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WC-132 WheelCommander Product Manual

1. lt Back Next gt Cancel WCWizard Velocity PID Loop Tuning Configuration Wizard Setting up and tuning the control loops is easy using an asynchronous serial level converter or USB serial port converter and WCWizard the WheelCommander configuration wizard which runs under Windows 2000 Windows XP Windows Vista and Windows 7 The wizard helps you perform the following set up the serial port parameters and or I2C slave address upload new firmware define the robot chassis geometry wheel diameter and spacing forward direction configure motor connections servo vs H bridge H bridge interface details invoke the WheelCommander s built in motor calibration routine interactively tune the velocity PID parameters with a graphical velocity display interactively tune the position PID parameters test the robot using an interactive driving dialog aaa ca eS oS Please see the WheelCommander Wizard User s Manual for details WheelCommander WC 132 Product Manual 31 Connecting to a PC We recommend the Acroname 4 pin extension cable p n C10 SER INT CONN EXT figure 4 together with either the Acroname USB Serial Interface Connector p n S27 USB SERIAL figures 5 and 7 or the Serial Interface Connector p n S13 SERIAL INT CONN figure 6 Figure 4 Figure 5 Figure 6 USB Mini b USB Status ig WC Stans A jf fT GND soar Ge FI STX Data In i a S o H VCC ge E N SRX Data Out gF
2. yO s KDdP 2 Right Position Error Right Correction Nubotics WheelCommander c 2009 Noetic Design Inc Figure 11 Position Steering Tuning Differential Drive Steering Parameters Constants KdpP steering position proportional constant KdiP steering position integral constant and KDdP steering position differential constant set the PID parameters for maintaining straight line motion when executing position commands Often KdiP is zero and KdpP is a small value near one If you are not using WC Wizard you will need to monitor the current angle using the Get Angle command 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 KdpP and or KdiP 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 WheelCommander WC 132 Product Manual 39 VV heelCommander Hardware Information J7 J10 Vdigital J2 J9 Left Servo Comms J1 Vservo Right Servo bJ J12 I2C optional G cn EEE a 9 optional H bridge z bma Y H bridge board to board gt o board to bo
3. This command lets you confirm that your program is talking to a WheelCommander the Wc part of the name string and also to determine the current firmware version 5 ASCII characters are always returned regardless of physical interface type asynchronous serial or 12C NOTE the firmware version is returned in ASCII HEX so a return value of 25 means firmware revision 37 Example Host sends N n WC 132 returns NWc25 n WheelCommander WC 132 Product Manual 15 Name Status Code Ss 0x53 Params none Returns S mnop 16 bits of status see p 12 for bit definitions Description This command lets you determine the current operating mode of the WheelCommander Name Odometry Code O Ox4F Params c 0 for left 1 for right 2 for left followed by right Returns O mnoparst 32 bit signed value Description This command lets you retrieve the current raw encoder tick count for the specified wheel Name Calibrate Code K Ox4B Params none Returns a or n Description This starts up the lengthy calibration process It only needs to be performed successfully once for a given robot design Repeat this procedure if calibration fails if you change servo models or motor types if you change wheel diameter or wheel base distance between wheels or if you change the motor supply voltage by a large margin A return value of a indicates that calibration is complete While cali
4. a and is returned for all set or action commands that were valid and successfully processed WheelCommander WC 132 Product Manual 5 Nack is the 8 bit value Ox6E ASCII n and is returned for all commands which are invalid for any reason bad CommandCode illegal characters in the parameter fields wrong command length premature command termination due to receipt of a Sync command or failure to perform the command CommandCode and associated parameters are returned for all valid get commands in order to return the values queried unless short mode is on in which case just the parameters are returned Asynchronous Serial Transport In asynchronous serial mode EndOfLine can be indicated by your robot controller using an actual ASCII LineFeed character n or Ox0A an ASCII CarriageReturn character r or 0x0D or even an ASCII Null character 0 or 0x00 The WheelCommander will always indicate EndOfLine back to your controller with a LineFeed White space the ASCII space character 0x20 or the tab character 0x07 will be ignored Parameters are specified in hexadecimal format with the most significant byte first For example the value 21 decimal equals 0x15 in hexadecimal and so in asynchronous serial mode it would be represented by two ASCII characters 1 0x31 followed by 5 0x35 The various possible parameters are short byte there is a special short form of a single byte pa
5. Acceleration values much larger than the requested velocity can expose a known bug in the trapezoidal control code WheelCommander WC 132 Product Manual 51 e I will be using the Nubotics WheelCommander WC 132 to control 12 Volt DC encoder motors with external H Bridges The power source for the motors is a 12Volt lead acid battery When the battery discharges its voltage will drop and a 100 PWM at low charge may result in a lesser voltage to motors than a 100 PWM at full charge Hence do I need to supply a constant regulated 12V to the H Bridges for powering motors so that the wheel commander works effectively and is immune to voltage drop due to discharging of the battery You only need to do this if you must operate the robot at maximum velocity regardless of battery state Normally you should set the maximum commanded velocity that your control program ever issues to the WC 132 to a value that works well all the way to the lowest safe discharge level of the battery for lead acid this is usually 10 8 volts and under the worst expected conditions regarding friction and slope of ground This way regardless of battery level the maximum required PWM is kept below 100 If instead you were to set the maximum commanded velocity to the maximum speed the robot can run at when the battery is full which requires 100 PWM then indeed there is little the WC 132 can do to get the robot to stay at maximum speed when the battery is low In
