WC-132 WheelCommander WheelCommander Wizard User`s Manual
Contents
1. Velocity Tuning Steering The steering velocity Proportional constant steering velocity Integral constant and steering velocity Differential constant are used to tune the ability of your robot to drive in a straight line Often the Proportional constant can be zero The Integral constant should be nonzero but not too large or the platform will overcompensate and not drive straight and or become unstable With these settings the steering velocity loop essentially uses a difference in position of each wheel as the error term if one wheel gets ahead of the other it s velocity controller is told to slow down while the other is told to speed up To tune the steering watch the rotation rate and or current angle in the bottom graph These should remain near zero during a long move If the angle grows continuously during a move try increasing the Proportional and or the Integral terms but not too much or it will become unstable and not track straight NOTE running the robot at top speed can result in poor tracking straightness as the control systems can become saturated Try running 5 10 below Vmax The image below shows typical graphs for a small robot using RC servos with the steering not properly tuned resulting in an angular drift 24 j Yelocity PID Loop Tuning E e E jojx Velocity vs Time a f E 2nd Vel Rot Alternate Stop Ist Vel ps 2nd Vel fi 3 Step Cycle Time fa 1st Rot fo ai eao 2nd2. s OOPIC in I2C mode check on Short Cmd Mode this reduces the amount of data returned by each command The Notify Motion Complete checkbox enables in serial port mode only asynchronous reporting of the completion of a motion command Step 5 Apply Communications Changes sioixi Current Status JReady COMS 38400 baud m Communications Parameters Connection Info Specific 20 Address gt Protocol Options Serial Port fis E I Inter char Delay for BasicStamp COMS po F Short Cmd Mode OOPIC R5232 Baud Rate I Notify Motion Complete heelCommander rrr We v 39 Lz BlueR adio Wireless Firmware Updates E ha J Firmware Recovery I SetBaud on Fest Data Mode a Special Update Fw F Write EEPROM Apply X Change settings lt Back Cancel Help Click Apply to send the communications changes to the WC 132 The Current Status should change to indicate that the connection has been updated Step 6 Update Firmware Comm Settings i s Current Status Ready COMS 115200 baud la xi Communications Parameters Specific 12C Address fis as R5232 Baud Rate 115200 ka BlueRadio Wireless Enable I Set Baud gt fast Data Mode J Write EEPROM Connection Info Serial Port COM5 wheelCommander We v 39 Protocol Options I Inter char Delay for BasicStamp E Short Cmd Mode OOPIC Tl Notify Motion Complete Firmware Updates Firmware R
3. COM1 4 COM2 Valid BlueRadio Wireless 4 i I Enable YA COMS Valid E a I SetBaud M fast Data Mode I Write EEPROM het ge Search i Cancel Help When you launch the Wizard it will quickly find and display all valid serial ports and I2C dongles in the Connections Found box be they your PC s built in serial ports or USB to serial interfaces The checkboxes to the left of the port names allow you to control whether a given port will be searched for the presence of a WheelCommander or other Noetic Design Inc product A greyed out check means skip this port a black check means search it By default the Wizard will search all detected ports which is useful if you don t know which port your WheelCommander is attached to However once you know which port you should uncheck the other ports to speed up the search process in the future 4 Step 2 Configure Port LT aolx Current Status Directions 1 Check Uncheck connections to search et ore 2 Select a port choose baud rate and optional wireless settings 3 Hit Search 4 Select device to configure Search Parameters Search Results Connections Found R5232 Baud Rate Devices 115200 Description xA COMI Walid V COM2 Valid BlueRadio Wireless i Enable YICOMS Valid u Fi Set Baud IM East Dats Mode write EEPROM Change Change the baud rate and or radio settings for the selected port Searc
