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1. People of different heights were going to be using the console for driving and would be frequently getting into and out of the seat for testing and demonstrations Height adjustability was added to the seat along with mobility of the desk to bring the pedals and steering wheel closer to the user Console electrical components needed to be mounted in the console for protection Access to the inside of the console is also frequent necessary for monitoring of component performance An access hatch was created in the console along with the addition of mounting locations for the interfacing electronics and access points for sub connections Data logging programming and MATLAB usage made version control of programs problematic for the final deliverable A computer was procured for the project which was secured to the console as a dedicated programming station The console needed to be mobile for various demonstrations and testing A robust subframe was fabricated for connecting the chair desk and computer Casters were added to allow for easy moving A pull rope with quick mounting catch was also made to making movement easier The image of the camera became blurry on the screen after testing There is a small set screw that holds the lens at a fixed adjustment on the camera that can come lose through vibration This was adjusted until the image was clear again and tightened
2. Issues were encountered with trying to power the console Freedom board with external power sources while allowing for serial connection over the Open SDA port A separate cord and USB adapter or the computer when data logging are used to power the console board through the Open SDA port from those used to power the rest of the console Dead pins on the console Freedom board were encountered in interfacing PTE1 and PTD7 Suitable working pins were substituted to enable functionality Computer The motors were emitting a high pitched noise while the car was powered on and the H bridges were supplying a 50 duty cycle signal The motors were initialized with 9000 Hz frequency using the TFC library which reduced audible noise completely Hardware interrupts from the wheel encoders were disrupting the wireless communication It caused noticeable lag in the system The solution was to multithread the car code A thread for each encoder was created Communication problems were difficult to debug when the data was redirected through Matlab The solution was to remove Matlab and transmit the data directly through the XBee s There was difficulty with calibrating the Logitech pedals The pedals used potentiometers however originally they drew power from a USB port on the computer The problem was that the range of potentiometer values changed for no apparent reason It was determined that the US
3. Developer Guide RC Camera Car P14226 IX Additional Information A Imagine RIT The demonstration at Imagine RIT went very well and the exhibit was a huge hit with both children and adults The basic setup we used was keeping the car in the direct drive mode no PID or open loop feedback with a capped max speed of around 0 7 PWM The console was near the front of the Freescale Cup track area and participants drove the car around one of two tracks in the morning session while students were testing their cars for the competition Later in the afternoon following the competition the entire track was available for participants to drive We actually had a line all the way up until 5 PM then the students from the competition wanted to drive the car without speed limits Needless to say the exhibit was awesome Participants were given a few laps to drive the car 5 and were asked a series of short survey questions afterwards to gain feedback on their experience Most of these questions collected data for the test plan document but we also had a comments section for any input given The comments can be seen below Appearance e It was good I like it very much e It looks like it took a long time to build e The X on top is cool e The project is professional e The setup looks cool and safe Suggestions e Brighter colors for the components could improve experience e The car needs fiberglass body e The steering is a little sensi
4. This results in a binary counter that determines the direction of movement based on the previous number that was received When the encoders are both seeing the gap in the encoder their signals will be 00 When one starts to get covered up but the other is still uncovered the signals will read 10 When both encoders are covered the signal will read 11 When the second encoder is covered and the first encoder is uncovered the signal will read 01 These numbers can be converted into decimal and based on which number the encoders were reading previously will determine if the encoders have changed direction To better understand this the following tables show the two possible rotations and all possible encoder positions Developer Guide RC Camera Car P14226 CCW Rotation Encoders Encoders A B A B 0 1 0 1 1 1 1 0 1 0 0 0 Below is an oscilloscope screen capture of the voltage levels of the two encoder signals reacting to movement can be seen ES Agilent Technologies SUN FEB 09 04 24 20 2014 Measure Current Mean Min std Dev Count Freq 339HZ 305 00HZ 280HZ 35 355Hz Pk Pk 5 2DV 5 5300V 5 50V 34 641mvV Mint 130mV 355 00mV 370mV 30 000mvV Max 5 18V err elk 3 18V 30 000mvV Freq 1 339Hz Pk Pk 1 5 25V Min 1 130mV Max 1 5 13V Source ey Select Measure settings Clear Meas Statistics 1 Pk Pk Pk Pk e a e a D a Encoder PWM Developer Gu
5. unsigned char wheel pos char unsigned char wheel neg char unsigned char gas char uUneigned char brake char int encoder lelt int int encoder rignt int The encoder signals are read as interrupts on pins PTDO for left and PTA13 for right These pins look for high states of over 2 0V and low states of below 0 8V The timers are used to measure pulsewidths between consecutive falling edges caused by one set of teeth passing each optical switch The timeout value is used to limit the pulsewidths read by the encoder so that the code can determine when the car is not moving rather than how long the last pulsewidth read was The min_pw and max_pw were added for transmission purposes and to deal with some of the noise issues from the h bridges Values faster than 5 ms as impossible for our car given out limitations and values slower than 96 ms basically mean the car is moving slow enough to consider it not moving The pulsewidth values for each side are written to this maximum value at the start and a previous value variable is declared for each encoder to store the last received value INTERRUPT Information intertuptin encoder lerr PIDU Interr ptIin encoder right PITAL3 Timer tiner lefty timer rigiri float time out 150 07 ms between pulses too long for encoders to be detecting a speed float min pw 5 0f ms minimum pulsewidth that should be considered as a possible speed Developer Guide RC Camera Car P14226 float
6. v Ea Z tanh 9 v E via 3 tanaan 10 Where V m s is an input to the system and represents the central tangential speed of the vehicle in the microcontroller code V comes from the throttle input When implementing the control system on the KL25Z equations 9 and 10 were used to reduce calculation time and complexity instead of equations 3 8 G Notes Equation 3 assumes an average steering angle 6 for the front wheels This angle would be the average of the inner and outer wheel steering angles because they differ slightly due to the Ackerman principle however for us 6 comes from Eq 2 In addition using a bicycle model with a high speed turn would vastly complicate Eq 3 to _ b Wr Wr Wr Far Y R 57 3 k m Z 11 SIDE VIEW Where 6 deg is the average steering angle b m is the distance between the front and rear axles Wr N is the weight felt by the front wheels W N is the weight felt by the rear wheels V m s is the tangential velocity Car N deg is the cornering stiffness for the front wheels Car N deg is the cornering stiffness for the rear wheels and Fy N is the tractive driving force coming from the rear wheels g m s is the acceleration due to gravity and 57 3 is the conversion factor used if 6 is in degrees Developer Guide RC Camera Car P14226 Radial slip is currently unaccounted for due to the no slip assumption The differential drive feedback
7. 5 Main Loop The main loop of the code first sets up the XBee communications initializes and enables the needed TFC library components for the motors sets the h bridge PWM to 9000 Hz to eliminate the buzzing noise and sets the motors to 0 so the car does not move Main Loop int main Initialize Serial Comms XBee baud baud_ rate TFC Setup TO sae TFC InitMotorPWwM 9000 switching frequency of H Bridges that yields no audible noise 1000 9000 Hz TFC SetMotorPwM 0 0 make sure motors are off TEC HBRI DGE ENABLE z The DIP switch setting is then read as noted in the previous section for selecting the car code The encoder threads are then initialized Thread Setup Thread thread 1 encoder thread left Thread thread 1 iencoder thtead right A buffer message size of twenty characters is used for the code as that gives plenty of room for the message for the console The message is only four characters and a new line character being sent from the console The rest of the loop runs indefinitely on a while true loop char message 20 while true Before running any of the serial based commands the code checks the TFC hardware for potentiometer settngs and battery voltage converting and storing these values for later use The servo adjustment gives about 5 degrees of change on either side of the zero for fine turning of the steering servo The speed capping servo limits the speed down from 1 0 PWM to 0 5 PWM at
8. Encoder were reading static non zero values A timeout was added to the code that writes when the car was not moving corresponding the speed of the wheels to zero 1f a long to the last pulsewidth length that triggered time has elapsed since the last interrupt was the interrupt detected After testing it was determined that a five point median filter was actually making the Median filtering was targeted as a possible data worse due to the consistent high solution to the issue of noise in the encoder frequency nature of the noise Capacitors data cannot be used as low pass filters as this reduces the square wave produced by the encoder circuit to a useless range Encoder pulsewidths were capped at high Noise pulsewidths in the encoder readings and low values If the value seen was sometimes yielded values smaller than Bar unrealistically small the value is set to the anything possible by the car Very slow i i previous reasonable value If the value is movement also yielded values outside the G l too large it 1s set to the maximum range that could be transmitted to the console i i l pulsewidth which corresponds to no using characters movement Throttle and brake input was added together The gas pedal spring data not always return to produce only one signal from the user A the pedal back to exactly the same position deadzone was established to ignore input so the car would sometimes statically run unde
9. if wheel float gt 0 turning left left target speed in speed right target speed put speed else turning right left_target_speed out _ speed right target speed in speed If the PID is not enabled and the gas float is greater than zero we want to map the user throttle input directly to the motor PWM for both wheels in the range of 0 5 to 1 0 PWM A cap is then implemented to limit user speed if necessary This can also be helpful for testing as multiple fixed data points can be taken for max speed at a given PWM for curve fitting and establishing the motor deadzone else Running with capped speed and no PID left target speed gas float 2 0 5f 0 5 1 0 range for max speed issue if left target speed gt cap cap speed value left target speed cap right target speed left target speed Developer Guide RC Camera Car P14226 If the gas float is zero in either case set all speeds to zero so the car does not move else if gas float 0 stopped write motors to not move out speed 0 in speed 0 lert target Speed 07 right target speed 0 Similarly to the PID disabled case above if the gas float is less than zero in either case write the user input directly to both wheels in the range of 0 5 to 0 75 This is limited to less than one because people tend to drive too quickly in reverse and run into objects else going in reverse just use the gas float scaled left targ
10. the parameters given are Kc Ti Td and Rate Rate is the variable which describes the discrete time step to be used in seconds The discretization method is as follows Integral e t e t 1 15 16 Derivative Dr Where e t is the error between the set point and the process variable at sample time t The integral contains an if statement which only integrates if the input is not pegged at a limit This is to prevent reset windup Note that the derivative control is unfiltered F Important Note Wheel Speed Output The PI control loops operate on the reference velocity for left and right wheel speeds not inner and outer wheel speeds The reference inner and outer velocities are generated from throttle input and steering input The inner and outer reference velocities are then assigned to left and right prior to entering the control loops This is based on steering angle for instance 1f the steering angle is 20 degrees to the left the right wheel reference will be assigned the outer wheel speed This will change when the steering angle crosses zero G Simulink Model 1 System parameters See Section E of the Physics Theory Section for a table of parameters used The motors are modeled using a first order approximation with a single time constant Using velocity versus time data for an acceleration from rest to maximum speed an exponential curve was fit to the data The curve fit equation 1s ttd T Max Spe
11. ym Om ee Oe om wmeomememememene 27 aww 0D OOOO Gu Figure 8 Input Bus The two 3 pin male bus connections towards the bottom left are for the steering and camera servos It did not matter which servo pin was connected to which 3 pin header as the servos were scaled 1 1 ratio These connections were exactly the same as that for the original Freedom Board Motor Shield as it is simply a furthering of the male headers originally on the shield Towards Developer Guide RC Camera Car P14226 the top are the bus headers for other signals to and from the XBee module Table 3 shows the different pins being used Pin numbering starts from the left of Figure 8 Table 3 Input Pin Bus Layout Adapter Board Pin Pin Functionality Jumper Jumper Pin Number Number Number Left Encoder Collector 12 GND J9 12 Left Encoder Anode Right Encoder Collector J2 GND J9 Right Encoder Anode XBee TX J2 XBee RX J2 Right Encoder Input J2 Left Encoder Input J GND J9 NC TNR S 4 Servo Pin Extensions The servo extension pins as described in the previous Section are simply 3 pin male headers brought on the Adapter Board from below via the Adapter Board placement harness This does not change functionality in any manner and only acts as male pins coming out of the Adapter Board rather than the motor shield itself Figure 9 shows the servo pin extension Figure 9 Servo Pin Extension 5 E
12. 0 Bold msoFalse NameComplexScript mn cs NameFarEast mn ea Fill Visible msoTrue Fill ForeColor RGB RGB 89 89 89 Fill Transparency 0 sFiLi lt Solid Size 14 Italic msoFalse Kerning 12 Name mn 1t UnderlineStyle msoNoUnderline Spacing 0 Strike msoNoStrike End With ActiveChart SetHlement msoEKlementPrimaryCategoryAxisTitleAdjacentToAxis Selection Caption Time Developer Guide RC Camera Car P14226 Selection Format TextFrame2 TextRange Characters Text Time s With Selection Format TextFrame2 TextRange Characters 1 8 ParagraphFormat TextDirection msoTextDirectionLeftToRight Alignment msoAlignCenter End With With Selection Format TextFrame2 TextRange Characters 1 8 Font BaselineOffset 0 Bold msoFalse NameComplexScript mn cs NameFarEast mn ea Fill Visible msoTrue Fill ForeColor RGB RGB 89 89 89 Fill Transparency 0 sFillecorid Size 10 Italic msoFalse Kerning 12 Name 4 mn 1t UnderlineStyle msoNoUnderline Strike msoNoStrike End With ActiveChart Axes xlValue Select ActiveChart SetHlement msoElementPrimaryValueAxisTitleNone Selection HasTitle True ActiveChart Axes xlValue xlPrimary AxisTitle Text Speed m s The following code can be modified to adjust y axis limits quickly as these are critical to data viewing and interpretation Currently they are from 0 to 2 m s which completely encompass
13. 58 0 84 0 53 0 33 4 0 109 1 87 0 84 0 53 0 33 5 0 254 0 58 0 29 0 53 0 33 6 0 402 0 60 1 40 0 53 0 33 T 0 547 0 60 0 29 0 43 0 33 g 0 695 0 60 0 73 0 53 0 33 9 0 840 0 62 0 45 0 53 0 33 10 0 988 0 60 1 29 0 53 0 33 11 1 133 0 58 0 34 0 53 0 33 The way the VBA macro works in the background is that once you click Ok in the ActiveX control window following data collection the program will scan the five data columns for data and plot these points with formatting in cell G9 of the active sheet If you want to trim the data quickly you can hit the Trim Plot Data button above the graph and enter the start and end time of the data you want to look at in the window as seen below left Developer Guide RC Camera Car P14226 in the chart They don t have to be exact Start tine a End time a ea ES If the data set is good click the Save Data button and you will get a window as above right Enter a quick name for that data set that records what was being done in the testing for reference and click Ok The data will be saved in a separate sheet along with the plot and title label as seen below F G H I J Enter Max Speed m s This data was recorded Data Collection Testing l 5 1 2014 13 13 Speed Data LeftEncoder Speed m s Right Encoder Speed m s Right Target Speed m s Left Target Speed m s 2 00 E 3 VBA Program Documentation The VBA program is quite involved but i
14. and off the PID controls depending on what type of testing you want to do If the PID controls are off the cap variable is the only parameter that needs to be changed as this sets the limit of the PWM set to the motor at max throttle input Reasonable values are within the range of 0 6 to 1 0 PWM This allows for data collection at different fixed speeds It is important to note that there is a finite resolution of this limit which seems to be two decimal places With the PID controls enabled the PID coefficients on the car and the max speed value on the car and in the VBA code are critical to collecting correct data The max speed will limit the target values of the throttle input so that data without noise can be collected This value decreases with increased turning angle to around 0 6 m s with a max value of m s for straight runs of the car with a step input D Verifying Results Of course the goal of this testing is to see that the wheel speeds and setpoints of the car are around the same value and that the approach to these values reflects changes in the PID coefficients accordingly with the theory Some sample data can be seen in the Physics Theory section The current setup is limited by undersized motors and signal noise from the h bridges when operating at high PWM values so few modifications are currently possible See the Difficulties Documentation in the Additional Information section for more information on these limitations
15. both XBees will be 0 which means there is no direct pairing For further settings and more detailed explanations of the functioning of the program consult the Digi website and the Getting Started Guide for our specific modules Parameter Ch PAN ID DL MY DD IC IR An additional program that is useful for debugging is the Putty terminal window application This can be configured to read what data is being transmitted to and from the XBees This program is a bit more in depth for how it can be used so consult tutorials for doing so The XBees used for this project seem to be prone to bricking or going into a mode that yields them unusable when used incorrectly so some information will be given here on the issue The following link here can give some insight into how to sort out the problem but the general gist can be summed up as follows e Connect the XBee that seems to be causing problems normally the LEDs will not blink quickly as they should when data is being sent to the Xbee Explorer USB breakout board Connect this to the computer and open X CTU e The newer version of X CTU may have some troubleshooting functionality we have not had any issues since the new version was released but what you can do is set the Baud to 115200 and the flow control to Hardware This forces the XBee into its max hardware settings Once you change this setting try reading the XBee data to see if the current ve