6. Simple velocity motions keep running until Coast Brake or Reset Motion Parameter commands are issued or until another Go command takes over However if Set Position Set Distance and or Set Angle commands were issued regardless of the other commands then the position PID loops will be active this is a controlled position motion Controlled position motions will eventually terminate as indicated by the Motion Goal Reached status bit bit 4 of the Status command s 16 bit return value This can be polled to determine when a motion is complete Alternatively in asynchronous serial mode the Notify mode bit enables asynchronous notification of motion completion by means of returning the WheelCommander WC 132 Product Manual 27 current position in the same format as the Get Position command s return value As yet another alternative the interrupt system can be enabled such that a digital output line is asserted when a motion is complete Name Upgrade Firmware Code U 0x55 Params mnop a 16 bit unlock password Returns Description This command is for internal use only WheelCommander WC 132 Product Manual 28 WEC 1 82 Installation and Configuration Parts List 1 1 63 x 2 14 4 layer printed circuit board preassembled 2 Two WheelWatcher compatible 4 color coded dual ended cables 3 One I2C 6 color coded cable 4 Optional analog and digital I O cable harness You Provide 1 Servos or motors and
7. as well as sometimes b the y intercept value You can try reducing each of these values after querying what they are set to F 05 n will query the current KpV for example See the User Modifiable Constants Table for the addresses of these constants If you still cannot make it stable then try reducing Lb and Rb constant addresses 34 35 and 47 48 It may be that the calibration procedure resulted in too large of a b value so that it is not possible to output a small enough servo control pulse to go as slow as you require Also you may need to reduce KdfV and KdiV the steering control constants as instability of the steering PID loop will make it hard to tune unstable wheel loops If all else fails you can start from scratch rather than work from the default values First set KpV KiV KdV KdpV KdiV and KDdV to zero and KfV to 16 Next adjust KfV until a smooth wheel velocity is produced If no value except 0 does this then reduce b by 10 and try again Once you find a KfV value that outputs a consistent speed adjust it to be near the goal value The point of KfV the velocity feedforward term is to set a starting point for the control loops that is in the ballpark of the goal velocity under normal loads This frees the PID loop to only controlling for error due to voltage drop friction or variable loads Now increase KpV slowly until it becomes unstable Drop it back to be just on the edge Next increase KiV This w
8. command R was executed While this can be combined with a Set Distance or Set Position command the motion of the robot may not be what you expect It is better to use this with a zero distance change so that the robot rotates in place WheelCommander WC 132 Product Manual 25 Firmware versions 37 and above are able to combine Position Distance and Angle commands to move the platform over a controlled arc In the hypothetical robot in the Set Velocity command description angle changes of less than 10 20 degrees may not be especially well controlled Name Get Angle Code W 0x57 Params none Returns mnop the current measured angle 0 359 degrees through which the platform has rotated available in any Axis Control mode Description This returns the current angle in degrees that the robot has rotated relative to the origin which is assumed to be position 0 and angle 0 either the last time the robot was powered on or the last time the Reset Motion Parameters command was executed This can be useful for example while sweeping fixed sensors sensors mounted in fixed position on the robot platform by rotating the robot the angle read can help you determine the location of a given object during the sweep It can also help you estimate the robot s position and angle pose in the room s frame of reference but this requires you to constantly monitor angle and position values and accumulate estimates of how t
9. flip of a bit position angle velocity and rotation rate are all readable at any time for either the platform or each individual wheel Benefits drives standard RC servos modified for continuous rotation OR DC gearhead motors with external H bridge asynchronous serial OR I2C command interfaces autoswitching upon receipt of first valid command for easy hookup easy to interface with external H bridges in sign magnitude or locked antiphase modes designed for use with Nubotics WheelWatcher Incremental Encoders can also be used with Nubotics Unicoder Magnetic Encoders with proper adapter supports 3 party encoders in either decoded clock direction format as per the WheelWatcher encoders or in Channel A Channel B quadrature format supports any encoder resolution up to 1024 per wheel rotation well isolated servo digital and analog power and ground planes to minimize noise designed to stack with future Nubotics WheelDriver motor driver board digital and servo power voltages readable via two dedicated analog inputs and resistor divider networks helps your robot controller be self aware Note The new WW 11 and WW 12 WheelWatcher encoders work best with the WheelCommander motion controller using quadrature format Simply connect Vcc Gnd ChA and ChB for each encoder to the WheelCommander and leave Mode floating or tie it high with a 10K pullup resistor WheelCommander WC 132 Product Manual 2 Description Thank you for purc
10. for trigger condition Watch hi 0 Interrupt when asserted high if digital or above hi limit if analog Watch lo 0 Interrupt when asserted low if digital or below Io limit if analog 0 If digital 0 level triggered 1 edge triggered ignored for analog 1 This pin is causing the interrupt Example WheelCommander WC 132 Product Manual 18 A photoresistor is connected in a voltage divider arrangement with a fixed resistor with the fixed resistor tied to Vdd and the photoresistor tied to Vss the center tap is connected to analog input 2 You want the interrupt pin to trigger when the room is dark which happens when the resistance of the photoresistor grows large pulling down analog input 2 Say you pick a voltage cut off of 0 5v which corresponds to an 8 bit ADC value of 0 5 5 0 256 25 decimal or 19 hex You need to set the interrupt flag bits to watch lo monitor and input Issue the following command Host sends H 02 2C 19 FF WC 132 returns a Name Get Digital Input Code J Ox4A Params mn a single 8 bit value specifying which digital input to read value values are 0 to 7 Returns J mn op where op is an 8 bit value whose least significant bit contains the logic level of digital input mn Description Digital inputs 0 through 3 are located on the front right side of the PCB and are labeled DO D3 In dual dir bits mode D2 is the right motor inverted direction line and D3 is the l