4. brings the count back down to 1 Inaccuracies of a few counts are typical when doing this by hand 16 Motor and Encoder Settings nMagntudej 17 Step 9 Calibrate Motors lolx Calibration Results Status JCalibrating Max Speed 139 Left Right Drive Slope m 124 148 Drive Intercept b 700 J 2092 Servo Zero Position 366 375 Reverse Motor Direction Iv Vv lt Back Next gt Cancel Help The WheelCommander includes a built in routine for testing and configuring the motors The steps it performs are 1 For servos only finds the zero position for each servo the pulse width that results in no motion 2 Measures maximum velocity of each motor 3 Determines direction of rotation of each motor with respect to the encoders some servos rotate in the opposite direction compared to others so this important step corrects this 4 Finds the output value servo control pulse width or motor PWM value corresponding to 10 of maximum speed and 80 of maximum speed 18 5 Calculates the coefficients of a linear equation for each wheel the m and b terms of y mx b where y is speed measured by the encoders and x is servo pulse width or PWM value used to enable the WheelCommander to smoothly control velocity over a large useful range b ensures that starting friction and the servo s deadband is overcome even at low velocities and m essentially sets the largest minimum output valu
5. stored in on board EEPROM so your WC 132 will remember them even with the power off 20 Step 10 Make Custom Settings Changes iadjust Constants acxl Change Value a Set Reset to Defaults This dialog is for advanced users only Current Constants select to edit 5 m on Z E SROSNNAHHSEAISAHNO ASH O Klz_l 111 Kiel 119 12C Address proportional velocity integral velocity differential velocity velocity feedforward unused proportional position integral position differential position ddrive proportional position ddrive integral position ddrive proportional velocity ddrive integral velocity rotation hysteresis position hysteresis positional velocity threshold velocity threshold wheel base lo wheel base hi wheel circumference lo wheel circumference hi Iservo zero lo Iservo zero hi rservo zero lo lt Back Cancel Help This dialog is provided just in case you ever need to modify the WheelCommander s EEPROM constants directly Normally you should rely on the various pages of this configuration wizard to set the constants for you in a more controlled manner 21 Step 11 Tune Velocity PID Control Velocity and Rotation vs Time a E lojxj Velocity vs Time 0 Vel 0 Pos Jet vevRot Zndvelikot Alternate eo N ist Vel i g 19 Shba Step Cycle Time fa ee 2nd Rot 50 100 20 s 2 Rotation Rate vs Time 0 Rot yea Parameters 20 0 Ang Pro
6. Mode 00PIC RS232 Baud Rate I Notify Motion Complete 115200 i r BlueRadio Wireless Fule Pse I Enable TD Firmware Recover I Set Baud I Fast Data Mode T Special Update Fw F write EEPROM Upload Finished xi Firmware uploaded successfully f lt Back Next gt Cancel Help It will start the download process during which the red and green LEDs will alternately blink and the Current Status will indicate the percent complete An Upload Finished message box will pop up indicating that it is complete NOTE do not switch away to another window during an upload if you do the wizard page will not refresh correctly until the upload is complete Click next to continue 11 Step 7 Configure the Robot Platform Platform Settings loj x m Chassis Geometry and Specifications Flip Platform Forward Backward IV Counter Rotating Shafts Wheel Base distance between wheels an Wheel 055561 565 fi 11123129 Je 2 Radius Diameter Circumference 1 m Platform Info Firmware Revision 33 Digital Supply volts 525390625 Refresh Motor Supply volts E 953125 This page of the wizard allows you to specify the information the WC 132 needs to know to correctly convert between real world velocity position and angle values and low level control of each wheel The information required includes e Flip Platform Forward Backward change
7. NUBOTICS wc 132 VVheelCommander VVheelCommander VVizard User s Manual E zlBjxj Current Status Directions 1 Check Uncheck connections to search p r 2 Select a port choose baud rate and optional wireless settings 3 Hit Search 4 Select device to configure p Search Parameters Search Results Connections Found R5232 Baud Rate Differential Drive Motion Controller for Standard RC Servos and DC Gearhead Motors DRAF T Copyright 2009 Noetic Design Inc 1 01 3 10 2009 VVheelCommancder Wizard Overview This program helps owners of the Nubotics WC 1 32 VW heelCommander differential drive controller set it up for use with their mobile robot Features e Connects to a WheelCommander using any serial port built in or USB dongle or I2C dongles from TotalPhase or Diolan Provides a firmware updater Helps you enter physical dimensions of your robot Offers display of current status of unit including supply voltages Helps you enter encoder and motor parameters for either RC servos or DC motors Coordinates calibration and displays results e Gives access to EEPROM constants directly if needed e Offers interactive PID loop tuning tools Benefits e Eliminates the need for the WC 132 owner to write their own throw away setup code for the board e Provides method for tuning PID parameters that would be difficult to do via an embedded master robot controller Description Thank you for pur