16. chtObj As ChartObject For Bach chtObj In ActiveSheet ChartObjects chtObj Delete Next Sheets COM Shapes AddChart2 240 xlxXYScatter Select Developer Guide RC Camera Car P14226 ActiveChart SetSourceData Source Range COM SAS1 SES425 repopulate chart With Selection Top Range G9 Top fadj ust Lop Left Range G9 Left End With For all charts in the active sheet the following formats the plot with titles colors axis labels legends and data marker types This section was recorded directly using the record functionality VTAKKKKKKKKKKKKKKK Format Chart KAKAK KKK KKAKKAKARAKKAKKAKAKAKKAKAKA KK AK KK AK KKAK EKA For Each chtObj In ActiveSheet ChartObjects chtObj Activate ActiveChart ChartTitle Select Selection Format TextFrame2 TextRange Characters Text Speed Data With Selection Format TextFrame2 TextRange Characters 1 10 ParagraphFormat TextDirection msoTextDirectionLeftToRight Alignment msoAlignCenter End With With Selection Format TextFrame2 TextRange Characters 1 5 Font BaselineOffset 0 Bold msoFalse NameComplexScript mn cs NameFarEKast mn ea Pill lt Visible msoTrue Fill ForeColor RGB RGB 89 89 89 Fill Transparency 0 FAL Solid Size 14 Italic msoFalse Kerning 12 Name mn 1t UnderlineStyle msoNoUnderline Spacing 0 Strike msoNoStrike End With With Selection Format TextFrame2 TextRange Characters 6 5 Font BaselineOffset
17. correspond to noise as noted in the initialization For very short pulsewidths noise data the pulsewidth value is written to the previous good value so that that data stream is slightly cleaner to look at Encoder Data Capping if pulsewidth left val gt max pw pulsewidth left val max pw else if pulsewidth left val lt min pw pulsewidth left val pulsewidth left val prev else Developer Guide RC Camera Car P14226 if pulsewidth right val gt max pw pulsewidth right val max pw else if pulsewidth right val lt min pw pulsewidth right val pulsewidth right val prev else For the transmission of the data over the XBee to the console the encoder values are translated by 30 to always be in a safe range for character transfer XBee Data Transmission encoder left int pulsewidth left val 30 encoder Fright ant pulsewidth right val 320 We now have to send the encoder data back to the console Similarly this uses a writeable command that first checks to make sure the buffer on the console is not already filled with data If it is the car does not send the data at all If the buffer is empty the character encoder pulsewidths are then transmitted as a string with a new line character Having this in line with the code seems to work the best based on our testing XBee Data Transmission if XBee writeable XBee printf ScSc n unsigned char encoder left int unsi
18. data was successfully collected from the Xbee all the way to the other end which was measured to be approximately 141 ft The XBees also transmitted through glass to the outside but the range was greatly reduced Walls seemed to cause packet loss after the 141 foot mark but for our purposes this is more than adequate B Camera Distance Stats and Info Range testing of the wireless camera modules was done in the Brinkman hallway of building 9 as well Starting with the monitor and receiver at one end of the hallway the image was still acceptable quality at 141 ft the end of the hallway The image had some interference while moving at all distances The image was still broadcast as far away as Xerox auditorium estimated at over 200 ft away with many obstacles in between Based on these results it 1s clear that the camera range surpasses the XBee range which was the target of our design Following testing it seems that interference in the image quality can be caused by obstacles outside signals and sharp movement of the transmitter Most notably metal objects tend to cause significant interference and should be removed from the operating area A rendering of the field of view relative to what a person would see normally when using the camera can be seen below Only the horizontal limitations are considered as it 1s difficult to limit the view in the vertical direction As can easily be seen the limitations of camera FPV are notable but still
19. debugging Separate external pullup resistors were calibrated and integrated into the XBee shield that yielded good voltage ranges for the encoder circuitry The PULLNONE functionality of the interrupts was used Noise issues caused by the motor shield led to multiple configuration attempts for powering the XBee shield as can be seen by the extra open pins on the shield Power and ground for the shield was pulled from the 3 3V source for the speed sensors from the TFC shield to reduce external wiring XBee communications kept dropping out once two way communications were enabled Clearing the area around the front of the car XBee of electrical components was observed to greatly reduce the issue Two way data communications were otherwise inconsistent A compromising range of 50 ms between transmissions was reached and printf and scanf commands in the code were enclosed in readable and writeable conditions to prevent buffer overflow Excessive encoder noise was encountered at higher H bridge PWM values H bridge saturation was limited in coding to 0 75 PWM for the PID control The max speed output of the PID was also limited to a range which did not produce much noise in the signal separately for straight driving and turning as turning requires higher PWM values to the outside wheel Steering servo values and camera servo values are frequently different due to slop in the steering servo gearing and f
20. int Asc brake char The pulsewidth values are calculated by removing 30 from the integer value of each data character which is the opposite of the data transmission step in the car code Convert Encoder Data pulsewidth left val encoder left ant 30 Gonvert to original pulsewidths pulsewidth right val encoder right int 30 The conversion from the pulsewidths to wheel speeds is identical to that seen in the car code in VBA format Developer Guide RC Camera Car P14226 If pulsewidth left val max pw Then left wheel speed 0 Else left wheel speed End If If pulsewidth right val right wheel speed 0 Else right wheel speed 16 83 pulsewidth right val End If 16 83 pulsewidth left val max pw Then The conversion of steering data to wheel float and steerplus values is also identical to the car code for consistency Convert Steering Data If wheel neg int 35 Then wheel float wheel pos int 35 92 Else wheel float wheel neg int 35 92 End If st erplius Abs wheel float 0 611 If steer is zero make it something small rad If steerplus lt 0 001 Then steerplus 0 001 End If The conversion of gas and brake values to gas float and speed calculations used in the PID loop are also identical to the car code with the exception that obviously the VBA code does not include the ability to calculate the PID output the same way as the car code works This functionality may be a nice ar
21. is to convert the left and right encoder data into a tangential speed so that the signal makes sense for debugging purposes This is done by measuring the distance from the center of the wheel at which the optical switch is located and combing this with the knowledge that there are going to be 8 cycles of tooth no tooth to calculate the arc length subtended during a measured pulse width 7 ms When converted to yield m s the results are 16 83 V feedback Ts ms 12 16 83 V feedback Tsr ms 13 D PI Control Closed loop feedback will be used to determine the output inner and outer wheel speeds These loops require a reference signal which is based on the average velocity V and instantaneous turn radius R which is based on the steering angle see Physics Theory Section The closed loop feedback portions of the control system are to be tuned using PI control directly on the KL25Z freedom board as shown below CO COpias Ke e t gt f edt Ty 14 Where CO is the controller output V e t is the error at time t setpoint V encoder V PV is the process variable encoder V and Kc Ti and Td are the PID proportional integral and Developer Guide RC Camera Car P14226 derivative coefficients The PID coefficients can be modified by changing Kc Ti and Td in the code E Discretization of PID in MBED The continuous Eq 14 used by MBED must be discretized for use on the freedom board First in MBED
22. max pw 96 0f ms maximum pulsewidth that is possible for transmission float pulsewidth left val max pw float pulsewidth right val max pw float pulsewidth left val prev pulsewidth left val float pulsewidth right val prev pulsewidth right val The PID setup only needs the input limits and output limits specified as well as auto mode for each controller The max speed variable in meters per second is employed for quick modification of the inputs while the outputs are fixed at 0 0 min to 1 0 max to correspond to the same range of PWM values that can be written to the motors The PID controller works on scaling the inputs and working in percentages so attention to units in these assignments determines the functionality of the controller PID Initialization void initializePidControllers void leftController setInputLimits 0 0 max speed m s travel speed leftController setOutputLimits 0 0 1 0 working range of car leftController setMode AUTO MODE rightController setInputhimits 0 0 max speed m s travel speed rightController setOutputLimits 0 0 1 0 working range of car rrghtController setMode AUTO MODE 4 Encoder Wheel Speed The MBED RTOS library was used to provide multithreading support to the car program Multithreading was needed in order to handle the interrupts from the wheel encoders which have separate interrupt service routines ISR s and codes as well For each main interr
23. mount the servo horn arms Set the servo flat against the table and brace or clamp the plastic blocks behind the set of tabs one either side Again with great force screw the screws into the top holes until the blocks are tight against the servo plastic mounts from the back p Now slide the servo assembly in from the center of the car outward and screw the attachment blocks in from the bottom of the car as seen below The screws used for this are the tapered head screws all of which are the same length which should leave a flat finish and not catch the floor Developer Guide RC Camera Car P14226 Almost there Now all you need to do is adjust the length of the servo arms and attach the plastic end cap pieces to the metal hitch pieces on each wheel Here we removed the wheels using the provided metal tool Be careful not to lose the washers that are behind each wheel nut The difficult part is making the wheels straight when the servo is centered The servo arms and plastic ends have to be adjusted repeatedly to give the correct length for connecting to the hitch points and when the plastic caps snap into place the wheel rods will not be perpendicular to the car centerline which is where you want them A helpful hint can be seen in the image below which is what you do to get the plastic caps off of the hitch points when it turns out you need to adjust the arm length Simple put a flat head screw driver in as seen and pry CCW
24. negative character to extend the resolution of the steering wheel range to 186 characters If the encoder is clockwise of center the negative character gets written to the lowest value 35 and the wheel float value is based on the converted positive character less the lowest value and scaled from 0 to 1 A similar operation is employed for counterclockwise of center STEERING Calculations if int wheel neg char 35 wheel float int wheel pos char 35 92 0f else wheel float int wheel neg char 35 92 0f The steerplus variable is then calculated which converts the wheel float to an absolute value of the radian measurement of the angle of the wheels If this value is near 0 it writes the variable to a value of 0 001 to be small constant and non zero for further calculations steerplus wheel float 0 611f If steer is zero make it something small rad if steerplus lt O f steerplus steerplus 1 0f if steerplus lt 0 001 steerplus 0 001 Developer Guide RC Camera Car P14226 Steering and camera servo PWM values are then calculated using the wheel float using the scaling factors declared in the initialization different for each running scenario The centering value declared in the initialization is added to each calculation as this is the PWM corresponding to the center position of each servo with our current setup This value may vary depending on configuration of the
25. of corners II DIP Switch Conr iguration Switch setting TFC GetDIF Switchit if switch setting 0 PID Control and Open Loop Disabled PID Enable false Open Loop Enable false Camera scale 0 231 steering scale 0 33f else if switch setting 1 PID Control Enabled Open Loop Disabled PID Enable true Open Loop Enable false camera scale 0 517 steering scale 0 57 leftController setTunings 3 0f 1 0f 0 0f Kc taul tauD floats rightController serliunings 4 05 1 0 0 0f Ke taul taun floats max speed 1 0f m s used for PID output limits and setpoint calculations initializePidControllers PID Initialization else if switch setting 3 PID Control Enabled Open Loop Disabled PID Enable true Open Loop Enable false camera scale 0 5f steering scale 0 51 leftController setTunings 3 0f 1 0f 0 0f Kc taul tauD floats Developer Guide RC Camera Car P14226 rightControllerssetTunings 2 0 1 02 0 01 Fo taul tau floats max speed 0 6f m s used for PID output limits and setpoint calculations initializePidControllers PID Initialization else if switch setting 7 PID Control Disabled Open Loop Enabled PID Enable false Open Loop Enable true camera scale U zZat steering scale 0 57 else if switch setting 15 PID Control Enabled Open Loop Disabled PID Enable true Open Loop Enable false camer
26. progression can be seen below 0 N A PC Used for Computer Image HDMI2 N A HDMI1 N A Component N A Video Used for Camera Image 95 N A On the car side the battery voltage indicator should be attached to the white four wire battery connector as indicated in the image below This indicator monitors the voltage in all cells individually and will emit a warning when the voltage gets low Be aware that the indicator will beep loudly when plugged in for the first time The indicator can be stuck to the Velcro on the top of the battery and the battery can be stuck to the Velcro on the car as below The red black transmitter wire then needs to be plugged into the battery using the red plastic connectors Developer Guide RC Camera Car P14226 Developer Guide RC Camera Car P14226 V Car Electrical Information On Car Microcontroller amp Shield Modifications A RC Car Onboard Control The RC car operates utilizing the Freedom board provided by Freescale To successfully interface the motors on the RC car with the microcontroller the Freedom board motor shield Insert part number was fitted on top of the microcontroller board This however brought in significant limitations on the number of I O pins that could be utilized for other sensors To overcome this certain modifications had to be made on the motor shield These modifications required the construction of a separate module which further altered the motor shield an
27. reasonable for driving purposes C X CTU Updating and Bricking Issues The primary debugging program for the XBees is the X CTU software from Digi Download the XCTU Next Gen Installer v 6 1 0 Windows x32 x64 and install the software this is the newest version In this program you can Add or Discover the XBee Devices connected over USB using the buttons on the top left of the interface Once you go through these initializations should be all the default settings 9600 baud 8 data bits 1 stop bit no parity no flow control Developer Guide RC Camera Car P14226 etc you can modify the Configuration and monitor the Console outputs using the buttons on the top right of the interface If you simply double click the listed XBee device some basic settings that are worth mentioning can be found below The channel setting for both XBee devices yes you have to repeat this process with both XBees should be the same here we are on channel C as well as the PAN ID s of both devices Similarly DD IC and IR should be the same value for both XBees To make the XBees communicate directly with only the each other specifically one XBee has to be set with DL and MY values here we used 10 and 20 to keep it simple The other XBee should be set with DL equal to the MY value of the other XBee and the MY value of the second XBee should be the same as the DL value of the other XBee By default the DL and MY values on
28. spring does not always bring pedal back to zero gas float 0 Now the actual PID loop is employed For gas floats great than O not stopped or going in reverse if the PID is enabled in the initialization the outer wheel speed and inner wheel speed in ft s are calculated using the formulas determined in the Controls Section if gas float gt 0 going forward implement PID control if PID Enable true PID Calculations out speed max speed gas float 1 0 353 tan steerplus tangential speed of outer side or car m s im speed Max speed gas Float i 0 353 tan steerplus tangential speed of inner side or car m s Based on the wheel position if the car is making a left or right turn is then established which establishes the assignment of outer and inner wheel speed to either left or right wheel as the set point to be achieved by the car using the control system if wheel float lt 0 turning left lereController sseroelPoint in speed rugheControllery setser Point cut speed else turning right IetLController ser SL Polnliouc speed riolCCon troller setoet Point in speed The process values what feedback the system is seeing is then set as the encoder speeds calculated earlier directly this time as the wheel designation corresponds directly to the controller with the same name leftController setProcessValue left wheel speed encoder value rightController setProcessV
29. the minimum to prevent people from driving too fast during the demonstrations Developer Guide RC Camera Car P14226 To calculate the battery voltage thresholds the TFC shield and KL25Z board were powered by a variable power supply and the associated readings were recorded and plotted in the chart below Curve Fitting Analog Read to Voltage Conversion 9 00 8 00 y 6 2837x 0 0047 ed m ms J 7 00 R 0 9998 er gt 6 00 Tl m gt 00 a 4 00 errr gt 300 lt _ _ _ _ ae 2 00 r 1 00 o 0 00 0 00 0 20 0 40 0 60 0 80 1 00 1 20 1 40 Analog Read Float Voltage vs Float es e Linear Voltage vs Float Based on these values the different voltage thresholds for the battery level indicators were set in the code The car simply reads the battery voltage and lights up from 0 to 4 LEDs on the voltage range of 6 to 8 4V Hardware Adjustments steering pot value TFC ReadPot steering pot 1 to 1 float potentiometer reading cap pot value TFC ReadPot cap pot 1 to 1 float potentiometer reading steering center steering pot value 0 05ft tsteering center default 0 2 to 0 3 PWM servo center range adjustment cap Cap Gefault cap pot_valuctl 0L 0s25t 710 5 to 10 PWM speed cap range adjustment battery volt TFC _ReadBatteryVoltage 6 28f V voltage of battery if battery volt gt 7 8f voltage cutoff threshold for 4 LEDS TEC oetBa atteryLED Level 4 else if b
30. until the plastic cap pops off This may mar up the plastic slightly so don t do this many times If you can t get the rods perfectly straight it 1s better to have the wheels slightly angled forward than backward as this will steer more preferably The image below shows how well we did Developer Guide RC Camera Car P14226 P Now just put the wheels back on At this point you will probably want to mount the bumper This is as simple as that seen below The indent that corresponds to the plastic on the front of the chassis press together translate the bumper upward in the picture and the bumper is secured with screws and nuts Depending on how well Freescale did with your set the taped flat headed screws that look like every other screw on the bottom of the chassis may work but if they do not just use the same screws that you used for the servo horn arm mounts They do not protrude much below the chassis anyway so it works and is significantly easier to mount a nut on Helpful Tip DON T MOVE THE SERVO BY HAND OR PAST THEIR STOPS THIS WILL BREAK THE PLASTIC GEARS INSIDE Just saying Developer Guide RC Camera Car P14226 2 Freedom Board For our project significant modification was made to accommodate significant amounts of extra electronics that are not necessary for the car This included the addition of a Lexan mounting plate over the entire chassis which can be seen in the Modifications Section As for basic mount o