11. mechanical platforms some tuning of the control loops will be necessary Below we outline a manual method for tuning the loops If you use Windows you should try the WCWizard tuning dialogs as they help you visualize how well each change you make to the tuning constants works and take care of the drudgery of reading and writing the constants Note that PID loop tuning is considered a black art even by experts in the field so don t 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 Consts command F command code with parameter value of OxFFFF WheelCommander WC 132 Product Manual 34 Single Axis Left Right Velocity Control Loop Velocity feed forward KV Velocit i mae rs H bridge and motor Ve B a o KpV Co m b m Kt Js s a M zy i Output scaling L R l i s Lp filter Steering feedback ee Steering rotation rate pa Sc control block PR EA EEEE l 4 y Other side Nubotics WheelCommander c 2009 Noetic Design Inc Figure 8 Axis Velocity Tuning Related Constants KpV KiV KdV KfV F
12. modes Name Set Rotation Rate Code Y 0x59 Params mnop a 16 bit value specifying the number of degrees per second to rotate the platform Axis Control 2 ignored for Axis Control O or 1 Returns a or n Description This command sets a maximum rate of rotation of the platform in degrees per second Most servo controlled robots cannot rotate at much less than 10 degrees per second This does not affect a Position Distance or Angle movement Name Get Rotation Rate Code Y 0x59 Params none Returns mnop the current rate of rotation of the platform available in any Axis Control mode Description This command returns the current actual rate of rotation of the platform in degrees per second This can be used during either velocity or position control modes Name Go Code G 0x47 Params none Returns a or n Description This command starts a movement as specified by previously executed Set Acceleration Set Velocity Set Rotation Rate Set Angle Set Position and or Set Distance commands A Reset Motion Parameters command will discard previous settings Any settings made since then specify the motion to be made by this Go command If only Set Rotation Rate and or Set Velocity commands have been issued then the WheelCommander s velocity PID loops will be active this is a simple velocity motion In this case PID velocity and rotation control loops are in charge
13. that case speed as well as steering will not be well controlled Another reason to set the maximum commanded velocity below the maximum the robot can attain on a full battery is that it provides margin to allow the PID control loops to adjust for changes in friction slope of the ground and so forth as well as to ensure there is adequate margin for steering e Or should I not bother about this issue and connect the h bridges directly to the battery without a 12V regulator There is no need for a regulator normally Also it can be difficult to find such a regulator that can provide enough current for the motors and yet not be either costly or run hot If you use a linear regulator you would need the battery to always be more than 12v the amount more depends on the voltage drop of the regulator Or you could use a switching boost regulator but they are expensive and complex e This is based on the assertion that the control loops in the WheelCommander are taking feedback from the encoders and therefore will make all the required corrections even as the battery voltage drops over time As long as the commanded velocity does not require more than 100 PWM then yes the WC 132 control loops will adjust the PWM to maintain speed This ability to correct for battery level changes often requires the I term integral to be non zero e Can the Nubotics WheelCommander be used to drive a robot at an arbitrary speed set during runtime or only at
14. will ignore I2C connection requests from the master until the command is finished and the WC is ready This is a similar behavior to that of standard I2C serial EEPROMs which do the same thing during a write until the write is complete Your I2C master code will need to either retry the read phase until the WC responds or delay the read phase in anticipation of the long execution time The C B R and G commands take less than 100 ms to execute so a time delay is appropriate here The K command can take a minute or so so retries are the best option for this command to poll for completion Note also that the WheelCommander s slave I2C implementation utilizes standard I2C clock stretching to slow down transfers from the master as needed If the master is not capable of respecting clock stretch requests from the slave incorrect operation and communication errors can result WheelCommander WC 132 Product Manual 8 WC 1 S82 Command Set Modifier abbreviations c single character modifier usually ascii O or 1 mn 2 digit hex modifier 8 bit or single 8 bit byte in I2C mode mnop 4 digit hex modifier 16 bit or single 16 bit word in I2C mode mnopqrst 8 digit hex modifier 32 bit or single 32 bit dword in I2C mode Name Code Hex Params Response Read Meaning written Communication Commands Sync 2E we are synchronized Echo E nm echo back nibbles in reversed order Informational Commands Name NWCXX 5 byte strin
15. work properly the Sync command works but nothing else What s wrong The WheelCommander I2C slave mode requires the I2C master your controller to support clock stretching by the slave the WheelCommander For many commands the WheelCommander must perform some processing between reception of a command via an I2C master write transfer and a subsequent I2C master read request If the WheelCommander receives a read request when it does not have data ready yet it will assert hold low the SCL line to signal to the master that data is not ready When data is ready the WheelCommander will release SCL allowing the transfer to continue This clock stretching method is part of the Philips I2C standard It will be helpful to test and debug your I2C master code with other simpler I2C devices such as I2C serial EEPROMs to make sure it works prior to using it with the WheelCommander Further many I2C master hardware implementations will require you to implement certain time delays between operations The Microchip PIC I8F series of controllers for example require delays between issuing a STOP and any subsequent START of at least 4 7 microseconds 50 microseconds in SMBus environments Shorter times will result in unreliable behavior including but not limited to bus hangs e I ve been looking at the status word Reads fine However bits 15 and 13 are always at 1 These specify the state of the two clk lines Should these reflect the state of t