8. Rot je 100 20 sa Rotation Rate vs Time 2 Rot ea ics aonda 20 35 ng Proportional aa Differential Feed Forward Je Differential Drive Steering Parameters 100 Proportional Integral E a Hen _ a i af a fs ad 25 step ee ma Position PID Control vs Ti EN Position PID Loop Tuning o Position vs Time 0 Pos 960 Vel i ingi 2nd Pos Ang ltemate Stop tst PosIncr 100 Step Cycle Time fi 0 2nd Pos Incr F oo Velocity 89 1st Angle fo Acceleration 89 2ndAnge Jo Follow Trapezoidal Profile T7 100 Relative Moves I A nate vs Time 0 Ang m Position Parameters 38 Rot Proportional Integral Differential Velocity Feedforward Differential Drive Steering Parameters Proportional Integral Differential pa PA f a pa a ane ter Apply The WheelCommander s position control system uses the current velocity and acceleration values to produce a trapezoidal velocity profile over a commanded movement During a move velocity will increase at a constant acceleration to the specified maximum velocity will continue at that velocity until it is time to decelerate and will then decelerate smoothly to a stop at the goal position The position itself when plotted will describe what s referred to as an S curve shape This trajectory is used to set the goal position to which the PID control loop attempts to slew the position of each wheel It is important that the
9. ava I2C and Microsoft Visual Basic asynchronous serial examples For more information visit www nubotics com Produced by Noetic Design Inc 25 NW 23 PL STE 6 PMB 181 Portland OR 97210 Copyright 2004 2009 Noetic Design Inc All rights reserved March 1 2009 32
10. before starting the search If found the interface name and device name will appear in the Search Results on the right if you have more than one Nubotics device attached uncheck all but the one you wish to configure If not found check your robot s power source and connections The green LED should be on and the red LED should be off Click Next when ready Step 4 Change Communications Settings Comm settings oo loj xi Current Status JReady COM5 38400 baud m Communications Parameters Connection Info Specific 120 Address Protocol Options Serial Port fi 6 F Inter char Delay for BasicStamp COM5 re Tl Short Cmd Mode OOPIC I R te i i Ne ci ae 232 Baud Rate I Notify Motion Complete We v 39 32400 n m BlueRadio Wireless r Firmware Updates Enable J Firmware Recovery E TEHE I Special Update Fw i Cancel Help This page of the wizard lets you modify the Wizard s and the WC 132 s communications settings if required You can change the I2C slave address the serial baud rate enable or disable use of a BlueRadio Bluetooth interface or select special communications settings to make the WC 132 compatible with certain controllers If using a BasicStamp to control the WheelCommander check on the Inter char delay this makes the WheelCommander slow down the character to character timing so the BasicStamp can keep up If using a Savage Innovation
11. chasing a Nubotics WheelCommander This manual should help you find your way through the WheelCommander Wizard and get your robot running quickly Connecting to a PC Before you can use the Wizard you need a method to connect it to your Windows PC We recommend the Acroname 4 pin extension cable p n C10 SER INT CONN EXT figure 1 together with either the Acroname USB Serial Interface Connector p n S22 USB SERIAL INT CONN figure 2 or the Serial Interface Connector p n S13 SERIAL INT CONN figure 3 Figure 1 Extension Cable Figure 2 USB Connector Figure 3 Serial Connector Another option is to use the TotalPhase Aardvark USB I2C dongle figure 4 http www totalphase com products aardvark_i2cspi or the Diolan U2C 12 USB I2C interface board shown in figure 5 Drivers for both are built in to the Wizard These products while more expensive than USB Serial dongles also provide their own I2C and SPI GUI control programs and signal monitors and can be quite useful for robot builders Figure 4 TotalPhase Aardvark Figure 5 Diolan U2C 12 Step 1 Launch the wizard LT nlx Current Status Directions 1 Check Uncheck connections to search 2 Select a port choose baud rate and optional wireless settings 3 Hit Search i Connected r Search Parameters 4 Select device to configure Search Results Connections Found R5232 Baud Rate Devices z Description