31. will attempt to eliminate tangential slip but will not affect radial slip For this reason the radial slip may be estimated possibly by obtaining the centripetal force the car is experiencing and comparing it to the largest amount of centripetal force the tires can provide on the given surface This would require estimating the coefficient of friction as well as measuring radial speed or acceleration Developer Guide RC Camera Car P14226 JII Controls Application A Torque Vectoring Model Theory of Operation The goal of this torque vectoring control system is to improve the turning characteristics of the car by accounting for the difference in speed required from the inner and outer drive wheels during aturn This system will use closed loop feedback to determine the speeds at which each drive wheel should spin during a given turn B System Inputs and Outputs The required system input signals are e The wheel speeds of the rear wheels from the encoders pulse widths of time measured over the width of an encoder tooth converted later to m s e The steering angle of the steering wheel 0 deg later converted to 6 by Eq 2 The required system parameters are The track width of the wheels left right The wheel base forward back Wheel diameter First order approximation time constant The desired outputs of the system are e Left and right wheel speed C Signal Processing The only remaining calculation before the PID loop can work
32. 5 00 15 00 25 00 35 00 10 00 From iterating this map with new transaxle lengths it was decided that the new transaxle length should be anywhere for 40 to 60mm The old transaxle length was about 15mm b Practical Design of Front Transaxles The real transaxle would need to have additional length to stick out on either side The inner side needed to clear where it was mounted on the kingpin so that a snap ring could be fitted to Developer Guide RC Camera Car P14226 hold it in The outer side needed room for threads and a lock nut to hold the wheel in place from the outside Smm centerless ground rod made from tool steel was used in the construction of the transaxles Below is the technical drawing As can be seen when comparing the drawing to the picture a step up was added to the drawing after spacers had to be made with the given dimensions to reduce movement in the connection point This should be done in the initial machining for future parts For the CAD model check out Front Axle Extension To download any CAD file right click the Display link in the CAD directory and choose Save link as This will save a SLDPRT or SLDASM file to the desired location May Need ta Tum Radius Below Smm ta fit Bearing ID 8 300 453 0 492 ee 0 394 1 962 K a Z lt N iH 25 5 mm E Ring 0 197 0 162 00 118 0 091 0 157 O01 0 025 3 mm E Ring Dimensions in Inches Developer Guide RC Camera C
33. B ports on the computer did not output 5V consistently The solution was to use a 5V DC wall adapter to power the pedals This resulted in a fixed consistent range of potentiometer values It is difficult to keep track of the NIMH battery voltage powering the car Analog read and battery LED indicators built into the TFC shield and TFC library were used to signal decreasing voltage levels The center position of the steering servo sometimes needed to be adjusted slightly during testing for straight driving Potentiometer reading functionality on the TFC shield was enabled using the TFC library to allow for fine tuning of the servo center on the fly during testing The max speed of the car during demos needed to be adjustable to allow for different drivers during the demonstrations Potentiometer reading functionality on the TEC shield was enabled using the TFC library to allow for limiting of the max speed of the car during forward movement when control systems are disabled Developer Guide RC Camera Car P14226 Issues were encountered with the internal pullup resistors used on the Freedom board and TFC shield that were interfering with the use of interrupt pins for encoder reading External pullup resistors were removed from the TFC shield Separate pins from those used by the motor shield for speed sensing PTAI and PTA2 since these pins disable the UART functionality of the board for
34. Cells False End With WS Shapes AddChart2 240 xlXYScat ActiveChart SetSourceData Source WS Range AS1 5ES425 Chart With Selection Top Range F4 Top Left Range F4 Leftt End With Formatting the chart is very similar to the code seen earlier in the plot macro VARKER RK RR RK KKK Format Chart BRAK RAR RAKA KARA ARR RAK RRA RAR KR RRR Re For Bach chtOb In WS ChartOb ects chrtOb Activate ActiveChart ChartTitle Select er ter Select an just top repopulate Selection Format TextFrame2 TextRange Characters Text Speed Data With Selection Format TextFrame2 TextRange Characters 1 10 ParagraphFormat TextDirection msoTextDirectionLeftToRight Alignment msoAlignCenter End With With Selection Format TextFrame2 TextRange Characters 1 5 Font BaselineOffset 0 Bold msoFalse NameComplexScript mn cs Developer Guide RC Camera Car P14226 NameFarEast mn ea Fill Visible msoTrue Fill ForeColor RGB RGB 89 89 89 Fill Transparency 0 Pi cOlLG Size 14 Italic msoFalse Kerning 12 Name 4 mn 1t UnderlineStyle msoNoUnderline Spacing 0 Strike msoNoStrike End With With Selection Format TextFrame2 TextRange Characters 6 5 Font BaselineOffset 0 Bold msoFalse NameComplexScript mn cs NameFarEast mn ea Fill Visible msoTrue Fill ForeColor RGB RGB 89 89 89 Fill Transparency 0 sFill Solid S
35. DEVELOPER GUIDE LAB TOPICS AND ADDITIONAL INFORMATION RC CAMERA CAR P14226 TIM SOUTHERTON BRIAN GROSSO ALEX REID KEVIN MEEHAN LALIT TANWAR MATTHEW MORRIS Developer Guide RC Camera Car P14226 I Chassis Construction and Information A Assembly Instructions For assembling the Freescale Car Cup chassis the directions can be found on the site below which is part of the Freescale community site where all sorts of helpful information can be found Unfortunately not all of the directions are that helpful so some are copied here and modified to give extra clarity General Freescale Community Site for Freescale Cup Car Assembly Assembly of the car focuses on three main aspects namely mounting the steering servo mounting the freedom board KL25Z to the car and mounting the line following camera These items will be addressed individually 1 Servo and Steering Inside the kit are various mounting options for different servo manufacturers Look for the Futaba bushing of the servo as this is the most common em O Hitec LAL ra N 9 Futaba L a O 2 gt Spare SD 4 6 gt Z O N Lt IR o gt eY Sanwa Before doing anything you want to center the servo bushing for the car on the servo This means connecting the tab on the plastic piece to be so that it fits on the gearing of the servo pointing vertically upward WHEN THE SERVO IS AT ITS MIDDLE POSITION The only way to move the s
36. O Header Figure A Freedom Board amp Motor Shield Jumper I O Headers P14226 To describe these I O further Freescale has labelled the pins on the boards itself as well and each of these pins are given an alias for easy programming Figure B shows the aliases and the pins for each female jumper Table A shows the different pins and their mappings to the aliases for programming FIMI CAG PTA PTA CHI PTA3 E E PLACE FTA4 PTAS PICs FICS PTAL Ao Seah PID PIL D FIL PTE GND VREFH a Freedom Board Interface J Note All pinout documentation 25 of PICT PICI Po H HICA PING CH3 PICS Pru PTC1g PTCl1 PTCI2 PTES PTC PTE ry gee Ee PIEJ PICI PT PTALG PIB PAIN PUBL PIE PTB PTBE PLOS Aa kB FTL PTA CAG FTW CHi AAC SETS Ata SEJI ET CH PT CHO l V BATTERY e E e 7 Pav Use GND E J 5 EE PP Toa Hih E 3 2 SDA PIDs SH Figure B Freedom Board Interface Developer Guide Pin J9 01 J9 03 J9 05 J9 07 J9 09 J9 11 ota ae oo J9 15 PTES P5 9V_VIN J1 Pin 2 H Bridge An H Bridge is necessary for the fast switching of battery voltage and thereby controlling the speed of the motor A PWM signal is sent to the H Bridge where the optocouplers turn the motor on and off at high frequencies to reduce the overall voltage sent to the motors The H Bridges used for motor control are the ones fitted on the motor shield The H Bridge
37. ServoNumber float Position void setintervallfloat interval void TFC_SetMotorPWM float MotorA float MotorB void setSet Point float sp void TFC_InitMotorPWM float SwitchingFrequency void setProcessValuelfloat pv float TFC_ReadBatteryV oltage void setBias float bias void TFC_SetBatteryLED_Level uint8_t BattLevel float computelvoid B Console Code Documentation The console code makes use of the MBED QEI quadrature encoder library in order to capture the position and direction of the Logitech wheel A digital interrupt was connected to the centering signal from the Logitech wheel This provided the ability to correctly zero the position and direction of the wheel Analog inputs were used to read the potentiometer values from the Logitech gas and brake pedals The Logitech console drew power from a 5V DC adapter This provided the console with a constant voltage so that the potentiometer values remained in the same range The range for the pedals was determined by recording the raw values when the pedal was not pressed and when it was fully pressed This range was determined to be quite large Unsigned characters were used Developer Guide RC Camera Car P14226 to transmit the data therefore the pedal range was compressed down via a scaling factor Similarly a scaling factor was also used to compress the wheel position s range The unsigned char was chosen to be the transmission data type The char type was well suited for this task b
38. SetMotorPWM MotorA MotorB 7 J Sets the serve channels i param ServoNumber Which servo channel on the FRDM TFC to use 0 or 1 i O is the default channel for steering i param Position Angle setting for servo ina normalized 1 0 to 1 0 i LOrm ae void SetServo int ServoNumber float Position TPC Seller vo oervONumber Position Developer Guide RC Camera Car P14226 2 Code Selection and Modifiable Parameters DIP Switch Settings Switch Camera Steering Max Adjustable Max SES ESERES Oe es vl a PID Optimal Straight poe eo pe Po fo aro Open Loop a fin os asa eee Adjustable Max Any Other Combination Speed Cap No Transmit For the car code the KL25Z DIP switch was employed to allow the user to easily switch between a PID enabled car functionality and a straight user input to car output setup Following some testing it was determined that for the PID enabled version the optimum amount of turning for both the camera and steering wheels was around 30 degrees to aptly demonstrate the application of a controls algorithm at the desired speeds which corresponds to a scaling factor of 0 5 In the straight input setup the camera only turns half this distance and the wheels only turn two thirds as much Extended turning of the wheels at higher speeds tends to make the car handle too quickly for the average user and the camera turning angle tends to make users overshoot corrections upon coming out
39. a scale parL Steering scale 0 51 LefteControlli er settTunings 10r 1 07f 0 08 ke taul taud floats rightControLler seriunings 1 08 1407 0 02 2 Ko taul taD floats max speed 1 0f m s used for PID output limits and setpoint calculations initializePidControllers PID Initialization else if switch setting 14 PID Control Enabled Open Loop Disabled PID Enable true Open Loop Enable false Camera scale ULI steering scale 0 572 lefeControlLler sertunings 1 08 1 072 amp 08 7ko tail taun Tloats rightConrrolLler setTunings 1 0f 1 071 0 05 7 hc taul taul floats max speed 0 6f m s used for PID output limits and setpoint calculations initializePidControllers PID Initialization else PID Control and Open Loop Disabled PID Enable false Open Loop Enable false camera scale 0 25f steering scale 0 3317 For the functionality of the car the only major control parameter is the cap_default This can be used to cap the speed PWM of the car directly which can be any value between 0 6 and 1 0 to help draw data curves for establishing the deadzone With the value limited you simply run the car in a Straight line at full speed and record the speed of the car We used a timing gate to measure this but the encoders are also a valid option Variable Parameters for Performance float cap default 1 0f PWM adjustable for no PID output cap
40. alue right wheel speed encoder value The PID library compute function calculates the target output PWM for the car based on the PID algorithm set points process values and input output limits Developer Guide RC Camera Car P14226 lett target speed lerrController compute bight target speed rightController compute Due to limitation in the motor outputs due to noise the computed output PWM s are then limited to 0 75 PWM This highest value is also scaled back from a 1 0 PWM to allow the outer wheel to spin at its max speed at around 1 0 PWM when the car centerline speed is less than 1 0 PWM basically a geometry limitation Around 1 0 PWM the car experiences excessive noise in the data which we want to avoid left target speed left target speed 0 75r 7 0 0 0 75 PWM range for max speed noise issue right target speed right target speed 0 75f 0 0 0 75 PWM range for max speed noise issue If open loop control is enabled the car basically takes the wheel speed calculations from the PID loop and directly writes those values to the inside and outside wheels based on the steering angle This does not use any encoder feedback hence the open loop control else if Open Loop Enable true out speed 0 8f gas Iloat 1 0 353 tan stecrplus outside wheel PWM maximum less than 1 0 in speed p regae iloat 1 U 252 tanteteerplus inside wheel PWM scaled the same as the outside wheel
41. ar P14226 All dimensions are given in inches because that is how the lathes in the machine shop are set up All length dimensions are based off of the outside edge of the kingpin mount The 3mm E ring groove holds the transaxle from sliding outward The outer opening of the kingpin mount is a 3 5mm hex and the inner opening is a 3mm hole this hex in the previous transaxle prevented the transaxle from sliding inward In the new transaxle that hex is replaced by a step up and the step from 0 118 3mm to 0 162 and finally to 0 197 Smm prevents the transaxle from sliding inward The 5mm E ring slot was positioned to leave room for the washers two bearings and wheel rim but leave just enough overhang over the 0 125 diameter so that the locknut could tighten up and eliminate slop in the system The overall length of the transaxle is about 74mm it is about 50mm in the length used in the calculation which falls right in the middle of the range Due to the rod being about 5 03mm in diameter and the bearings being about 4 98mm in diameter the sections of the transaxles outside of the 5mm E ring groove had to be turned down slightly to allow the bearings to fit 7 Rear Encoder Wheel Adapters and Optical Gates a First Iteration Encoder The new wheels came with new requirements to be mounted on the car The old adapter for the wheels was a cylinder with two flats and a central hole for the alignment axle The new wheels required a 12
42. aracter of and an ending character of a new line and carriage Developer Guide RC Camera Car P14226 return If the write buffer is full already the code does nothing making the transmissions are not being overloaded XBee Data Transmission if XBee writeable f XBee printf Sscsc c c n r unsigned char wheel pos char unsigned char wheel neg char unsigned charjgas int Unsigned char brake int else Two way communications have not been able to be resolved as enabling this bit of code constantly causes the communications to disconnect so the car runs off on it s own We have narrowed down the problem to the scanf command on the console and none of the workarounds we tried seemed to work A switch was added then that enables or disables the functionality which is checked first A 20 character buffer is established to give plenty of room for the message being sent from the car The first two characters are then sent to the last character in the range 126 and the code checks to see if there is data in the buffer to be read If this is readable and there are a full 3 characters to be read the first two characters are assigned to characters in the code XBee Data Reception Assign a 3 character buffer 1f enableTwo char message 20 message l 126 message 2 126 if XBee readable if XBee scanf s3s amp message 1 Store Individual Characters encoder left char message 1 e
43. art from replacing the separate 3S LiPo 11 1V 35C battery for the transmitter when the battery indicator warning goes off The transmitter has a heat sink for thermal dissipation at the back of the car and has no user settings The camera is powered through this transmitter and data is transmitted through the same cable The servo that articulates the camera is controlled off of the microcontroller shield Testing of the runtime of the camera and transmitter from a single LiPO battery is as follows Starting at a max voltage of 12 5V the camera and transmitter broadcast a good quality image for 2 hours and 55 minutes setting the voltage indicator off at 10 1V During this time the heat sink reached a steady state temperature which is warm to the touch but not hot which is a worst Developer Guide RC Camera Car P14226 case airflow scenario and is desirable This is significantly longer than the runtime of the car battery so that metric 1s ideal Developer Guide RC Camera Car P14226 VI Wireless Communication Information A XBee Distance Stats and Info For this project XBee 802 15 4 XB24 2mW chip antenna modules are used for the data transmission From the detailed XBee guide these XBees operate in the 2 4 GHz range and have an operating distance significantly affected by Line of Sight and other interference sources Range testing of the XBees was done in the Brinkman hallway in Building 9 A table was set up at the end of the hallway and
44. as cut using a hot wire foam cutter to get the desired geometry However reasonable results can be achieved with a sharp knife After the shape was cut reliefs were cut into the back of the foam to allow for more compression A back bumper was added by simply cutting an additional piece of foam and using the existing standoffs for the frame as securing points The foam simply slides over the standoffs For the CAD model check out Bumper Frame Bottom and Top To download any CAD file right click the Display link in the CAD directory and choose Save link as This will save a SLDPRT or SLDASM file to the desired location Developer Guide RC Camera Car P14226 C Car Steering Servo and Drive Motor Specs As measured on the console and confirmed online the range of the steering wheel is 120 degrees The steering angles of the car wheels are targeted at 35 degrees to simulate normal car handling These values yield a steering ratio of 3 4 D Battery and Power Management Specs The Freescale Cup Car is powered by a 3000 mAh NiMH battery that is charged with the supplied Tenergy brick charger The status LED will be red while charging and green when charged The current level selector switch can be in either setting 2A will charge more quickly 1A will prolong the life of the battery but will take longer to charge This is a very robust battery that outputs 7 2 V nominal and 8 2 V at max charge and they can be fully discharged wit
45. at had to be low to reach the pedals children were below the height of the steering wheel which made them pull downwards to see the screen This broke the clamping mechanism which had to be held in place manually by a team member This was replaced by a bolted connection An additional option may be a small console specifically set up for small participants now that the functionality is fully developed With this some additional time could be spend on the aesthetics of the car and console fiberglass body brighter colors etc Developer Guide RC Camera Car P14226 B Controls Class User BOM Item Qty needed Total Price 84 99 Transmit driving controls XBee kit Qu Microcontroller Wireless Tx Rx kit Motor Controller Batteries Car Battery w Connectors Battery Chargers Car battery charger Drive wheel encoder system O O1 2 i Freescale Motor Shield Included with chassis kit _ Motor Shield Included with chassis kit 4 Ls Eon 6 61 Encoder 62 es a 8 Sos or O Co 9 4 i 4 3000 mAh NiMH 7 99 To charge the car batteries 23 14 Encoders are 3D printed 8 00 For wheel speed sensing Run the entire Console Optical Switches Console Computer mouse keyboard Car Chassis Kit Assorted other components 5mm rod x3ft 3mm E rings x 100 5mm E rings x 100 8 32 locknuts x 100 9 5 2 8 diameter wheels x2 9 6 bea