16. 00 7 230400 experimental 3 19200 8 460800 experimental 4 38400 PWM Output Frequency stored in constant addr 34 Mode PWM 1 Value WOPSOPNI D L APAL WP OTR S mw Q PwM Frequency 62HZ 125Hz 244Hz 488Hz 976HZ 1I953HZ 3906HZ 7812HZ 15625Hz 31250HzZ 62500HzZ NOTE the PWM output frequency range is expanded in firmware revision 37 and greater both going lower and higher than before Typical Robot Platform Measurements Robot Type Junun 1SORC MarkIII band wheel MarkIII o ring wheel Rogue Robotics Blue Parallax BoeBot WheelCommander WC 132 Product Manual wheel Base 35 1 89 mm 35 1 89 mm 65 1 165 mm 44 1 112 mm 82 1 209 mm 92 1 235 mm 86 1 219 mm 82 1 209 mm 13 Status Bit Definitions 3 Overrun n 1 5 z i Calibration Error Codes value Meaning Calibration completed ok Calibration is running Failed to find servo zero motion position Error left encoder attached to right motor and vice versa check wiring Failed to measure max speed of right motor check power and wiring 1 2 3 4 5 Failed to measure max speed of left motor check power and wiring 6 7 Failed to find stable low speed output value 8 Failed to find stable moderate speed output value 9 low and moderate speed output values are inconsistent 10 Curve fitting results are invalid 11 Uncalibrated please calibrate NOTE error
17. 10 is new in revision 37 firmware and above WheelCommander WC 132 Product Manual 14 Command Set Detailed Descriptions Name Sync Code s Ox2E Params none VI Returns i Description This command serves as an early test of communications with a WheelCommander to determine if the WheelCommander is present and the baud rate is set properly in asynchronous serial mode or that the I2C slave address matches between your master program and the setting of the WheelCommander It can also be used to cancel a partial command string in asynchronous serial mode only To cancel a partial command string in I2C mode stop the master transfer after the incorrect number of bytes for the specific command You can also use this command in asynchronous serial mode repeatedly until a is returned in order to reestablish synchronization between your program and the WheelCommander Name Echo Code E 0x45 Params mn 8 bit value to be echoed back Returns E nm 8 bit echo value with nibbles reversed Description This command is used to test communications between your master program and the WheelCommander The nibbles are reversed to ensure that your program is not communicating with some other device which happens to echo back characters in an unmodified fashion Example Host sends E12 n WC 132 returns E21 n Name Name Code N Ox4E Params none Returns NWcxx where xx is the firmware version Description
18. 360 90 y r radius of arc V 360 R 2 m t WE Vb Note R would be negative reer pl lisa Bee X 0 follows standard mathematical conventions Y 270 We T Wd Nubotics WheelCommander c 2009 Noetic Design Inc Figure 1 Inputs as W goaranae Kinematics of Position and Angle Movements D goal distance Wb wheel base We wheel circumference A acceleration limit V velocity limit Ending pose x2 y2 2 in world coordinates Distance traversed by each wheel DI D Wb W m 360 Dr D Wb W m 360 Velocity of each wheel VI V r radius of arc D 360 W 2 1 Vr V Dr DI ore of each wheel Note W would be negative N A D IDI in this example The Wheel rigi Commander coordinate system follows standard mathematical conventions 90 1y Wb Starting pose x1 y1 1 in world coordinates origin 180 X 4X 0 zd 270 We T Wd Figure 2 WheelCommander WC 132 Product Manual VI i Al Pcl Origin DI Vr i Ar Per Origin Dr Nubotics WheelCommander c 2009 Noetic Design Inc Communications The WheelCommander provides two different physical interfaces for transmission of commands and status information asynchronous serial or I2C The asynchronous serial connection is via J10 part of the 14 pin right angle connector along the top edge of the board and is TTL level not level shifted for easy connection to your microcontroller Connectio
19. MDOT OS Wreetcormencier Product Manual Differential Drive Motion Controller for Standard RC Servos and DC Gearhead Motors 1 14 11 23 2011 VV heelCommander Overview This revolutionary controller performs full motion control of a differential drive platform freeing the main robot controller to perform higher level behavior control Features based on wheel circumference and wheel base measurements accepts velocity rotation rate position and angle in real world units built in closed loop velocity and position control loops for each wheel additional closed loop velocity and position steering control of platform to ensure accurate straight line motion or each wheel can be separately commanded asynchronous serial RS 232 features o programmable baud rates 38400 default 115200 max o ASCII human readable commands o TTL signal levels not level shifted I2C features o programmable I2C slave address 8 bit I2C address is 20h default o binary SMBus compatible commands o up to 400KHz transmission rates o clock stretching must be allowed by I2C master 4 general purpose 10 bit analog input lines and 4 general purpose digital 1 O lines each with its own power and ground pin provisions for H bridge current sense field upgradable firmware via asynchronous serial two indicator LEDs one clear EEPROM jumper code examples for common master robot controllers available define the forward vs backward direction of motion with the
20. RTs STX Status Blue vat 0 57 SRX Status Green _ m Sas ri a fad Bs Boma 37 Figure 7 Note Do not connect the WC 132 directly to a USB to RS 232 converter nor to a standard PC serial port the high voltages present can damage the WC 132 and the inverted signaling will result in bad data WC 132 to S27 USB Serial Connections WC 132 Pin Name S27 Pin 310 1 RXD SRX Data Out 310 2 Vdd VCC J10 3 TXD STX Data In J10 4 Digital Vss GND Note this can be connected straight through using the C10 SER INT CONN EXT cable shown above WheelCommander WC 132 Product Manual 32 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 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
21. a dual H bridge 2 Wheels 3 Power 4 Robot controller or PC interface connection 5 Two encoders either WheelWatchers or oth er WheelCommander attached to two servos and two WW 01 WheelWatcher encoders Connections At a minimum you must connect e digital power to J1 6 2v or above ground wire goes towards left side in above photo e communications to your host controller asynchronous serial TTL levels not level shifted or 12C TTL levels external I2C pullups required asynchronous serial ground wire goes towards left side in above photo When ready to try motion commands you must connect e if using servos connect servo power to J2 any voltage your servos can handle may be wired to share the same supply with J1 ground wire goes towards left side of above photo and connect the servos to J7 and J9 black brown ground wires face towards center of board see above e or if using DC motors with an H bridge provide motor power to the H bridge as well as to J2 so the WheelCommander can measure the voltage of it including ground e WheelWatcher encoders or other encoders to J6 and J8 red and black wires face UP Note The new WW 11 and WW 12 WheelWatcher encoders work best with the WheelCommander motion controller using quadrature format Simply connect Vcc Gnd ChA and ChB for each encoder to the WheelCommander and leave Mode floating or tie it high with a 10K pullup resistor WheelCommander WC 132 P