12. circumference would need two bytes to be specified 8 0 01 800 0x0320 On the other hand using whole inches is also not desirable as there can be as much as 0 5 in error on each measurement which would result in very inaccurate odometry 0 5 distance error for every wheel rotation or approximately a 14 degree error on a 90 degree turn which is equivalent to only about 26 positions per 360 degrees Instead for many small robots we recommend multiples of 0 1 With that typical robot dimensions fit well in one byte and also result in 0 1 or better position error per wheel rotation and a 1 4 degree error on turns Another unit of measurement that works well is the millimeter A typical robot wheel is 209 mm in circumference with a wheel base of 89 mm 13 Step 8 Configure Motors and Encoders Motor and Encoder Settings E lol x gi jigg Note if unchecked RC servo mode is active instead DC Motor Control I Locked AntiPhase not Son Magnitude Z Dual Sign Pins 31 2 KHz ri PWM Frequency m Encoder Settings M Quadrature Signals 128 Encoder Resolution Ticks Rotation Encoder Counts Jo Left Encoder Tick Count Jo Right Encoder Tick Count Monitor Reset Counts lt Back Cancel Help This part of the Wizard is where you tell the WC 132 what kind of motors are attached and how to control them The WC 132 can produce the correct signals to drive either RC s
13. ctive high enable line 4 locked antiphase 2 a single signed magnitude PWM signal and an active low enable line An unsigned magnitude PWM signal means that a 0 duty cycle corresponds to 0 speed or no output and 100 duty cycle corresponds to full speed intermediate values result in intermediate speeds A signed magnitude PWM signal generated for cases 3 and 4 above is used for locked antiphase motor control rather than sign magnitude control In locked antiphase the PWM signal is at 50 duty cycle for 0 speed values between 0 and 50 for speed in one direction and values from 50 to 100 for speeds in the other direction with 0 and 100 being maximum speeds in the opposite directions Locked anti phase can work well for certain kinds of motors but not all motors motors with very low impedance are more efficiently driven using sign magnitude mode this includes many low cost hobbyist quality DC motors The choice of PWM frequency depends on a lot of variables Often experimentation is the best way to find the right frequency A good starting point is around 1KHz Lower frequencies may result in large current spikes shortening the life of the motor brushes which is not desired higher frequencies can result in lower efficiency Frequencies 15 below 16KHz can be audible and very annoying depending on the quality of the motor and its audio resonance points some cheap motors work as very good speakers too Finally many H bridg
14. ds 1 Vel is set to 80 of max 22 speed and 2 Vel is set to 20 of max speed as recommended values to use for tuning Set your robot up on a small box like a car up on jacks so that the wheels can turn but the robot does not move Click on the 1 Vel Rot button and watch the graphs you may need to move the main window to the right to fully uncover the graphs First we need to adjust the Feed Forward term to get the overall velocity to roughly match the requested velocity The calibration procedure should have already set the slope and intercept values m and b to ensure that a Feed Forward value of 16 results in an accurate velocity value But if the velocity is too low you need to increase Feed Forward if it is too high decrease it If the velocity is very unstable then reduce the two integral gains until it is stable Reduce the proportional gains too if the integral gains are zero and it is still not stable Now try running it at the lower velocity by clicking on the 2 Vel Rot button This will most likely be unstable the velocity will rise and fall quickly and not appear to be under control This can be a result of a number of factors usually that one or more of the constants is too large You can try reducing each of these values until it is stable If all else fails you can start from scratch rather than work from the default values First set all constants to zero and Feed Forward to 16 Tune just the Veloc
15. e designs have a recommended upper limit on PWM frequency it is wise to keep the setting at or below this This dialog also allows you to configure the WC 132 to use nonstandard encoders The default is meant to accept sign magnitude encoder signals such as those output by the WheelWatcher encoders from Nubotics These encoders include a quadrature decoder chip which converts the two channels of 32 stripes per rotation which are phase shifted by design by 90 resulting in a quadrature timing pattern into 128 active low clock pulses per rotation as well as a direction of rotation signal Alternatively by checking the Quadrature Signals check box you can use commercial industrial quadrature encoders such as those made by US Digital The encoder resolution should be changed to indicate the number of stripes per rotation As a troubleshooting tool this dialog also provides a display that allows you to monitor the encoder tick count as you manually spin the encoder shaft Click on the Monitor button as shown below to test your encoders Click on the Reset Counts button to reset the counts to 0 Spinning the shaft one way a full turn should result in the count changing by roughly the resolution value spinning the other way a full turn should change it the other direction For example with a resolution of 128 turning Robot A s left wheel clockwise one rotation results in a count of 129 turning the same wheel counter clockwise one rotation