46. ate at 5 VDC similarly to USB The level shifter used in this project was the BOB 11978 from sparkfun com This level shifter shifts between the two voltages 5 VDC and 3 3 VDC because it is meant for RS 232 communications The following pins were assigned the following values Value 5 VDC 3 3 VDC GND 0 VDC Centering Signal Input Centering Signal Output B Console Components The Logitech MOMO steering wheel donated to the team was analyzed for use without using the pre existing and historic drivers for it The original driver which existed can only be run on a Developer Guide RC Camera Car P14226 windows machine and still had numerous errors and bugs Also the readings from the controller could only be seen by using the GUI from Logitech Due to the lack of usability of the pre existing software it was decided that the analogue signals from the internals be taken in calibrated and then used directly Ideas of creating a self programmed driver were also brainstormed and it was decided that for obtaining only steering data it was too exhaustive of an effort to design and program a driver for it Utilizing the signals straight from the internal circuitry also enabled the use of a low powered microprocessor It must be given note that there were two sources of power to the steering controller the 5V from the USB and the 24V from the wall outlet The 24V supply was only connected to the motor When the 5V power su
47. attery volt gt 7 2f voltage cutoff threshold for 3 LEDS IFC SetBatteryLED level 3 else if battery volt gt 6 6f voltage cutoff threshold for 2 LEDS TFC oetBatteryLED Level 2 else if battery volt gt 6 0f voltage cutoff threshold for 1 LEDS TFC oetBatteryLED Level 1 else voltage cutoff threshold for 0 LEDS TPC SetBatteryhLaD hevel Developer Guide RC Camera Car P14226 To deal with issues encountered when data transmission is lost holding onto the last received command and having the car take off a readable command was employed to first check and see if there is any data in the buffer before trying to perform any operations It also checks to make sure that the length of the message is 5 characters so that no short packets are being read If there is no data in the buffer an else condition at the end of the code writes both motors to stop moving and sets the servos back to straight stopping the car instead of allowing it to take off This still does not always work and should be looked into for future work XBee Data Reception 1f XBee readable amp amp XBee scanf s5s amp message 1 The message data is then parsed into individual characters for steering wheel gas pedal and brake pedal inputs 7 Store Individual Characters wheel pos char message 1 wheel neg char message 2 gas char message 3 brake char message 4 The steering data employs both a positive and
48. battery as well as seen in Figure 14 The whole purpose of the core is to prevent eddy currents as the battery is being used to power the motors pw Figure 12 Ferrite Core Choke on RC Car Battery Developer Guide RC Camera Car P14226 A Figure 13 Ferrite Core Choke on RC Camera Battery 2 Filtering Capacitors Due to the use of H Bridges to control the motor speed there was a lot of noise on the power terminals of the motor shield which in turn caused all the pins to have the high frequency noise To remove this high capacity capacitors were added on the battery power terminal as well as the 3 3 volt and ground line on the Adapter Board These capacitors can be seen in Figure 14 and 15 below Figure 14 Capacitor Added Over Battery Terminals As seen in Figure 14 the center harness of the motor shield allows for connection of the battery power The left is connected to the positive terminal and the right is connected to the negative terminal of the battery The capacitor added is also seen in the figure Developer Guide RC Camera Car P14226 To the right can be seen the green screw in harness of the right motor The connections for this had to be reversed so as to make the car go forward as the motor on the right side is flipped The positive terminal of the motor is connected to the negative terminal of the harness and vice versa To the left can be seen a green screw in harness of the left motor The connectio
49. be used for driving on two wheels in the future while not negatively affecting the usability of the car for normal driving purposes Developer Guide RC Camera Car P14226 6 Front Transaxles a Length Calculation Since the wheels were larger the front wheels would now contact the chassis while turning if the original transaxle was kept Some geometry was done in mapping out the shape of the chassis and determining the length of the new transaxle A goal of 5mm clearance at a turning angle of 35 degrees for the inner wheel on a turn was assumed in the geometry as this was deemed to be the limiting case since the front bumper would not get in the way because it would need to be redesigned anyway An excel file was set up to iterate transaxle length given the parameters above and the radial distance inward from where the wheel rim met the transaxle and the inner edge of the tire which was 17 mm Front left Chassis shape mm Left turn 90 00 y 0 0089x 0 2145x 3 1826x 68 443 30 00 o 7090 Tire Bounds 6 _ Chassis 60 0 G fe clearance line Transaxle Tire Line 9 y 1 4281x 45 886 e 10 00 Qt tee e ees Poly Chassis oO seeeeeees Poly clearance IE line gt ii i Linear Transaxle eu Green dot is __ 2 30 00 F inner edge of eo i o tire i iii ii 0 7002x 1 7896 y 0 0091x3 0 0602x 1 7379x 55 452 6 0 09 25 00 15 00 5 00
50. changed from what they were originally This change can be seen below in Figure 3 ee J1 O Header a a TFC Controller Pins Used TFC Controller Pins Used SPEED SENSOR PTA 2 1 PTC7 SPERD SENSOR PTAZ 4 3 PTCO a J10 VO Header TFC Controller Pins Used PTO F PICS H BRIDGE TFC Controller Pins Used PTA12 PTC4 H BRIDGE PTE30 11 12 PTC1 H Bridge PTA4 U J PTCS Battery PTE29 PTC2 H Bridge PTAE PTC65 H Bridge PTE23 PTB3 POT1 PTCE amp PTCi0 H Bridge PTE22 PTB2 POT2 PTCS 6 PTC11 H Bridge PTE21 PTB1 Servo 2 H Brid PT 1 PT Steer Servo FRDM Board Pins FRDM Board Pins we E20 2 BO eering Servo FRDM Board Pins FRDM Board Pins J2 I O Header Pins for Xbee Perfboard TFC Controller Pins Used J9 VO Header TFC Controller Pins Used PTC12 ENCODER QRB1134 1 Line Scan Camera In ENCODER QRB1134 2 XBEE RX XBEE TX sw1 SW3 PTES V Battery Sw3 SW2 sw3 sw3 LEDs LEDs LEDs 7 PTDG Line Scan Camera In LEDs Pro FRDM Board Pins _PTD3S WU PTD 12 PTE1 FRDM Board Pins FRDM Board Pins FRDM Board Pins Figure 3 Freedom Board Motor Shield Jumper Modifications E Adapter Board An adapter board had to be made so as to be able to obtain access to certain pins on the micro controller board as the motor shield board restricted access to a majority of the pins This adapter board also enabled the placement of necessary passive devices such as pull up and pull down resistors for the encoder sig
51. ctions that were reinforced with other structures to provide a solid platform Little room was available for mounting electrical components on the original chassis and the position over the motor posed noise issues for the microcontroller A Lexan mounting plate that spans the entire chassis was created that increases the rigidity of the frame and provides ample mounting room for electrical components far away from motor interference areas The electrical components added that need to be accessed and monitored frequently were otherwise unprotected from outside forces A Lexan protection plate was mounted on standoffs above the electronics to allow for easy access from the sides while protecting from impacts from the top The car s existing bumper was very small and provided little protection Front and rear polyethylene foam bumpers were designed and added to the chassis that adequately protect the components from front and rear impacts Stock tires and wheels on the chassis did not provide adequate ground clearance for getting over small obstacles and did not allow for the addition on encoder functionality New tires and wheels with normal mounting connections for RC cars were purchased for the car Transaxles and a rear axle was fabricated to extend the car s track width to support the larger wheels and provide adequate room for 3D printed encoders to be mounted to the rear wheels Standard mounting
52. d utilized the pins in a manner that enabled easy access to various I O pins on the microcontroller board One important information to note is that all the external connections were done using combinations of male and female headers This helped the connection of the different inputs and outputs easy and removed the probability of an erroneous connection B Freedom Board Motor Shield The Freedom Board Motor shield is a shield that is used to control the motors and allow for other sensors such as speed sensors line camera and servos to be controlled This 1s mainly used in the Freescale Cup competitions but in order to be used for this projects use certain modifications were required Those modifications are described in the next Section This Section talks about the functionality of the shield as it arrived from the package Only parts of the shield that are still being used in the project are described below 1 Jumper Interface amp Pin Names The motor shield sits on top of the Freedom board and therefore occupies all the I O pins on the micro controller The different header names which will be referenced to in the later Sections of this guide are given below in Figures A Developer Guide Pro 2 freescale KL25Z 80 LQFP J1 I O Header J2 I O Header Reset KL252 USB RC Camera Car Capacitive Touch Slider J10 I O Header RGB LED J9 VO Header MMA84510 OpenSDA J10 I O Header J9 I O Header J1 I O Header J2 I
53. dition the outputs of the compensators are subject to the saturation blocks Note that the control loops work in m s this corresponds to a certain rotational speed of the motors which corresponds to a certain voltage but the DZ and Vsa values must be given in m s which means some experimenting must be done with motor pulse width modulation PWM values if each group is to determine values for itself Our version of this relationship is located in the vehicle parameters section The dead zone block in Simulink simply subtracts the DZ value for any input higher than DZ for positive inputs or relays a zero for signal less than DZ for positive inputs The velocity saturation blocks clip the velocity signal at the maximum minimum values given by Vsat and the torque saturation blocks clip the acceleration signal at the maximum minimum values given by Tsat The values for Vsar m s were obtained from the encoders as they simply correspond to the car s maximum speed at maximum PWM The values for Tsar m s7 were obtained from recording the velocity versus time data using the current arbitrary PWM cap in the car code The first few points were fit with a line to get obtain the maximum acceleration value Tsat m s The values for DZ were obtained while the car s wheels were on the ground by feeding increasing PWM values to the motors until the car began to move The value of DZ in m s is obtained from multiplying the motor s fractional PWM va
54. e Dim chtObj As ChartObject For Each chtObj In ActiveSheet ChartObjects chtObj Select ActiveChart Axes xlCategory MinimumScale tstart ActiveChart Axes xlCategory MaximumScale tstop Next Unload Me End Sub Private Sub CommandBucton2 Ciick Unload Me End Sub Private Sub Labell Click End sub Private S00 UserForm Initialize Empty NameTextBox TextBoxl Value Empty PhoneTextBox TextBox2 Value Ena Sub e Saving Data Macro Finally the save data macro is called in Module as below Sub ShowCoOM makes the COM block visible Sheets COM Shapes StrokeReaderl Visible True Developer Guide End Sup RC Camera Car P14226 The actual code is found in Module 2 as below The macro copies and formats the data to a new Sheet and formats the headers Sub savedata Dim WS As Worksheet Set WS Sheets Add copy paste and format data Sheets COM Range A F Co PY WS Range A F PasteSpecial Paste xlPasteValues WS Range A A NumberFormat 0 000 WS Range B E NumberFormat 0 00 WS Range F F NumberFormat 0 0 WS Columns A E ColumnWidth 15 6 WS Columns F F ColumnWidth 19 WS Columns G G ColumnWidth 20 Format headers With WS Range A G HorizontalAlignment xlCent VerticalAlignment xlBottom WrapText False Orientation 0 Addindent False IndentLevel 0 ShrinkToFit False ReadingOrder xlContext Merge
55. e Zero sigd falltecenter The while loop then runs indefinitely for transmitting data The 20 ms wait time is setup to mimic the car code wait times used in the PID loop This value was established experiementally through testing and works very well for smooth vehicle turning without overloading the transmissions while true XBee Data Transmission wait 0 05 data tx rx speed control The pulse count of the encoder is then sampled and stored with 624 pulses for a full revolution or one side of the steering stop to the other The gas and brake pedal values are then captured and converted to values between 35 and 126 for transmission purposes This gives adequate resolution for user input The range of 35 to 126 was established so that no bad characters are sent that interfere with communications reading and writing such as carriage return new line and quotes Record steering values wheel int int wheel getPulses Record pedal values and conver to character ranges gas int 126 gas pedal read u16 15000 500 should output 35 126 brake int brake pedal read_ul6 15000 460 35 should output eea S Developer Guide RC Camera Car P14226 Wheel pulses inside of the range 650 to 650 are then converted to positive or negative characters if the wheel is clockwise of center or counterclockwise of center respectively This is done to give the steering wheel effectively twice the range of values for greater resol
56. e sense to have a rigid chassis to which the electronics are mounted so these components were removed PROPRIETARY INFORMAT As can be seen many parts were removed and the result gave considerably more open space on the chassis The plastic T bracket was secured using two 8 32 flat heat screws with nuts and washers to prevent movement between the two sections This design is further reinforced by the adapter plate noted later which connects the front and rear chassis sections through standoffs 2 Servo Position Adjustment After some preliminary testing it was noted that more room would be available in the front of the car for bumper mounting and standoffs if the servo was reversed in orientation on the chassis The provided plastic servo mounting blocks also became loose frequently and required excessive work to fix Aluminum L brackets were used along with left over screws and nuts from the kit Developer Guide RC Camera Car P14226 to mount the servo in a reverse orientation using two of the holes already available in the chassis Two small plastic tabs had to me snipped off of the back of the servo screw mounts and two more holes were drilled directly in front of the mounting holes for increased support The new design allows for easier component removal and service and provides the same turning capabilities as the original mounting configuration 3 Prototyping Plate The hole layout of the original chassis was not suitable for ei
57. ea to explore in future work but for the time being we are only concerned in comparing the signal we are applying to the setpoint of the control loops left and right target speeds as calculated by out speed and in speed assigned using the steering logic with the wheel speed from the encoders that we are using as the process variable in the control loops This allows us to see the square value inputs we are applying against the actual speed we are seeing from the encoders Convert Throttle Data gas float gas int 92 brake int 92 If gas float lt 0 25 And gas float gt 0 25 Then Pedal spring does not always bring pedal back to zero gas float 0 End If If gas float gt D Then going forward implement PID control PLD Calculations out_speed max speed gas float 1 0 3535 Tan steerplus tangential speed of outer side of car ft s in Speed max speed gas fLoat L 0 353 Tan steerplus tangential speed of inner side of car ft s Developer Guide RC Camera Car P14226 If wheel float lt 0 Then turning left left target speed in speed showing target max speed in m s right target speed out speed Else turning right Lert target speeo Out speed right target speed in speed End If Bleeli gas float 0 Then stopped write motors to not move out speed 0 in speed 0 left target speed 0 right target speed 0 Elge going in reverse Just use the gas float scaled left targe
58. ecause of its minimal bit size The char type is 8 bits versus the integer type which is 32 bits Since wireless bandwidth should be conserved characters use 1s critical in order to maximize message throughput The code first calls the libraries and initializes the PC USB and XBee TX PTD3 and RX PTD2 communications It then sets up to read analog in values on PTB1 for the gas pedal PT BO for the brake pedal and reads QEI values using PTD5 and PTDO with 624 pulses per revolution based on testing PTA13 is setup as an interrupt pin for the zeroing signal and sets PTB8 as a digital in pin for enabling and disabling two way communications using the switch in the console j Libraries Finclude mbed h tinclude OGEIT n SERITAL Information Serial po USBIX USBRXJ Serial XBee PTD3 PTD2 int baud rate 9600 CONSOLE PIN Information Ama Login gas pedal PIB1 Analogin Drake pedal PTBO QEI wheel PTD5 PTDO NC 624 Tnterruptin zero sig PTAL3 DigitalIn enableTwo PTB8 toggle two way communication The wheel range is initialized at 650 to make sure that the values of the wheel are always inside the range since sometimes the count gets a bit messed up at higher turning speeds Then the wheel gas brake and encoder variables are initialized CONVERSION Variables Steering Wheel int wheel range 650 established through testing larger than actual range so no characters are lost int wheel in
59. ed 1 exp 17 For a total system weight of 1670 grams only affects time constant and a max speed of 0 95 m s the time constant was fit to be 1 4s Developer Guide RC Camera Car P14226 Speed Data Left Encoder Speed m s Right Encoder Speed m s Left Target Soeed m s Right Target Speed m s ome Curve FIT 3 00 2 50 Speed m s 1 000 3 000 5 000 7 000 9 000 11 000 Time s The above data is unfiltered and PI control was off The curve fitting was done by manually iterating the time constant as Excel s least squares approach was biased toward the earlier parts of the curve due to the higher slope and greater data point density as the car was moving slower In addition the noise would also throw off the least squares fit Only the left wheel was fit since it was not exact and the data from each wheel was very close 2 Control Loops The Simulink model is continuous in time and relies on signal generators for steering angle 6 in degrees and left and right input wheel speeds in m s The user can make these whatever he she wishes as long as 0 lt V lt 6 and 35 lt 6 lt 35 The system parameters are already in the Simulink model and once the input is given it goes through Eq 3 8 The feedback loops then operate on the reference speeds for the left V7 and right V wheels The control loops are unity feedback with a PID compensator a torque saturation Tsart fo
60. eld This also allowed access to the male pins through the female dual line headers a a U a ee eS gt AN T Oe ae ae 2 XBee Figure 6 Sitting Harness for Adapter Board The XBee module is used to communicate between the MOMO steering wheel and the RC car One of the XBee receiver transmitter modules had to be fitter on the RC car and was harnessed on the Adapter Board The XBee module was placed on female header pins as shown in Figure 7 below and was powered and connected by the input bus connections The only connections required were the power ground transmission and receipt Table 2 shows the pin layout Table 2 XBee Pin Connections Pin Functionality XBee Pin Number Jumper Number Jumper Pin Number Power Vcc 1 J9 8 Ground 2 J9 14 RX 10 J2 8 TX 3 J2 10 Figure 7 below shows the female harness for the XBee This harness requires the XBee to be placed in a certain direction so as to operate correctly The direction is induced by a sticker on the final Adapter Board Developer Guide RC Camera Car P14226 oee o0o0000000C Figure 7 XBee Harness 3 Input Bus The input bus is simply a collection of wires connected to a single line female header These wires carry the input signals from the various sensors and modules such as the encoders Freedom Board servos power etc Figure 8 shows the different input busses that are in use ss
61. emove any unnecessary signals coming in from the motor shield board due to prior connections Figure 1 shows the external wires that were attached to the Freedom board directly Developer Guide RC Camera Car P14226 Figure Motor Shield Direct Wiring Pin Functionality Pin Alias Jumper Location Jumper Pin Number Left Encoder Input PTAI3 J2 2 Right Encoder Input PTDO J2 6 XBee Receive PTD3 J2 10 XBee Transmit PTD2 J2 8 D Motor Shield Modifications Addition of Headers Originally the motor shield utilized the I O pins by enabling access to them with the use of certain male headers These headers were designed to perfectly accommodate for the sensors required to compete in the Freescale Cup These sensors were the Line Scan cameras speed Sensors and servos Additional male headers were added to fill both the slots on the motor shield board as can be seen in Figure 2 below These headers enabled the operation of two servo control signals one for the steering and one for the RF camera attached on the car Figure 2 Additional Headers on Motor Shield The servo headers can be seen on the right and are labeled n the board with serial numbers O and 1 The 3 pin female headers are attached to the servo wires and they connect to the male adapters Developer Guide RC Camera Car P14226 on the adapter board The motor shield jumpers were modified for access to custom sensors The jumpers on the motor shield were