22. able WheelCommander WC 132 Product Manual 45 Interfacing Examples Please check www nubotics com for Arduino Player Stage Parallax Basic Stamp asynchronous serial RidgeSoft RoboJDE java I2C and Microsoft Visual Basic asynchronous serial examples Acroname has published an example for using the WheelCommander with their BrainStem controller http acroname com examples 10013 10013 html RoboRealm an excellent commercial robot machine vision package now includes support for the WheelCommander http www roborealm com help Nubotics Wheel Commander ph WheelCommander WC 132 Product Manual 46 Frequently Asked Questions General Questions Where can I buy it Acroname easier robotics Click here What do the LEDs mean The RED LED DL1 will be lit after power on reset to indicate that stored EEPROM values are being used if off immediately after power on reset the red LED indicates that the Clear EEPROM jumper is active connecting pins 1 and 2 of JP1 If the Clear EEPROM jumper is active the serial port baud rate will be reset to 38400 and the I2C slave address will be reset to 0x20 During operation the red LED will be lit during active movement and off at the end of movement Further the red LED together with the green LED will flash through various combinations during the calibration procedure to indicate the current step number Finally the red and green LEDs alternately blink during firmware updates to indic
23. al control Non trapezoidal control means that the WC 132 will attempt to reach the desired position as fast as possible It does not try in any way to modify your goal position request You will need to control the velocity yourself by issuing incrementally larger goal positions until the real desired goal is reached the delta in position each time divided by the time between changes gives you your requested velocity Trapezoidal control on the other hand controls acceleration and velocity as it moves to a goal position The trapezoidal control code feeds a series of goal positions which change by increments determined by the currently required acceleration and velocity Note that the actual measured real world velocity that your robot will travel will be what you request only if the position control loop PID is well tuned In general you may want to use trapezoidal mode since this will do the position scheduling for you saving a considerable amount of communications overhead between your controller and the WheelCommander This will in turn ensure that all required processor bandwidth in the WheelCommander is available to process high encoder interrupt rate in addition to doing PID control were you to use high resolution encoders When using trapezoidal mode you will need to issue a non zero acceleration amount Values on the order of the requested velocity or a small integer multiple or fraction of it work well under most circumstances
24. al input lines Bits 0 through 7 contained in the second byte returned the first byte of the interrupt map indicate the interrupt status of the digital inputs A bit will be 1 if the digital input interrupt condition previously set up using the Set Digital Output and Interrupt Control command has been met otherwise bits will be 0 Bits 8 through 15 of the interrupt map the third byte returned reflect the interrupt status for the analog inputs Bit 8 corresponds to AO and Bit 15 corresponds to A7 Issuing this command will deassert the interrupt output line and clear the Int is Active and Interrupt Asserted flags Name Reset Motion Parameters Code R 0x52 Params none Returns a or n Description The Reset Motion Parameters command stops any current motion like Brake does and also clears out any current settings for acceleration velocity rate of rotation position and angle Name Brake Code B 0x42 Params none Returns a or n Description This command stops the velocity and position control loops When using servos the WC 132 pulses the servos with the zero motion value found during calibration effectively serving as a form of active braking In PWM sign magnitude mode the PWM output pins will be set to 0 duty cycle which unfortunately provides no active braking In locked antiphase mode the PWM output pins are set at 50 duty cycle with the motors enabled re
25. ard connectors m ge a T s connectors J6 J8 i Left Encoder Right Encoder J3 J4 Analog In Digital 1 0 Figure 12 Connectors The silk screen on the back of the board not pictured shows the reference designators J1 J2 etc Connector Pinouts Ji digital power J1 1 vin J1 2 digital vss ground to right in figure 8 J2 servo power J2 1 Vservo J2 2 servo Vss ground to right in figure 8 WheelCommander WC 132 Product Manual 40 J10 serial communications J10 1 RXD linked to I2C SDA if RC11 amp RC12 present J10 2 vdd 5v out normally not connected except to power external asynchronous serial level converters J10 3 TXD linked to I2C SCL if RC11 and RC12 present J10 4 digital vss ground to right in figure 8 J12 I2C This connects directly to the I2C pins on the processor bypassing RC11 and RC12 which connect the I2C SDA and SCL lines to the communications connector J10 in some versions of the WC 132 If RC11 and RC12 are present located between the I2C and JTAG connectors you could use J12 as an alternate communications connector for I2C or asynchronous serial if it is more convenient for you Production boards will omit RC11 and RC12 to separate the asynchronous serial and I2C busses in which case J12 is the only way to command the WC 132 via I2C IMPORTANT NOTE I2C cable color coding Some models ship with a preassembled I2C cable that plugs into a right angle con
26. arhead motor instead of RC servos available when using servos A5 right H bridge current sense available when using servos A6 Vin J1 voltage divider multiply 10 bit ADC value by 5 1024 40 1 10 0 01958 or divide by 51 07 to convert to volts A7 Vservo J2 voltage divider multiply by 5 1024 100 9 10 0 04927 or divide by 20 30 to convert to volts J4 digital I O signal is topmost row ground is bottom most note supply is digital power and ground D3 D2 D1 DO Signal 34 12 J4 9 34 6 J4 3 Power Vdd 34 11 34 7 34 5 34 2 Ground vss 34 10 34 7 34 4 34 1 Note D2 is used for the Right Motor Inverted Direction in dual dir bits sign magnitude mode in this mode it is not available for other purposes Likewise D3 is used for the Left Motor Inverted Direction Other digital inputs D4 JP1 pin 2 clear EEPROM jumper never use as an output or general purpose input but you can read this to determine whether the shunt is WheelCommander WC 132 Product Manual 42 installed on pins 1 2 D5 J16 pin 3 right DC motor direction available when using servos D6 J16 pin 4 Cleft DC motor direction available when using servos D7 J5 pin 3 CSPI SCK signal which is not used in current Firmware so D7 is available for general use J16 H bridge direction control J16 1 digital vss J16 2 vdd J16 3 Right Motor Direction sign magnitude mode Enable Clocked antiphase mode D5 J16 4 Le