16. e needed to attain full speed 6 Stores the measurements in EEPROM for use in the future If your robot uses DC motors with an external H bridge instead of servos we still recommend running calibration to determine motor rotation direction maximum speed and m and b values In this case step 1 is automatically skipped While the factory default values for the servo zero positions maximum speed and m and b may function as is out of the box it is highly recommended that you run the calibration procedure prior to tuning the PID loop parameters TIP Place the robot on a small box or stand and run the calibration with the wheels off the ground To calibrate hit the Start button then wait while the calibration routine runs 19 Calibrate Motors p o xi Calibration Results Status Calibration Complete Max Speed 156 Left Right Drive Slope m 126 103 Drive Intercept b 768 231 Servo Zero Position 367 375 Reverse Motor Direction M M lt Back Next gt Cancel Help NOTE Do not change the Reverse Motor Direction checkboxes The Reverse Motor Direction checkboxes are set automatically as result of the calibration procedure there is no need normally to change them The same is true for the other fields We provide the ability to hand modify these values just in case you ever need to but normally you do not When calibration is complete hit Next The values found during calibration will be
17. ecovery Special p ns b r ipev r ser r susasi dar Update Pw lt Back Nest gt Cancel Help In addition to changing communication settings this page of the Wizard also allows you to update the firmware of your WC 132 If there is no newer firmware available click Next to move on to the next page and move on to Step 7 below NOTE flashing firmware should only be done with a serial port connection not using I2C or a wireless interface such as Bluetooth First download the latest firmware place of your hard drive from the Nubotics website saving it in a convenient Click on the Update FW button and select the file you just downloaded as shown in the next image Open 21x Look in E WheelCommander Setup Wizard e ter Fe My Recent Documents Desktop we 132_beta _ 39 bin My Documents e g My Computer ae File name Jove 132 beta 39 bin h F I VETON fedw Fme Fies 0 TC Places T Open as read only Select the firmware file it will have an extension bin and contains an encrypted binary copy of the WC 132 firmware Select Open to start the firmware update process 10 gt Comm Settings O xi Current Status Upload complete m Communications Parameters Connection Info Specific 12C Address p Protocol Options gt fe 0 d J Inter char Delay for BasicStamp al J Short Cmd
18. ervos modified for continuous rotation or DC brushed motors driven by an H bridge further it supports a couple of styles of H bridges If you are using RC servos and WheelWatcher encoders the defaults shown above will be correct If you are instead using DC motors with an H bridge to drive them you need to find out 14 a couple of things first 1 what control signals do the H bridges offer to control speed and direction of rotation 2 what control signals can the WC 132 generate 3 what additional circuitry if any are needed to connect the two together 4 what is the best PWM frequency for my application The WC 132 was designed to support the control signals for many common commercially available H bridges such as the Texas Instruments SN754410 dual motor H bridge chip or its predecessor the L293 the L298 or the ST VNH2SP30 or VNH3SP30 used in Pololu s various high current motor drivers Note that these specific H bridges require mode 2 below two direction control signals And this list is not complete many others should work too when properly connected The WC 132 can generate these combinations of signals for each motor 1 sign magnitude 1 a single unsigned magnitude PWM signal and a single direction control signal 2 sign magnitude 2 a single unsigned magnitude PWM signal and two direction control signals one the inverse of the other 3 locked antiphase 1 a single signed magnitude PWM signal and an a