62. er teeth were moved closer to the wheel hubs to provide optimum spacing with the optical sensors mounted on the back The color was also changed from black to white to obtain better values from the photo sensor In addition the hex was widened by about 0 5mm to eliminate slop The inner diameter of the encoders were drilled out with a 7 drill to 0 201 5 1mm to allow them to spin freely on the alignment rod Depending on the material used in 3D printing the interface between the encoder and hub may be tight and require minimal amounts of material to be removed to slide on easily For the CAD model check out Encoder Wheel Mount rev2 To download any CAD file right click the Display link in the CAD directory and choose Save link as This will save a SLDPRT or SLDASM file to the desired location The new encoders were made larger so that the optical switches could read the rotational data while being mounted rigidly to the chassis with screws The design also allowed for adjustability in the disk to switch distance which was set at the optical 3mm gap The connecting wires had to be replaced with more flexible connections to accommodate wiring constraints on the chassis Be careful when drilling the screw holes into the side of the plastic where seen below There is limited extra material in this location so size the mounting screws and tighten appropriately Developer Guide RC Camera Car P14226 8 Rear Axle Alignment Rod A
63. ervo to the center position is by feeding it power ground and a PWM signal The easiest way to do this is using an Arduino but since this is not a Freescale item I will not go into much detail Anyway this Youtube video gives you the code you need to center a servo with an Arduino Uno and additionally you can just modify the sample code for the Sweep Arduino Example to do this The example is helpful because it will show you the full range of motion of the servo giving you an idea of what can go wrong These servos only spin 180 degrees so 1f you don t mount the connecting pieces so that the wheels are straight when the servo is at the center you might limit your turning capabilities in one direction of burn out the servo Remove any existing servo horns and screws when you understand the servo s range of motion When everything is centered in looks right you should see something like the images below MAKE Developer Guide RC Camera Car P14226 SURE THE TAB POINTS TO THE SAME SIDE OF THE SERVO AS BELOW OTHERWISE YOU WILL HAVE TO MOUNT THE OTHER COMPONENTS IN THE OPPOSITE ORIENTATION Lr oy You will need the pieces shown below You will screw this into the servo Pieces are notched so assembly is straight forward Mount the yellow servo plate assembly to the servo as shown below Make sure to add the small yellow washer pictured below in between the servo plate and the screw Tighten well a servo produces a good amount
64. es our target speeds Legend and y axis limits ActiveChart SetHlement msoElementLegendTop ActiveChart Axes xlValue MaximumScale 2 ActiveChart Axes xlValue MinimumScale 0 Change target speeds to lines not points ActiveChart FullSeriesCollection 4 Select With Selection Format Line Visible msoTrue ForeColor ObjectThemeColor msoThemeColorAccent2 ForeColor TintAndShade 0 ForeColor Brightness 0 End With Selection MarkerStyle 4142 ActiveChart FullSeriesCollection 3 Select With Selection Format Line Visible msoTrue ForeColor ObjectThemeColor msoThemeColorAccentl ForeColor TintAndShade 0 ForeColor Brightness 0 Transparency 0 End With Selection MarkerStyle 4142 Developer Guide RC Camera Car P14226 Next End Sub d Trimming Data Macro Similar to the plot macro above this macro is only used when trimming data and was recorded using Excel s macro functionality It uses the User Form that can be found under VBAProject File_Name gt gt Forms gt gt TrimPlotUserForm and is displayed by clicking the button on the main sheet Sub TrimPlotData trims the maximum and minimum time on the chart to focus on an area of interest TrimPlotUserForm Show End Sub To access the code you must open the above mentioned form right click the form and click View Code It is as seen below Private Sub CommandButtonl Click tstart Val TextBoxl Value tstop Val TextBox2 Valu
65. et speed gas float 4 0 5f 0 5 0 75 speed ok for reverse rignt target specd left target speed Finally in one write the motor speeds are actually written to the motor encoders Here there is also some debugging code for printing the values back to a putty terminal window Writing Motor Speeds and Debugging TPC SetMotorPWwM right target speed deit target speed 7 PC PEIMEL SC CeC Cee Cec La Zr ie Zi es 2i n e wheel pos har wheel neg chargas char brake char das Tloat wheel float s ervo Iloat ERN e a a A a a aa a a ek ih tr pulsewidth Leit med pulsewidth right med ert wheel speed r ight wheel Speed out Sspeed in pead delt target Speed right ta roget speed 7 PC PLAICE ai 20 ie Ze ee Ze ea Ze ee 2 eer ee om sie t wheel specd right wheel specd gqas Iloa touL speed in speed 1 eit target specu ight target Speed if readable Mentioned above if the car loses data reception the car needs to be written to stop so that it does not take off with the last command given to it else if data lost stop car movement completely TEC SetMotorPwM 0 0 7 TBC SeloeEevo servo Choniel Vsz2o 7 TEC SeGUSerVO Camera Channel U 26r 7 else readable while loop main loop Developer Guide RC Camera Car P14226 VIII Testing A Uploading Code There are separate codes that have been developed in MBED for the console and car which can be uploaded to the KL25Z boards on the car and console using t
66. f the Freedom Board to the Freescale Cup Car see the video below as it proposes the easiest solution with parts provided 3 Line Scan Camera Similar for our project the line following camera was not needed for anything so little was done in the mounting of this component The method seen below from the link above is the easiest way to mount the components with some of the parts provided which seems to just use the servo attachment posts and some L brackets These brackets can be purchased from Parallax for cheap here or from Home Depot here For reference previous teams have needed to mount the camera significantly higher for viewing area but this can be done by adding a post between the L brackets and camera The rest is up to you Bi To attach the camera we found useful to prepare two metal L shaped pieces made from aluminum With the help of black plastic distance posts already available in the kit and these metal stands you may freely change the position of the camera over the surface See link above in header for CAD files Developer Guide RC Camera Car P14226 B Modifications 1 Suspension Removal The first design feature that was deemed useless for our project goals was the rotary joint suspension system implemented on the back of the car This allows for three wheels to be on the ground when going over uneven terrain but due to the ground clearance of the car this effect cannot be realized For our purposes it makes mor
67. float right wheel speed float out_speed floot in speed figat leit Target speed float right target speed The hardware information declares the variables used by the switches potentiometers servos and battery level reader The steering and camera servo center defaults are declared separately so that they can be modifed in the future without issue HARDWARE Information ing SWLECh Setting int steering pot 0 int Cap pot 1 Developer Guide RC Camera Car P14226 int servo channel V int camera channel 1 float steering center default 0 25f adjustable center steering servo position value float camera center default 0 25f adjustable center camera servo position value clog Camera scale rilor steering scale float steering pot value float Cap pot value Pieat battery volti figat stesring center LlLoaw cap The serial communication from the XBee is initialized with TX on PTD3 and RX on PTD2 The pe serial can also be enabled for debugging but this interface cannot be used at the same time that the board is powered with the battery so debugging is limited on the car currently The baud rate variable was added for quick modification The unsigned characters correspond to these values read in from the XBee to be converted to user input The encoder left and right integers are used to send data back over the XBees to the console SERIAL Information Serial XBee PTD3 PTD2 int baud rate 9600
68. gned char encoder right int else Finally the wheel speeds seen are written to 0 if the max pulsewidth is currently being seen For any other values the pulsewidth is converted to m s using the formula developed in the Physics Section based on the geometry of the encoder ENCODER Conversions if pulsewidth left med max pw left wheel speed 0 else left wheel speed 16 83 pulsewidth left med if pulsewidth right med max pw right wheel speed 0 else right wheel speed 16 83 pulsewidth right med The gas float value 0 to 1 is established by taking the relative difference between the gas and brake characters This was a simple coding solution that allows for no output to the motors when both pedals are being pressed as a safety Developer Guide RC Camera Car P14226 During testing with the car a deadzone for the gas pedal was required This was caused by the spring used to return the pedal to the zero position being too weak which sometimes lead to static input values without the user even touching the pedal This was accounted for in the coding through testing by ignoring inputs below a certain limit 0 25 The modification was done here as it is most effective to account for after all other data conversions have been completed THROTTLE Calculations gas float int gas char 92 0f int brake char 92 0f if gas float lt 0 25 amp amp gas float gt 0 25 Pedal
69. he direction found in Section VII These codes are also documented in Section VII so that changes can be made for future modifications B Logging Data 1 Serial Data The design of the car and console code is to transmit data back to a computer as serial over a USB cable connected to the Open SDA port of the console KL25Z This data comes in the form of six characters followed by a new line and a carriage return that represent the following quantities Carriage Return N A N A Encoder Left Char Left Encoder Pulsewidth 35 126 Encoder Right Char Right Encoder Pulsewidth 35 126 Wheel Pos Char Scaled Wheel Displacement CW 35 126 Wheel Neg Char Scaled Wheel Displacement CCW 35 126 Gas Int Scaled Gas Pedal Displacement 35 126 Brake Int Scaled Brake Pedal Displacement 35 126 New Line N A N A 1 2 3 4 5 6 7 8 Characters two and three come directly from the car over XBee recorded as the pulsewidths seen between encoder falling edges in milliseconds Characters four through seven are the same values as those sent to the car from the console based on user input from the steering wheel gas pedal and brake pedal The first and last character are for data formatting The character ranges of 35 126 were established based on the unsigned character limitation with normal ASCH characters The minimum of 35 was established to not try and use any bad transmission characters new line carriage return etc along
70. hile 0 varies from 120 degrees to 120 degrees 6 0 2 Use steering angle 6 to determine turn the radius R The no slip assumption implies that this is a low speed turn which assumes that lateral forces are negligible and the turn radius is independent of the car s speed _ _ lm tan 6 deg 3 Note that if the steering angle becomes zero R will tend toward infinity In order to avoid this the code simply contains an if statement that says if lt 0 001 then 6 0 001 This will result in a turning radius so large that the wheels will spin at the same speed but the code will believe the car is turning right Use the known track width w in meters to determine the radius of the turn as seen by the inner Ri and outer rear Ro wheels in meters Ro m R 2 4 Use forward speed input and central turn radius to get the angular speed of the car through the turn w 4 Developer Guide RC Camera Car P14226 Use the rigid body assumption all parts of car have the same angular speed through the turn at a given time to map the inner Ai and outer Ro radii to an inner and outer tangential speed nE Rim o 7 vE Riim wf 8 S These tangential wheel speeds are what the PID loops use as the set points Equations 3 8 are useful for debugging purposes as the intermediate values have easy to grasp physical meanings however equations 3 8 can be reduced to n
71. hout issue with damaging the battery These batteries do not have a quick charge time 2 4 hours so two batteries are supplied with this car so that one can be charged while the other is being used The camera and video transmitter on the car are powered by a separate 3S 35C 11 1V LiPO battery pack This battery pack is estimated to have a run time of two hours and we have an additional battery pack for continuous use of the system The batteries are charged with the silver Tenergy balance charger simply plug the white connector into the four pin connector port Make sure the switch 1s set to LiPO and the 1 4cells Li Po LiFe LED will be red while charging and green when fully charged Developer Guide RC Camera Car P14226 II Physics Theory Torque Vectoring for Cornering Performance A Goal Define a desired wheel speed input signal to serve as a reference signal in the tangential speed control loop for the inner and outer wheels on a turn Use these reference speeds to change the left and right wheel speeds to alleviate wheel slip through turns B Assumptions e No slip e Car moves as rigid body through turn C Inputs e Tangential forward speed of car generated from throttle input e Steering angle angle of front wheels D Notation p Variables R radius m V tangential velocity m s w track width of vehicle m b wheel base m steering angle of front wheels deg angular speed through tur
72. ht char As String Dim wheel pos char As String Dim wheel neg char As String Dim gas char As String Dim brake char As String Calculation Integers Dim max pw As Integer Dim encoder left int fe Integer Dim encoder right int As Integer Dim wheel pos int As Integer Dim wheel neg int As Integer Dim gas int As Integer Dim brake int As Integer Dim pulsewidth lert val As Integer Dim pulsewidth right val As Integer Calculation Doubles P olie time rer AS Double global reference Line reset when connection checked Dim max speed As Double Dim time system As Double Dim time sample As Double Dim left wheel speed As Double Dim right wheel speed As Double Dim wheel float As Double Dim gas float As Double Dim steerplus As Double Dim out speed As Double Dim in speed As Double Dim left target speed As Double Dim right target speed As Double b Received Data The program starts at the Private Sub line and the general structure is a set of cases that correspond to events caused by checking connect or unchecking disconnect the Connect box in the ActiveX control When the connection is disconnected you can see that the program simply runs the plot macro which will be documented later When the connection is connected the program selects all of the existing data in columns A through E and clears the contents It also initializes the cell row index for printing the first line of data the reference time Timer is an in
73. ide RC Camera Car P14226 2 Optical Gate The centering on the wheel is done by utilizing the signal from the optical encoder attached at the axle of the wheel There is a white reflective strip present which triggers the optical sensor whenever it passes by the receiver transmitter to detect that the wheel has been centered Originally with the windows software installed the steering wheel would go into a centering reset routine where when the white strip would pass over the optical sensor and the motor would stop rotating and record that as the center position rt Agilent Technologies SUN FEB 09 03 16 47 2014 Measure Current Mean Min Max Std Dev Count Freqi No edges 6 8585Hz 1 060Hz 29 000HzZ 8 4517Hz 19 Pk Pki 4 94V 2 2261V 500mV 5 90V 1 4842V 224 Mint 130mvV 2 9941V 600mV 4 25V 1 5213V 224 mm No edges Pk Pki 4 94V Mini 130mV Select Measure Settings Clear Meas Statistics r Min Min E lt lt w Steering Wheel Centering Reflective Strip Steering Centering Optical Sensor Signal Since the windows software was not being used raw signals from the pins of the encoder were to be recorded Whenever the white strip as seen in Figure 3 passed over the optical sensor there was a sharp drop in voltage detected This drop can be used to determine that the center position has been achieved and the encoder count set to zero at this point With the center determined the direction pulled from the diodes and the e
74. in MBED lt the best reference is the handbook dedicated to the board The major steps required in setting up the board with any new computer are as follows 1 Upgrade to the latest firmware 2 Install the Windows serial port driver 3 Create and download a program to the KL25Z 4 Press the reset button to run the newest program A Coding Logic Flow Chart The following UML was created to show an overview of the coding done in this setup This shows the interplay between the console and car microcontrollers along with the libraries used for on each system Console void initialize PidControllers void void ts_left void ts_right T void encoder_thread_left void const args void center int main P l y void encoder_thread_right void const args void TFC_TickerU pdate i RTOS Thread int main Je eo ew ow ow ow ow ow ow ow ow ow oe d QEI PinName channelA PinName channe lB PinName index PID float Kc float taul float tauD float interval _TFC_LHBRIDGE ENABLE i c int pulsesPerRev Encoding encoding X2_ENCODING void setinputLimits float inMin float inMax void TFC_Init void reset void void setOutputLimits float outM in float outM ax uint8_t TFC_GetDIP_Switch int getPulsed void void setTunings float Kc float taul float tauD float TFC_ReadPot uint8_t Channel void reset void void TFC_SetMotorPWM float MotorA float MotorB void setModelint mode void TFC_SetServoluint8_t
75. ine Visible msoTrue ForeColor ObjectThemeColor msoThemeColorAccent2 ForeColor TintAndShade 0 ForeColor Brightness 0 End With Selection MarkerStyle 4142 ActiveChart FullSeriesCollection 3 Select With Selection Format Line Visible msoTrue ForeColor ObjectThemeColor msoThemeColorAccentl ForeColor TintAndShade 0 ForeColor Brightness 0 Transparency 0 End With Selection MarkerStyle 4142 Next The rest of the code makes the window into which you input the saved data name and creates the text box on the new sheet accordingly Sheets COM Activate Re selects the COM worksheet Make a note on the circumstances of your data note InputBox Input the scenario this data represents Data Description WS Range G1 WS Range G2 This data was recorded Now Add a textbox with the note in it Dim shp As Shape Set shp WS Shapes AddTextbox msoTextOrientationHorizontal 100 100 200 50 add shape With shp TextFrame Characters Text note add text to display Top Range J1i Top fac just top Left Range J1i Left adjust left TextFrame AutoSize True turn on autosize Fill ForeColor RGB RGB 255 255 204 ehoose Till calor Line Weight 1 adjust width Line ForeColor RGB RGB 255 0 18 choose color Line DashStyle msoLineSolid choose style End With Developer Guide RC Camera Car P14226 End Sub C Implementing Model Changes On the car you can turn on
76. ize 14 Italic msoFalse Kerning 12 Name 4 mn 1t UnderlineStyle msoNoUnderline Spacing 0 Strike msoNoStrike Bnd With ActiveChart SetHlement msoEKlementPrimaryCategoryAxisTitleAdjacentToAxis Selection Caption Time Selection Format TextFrame2 TextRange Characters Text Time s With Selection Format TextFrame2 TextRange Characters 1 8 ParagraphFormat TextDirection msoTextDirectionLeftToRight Alignment msoAlignCenter End With With Selection Format TextFrame2 TextRange Characters 1 8 Font BaselineOffset 0 Bold msoFalse NameComplexScript mn cs NameFarEast mn ea Fill Visible msoTrue Fill ForeColor RGB RGB 89 89 89 Fill Transparency 0 yd bw SOLO Size 10 Italic msoFalse Kerning 12 Name 4 mn 1t UnderlineStyle msoNoUnderline Strike msoNoStrike End With ActiveChart Axes xlValue Select ActiveChart SetElement msoElementPrimaryValueAxisTitleNone Developer Guide RC Camera Car P14226 Selection HasTitle True ActiveChart Axes xlValue xlPrimary AxisTitle Text Speed m s Again the new chart y axis limits are set here which could be modified to be more efficient Legend and y axis limits ActiveChart SetHlement msoElementLegendTop ActiveChart Axes xlValue MaximumScale 3 ActiveChart Axes xlValue MinimumScale 0 Change target speeds to lines not points ActiveChart FullSeriesCollection 4 Select With Selection Format L