27. ate an error code which should help diagnose the problem In the situation you described the problem is most likely that you have swapped the encoder connectors or the motor connectors e When calibrating should I insert a sizeable delay before reading an a result or immediately accept an error result and poll the status word for calibrate complete If using a delay what would be a suitable value Once calibration is initiated by writing the K command in I2C mode it will ignore its own address and not respond to read or write requests until the calibration completes either with or without error When the WC 132 finally does respond to your request it will return either an a or an n Then you can issue a Q command In serial mode it will output an a character or an n character when calibration is complete after which you can issue a Q command One scheme for dealing with this after writing the K command is to periodically poll say every 100ms the WC 132 until it responds to a read request then obtain the status You could implement this inside your firmware by having it retry STOP delay START issue address plus read bit every 100mS until you receive an ACK e How long does calibration take It really depends on the motors or servos and how they respond but normally approximately one minute e I ve got the system moving but when I execute a Set Position to 100 then a Go I get the following one mo
28. ate that an upgrade is in progress The GREEN LED DL2 will be lit when the command receiver is idle and off while in the middle of receiving and parsing a command Further it together with the red LED will reflect the current stage of the calibration procedure and will also alternately blink with the red LED during firmware upgrades What kind of encoders will it work with The WC 132 WheelCommander firmware rev level 28 is only compatible with 128 pulse per wheel rotation encoders which output the decoded quadrature signals of CLK and DIR Future firmware versions might support programmable encoder resolutions as well as the use of raw quadrature ChA ChB signals Do I need to zero out my servos by adjusting their potentiometers No you don t You just need to make sure the potentiometer is relatively close to the center so that full speed operation in both directions is possible The built in calibration procedure will detect the exact pulse width needed to prevent servo motion If I command the WheelCommander via serial what can I do with it s I2C port or vice versa Currently firmware version 28 the unused command interface is inactive and inaccessible Future firmware versions might provide a passthrough capability so that a serially commander WC 132 can communicate with I2C sensors and transfer sensor data back to your master controller WheelCommander WC 132 Product Manual 47 e I can t seem to get I2C commanding to
29. bration is running the WheelCommander will not respond to commands using either transport method In I12C mode it will even ignore its own slave address this can be used to poll the WheelCommander for completion without keeping the I2C bus busy Your master program may continue to use the I2C bus to access other devices in the meantime Name Calibration Status Code Q 0x51 Params none Returns Qmn an 8 bit status code see p 13 for values Description After calibration completes a return value of n indicates the calibration procedure failed Execute this command Q to determine the type of failure WheelCommander WC 132 Product Manual 16 Name Set I2C Slave Address Code T 0x54 Params mn an 8 bit values whose 7 most significant bits are the same as the 7 most significant bits of the I2C standard s slave address byte Returns a or n Description This command is a short cut for the Set Constant command to modify the I2C slave address Either method instantaneously changes the current slave address Name Set Constant Code F 0x46 Params mn op two 8 bit values mn is the constant number to change and op is the value to change it to Returns a or n Description This command lets you directly modify any user modifiable constant in the WheelCommander see the table on p 10 for details Please do not modify any constants if you don t know what you are doin
30. d 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 its velocity controller is told to slow down If you are not using WC Wizard you will need to monitor the current rotation rate and or current angle using Get Rotation Rate or Get Angle commands These should remain near zero or whatever the starting angle was in the case of Get Angle during a long move If the angle grows continuously during a move try increasing KdpV and or KdiV 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 WheelCommander WC 132 Product Manual 37 Single Axis Left Right Position Control Loop Velocity feed forward s Ke Position Wig KIP Command 4 H bridge and motor Pc g er KpP 7 Kt Js i Output scalin lk KdP P 9 EE l i 3 Lp filter Steering Y l feedback Command a Steering control block Sc a 4 a E Other side Nubotics WheelCommander c 2009 Noetic Design Inc Figure 10 Position Tuning Once velocity control is working well
31. d m essentially sets the largest minimum output value needed to attain full speed 6 Stores the measurements in EEPROM for use in the future WheelCommander WC 132 Product Manual 33 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 Whether or not you are not using WC Wizard place the robot on a small box or stand and run the calibration with the wheels off the ground If you are not using WC Wizard calibration can be performed by issuing the Calibrate command K n and wait for either a indicating success or n You can then query the Calibration Status code Q n which should return Q 01 n A value of 01 means calibration completed ok See the Calibration Error Codes table for other values PID Loop 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 with higher or lower supplies or different
32. der The RED LED will be on and the GREEN LED will be off indicating the Clear EEPROM jumper is present BE SURE TO REMOVE THE JUMPER or move it back to between pins 2 and 3 before the next power cycle after you correct the baud rate or I2C Slave address Clearing the EEPROM resets the baud rate to 38400 and the I2C address to 0x20 The normal position for the shunt is over pins 2 and 3 which are the two pins towards the center of the board WheelCommander WC 132 Product Manual 44 Specifications Servo Control 2 5 msec at 50Hz asynchronous serial Baud Rate 1200 115200 Baud Note 3 I2C Trans Rate 400 KHz Digital Tec TED 200 recommendations Note 1 DC Input Logic Lo w 0 5 0 2 Vcc DC Input Logic High Vcc 0 5 H bridge PWM a Kz fe A D Inputs Dedicated 4 General Purpose 4 A D Resolution 0 bits Digital 1 0 Dedicated 4 General Purpose 4 Note 4 Note 1 servo life may be shortened with supply voltages above its rated value usually 6v although maximum speed will be increased Note 2 at 10 bit A D resolution the smallest value above zero a reading of 1 corresponds to 4 88 mV A reading of 1023 corresponds to Vcc Note 3 230400 and 460800 can be enabled on the WheelCommander side but are currently untested and unsupported Note 4 when using RC servos three of the dedicated are available for general purpose use When using DC motors with dual external H bridges only one of the dedicated digital I O lines are avail