19. gital pins and bits 8 15 are the analog Not all of these pins can be used as some are required by the system for standard functions such as controlling motor direction The remainder of this page consists of a table providing detailed status and control over each I O line lt TO DO document which regions are clickable and what they do gt 30 Step 14 Drive the Robot Drive Robot E ioj x Query Velocity Rotation M Enne bumen fo Jo I Active Low M H Right DIO Hi Left More Stop Right More m Let DIO F Hit Bwd Slower Distance Angle Velocity Rotation lt Back Next gt Cancel Help This page of the wizard gives you a simple dialog with which to test driving your robot platform You can either specify a specific velocity and or rotation rate by typing them into the text boxes below their respective labels or you can click the Fwd Bwd Left Right buttons to adjust them by small increments The current distance travelled angle turned and current velocity and rotation rate are displayed below the buttons lt TO DO document what the Enable Bumpers Active Low and Right Left DIO values do gt 31 Step 15 Done LO sax Your WheelCommander is now ready for use Please see www nubotics com for example code users manual and more Thank you for your business Interfacing Examples Please check www nubotics com for Parallax Basic Stamp asynchronous serial RidgeSoft RoboJDE j
20. h Cancel Help By default the WC 132 WheelCommander and the Wizard are set to 38400 baud so the first time you run the Wizard you do not need to change the baud rate This page allows you to change the current baud rate for searching for a WC 132 this is useful later on if you have already changed the baud rate in your WC 132 and are either connecting to it from a different computer or from a different port number This page is not for changing the baud rate of the WC 132 itself you do that on the next page of the Wizard The baud rate list box and BlueRadio settings will be greyed out until you pick a port to modify by clicking on the interface name on the left make the change required then hit Change Step 3 Search Current Status Not Connected Directions 1 Check Uncheck connections to search 2 Select a port choose baud rate and optional wireless settings 3 Hit Search 4 Select device to configure Search Parameters Connections Found R5232 Baud Rate 38400 w Search Results Devices Description Valid Valid Connected W BARRA ai ICOMS WheelCommander I Enable I Set aud I East Data Mode I write EEPROM Change V COM2 MICOMS Search Click on the Search button to start the search The Wizard will spend a few seconds on each port before going to the next one Be sure to have your robot connected and powered on
21. ity Parameters and leave the Differential Drive Steering parameters at zero Adjust Feed Forward until a smooth wheel velocity at or below the desired velocity is produced The point of Feed Forward is to set a starting point for the control loops that is in the ballpark of the goal velocity under normal loads it effectively bypasses the PID controller and feeds a speed request straight to the motors This frees the PID loop to only control for error in velocity due to voltage drop friction or variable loads without also having to provide all the output required to just move at all Continuing with the tuning increase the Proportional term slowly until velocity control becomes unstable Drop it back to be just on the edge Next increase the Integral term This will usually take any sag out of the velocity to be at or very close to the goal velocity Increase this until unstable then drop it a back to the edge Do the same with the Differential term You should now have good control at low speeds Verify the scalability by increasing the goal velocity by small steps e g increments of 10 If the tuning is good and the scale is good it should continue to match the goal velocity up to Vmax 23 As a final test click on the Alternate button Every Step Cycle Time number of seconds it will switch between the 1 and 2 velocity and rotation rate settings Watch the graphs and fine tune the control loops to get nice looking stable graphs