77. k 1 5K PTC11 5V USB OUT i White PTA13 P3V3 Yellow PTA20 Yellow PTDO P3Vv3 Ey R1 0 Blue PTD2 SDA PTD 0 Dark Green PTD3 PTES TKI TXO 10 PTD1 PTE4 RXO Level RXI Gi GND PTE3 LV Shifter HV 1u VREFH PTE2 GND GND PTEO PTE11 RXO RXI PTE1 PTE10 FE TXO PTC12 PTE9 PTC13 PTE8 PTC16 PTC17 PTA16 O PTA17 PTE31 NC PTD6 PTD7 Xbee RX Blue Mbee TX Dark Green Above is a schematic that represents the connections made in the MOMO console These connections are made to enable the sensors in the MOMO console to communicate safely with the FRDM Board The FRDM operates at 3 3 V for most of its input signals while the MOMO console s sensors operate at 5V To protect the FRDM board the above circuitry has been designed For the Encoder 1 amp 2 Gas Pedal and Brake Pedal a resistor network was created The Wheel Centering Signal requires a level shifter A level shifter is a series of MOSFETS and resistors designed to step up or down a voltage to the desired range In this case the level shifter is only being used in one direction and it s to step down the centering signal voltage to 3 3 V Developer Guide RC Camera Car P14226 The level shifter requires two different voltage supplies to operate The HV High Voltage pin is connected to the power supply from the MOMO console This was previously attached to FRDM board s power supply but it was found that the FRDM did not provide enough current to make the output signal fr
78. lly for RC planes that normally operates using a battery for power Because of this on startup the module will beep a number of times corresponding to the number of cells of the battery input voltage and will continue to beep if the voltage drops below some specified levels Being as in our application the module is powered by a wall DC converter the voltage was dropped to within the specified levels for a 2S LiPo battery as specified in the user manual This was done using a simple voltage regulator circuit The kit comes from Ready Made RC and can be found here Consult the user manual if the video is not being broadcast as the button on the front of the module scrolls through the available channels if pressed and simply needs to be pressed into the correct channel is found again As a final note during operation the receiver will get slightly warm which is expected and does not cause issue The current setup of the wireless video involves plugging the receiver through the DC barrel jack into the DC wall converter labeled Video RX The wiring harness is then plugged into A V 1 on the video receiver and the yellow RCA on the left hand side of the screen ok ey 5 y Hi E i Developer Guide RC Camera Car P14226 To see the image being broadcast the TV channel has to be adjusted to Video This is done using the Channel and keys on the right hand side of the monitor The selection options in order of decreasing
79. location for the servo on the chassis was inconvenient used weak components and in the way of more useful supports for the Lexan mounting plate The servo orientation was reversed and more robust mounting brackets were used to mount the servo for easy accessibility Fabricated rear axles was making a squeaking noise while turning from rubbing on the inside of the encoder plastic Grease was put on the rear axle that reduced the noise completely and reduce rolling resistance Encoder optical switches were not reading the same values The switches were moved so that an optimal distance of 3 mm was achieved between the emitter and encoder face The mounting locations are somewhat adjustable to accommodate this issue Encoder optical switch wires were very stiff and could not be used with chassis Wires replaced with flexible speaker wire and servo headers for easy connection to the XBee shield Quick connection of the light camera battery and voltage monitor were necessary for quick change out Velcro was used to secure both components in a minimal configuration Developer Guide RC Camera Car P14226 Multipath interference was targeted as the cause of noise in the camera signal The transmitter was mounted as high as possible on the console and the transmitter was moved to the highest point on the car to reduce the number of objects in the way of the signal path between these components
80. ls are attached to potentiometers which vary the voltage according to the depression in the corresponding pedals These voltage values can easily be read and calibrated to determine the depression to voltage value and accordingly use to set the PWM increase or decrease in the motor signal The pin outs can be seen below in the figure GAS http www tytlandsvik no momo Pedal Pin Layout 4 Communications Switch As final modifications to our system based on testing a switch was added to the console that switches between two way communications scanning the received data on the console and one way communication to the car This switch connects PTB8 to ground on the console K1I25Z This was added due to the fact that enabling scanning seems to cause the XBees to occasionally lose communications Since this functionality is only needed for data logging this switch makes it considerably easier to demo removing the need to upload new code We were unable to resolve this issue with the communications but it would be an area to investigate in the future On P14226 RC Cam m Southert On Briar Meehan Lalit Ta Or era Car a vex Reid mwar Matthew hag Developer Guide RC Camera Car P14226 C Video RX The video from the RC car camera is transmitted over RF at 5 8 GHz well outside the range of most other wireless communication protocols to the receiver module on the console This module is a Uno 5800 module designed specifica
81. lue at the edge of the dead zone by the maximum speed of the car in m s Developer Guide RC Camera Car P14226 4 Logic Lastly the Simulink model must decide which reference velocity to send to the left right wheels This is accomplished by using a variable called sig which equals 1 when gt 0 and equals 0 when 6 lt Q So sig is 1 when the vehicle is turning right Sig is defaulted to read to the right due when 6 0 to avoid the turn radius going to infinity Sig is then used as the switch criterion for the two switches required before the control loops to determine whether left or right is inner or outer On a right turn right will be the inner wheel IV Console Electrical Information The driving console Logitech MOMO steering wheel features a KL25Z microcontroller More information about this microcontroller can be found at the MBED handbook page The wheel is powered with the stock USB connector and the signals from the different internal components are conditioned and fed into the microcontroller A Electronics Modifications 1 Schematic ENCODER 1 Dark Green ENCODER 2 Blue GAS PEDAL Light Green PTA1 RTC CLKIN BRAKE PEDAL Grey R5 PTA2 PTC2 CENTERING SIGNAL Yellow PTD4 PTB3 SV MOMO Power Supply Red PTA12 PTB2 PTA4 PTB1 Green PTAS KL25z PTBO Blue PTC8 FRDM BOARD PTE30 PTC9 PTE29 PTC7 PTE23 PTCO PTE22 PTC3 PTE21 PTC4 PTE20 1 5k PTC5 VIN R2 PTC6 GND PTC10 GND Blac
82. male headers each internally connected to the appropriate I O pins Figure E shows the connections for the steering servo This is similar to the additional servo connection available To control the servo the necessary signals required are the power source ground source and input signal source The camera servo had the same schematic except for the signal line being PTB1 instead of PTBO STEERING SERVO V_BATTERY Ey J12 40454 3 Figure E Servo Connections C Freedom Board Modifications Removal of Pins amp Direct Connections Certain pins had to be removed from the motor shield and direct connections had to be made so as to enable the use of the encoder signals to accurately calculate the speed of the rear wheels as well as to accommodate for the sending and receiving of data by using an XBee Table 1 shows which of the pins were used removed and the function implemented on those pins The pins were chosen in such a manner that after the removal of the connection between the motor shield and the Freedom board there was no loss in original functionality Only the pins removed for XBee transmission and receipt of data affected the original functionality as those pins were being utilized for the Line Scan camera This however did not affect the operability of the car since the Line Scan camera is not utilized for the purposes of this project The removal was necessary to avoid any cross talk between the motor shield s H Bridge and also to r
83. mm hex to transmit torque So an adapter to go between these two shapes had to be designed Since there was currently no good way to measure wheel speed on the original chassis it was decided that these new adapters for the rear wheels would also act as encoder disks The concept for out encoder design stems from a commercially available speed sensing encoder set that can be found here The optical gates used for this project were donated and datasheets can be found here These are reflective optical switches that are to be mounted to the chassis facing the encoder A prototype of the encoder idea was 3D printed before new front wheels were considered for testing purposes and design feedback This design was later updated when the new wheels were added For the CAD model check out Encoder Wheel Mount To download any CAD file right click the Display link in the CAD directory and choose Save link as This will save a SLDPRT or SLDASM file to the desired location Developer Guide RC Camera Car P14226 b Second Iteration In order to provide a platform for balancing on two wheels the track width of the front and back wheels had to be the same The new front transaxles and wheels put the new track width target at 8 4 The new encoders had to be designed to meet the same value for the rear track width The position to mount the optical sensor also changed So between iterations the encoders got longer larger in diameter and the encod
84. n rad s e Subscripts r right side of car l left side of car i inner side of car on a turn o outer side of car on a turn No subscript means the variable applies to the center of the car Developer Guide RC Camera Car P14226 E Vehicle Parameters Parameter Symbol Value Wheel Base 0 1981 Track Width 0 1397 Tire Radius 0 0356 Time Constant 1 4 Total Weight 1670 Steering Angle 35 lt lt 35 Tangential Velocity 0 lt V lt 6 ideal Dead Zone 2 78 0 5 PWM Velocity Saturation DZ 1 52 0 75 PWM Torque Saturation DZ 0 7 0 75 PWM 1 Saturation and Dead Zone values Note that the Dead Zone value DZ is reported by what speed the 0 5 Pulse Width Modulation PWM corresponds to ideally as that is the PWM required to get the car moving while it is on the ground The Saturation values Vsat and Tsat reported in terms of Saturation minus the Dead Zone for convenient use in Simulink since the control loops in the Simulink model are in terms of m s the placement of the saturation blocks immediately after the compensators requires that dead zone already be taken into account The value of Tsat was obtained from the graph in the System parameters of the Controls Application Section The method used to determine Tsat can be found in the Non linearities section Also note that the motor saturation is arbitrarily capped at 0 75 PWM instead of 1 0 PWM This is done as 1 0 PWM i
85. nals It also housed pins that provided power and ground On top of this adapter board an XBee module was also placed To access the trimming potentiometers placed on the motor shield two holes had to be drilled into the Adapter Board These can be seen in the figures below as well k Fn ae en ell D ee ay WY VW YY oF ec Figure 3 Adapter Board Top View Figure 4 Adapter Board Bottom View The schematic for the adapter board can be seen in Figure 5 below This schematic was made in CadSoft Eagle 6 5 software In the center can be seen the XBee module To the top are the JP10 and JP9 headers Also on the extreme top is the capacitor and switch additions described in later Sections fitted across the battery The battery used was a 7 2 Volt 3000 mAh NiMH battery pack The extreme bottom has the other side of the jumpers from the motor shield to which further input and output signals are made Towards the right can be seen the speed encoders which are actually attached externally to the wheels ppeed Encoder IN 1 Figure 5 Schematic of the Adapter Board 1 Placement of Adapter Board The adapter board was placed on top of the motor shield This required some modifications which were described in the previous Section by the addition of male headers A harness as can be seen in Figure 6 below was attached on the Adapter Board and it sat perfecto on top of the male pins of the motor shi
86. ncoder Input Bus Described previously and with the pin layout from Table 3 the encoder pin bus can be seen on the left side of the Adapter Board in Figure 10 below These pins act as connections to the encoder placed on the wheel Figure 10 shows these pins Developer Guide RC Camera Car P14226 Rs ye OQ00 g Wopewen eee pmemenenens sw ww OOOO Gu ome Figure 10 Encoder Pin Bus The pins for the two encoders are similar and are divided into 3 pins The pin layout can be seen on the QRB1134 data sheet but on the Adapter Board the pins are as follows 1 Leftmost pin in Figure 10 Collector Pin 2 Middle pin in Figure 10 Emitter and Cathode Pin 3 Rightmost pin in Figure 10 Anode Pin Finally with all the connections made the adapter board placed on top of the motor shield can be seen in Figure 11 amp 12 below Figure 11 Adapter Board on top of Motor Shield Side View 1 Developer Guide RC Camera Car P14226 en ae ees gt Figure 12 Adapter Board on top of Motor Shield Side View F Other Modifications Certain other modifications were made to the overall setup to reduce noise and obtain better signals as inputs 1 Ferrite Core A ferrite core was added as a choke to the two batteries being used to power the whole apparatus One choke was placed on the positive and negative terminals on the RC car battery as seen in Figure 13 and another choke was added to the RC Camera
87. ncoder PWM count reset all the necessary signals for effective and accurate steering are now set and can be utilized All signals have a certain chance of error When a computer is counting the encoder tics and an error occurs the computer has no way to know that it is in error and therefore will keep it in the encoder count This results in a long term offset between where the computer thinks the steering wheel is and where the steering wheel actually is With a fine toothed encoder these errors are negligible But as with all errors they are undesirable and can add up to significant problems further down the road The constant resetting of the encoder count by the centering signal removes this error as a problem Now the only error that can occur has to occur within the time it takes for the user to turn the wheel from the center to one side as far as possible and back to the center The error becomes virtually nonexistent because of this narrow window in which it has to occur The centering signal similarly to all the signals on the MOMO console operates between 0 5 VDC This is an industry standard however the FRDM Board requires that all signals operate between 0 3 3 VDC which means this signal needed to be conditioned Developer Guide RC Camera Car P14226 3 Pedal Potentiometers The MOMO pedals are designed to replicate the accelerator and the brake pedals of an actual car The signals are sent as voltage values The peda
88. ncoder right char message 2 Once the messages are read the car characters are combined with the characters from the user input and sent to the computer over the USB connection as 6 characters with a new line and a carriage return If there are not three characters to be read or if the read buffer is empty the code does nothing Send Characters pe printft ScScScScsc c n r unsigned elietysncoder left char unsigned char encoder right char unsigned char wheel pos char unsigned char wheel neg char unsigned char gas_ int unsigned char brake int fai Scant if readable else else readable while true Developer Guide RC Camera Car P14226 main C Car Code Documentation 1 KL25Z Motor Shield Functions Several functions from the TFC motor shield library were used in order to easily interface with the KL25Z motor shield MBED library include TFC h Initialize Motors and HBridge void Init TEC Init TFC SetMotorPWM 0 0 TEC HBRIDGE ENABLE Sets the PWM value for each motor param MotorA The PWM value for HBridgeA The value is normalized to the floating point range of 1 0 to 1 0 param MotorB The PWM value for HBridgeB i The value is normalized to the floating point range of 1 0 to 1 0 l0 28 0 Full Reverse on the H BPridge and 1 0 is 100 Poll Forward on the H Bridge void SetMotorPWM float MotorA float MotorB TFC
89. new rear axle which only serves to align the rear wheels and keep them from falling off had to be designed to accommodate the new length of the encoders and to allow the locknuts on the threads to tighten up against the wheel to eliminate slop For the CAD model check out Back Drive Rod To download any CAD file right click the Display link in the CAD directory and choose Save link as This will save a SLDPRT or SLDASM file to the desired location 7 023 Dimensions in Inches 8 32 0 453 Threads Both Sides The rod is from the same piece of 5mm center ground rod made of tool steel The inner diameter of the wheels were also drilled out with a 7 drill to 0 201 5 1mm to allow them to spin freely on the alignment rod 9 Bumper Modification The bumper design that would allow for the significant chassis weight increase and adequately protect the electronics went through many iterations as quick analysis techniques do not really exist for impact testing Instead we went through some material and design testing before coming to an acceptable final product The design consists of two Lexan plates that sandwich a piece of polyethylene foam and are held together with screws and nuts Two holes for the original bumper had to be enlarged to mount the new bumper with 8 32 screws The foam as free from senior design it is suggested to find packing material rather than buying foam which can get expensive and w
90. ns for this were similar to the power harness connection with the positive side of the harness left connected to the positive terminal of the motor and the negative side of the harness right connected to the negative terminal of the motor Figure 15 Capacitor Added Over Power and Ground Pins In Figure 15 can be seen the capacitor added on top of the power pins for the adapter board This capacitor sits over the 3 3V and the GND pin which powers all the circuitry on the adapter board These capacitor placements known as decoupling capacitors or bypass capacitors are generally placed across the power and ground for any electronics that needs to be isolated from noise Furthermore to reduce the motor noise additional capacitors were added to the motor terminals as can be seen in Figure 16 and 17 below Developer Guide RC Camera Car P14226 L3 4 5 i mn t f 4a a g ANA Ry Ea Figure 16 Motors without Capacitors Figure 17 Motors with Capacitors One major drawback to working with motors is the large amounts of electrical noise they produce which can interfere with your sensors and can even impair your micro controller by causing voltage dips on your regulated power line Large enough voltage dips can corrupt the data in the micro controller or cause it to reset The main source of motor noise is the commutator brushes which can bounce as the motor shaft rotates This bouncing when coupled with the ind
91. o and including the new line character from the left side of the string to the new string data_chars The Mid function then parses off each character individually from the data_chars string according to the position in the string for character length Since the first character is the carriage return this value is ignored and the data starts at the second position Parse Data from Buffer and Remove data chars Left buf LF encoder left char Mid data chars a 1 Parss data trom data Chars string Starting at position 2 with character length encoder right char Mid data chars 3 1 wheel pos char Mid data_ chars 4 1 wheel neg char Mid data_ chars 5 1 gas char Mid data_ chars 6 1 brake char Mid data_ chars 7 1 Now that the data is stored in individual characters the string just parses is removed from the buffer using the Right function from the right side of the string for the length of the total buffer less the distance to the new line character buf Right buf Len buf LF Cut the parsed data from the buffer With the data removed the characters are now converted back to the corresponding decimals from 35 to 126 as done in the mbed code Convert Received Data encoder left int Asc encoder left char convert ASCII characters to integers encoder right int Asc encoder right char wheel pos int Asc wheel pos char wheel neg int Asc wheel neg char Gas int Asc gas char brake