33. e mediated construct this has no connection whatsoever to the hardware interrupts inside the WC 132 s microcontroller It is provided to enable your main robot controller to know when it should poll the WC 132 rather than have to poll continuously The interrupt pin will be deasserted when the user issues the Query Interrupt command below Interrupt System Control Flags and Status Flags Pin 0 Which digital output pin to use as the interrupt signal Int is Active 0 The interrupt is currently asserted Motion Complete 0 1 Generate interrupt when motion command has completed 0 0 set low to indicate interrupt assertion 1 set high Active High WheelCommander WC 132 Product Manual 20 7 Int Enable 0 0 disable interrupt system 1 enabled Name Query Interrupt Code I 0x49 Params none Returns I xy mnop xy interrupt status flags mnop interrupt map Description This command allows you determine the source of an interrupt which the host learned about either through the hardware interrupt line set up previously with the Interrupt Control command or by seeing bit 13 Interrupt Asserted of the Status command s return data being asserted The first byte returned after the optional command echo T is the interrupt status flags as defined above in the Interrupt Control command The next two bytes are a 16 bit map of the interrupt status for all analog and digit
34. eft motor inverted direction line so they won t be available for general purpose use in that mode D4 is hardwired to the Clear EEPROM jumper so you can use it to read the current state of the jumper D5 right motor direction in sign magnitude mode or right motor enable in locked antiphase mode D6 is the same as D5 but for the left motor D7 is connected to J5 pin 3 and is normally unused NOTE all digital input pins have pullups enabled these pullups are located inside the microcontroller on the WC 132 and are normally between 20K and 50K ohms Name Set Digital Output and Interrupt Control Code J Ox4A Params mn op two 8 bit values where mn is the digital output to change 0 to 7 and op contains the digital input interrupt control flags Returns a or n Description This command lets to change the specified digital I O pin direction interrupt generation ability and also set its level 0 or 1 if it is an output The firmware currently allows you to change any of the 8 digital T O lines but this can be dangerous in various motor control configurations as D5 and D6 and sometimes D2 and D3 can already be in use D4 is hardwired to the clear EEPROM setting so please never set this high or you could cause a short circuit the clear EEPROM jumper when present connects D4 to ground D7 is available on pin 3 of J5 WheelCommander WC 132 Product Manual 19 NOTE all digital input pins have pullups e
35. ers want the 8 bit value For example the Ridgesoft RoboJDE s I2CMaster transfer method wants the 8 bit value whereas the Savage Innovations OOPIC wants a 7 bit value In I2C mode EndOfLine is indicated implicitly by means of the number of bytes written to the slave the WheelCommander by the master your robot controller After writing the slave address CommandCode and parameter bytes as required by the command the master simply ends the transfer by signaling a STOP condition after receiving ACK on the last byte The master can optionally request the return value of the command using a REPEATED START or a separate START in read mode and request a single byte For complex query commands which both require you to write one or more parameters and also read one or more return values you would first issue a START the slave address with the WRITE bit set the CommandCode and any required parameters a Repeated START condition the slave address with the READ bit set and then the return values can be read Your master would read as many bytes as it required or until an I2C NACK condition occurred It would then signal a STOP condition Alternatively in a single master environment separate START STOP conditions can occur for each phase of a complex query command first write the command and its parameters if any which may be required to specify what is being queried e g which digital I O pin then a read transaction will read the Co
36. eturned for illegal commands ill formed commands long running command In I2C mode the WC will ignore connections until ready denotes commands available in firmware revision 37 or higher denotes commands changed in firmware revision 37 or higher which are no longer compatible with earlier versions WheelCommander WC 132 Product Manual 10 User Modifiable Constants Address Default Meaning 0 1 not used reserved not accessible 2 80h mode see below 3 4 asynchronous serial baud rate see below 4 20h I2CADR_ I2C address 5 6 axis velocity P proportional gain 6 4 axis velocity I integral gain 7 1 axis velocity D differential gain 8 16 axis velocity feedforward gain 9 1 axis velocity output gain deprecated in firmware 37 and above 10 6 axis position P proportional gain 11 4 axis position I integral gain 12 1 axis position D differential gain 13 4 steering position P proportional gain 14 0 steering position I integral gain 15 0 steering velocity P proportional gain 16 4 steering velocity I integral gain 17 1 angle hysteresis difference between encoder counts tolerated without correction 18 1 position hysteresis error tolerated per axis below which motion deemed complete 19 2 position velocity threshold velocity of axis must be lt to declare motion complete 20 2 velocity threshold how close actual velocity must be to declare at speed F 35 wheel base in cu