22. l User Interrupt Status Digtal Output Pin fE i splays Aia 0000000000000000 Interrupt is Active Active Int Pall Motion Complete Int Enabledi I MotionlntEn Active High I F Active High oe Interrupt is Enabledi I Int Enabled IS Motion Complete NOTE these settings are volatile they are forgotten after the WheelCommander is reset or power cycled Pin Type Value Monitor input Set Edge slot to shit Hi 1 0 1 OOOO b b k oon oo oa SDO TD S AD SADI RON SODN DA ON Oo ELELELEKEOQOQOQJOO SQSSSSOSSOSOSOSO Ah eh e ia C sk id S eel SSSSSSSHISOTO SH Hd TEJ SOQOOSDQSOQOOSOOQO DOO GOOO oooooo0 aco 0 Gc SSSSSSSO lt Back Cancel Help The WC 132 provides 4 analog inputs and 4 digital input output lines along one edge of the board each with its own power and ground pin These are intended to be used with sensors or simple actuators There are some additional analog inputs and digital I O lines as documented in the WheelCommander Product Manual available from other points on the board The WheelCommander provides two mechanisms for monitoring its inputs polling and monitoring Polling is done by simply providing commands for your main robot controller to read the current analog value or digital logic state of one or more inputs This is fine if the sensor attached to the input is slowly changing but some kinds of 29 sensors are not So the WheelCommander offers a seco
23. me 5 2nd Pos ner 100 Velocity po 1st Angle Je Acceleration po 2nd Angle Je Follow Trapezoidal Profile 1V Relative Moves I Position Parameters Proportional Integral Differential Velocity Feedforward Angle vs Time 4 Ang 20 Rot Differential Drive Steering Parameters Proportional Integral Differential zi Apply lt Back Next gt Cancel Help Position Tuning Forward Reverse Proportional Integral Differential and Velocity Feedforward are the constants for tuning the position loop As in the velocity control system the velocity feedforward term should normally be 16 The default values should work well WCWizard will by default execute alternating delta position commands of 100 units when you click the Alternate Incrs button The position graph will show position vs time If the position loop is tuned properly little or no overshoot of the goal should occur and it should dampen nicely and not oscillate until the next position command see the above graph If it overshoots reduce the Proportional and or Integral terms If it oscillates increase the Differential term but not too much or it will oscillate even more 27 If the cruising speed is incorrect too high or too low adjust the Velocity Feedforward value As in velocity PID tuning if adjusting the defaults does not result in stable motion you might try starting from scratch Set all con
24. nd mechanism monitoring resulting in a hardware interrupt to your main robot controller This page of the Wizard demonstrates the Monitoring feature This feature allows you to configure trigger conditions for each input line When a trigger condition is met a user specified output line will be asserted indicating to your main robot controller that a trigger has occurred Your main robot controller can then check the status to determine which trigger condition s caused it The output line to use referred to as an Interrupt line is specified by the user in the upper left part of this page of the wizard Set the pin number in the Digital Output Pin box The Interrupt Is Active checkbox will reflect the current interrupt trigger state normally do not change this checkbox The Motion Complete Int Enabled checkbox when checked indicates that you also want a trigger to occur when a movement has completed this is alternative to the Notify checkbox on the Communications Settings page The Active High checkbox when checked causes the output to go high when a trigger occurs otherwise it goes low The Interrupt Is Enabled checkbox provides a way to globally enable or disable the trigger system To the right of this part of the wizard is the User Interrupt Status section Click the Poll button to read the current value of the interrupt status word each bit represents the trigger state of all 16 possible analog and digital inputs Bits 0 7 are the di
25. portional Integral Differential Feed Forward Differential Drive Steering Parameters 50 100 Propottional Integral Differential Appl 4 fa 4 1 a Apply lt Back Next gt Cancel Help PID Tuning The control loops for velocity rotation rate angle and position are set to factory specified values that work adequately with servo based robots with a 6 volt servo supply on a MarkIII robot base using GWS servos For other servos or DC motors or with higher or lower supplies or different mechanical platforms some tuning of the control loops will be necessary Note that PID loop tuning is considered a black art even by experts in the field so dont be frustrated if it takes a while to make it work well this is common for setting up and tuning all kinds of PID loop controlled industrial machinery First start with the default settings If you need to start over you can restore the all of the factory settings including baud rate I2C address mode and PID parameters by issuing the Reset to Defaults command on the Adjust Constants wizard dialog Velocity Tuning Forward and Reverse Most typical servos cannot spin the wheels faster than 10 inches per second usually more like 6 to 8 This value is automatically measured during the calibration procedure It is also displayed in WCWizard on the Calibration dialog This max speed value is used by the wizard to initialize the 1 Vel and 2 Vel fiel