92. oTek R C 5x11x4mm Metal Shielded Speed Clutch Bearings 10 http www homedepot com p LEX AN 10 in x 8 in Polycarbonate Sheet 3 1 GE XL 1 2020901342N SyclvZbrd http www mcmaster com 93505a825 r1rg66 http www mcmaster com 9 1780a770 rlrcyn Developer Guide C Difficulties Documentation RC Camera Car P14226 Many unforeseen challenges were tackled in the course of completing this project This Section mentions many of them as a means to prevent future groups working on this project from having to deal with the same issues Difficulties Documentation Difficulties Solution Electrical FRDM KL25Z Board has 3 3 V inputs only Use drop down resistors and a level shifter to change sensor voltage ranges Centering signal was not reaching high enough voltage levels when going through the level shifter This was due to the level shifter receiving its power from the FRDM board which cannot provide enough power to achieve the desired voltages The level shifter is now powered from the MOMO s 5V power supply Encoder values are very noisy Capacitors were added to the motors and power supplies but this was not enough Encoders are still noisy Problem comes from the H Bridge The system was very electrically noisy in general Ferrite cores were added to the batteries to help reduce noise propagation Wires often slipped out of their positions during operation Headers and harnesses
93. of torque and will slip if not tight but remember this is metal on plastic so you can strip the connection Assemble the short arm and long arm The plastic pieces are identical in this case but the rods are of different length This process is most easily accomplished with two pairs of pliers or a small adjustable wrench one to grab the metal rods and the other to tighten each end individually These will take some adjusting so just get the threading started and leave for later Developer Guide RC Camera Car P14226 Once finished the metal balls need to be installed in the open plastic ends The easiest way to do this seems to be to put the balls down on a table using the hole to sit flat then push the plastic end down over the ball until you hear a snap This will take some force so alternatively do the same process with a pair of pliers While doing this locate the black round headed screws pictured These are used for mounting the arms to the servo horn Screw the plastic screws into the servo horn as seen below This also takes some force as the plastic is not threaded If this is not going well mark the position of the servo horn remove the yellow pieces and clamp that to assemble this separately before reattaching in the same orientation Developer Guide RC Camera Car P14226 Now the servo has to be mounted to the chassis Locate the small plastic blocks seen below along with two more of the same screws you used to
94. om the level shifter reach 3 3 V The LV Low Voltage pin on the level shifter is attached to the FRDM board s 3 3 V output The output pin labeled RXI has a low pass filter attached between it and the input pin on the FRDM Board This is because the signal was noisy when first measured 2 Wiring Harness Pinout Red Xbee TX Dark Green I TEE 1 Dark Green Xbee RX Blue Steering Encoder 2 Blue Steering Encoder 1 White Gas Light Green Steering Encoder 2 Yellow Brake Grey Gas Green 3 3 V Yellow Brake Blue GND Black Centering Out White 3 Signal Conditioning There are many different kinds of signal conditioning and depending upon what the project requires only a few will be needed for any project The most common is filtering which is useful for isolating desired signals and reducing noise The MOMO console does this often throughout its system so the only filtering needed was for the centering signal which was just to remove a little noise In this case a low pass filter with a time constant of 0 1 was used The other kind of signal conditioning used for the MOMO console was a voltage level shifter Level shifters are most commonly used when trying to communicate between two different systems that operate at two different voltages The most common example of this 1s communicating with almost any microcontroller and serial RS 232 logic on a computer RS 232 operates at 3 3 VDC while most micro controllers oper
95. ping Developer Guide RC Camera Car P14226 3 Initialization and Declaration The libraries included correspond to those seen in the UML diagram given previously Each will be discussed as it is used in the code Libraries rinclude rtos n include mbed h Finglugde TRC h include PID n The PID rate set for our car is 0 05 or 20 updates per second as this was determined to be adequate The PID constants were determined using the characterizations seen in the Controls Section Due to the fact that both motors showed essentially the same performance the same values were used for both left and right PID controllers The max_speed variable is declared so it can be modified later on in the code J PLiD TAtormacion define RATE 0 05 derine Ke 1 0 define Ti T0 define Td 0 0 PID leftController Ko T1 Td RATE PID rightController Ko Ti Td RATEJ float max speed m s adjustable for PID speed calculations The calculation parameters were initialized as floats as storage space is not currently a limitation Only the gas and wheel floats need an initialization as all others are calculated from these quantities The Booleans are used for enabling and disabling PID and open loop controls later in the code CALC Information bool PID Enable bool Open Loop Enable float gas float U float wheel float 0 fleat Steering servo float fioat camera servo float float steerplus float left wheel speed
96. pins are already connected to the micro controller through the jumpers and these pins can be seen in Figure C below Care must be given to not use these pins for any other use as the H Bridges are necessary for RC car control PTC3 PTC4 PTE23 PTE21 PTE20 PTC PTC2 PTE22 3 FIMO_CH FTMO CH3 ADCO SE7a FIMO_CH0 FIMO_CHI1 ADCO SE3 Potentiometers H BRIDGE_CONTROL H BRIDGE_A IN1 H BRIDGE_A IN2 H BRIDGE_A IFB H BRIDGE_ENABLE H BRIDGE FAULT H BRIDGE_B IN1 H BRIDGE_B IN2 H BRIDGE _B IFB P n f so f Paas f noo Pe Signal Pin Signal Pin i Signal tos Poa J10 PTS J111 J1 13 J115 RC Camera Car P14226 J10 Pin Signal i Signal J1001 PTE20 J1002 PTBO PTE21 J10 04 PTB 110 06 PTB2 J2 NC TE Table A Pin Map for Freedom Board MOTOR A J4 U_H BRIDGE BP TT b Do _ H BRIDGE_CONTROL MOTOR_OUT lt HBRIDGE OUT H BRIDGE_A OUT1 HARDO A OUL H BRIDGE B OUT2 MOTOR B J11 y 282857 2 Figure C Motor H Bridge Connections Potentiometers on the motor shield are necessary to trim the servos These potentiometers are used for two servo trimming and centering The connections to these potentiometers which are on the motor shield can be seen in Figure D below Developer Guide RC Camera Car P14226 PTEG Ate el Figure D Potentiometer Connections 4 Servos To connect to the servos the motor shield has two placements of
97. powered and the USB has to be connected The car also has to be on First press the reset on the car KL25Z then press the reset on the console KL25Z The car XBee LEDs for TX and RX should light up and blink quickly one blue one red and the RSSI LED should be steady red meaning signal strength is strong On the console the red RSSI and blue connection LEDs should be on If this does not work first check to make sure that the wiring harnesses in the console on the perfboard are well seated in the pin headers as this can cause disconnection To check if data is being read correctly on the port you are using you can first open a Putty window chose the Serial connection type enter the COM number of the port and hit open You should see a stream of data characters being printed with carriage returns If the data ever stops hit the reset button on the console and it should begin again Again this is signaled by the blinking LEDs on the car XBee Once data is being read correctly all that needs to be done in Excel is checking the Connect box in the ActiveX control window as above and clicking Apply You should see data start to be displayed in the Excel document as below even without clicking Ok in the ActiveX control To stop data collection simply uncheck the Connect box and click Apply again A B C D E 1 Timer i Lett Encoder Speed Right Encoder Speed Left Target Speed Right Target Speed 2 5 m s m s m s m s 3 0 016 0
98. pply was not connected all the signals read noise when the steering was moved This was postulated to be due to the back EMF from the motor Determining that only the 5V supply is needed was a major discovery and only this USB is used to power the steering wheel electronics The concept for steering requires the following known quantities Turn Direction Obtained from the quadrature encoder signal Turning Displacement Obtained from the encoder PWM which will be calibrated to encompass the whole steer angle with PWM count This will require the wheel to be centered Centering Location The steering wheel center position is determined from the optical centering sensor present on the wheel axle 1 Quadrature Steering Encoder Quadrature encoders are a type of encoder used to determine angular velocity and direction Normal encoders cannot tell direction on their own If one were to start turning the encoder in the opposite direction the encoder would just keep counting tics the same as if the direction hadn t changed The way quadrature encoders solve this problem is by using two encoders that are slightly offset by each other The encoder plate needs to have slits in it that are big enough for both encoders to see though it at the same time and have the space between each gap big enough to block both encoder signals when positioned over them What the encoders generate are two PWM signals that are offset by 90 degrees from each other
99. r reset timer column max speed ActiveCell Value m s actual max speed max pw 96 ms pulsewidth When the program receives serial data it then enters the DATA event and adds the received data to the buf string The program than uses the InStr function to look through the buf string for the new line character ASCII decimal 10 recording the length of the data to that character as an integer in LF If less than 8 characters are received the length of the whole string we are sending it parses that data off of the buffer and exits the loop and waiting for new data Case EVI DATA Incoming seraal data buf buf data Incoming serial data accumulated in buf Do Read from Buffer LF InStr out Chr 10 Scan butter for ASCII lt LF gt If LF lt 8 Then Waiting for full ASCII string to lt LF gt to be received buf Right buf Len buf LF Cut the parsed data from the buffer Exit Do Ena I The system time at the time of data reception is then recorded as time_system The time_sample is then calculated as the time difference between this time and the reference time effectively making a timer that starts at roughly 0 seconds for recording data sample times Developer Guide RC Camera Car P14226 Establish Time time system Timer time sample time system time ref Data parsing uses some of VBAs canned string functions First the Left function 1s used to copy the string of characters from the buffer up t
100. r a certain limit that corresponded to without input the highest value seen in the throttle return range Developer Guide RC Camera Car P14226 Gas float throttle input values at O were causing strange output from the PID loop The reverse functionality also was to be isolated from the PID loop Separate conditions for no throttle input and reverse were made that bypass the PID loop The car kept taking off with the last signal received when data transmission was lost The motors are written to zero when data 1s not received but this still does not seem to work Speeds in reverse and otherwise were limited to mitigate this issue One way communications never have the issue of dropping signals Functionalities in both car and console code for turning on and off data transmission were made Wheel range pulse signals from the quadrature encoder varied depending on the speed of turning the wheel from one extreme to the other A range of 650 was set that is larger than any values seen by a small margin to allow for reading of all values within range A centering signal was also read in as an interrupt to reset the values to around zero whenever the center was passed This sensor was already in the console electronics Gas pedal and brake pedal voltage ranges differed in orientation from low to high and high to low Ranges were converted to be near the same from low to high for simplicit
101. r acceleration a max speed saturation Vsar and a 1 order approximation of the motors as seen below Developer Guide RC Camera Car P14226 rightout 1397 Derivative Torque Integrator V Sst 1 Right Motor Output right speed Calculates reference Sst 1 m s velocitites based on Inner Wheel Ref Velocity m s Vrefright turn radius calculsted from inputs 1 Inner Wheel Feedback Track width m Right Wheel Ref Right Wheel Speed Sensor Velocity m s Vrefleft Outer Wheel Ref Velocity m s Left Wheel Ref aloe Velocity m s Ope 45 Derivative1 Torque Integrator V Sat2 Left Motor Output left speed Sat 2 m s Outer Wheel Feedback Left Wheel Speed Sensor Right or Left slowly turn right1 Relational 1 or 0 Operator The PID coefficients in Simulink can be changed by double clicking on the PID blocks and adjusting P I and D The PID model implemented by Simulink is as follows CO e t P rf o 18 Where CO is controller output Note that these values differ from Eq 14 so any tuning done in Simulink will need to be converted to the format in Eq 14 for use on the car Also note that N is a coefficient used to filter the derivative control 3 Non linearities Non linearities are taken into account in the Simulink model as well The speed input is subject to the dead zone block before it enters the sub system containing equations 3 8 In ad
102. requent contact with objects It was also determined through testing that adjusting the camera the same range as the wheels only worked for PID control slow speed and needed to be limited during higher speed driving Completely separate assignments for the camera and steering servos were established in the code Developer Guide RC Camera Car P14226 Transmission signals were converted to ASCII characters in the range of 35 126 to simply transmission This range allows for the start bit of 33 corresponding to and Issues were encountered with sending does not interfere with the new line or multiple values over the Xbee s for signals carriage return characters found at 32 and below With the XBee s in transparent mode they only read the characters as characters and not other transmission functions so this is safe Separate positive and negative characters Character data transmission limited the corresponding to displacements CW and resolution of the steering wheel which has a CCW of center respectively were used to large range transmit the steering signal Separate modes of operation were necessary for PID control open loop control data l l aie Pa SP he Fixed configurations are enabled through transmission standard driving with capped l i coding at startup based on TFC shield DIP max speed and other parameters that could i l l l l switch settings be easily selected without uploading new code
103. rings x10 9 8 am 200 00 Freescale Cup chassis KL25Z motor shield ON 1 for whole class 1 for whole class 1 for whole class 1 2 3 1 5 5 1 6 1 6 2 7i 7 1 9 1 9 2 9 3 For new wheel layout 9 4 9 5 18 98 3 98 Adapter Plate chassis modifications 1 22 stand offs for back Lexan plate 1 94 stand offs for front of Lexan plate Total Price 373 84 http www freescale com webapp sps site prod_summary jsp code FRDM KIL25Z amp tab Buy_Parametric_Tab amp nodeld 015210045A amp pspll 1 amp fromSearch false http www parallax com product 32440 https community freescale com docs DOC 93914 8x 10x 1 Lexan sheet Stand offs 75 in Stand offs 2 in NINI N NIN e Si NO http www tenergy com 11204 01 5 ttp www tenergy com 01025 http edge rit edu edge P14226 public Detailed 20Design 20Subdirectory CAD http www digikey com product detail en QRB1134 QRB1134 ND 187533 E 8 http www freescale com webapp sps site prod_summary jsp code TFC KIT amp tab Buy_Parametric_Tab amp fromSearch false http www mcmaster com 88625k64 r1qj8m http www mcmaster com 98543a101 r1qh4b http www mcmaster com 98543a112 r1qih6 http www mcmaster com 9063 1a009 rlqkau http www amain com product_info php cPath 1_25_2981_2983 products_id 25167 1 n Vaterra Gravel Spec Pre Mounted Tire Set 2 http www amain com product_info php cPath 1576_63 products_id 5728 n Pr
104. rsion is recognized e Once done with this working or not change the XBee settings back to 9600 Baud and hardware flow control and repeat the process After this you should be able to remove the flow control and use the XBee as intended Some important settings to check are below e Protocol should be XB24 802 15 4 and the version this was developed with is 1OEC Developer Guide RC Camera Car P14226 It would be advised for this setup to never update the firmware for either XBee as the current configuration is stable and further changes are unnecessary D Using Xbee s with MBED XBee modules were used to transmit data between the console and the car In MBED the XBee is treated as a serial device In the console code PTD3 and PTD2 are the RX and TX pins that connect to the XBee s data pins In order to transmit data the printf and scanf functions were used Seen below are some statistics gathered for data transmission of the XBees used XBEE data rate 250 000 bits sec Packet size 48 bits Maximum packet frequency 5208 packets sec Developer Guide RC Camera Car P14226 VII KL25Z and MBED As both the console and car use KL25Z microcontrollers we used mbed as our primary compiler This online software is openly available and has a wealth of documentation and premade libraries submitted by an online community of users that allow for easy implementation of many basic functions For official directions and getting started with the KL25Z
105. s This design allows for some protection from outside forces while still allowing access to the electronics for modification This standoffs are simple 3 5 long 8 32 aluminum hexes A schematic of the plate to be fabricated is below with dimensions again in inches for fabrication purposes For the CAD model check out Protective Plate To download any CAD file right click the Display link in the CAD directory and choose Save link as This will save a SLDPRT or SLDASM file to the desired location Developer Guide RC Camera Car P14226 7 047 0 787 a l N F p 0 276 3 858 0 276 2 854 1 280 x 0 177 THRU 4x 0 177 THRU 5 Wheels The original Freescale cup chassis wheels were 2 inches in diameter This left only a few millimeters in terms of ground clearance In addition the locknuts attaching the front wheels stuck out such that the future goal of driving on the two side wheels would not work In order to better accommodate this goal for future iterations of the project softer larger tires were deemed more useful Fitting the car with monster truck tires would be out of the question due to the limited power of the small motors For this reason it was decided that the tires should be in the vicinity of 3 inches in diameter The new tires obtained are 2 8 inches 70mm in diameter and much better suited softer bigger and no pieces sticking out to the task of providing a platform that could potentially
106. s just too noisy to get useful encoder data The arbitrary PWM cap affects the value of the Vsat and Tsar and if that value changes from 0 75 PWM then Vsat and Tsar must be re calculated All values in this table appear as they are used in the Simulink model no addition conversions are needed Use the chart below to convert from PWM to speed if necessary Car Speed versus PWM while on the ground Actual Speed Ideal Speed Linear Actual Speed Linear Ideal Speed 7 0 6 0 5 0 y 5 7267x 3E 14 4 0 3 0 2 0 Car Speed m s 1 0 y 5 7267x 2 7753 0 0 2 0 4 0 6 0 8 1 Motor PWM 0 0 Developer Guide RC Camera Car P14226 The data was obtained by passing through a timing gate 3 times at each PWM averaging the results and drawing a trend line The ideal speed line is drawn with the same slope as the Actual Speed line but with no Dead Zone use this to determine what the input speed should be in Simulink F Method The average steering angle 6 corresponds theoretically to the average of the left and right Ackerman steering angles 2 1 However due to slop in the steering linkages 6 is assumed to be a linear function of the maximum turning angle of the wheels and the console steering wheel itself The angle of the console steering wheel is known from the encoder in the steering wheel Both and are in degrees The value of 6 varies from 35 degrees left turn to 35 degrees right turn w
107. servo horn on the servo as well as the PWM being sent by the specific microcontroller being used steering servo float wheel float steering Scale steering center 30 degrees to 30 degrees depending on scaling Camera Servo iloat wheel tloac Camera pcale camera center default 30 degrees to 320 degrees depending on Scaling As a final check the servo values are only written to the corresponding servo if the values are within the range of 1 to 1 to prevent damaging the servo motors if steering servo float gt 1 0f amp amp steering servo float lt 1 0f amp amp camera servo float gt 1 0f amp amp camera servo float lt 1 0f TEC Se USerLVOtServO Channelsstesring servo float TFC SetServo camera channel camera servo float To prevent reading random values repeatedly from the encoders when the car is stopped corresponding to the last pulsewidth seen a zeroing function 1s used on each encoder This function reads the time since the last interrupt and sets the value to the maximum pulsewidth 126 if it has been more than 150 ms resetting the timer again afterwards Encoder Data Zeroing if timer left read_ ms gt time out pulsewidth left val max pw timer left reset if timer right read ms gt time out pulsewidth right val max pw timet right reset Similarly the median pulsewidths are then capped to prevent any impossible values from making it through which
108. t wheel values int wheel pos char character range conversion for positive wheel values extend range to 93 2 characters int wheel neg char character range conversion for negative wheel values extend range to 93 2 characters Pedals int gas val gas pedal values int brake val brake pedal values int gas int character range conversion of gas pedal values int brake int character range conversion of brake pedal values Encoders unsigned char encoder left char received left encoder character range data Developer Guide RC Camera Car P14226 unsigned char encoder right char received right encoder character range data The centering ISR is setup to only reset the wheel count whenever the interrupt is triggered by the wheel passing the center position with the optical gate Debugging code is also commented out which can help for testing Centering ISR void center 7 eCeprinct Center r n for debugging Reset count to 0 when falling edge detected wheel reset The main loop contains three major parts It reads the raw wheel and pedal information Then it adjusts the ranges and checks for invalid data Finally it transmits the data to the car via the XBee The first part enables the serial communications and interrupt ISR on falling edges int main Initialize XBee and PC communications pc baud baud_ rate XBee baud baud race Interrupt Centering ISR on signal falling edg
109. t can be modified by pressing Alt F11 and selecting VBAProject File_Name gt gt Microsoft Excel Objects gt gt Sheet COM Additionally you can use the Developer Tab in Excel If your Developer Tab is not visible follow these directions In the Developer Tab click the Design Mode button and double click on the COM ActiveX control This will open the code a Initialization The first part of the code is just initializing the variables in the code for completeness VBA does not require this but by uncommenting the top line the hard data type functionality will be enabled which may help for checking with issues caused by modification The received characters include the buffer cell printing buffer length and character string arrays used for data reception and parsing The calculation integers are the limits used in the mbed code along with the integer conversions of the ASCII data characters The calculation doubles are the same floats used in the mbed code for storing the values calculated from the physics and controls equations The reference time value is initialized as public to enable functionality throughout the program cases Developer Guide RC Camera Car P14226 OpEion EXPLICIT Received Characters Dim buf As String Buffer for incoming serial data Dim cell idx As Integer The tow number cell to store a received barcode Dim LF As String Dim data chars As String Dim encoder left char As String Dim encoder rig
110. t speed gas float 4 0 5 0 5 0 75 speed ok for reverse right target speed leit target Speed end I Finally the values calculated are written to individual cells using the Cell function row column and incrementing the cell index each time The placement of the cell index before the cell assignments is why the data starts printing in row three Write to Cells cell idx cell idx 1 increment the row number of cell where the barcode will be stored Celis cell idx 2 time sample Celis celd idz 2 left wheel speed Celis cell 1d 3 right wheel speed Cells cell idx 4 leit target speed Cells cell idx 3 right target speed Loop End Select End Sub c Plot Macro The macros used for plotting and recording data as not as critical to the basic functioning of the program but they do make data collection and evaluation more efficient Again these macros only work for 2013 and should be modified for 2010 functionality These macros were created using Excel s macro recording functionality so they will only be minimally documented as it is very easy to record your own macros that do anything you want to the data sets created These macros can be found in in the VBA interface under VBAProject File_Name gt gt Modules gt gt Module 1 and Module 2 The plot function first deletes all charts in the main sheet and creates a new chart in cell G9 Sub plot deletes the old plot and creates a new one of all the data Dim
111. ternal system clock call function in VBA that returns the number of seconds since midnight the max speed constant and the max pulsewidth constant The last two values are the same as those initialized in the mbed code Private Sub StrokeReader l Commivent ByVal Evt AS StrokekesaderLib Event ByVal data As Variant Select Case Evt Can be EVT DISCONNECT or EVT DATA or EVT SERIALEVENT Developer Guide RC Camera Car P14226 Case EVI DISCONNECT at USS Serial port adapter as Just disconnected from the PC plot goes to plot sub Range Al FormulaR1Cl Timer Range A2 FormulaR1Cl s Range B1 FormulaRICl Left Encoder Speed Range B2 FormulaR1Cl m s Range C1 FormulaR1ICl Right Encoder Speed Range C2 FormulaR1Cl m s Range D1 FormulaRI1Cl Left Target Speed Range D2 FormulaR1Cl m s Range H1 FormulaR1ICl Right Target Speed Range E2 FormulaR1Cl m s Range F1 FormulaR1Cl Enter Max Speed m s Range Al Select Case EVT CONNECT ActiveSheet Range a3 ActiveSheet Range a3 End xlDown ClearContents ActiveSheet Range b3 ActiveSheet Range b3 End xlDown ClearContents ActiveSheet Range c3 ActiveSheet Range c3 End xlDown ClearContents ActiveSheet Range d3 ActiveSheet Range d3 End xlDown ClearContents ActiveSheet Range e4 ActiveSheet Range e4 End xlDown ClearContents Cell idk Z start at row 3 time rei Time
112. ther the Freescale microcontroller or any of the other electronics we needed to add for this project For this reason we decided to make a prototyping plate out of Lexan This plate attaches to the car at several points to increase rigidity is elevated on stand offs and contain the hole pattern of all of the parts we are attaching to the car In the diagram below all dimensions are in inches for machining purposes For the CAD model check out Fixed Adapter Plate To download any CAD file right click the Display link in the CAD directory and choose Save link as This will save a SLDPRT or SLDASM file to the desired location Additional CAD work and component testing had to be done to optimize the hole layout for all of the components This yielded the following CAD rendering which shows where all of the components mount on the frame Of course this differs slightly from the final product but it gives a good idea of the final objective of the design For the CAD check out Fixed Car Components To download any CAD file right click the Display link in the CAD directory and choose Save link as This will save a SLDPRT or SLDASM file to the desired location Developer Guide RC Camera Car P14226 10 000 3 051 1 083 4 Protective Plate To protect the electronics added to the car an additional Lexan plate was added above the adapter plate and separated by standoff
113. tive e We could make the controls a little better e We could make it a little faster Issues e The car gave a participant vertigo e Young children need to sit on parent s laps because they cannot touch the pedals Observations e Pulling on the wheel can break it since it is not load bearing e tis hard to separate the camera delay from the control delay e Sometimes the car wouldn t drive straight and the video cut out As the car speed was limited using a potentiometer on the car and operators were already busy enough trying to deal with the influx of people adjustments could not be made to increase speed on an individual basis Having this adjustability on the console would be a nice touch for future work but would require changing our communications significantly The sensitivity of the controls could be adjusted in a similar fashion Though our design attempted to make the console adjustable for people of all sizes very small children seem to be outside of this range For the future it would be helpful to make the pedals fixed to the table base and adjustable in height with around a foot of travel upward More Developer Guide RC Camera Car P14226 adjustment in the height of the seat and being able to reduce the height of the top table surface may be desirable Effectively the lack in adjustability made it difficult for children to press the pedals which would move on the table base and had to be held in place Since the se
114. uctance of the motor coils and motor leads can lead to a lot of noise on your power line and can even induce noise in nearby lines The solution is to solder capacitors across your motor terminals Capacitors are usually the most effective way to suppress motor noise and as such we recommend you always solder at least one capacitor across your motor terminals Typically you will want to use anywhere from one to three 0 1 uF ceramic capacitors soldered as close to the motor casing as possible For applications that require bidirectional motor control it is very important that you do not use polarized capacitors The capacitors seen in Figure 17 were soldered across the motor terminals directly for each motor to achieve sufficient noise suppression Instead of electrolytic capacitors the ceramic capacitors were used to account for the dual direction nature of the motors since both reverse and forward direction operations are being performed by the RC car Other precautions that were observed to reduce noise were that the motor power wires were kept very short and the motor lead wires were spiraled around each other to decrease the noise as well Care was also given to keep the motor power cables away from the electronics such as the XBee for fear of induced currents on the signal lines 3 Power Switch A power switch was added to the car for safety purposes Although it is not included in the Freedom board documentation if the board is powered b
115. upt thread the timer is first reset to 0 and started when the thread is first called in the main loop The mode of the interrupt pin is then called as a PullNone which means that it does not use the internal pullup resistor of the KL25Z board for reading input The KL25Z board does not have an internal pulldown resistors so this step is critical as external pullup resistors are used in the encoder circuit on the XBee protoboard that correctly limit the ranges of the output to trip the encoder The interrupt is then attached to the corresponding ISR using falling edges as triggers INTERRUPT Code LEFT Main Thread wold encoder thread left void const args Cimer ett reser tiner Jerucstart it encoder left mode PullNone encoder Jeftstallyecs lert RIGHT Main Thread void encoder thread right void const args timer right reset timer right Stari encoder right mode Pul lNone encoder right fall amp ts right Developer Guide RC Camera Car P14226 On trigger the ISR s use the timer read function in milliseconds as integers to read the elapsed time since the last falling edge The time 1s reset for timing the next interrupt These ISR s are kept short to reduce processing time on triggering LEFT ISR void ts _ left Q pulsewidth left val timer left read_ms timer left reserc RIGHT ISR void ts _right pulsewidth right val timer right read_ ms Cimer cightiwreselt 7
116. ution The values are converted to the range of 35 126 and depending on which side of center the wheel is on the other character is written to the lowest value 35 If the reading is outside of the range the code does nothing Constrain steering range and convert to character range if wheel int gt 1 0f wheel range amp amp wheel int lt wheel range if wheel int gt 0 wheel pos char wheel int 7 35 35 126 wheel neg char Tor else wheel pos char 35 wheel neg char wheel int 7 35 1 35 126 else Due to the springs in the pedals not always returning the values to the same position the values of the pedals were always capped to the range of 35 to 126 to make sure no bad transmissions occur cap gas values to account for potentiometer inconsistency a 4gas int lt 33 gas int 35 if brake int lt 35 brake int 35 if gas int gt 126 gas int 126 if brake int gt 126 brake int 126 For debugging it is useful to print out the values that are being sent as characters so that you can see what might be going wrong with the transmissions This is commented out in the code Debugging pe printt sd tsd ted tsd n r wheel pos char wheel neg char gas_int Drake ntj ee prinkt Enabler 2d n r enablelwo Once everything is setup the input is convered to unsigned characters and sent over XBee as four characters with a start ch
117. utorial can be found here In the macro enabled Excel sheet that is included in the Final Documents Subdirectory on EDGE the interface you will see on the right hand side of the screen is as seen below The small ActiveX control box labeled COM will not be visible but this 1s made visible by clicking the Show COM button The Enter Max Speed m s box F2 is used as the input for the coding as it is in the car code Normal values will be either 1 0 for straight runs and 0 6 for turns depending on the DIP switch setting F G H I J Enter Max Speed m s 1 0 COM Show COM Save Data Trim Plot Data Speed Data Left Encoder Speed m s Right Encoder Speed m s Left Target Speed m s Right Target Speed m s If you double click the COM ActiveX control you will get a window that looks like the image below This is used to record the data directly The port number for data transmission will vary from computer to computer but it can be found by typing Device Manager into the Windows search bar Under the Ports heading you should see the Freescale board with the associated port number listed when the device is connected The rest of the settings stay the same as below StrokeReader Control Properties General Port Number Connected Baud rate 9600 Parity NO PARITY Data bits Stop bits 1 Developer Guide RC Camera Car P14226 To take data the console has to be
118. were created for each wire so the wires fit more securely and could not be misplaced in the boards Camera feed would occasionally drop out while operating indoors Replaced antennas to give the wireless signal more axes of operation Indoors is still not best for operation but rooms with higher ceilings are best Connecting and disconnecting the battery for testing was inconvenient and inefficient A simple switch was added to the chassis that allows for easy code development and testing on the chassis The addition of a separate LiPo battery added the possibility of the voltage dropping too low and making the battery unusable during testing A LiPo battery level indicator with audible alarm was added to signal when voltage is getting low Default motor wires included unnecessary connectors that made connecting to the TFC shield inconvenient New wires were added at the optimal length for the chassis layout The encoder wires were also possibly targeted as a cause of the noise seen as they sit directly on the motors Tin foil was added over the motor area around the wires to protect against signal interference Video receiver was designed to be powered by LiPo batteries at fixed voltage ranges that did not readily correspond to DC wall A voltage regulator was added to a DC wall adapter to provide the desired supply voltage adapter values Developer Guide RC Camera Car P14226
119. with the quote character 34 since this is used in VBA for reading strings 2 Using the Excel Sheet The following documentation is for the 2013 version of Excel Previous versions still support the ActiveX control and main VBA functionality but the macros do not work in previous versions as VBA has changed its syntax for chart formatting A working version for 2010 can also be found on EDGE which effectively just has the same main macro and slightly modified plotting macros In essence the strategy is to give the computer the same raw data that the car is seeing before it is converted to useable quantities to better understand how the car is functioning and to make data transmission easier To log data an Excel VBA code was developed that relies on the StrokeReader ActiveX control for Excel This control is a serial port interface with event driven asynchronous data transfer that can be downloaded here Due to budgetary limitations we area only using the free version but a license only costs 7 so it might be worth the investment for Developer Guide RC Camera Car P14226 future development This interface was developed for scanning barcodes but it provides a convenient interface for all serial data communications The basic background VBA macro associated with this control was modified extensively for our application in the specific Excel sheet being used For additional information about including this control in other applications a good t
120. y Steering wheel gas pedal and brake pedals sometimes read inconsistent values Value maximum and minimum caps were added to prevent the transmission of bad characters over XBee Controls Steering inputs near zero led to singularities in the wheel speed calculations Steering inputs less than 0 001 radians were limited to that value to correspond to roughly a straight signal without division by zero Accumulated error needed to be reset when running the car from time to time Every time the car comes to a stop the error is reset for the next movement Assignment of the correct wheel to assign outer and inner speeds based on turning signal was confusing The car was tested unloaded at slow speeds while holding one wheel constant to determine when PID was functioning correctly Open loop feedback led to the possibility that the outside wheel could be written to a value greater than 1 0 PWM Both inside and outside wheel speeds were limited linearly so that the highest value the outside wheel could see is slightly less than 1 0 PWM This logic did not need to be employed in the PID loop as saturations at 0 75 PWM were already in place due to noise issues Developer Guide RC Camera Car P14226 Mechanical The original car suspension system added no functionality to the car and made mounting components difficult The suspension system was removed and removed with fixed conne
121. y an external battery source in addition Developer Guide RC Camera Car P14226 with the USB programming interface the micro controller seemed to get damaged every time The cause for this was unknown but the solution was a very simplistic one A power switch as seen in Figure 15 was added to turn the battery power off whenever the microprocessor needed to be programmed The schematic can be seen in Figure 16 ee EE 15 Power Switch and Wire Connections Placed Discretely On Car Chassis 4 Figure 16 Schematic for Switch 4 Encoders To successfully apply the use of control systems and a PID loop the wheel speeds were needed to be measured For this encoder sensors were attached to the wheels The sensors used were the QRB1134 sensors The wiring for these sensors can be seen in Figure 17 below The collector emitter anode and cathode internal wirings can be seen in the sensor datasheet or in Figure 18 Developer Guide RC Camera Car P14226 NLE Ta Way u hi A gh eft Encoder Colector gno de dlector end de a6 Fi Enit er J athode z fathode Figure 17 Encoder Sensor Wiring Diagram Signal Que Put A Anode Orange gt Ceollectsor White E Catode Green E Emitter Blue Figure 18 Encoder Sensor Hookup 5 Camera TX The camera and transmitter used for the car are standalone modules that can be seen in the links under the Video RX Section Nothing should have to be modified with the setup ap

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