26. requested acceleration and velocity limits are within the capabilities of your robot platform otherwise the trajectory will not be able to be followed and can result in unstable operation overshooting of the goal and oscillation around it Tuning of the PID control loop follows similar concepts as for tuning the velocity control loops First you need to stimulate the system by setting maximum velocity and acceleration values a goal distance and or angle to move over and an optional loop time Step Cycle Time and an optional second position and or angle to move to These moves can be either absolute or relative depending on the state of the Relative Moves checkbox this corresponds to the difference between the D W and X and Z commands described in the Product Manual The Follow Trapezoidal Profile should 26 normally be left checked on NOTE Firmware revision 37 does not work properly if Trapezoidal mode is not set Trapezoidal mode enables smooth acceleration cruising and deceleration using either the default of 1 2 of the maximum velocity as measured during calibration or the value specified before Go using the Velocity and or Acceleration commands If Trapezoidal mode is not set the PID loop will be commanded to move immediately to the requested position and or angle with no limit on velocity or acceleration Ei gt Position PID Loop Tuning 10 x Ast Posf ng 2nd Pos Ana if Ist Pos Incr fi 00 Step Cycle Ti
27. stants to zero with Velocity Feedforward set to 16 Command a move and watch the Vel number in the upper graph adjust the Velocity Feedforward until you get close to the correct value Increase the Proportional term until unstable then back it down Do the same with the Integral term Add some Differential term to reduce overshoot and ringing around the goal Position Tuning Steering The steering position Proportional constant steering position Integral constant and steering position Differential constant set the PID parameters for maintaining straight line motion when executing position commands Often the Integral term is zero and the Proportional term is a small value near one You will need to monitor the current angle and rotation rate in the bottom graph while executing a long Set Position command If well tuned the current angle should stay near 0 though it may deviate a few degrees back and forth during a move If it gets progressively off track one direction or the other try increasing the Proportional and or Integral terms though if these are too large it will become unstable and not track straight either The same issue regarding running at maximum velocity applies here as well set the velocity 5 10 below maximum before issuing your position command in order to insure the PID loops have adequate headroom to control steering 28 Step 13 Explore I O Control 1 0 Control E loj o x User Interrupt Contro
28. this if the robot drives the wrong direction during later testing e Counter Rotating Shafts most differential drive robots are built such that the motors face away from each other thus when the robot moves forward the left motor rotates counter clockwise while the right motor rotates clockwise check this box on if this is how your robot works or off if your robot s motors both 12 point towards the same side of the robot e Wheel Base the distance between the contact points of the two wheels this is needed to convert the desired angle or rotation rate of the base to forward and reverse motion of each wheel e Wheel Radius Diameter or Circumference likewise the WC 132 needs this information to convert desired distance or velocity into the correct amount of rotation of each wheel this part of the wizard allows you to change any of these three values and the other two will be automatically calculated for you Units of Measurement The WheelCommander does not need to know what units of measurement you are using to specify the wheel base wheel circumference velocity and position they just need to be consistent and use numerical values of reasonable magnitude they must fit within two bytes but also should offer enough precision that determination of the angle of the platform can be done with the desired precision using integer arithmetic For example for a wheel 8 in circumference you could use multiples of 0 01 because the
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