37. ft Motor Direction Enable D6 J15 H bridge current sense J15 1 analog Vss J15 2 analog Vdd J15 3 Left Current Sense A4 J15 4 Right Current Sense A5 J13 H bridge left PWM J13 1 PWM out J13 2 Vmotor monitor note this is for low current voltage monitoring only not for supplying power to an H bridge external wiring is recommended J13 3 Vmotor Vss low current ground J14 H bridge right PWM J14 1 PWM out J14 2 Vmotor monitor J14 3 Vmotor Vss J5 SPI J11 JTAG These connectors are currently not usable by customers but are for factory use only The only exceptions are J5 SPI pin 2 which is 5v J5 SPI pin 6 which is digital ground J5 SPI pin 3 which is Digital I O line D7 and J5 SPI pin 5 which is an active low RESET pin If you would like to give your robot controller the ability to hard reset the WheelCommander you can do so with this pin It must be at a logic high level for the WheelCommander to run JP1 clear EEPROM D4 You can restore the all of the factory settings including baud rate and I2C address as well as PID parameters and platform setup values by issuing the Reset Consts command F command code with parameter value of OxFFFF Alternatively to recover from communications misconfigurations only install a 2mm WheelCommander WC 132 Product Manual 43 pitch shunt on the Clear EEPROM jumper header over pins 1 and 2 then power cycle the WheelComman
38. g Also the EEPROM locations used have a finite lifespan Please do not use the Set Constant command except at robot startup if needed rapid and continuous rewriting of an EEPROM location will eventually literally wear it out Name Reset Constants to Factory Defaults Code F 0x46 Params FF FF two 8 bit values with all bits set to one Returns a or n Description This will result in all user modifiable constants to be overwritten with factory default values This may be useful to recover from configuration errors or to start clean when moving the WheelCommander to a new robot platform WARNING this will reset every constant including baud rate and I2C address so use this command carefully Name Get Constant Code F 0x46 Params mn a single 8 bit value specifying the constant number to read Returns F mn op where op is the 8 bit value of constant number mn Description This will return the current value of any of the user modifiable constants In asynchronous serial mode you can currently only read a single constant at a time In I2C mode you can continue reading as many constants as you require up to 30 constants in one command WheelCommander WC 132 Product Manual 17 Name Get Analog Input Code H 0x48 Params mn a single 8 bit value specifying which analog input to read valid values are 0 to 7 Returns H mn opqr where the least significant 10 bits of the 16 bit val
39. g device name Wc Wheelcommander firmware version XX Status current device status See below C mnopqrst Retrieve current encoder tick count for wheel c Odometry where c 0 for left 1 for right 2 for left followed by right Control Commands calibrate automatically configure motors cal Stat return calibration status I2c Addr set I2C slave address to 7 bit value mn Set Const set constant number mn to value op Reset Consts reset all constants to factory defaults Get Const gets value of constant mn Analog Input read analog input xy mnop is the 10 bit analog value set analog input bit xy s interrupt control Analog flags to mn lower limit to op upper to qr see control below Digital Input Set digital I O pin xy to be an input read its value and return as mn 2 set digital I O pin xy s interrupt control flags Digital to mn see below Output xy specifies the digital output pin to assert Interrupt as well as other parameters see below Output CY xy mnop returns interrupt status byte xy see below as Query well as a 16 bit map of pending interrupts Interrupt Motion Commands Reset resets all motion values stops motion Brake active braking stops current motion Coast turn off motors stops current motion low power consumption mode Axis Control separate or coordinate the axes c is O left wheel 1 right wheel 2 both default WheelCommander WC 132 Pr
40. hasing a Nubotics WheelCommander This revolutionary new product is unlike any other servo or motor controller on the market The Nubotics WheelCommander coordinates the motion of both wheels of a differential drive robot using odometry provided by Nubotics WheelWatcher encoders or other encoders It uses real world units of measurement to specify distance velocity angle and rate of rotation It provides battery voltage monitoring motor current monitoring as well as four general purpose digital I O and four analog input lines And it can work with simple low cost RC servos and yet provide accurate dead reckoning and speed control Kinematics The WheelCommander offers two separate motion control systems which you are free to use depending on your needs The first is the velocity and rotation rate control system This system is useful when your main robot controller needs to parametrically control the motion of the robot in response to periodically changing sensor data such as sonar or IR range finders The second is the position and angle control system This is useful when you need the robot base to reproduce a predetermined sequence of movements over specific distances and turning angles Both of these systems provide feedback in the way of odometry information which your robot controller can use to infer the robot s position in world coordinates this is not done within the WheelCommander due to the need to perform trigonometry to calcula
41. he LEDs on the Wheel Watchers As I turn each wheel the Dir bits follow the LEDs This is normal The red LEDs are hooked to ChA in other words a buffered version of the signal detected by one of the photosensors The green LED however hooks to the decoded direction output of the LS7084 chip this is the same as the State of x Wheel Dir Line in the status word bits 12 and 14 The State of x Wheel Clk Line bits 13 and 15 reflects the value of the clock output of the LS7084 not ChA so they are not the same The clock output of the LS7084 only pulses low for tens of microseconds upon detection of an edge transition on either ChA or ChB so you would be lucky indeed to see bits 13 or 15 go low In hindsight these bits are not very useful except to confirm that the WheelWatcher encoders are connected e After I enable PWM mode by setting constant 2 to 0x98 I see pulses on the servo outputs still Is there something I have missed The servo output pins are connected to the PWM output pins so you will see the same signal WheelCommander WC 132 Product Manual 48 e I m using the WheelCommander with an external H bridge and PWM mode When I try to run the Calibrate command it runs one motor 100 on the other nearly 100 off for 4 seconds then turns both wheels off and then nothing What s wrong The Calibration Status command when issued after the Calibrate command as explained on pages 24 25 in the manual will indic
42. hese values affect the robot s pose This can be used during either velocity or position control modes Name Set Relative Angle Code Z Ox5A Params mnop a 16 bit relative angle in degrees to rotate the platform Axis Control 2 ignored for Axis Control 0 or 1 Returns Description This command sets a goal angle in degrees through which the robot platform should be rotated in a controlled manner This is relative to the robot s current pose i e repeating a Set Relative Angle command of 90 degrees will rotate the robot by 90 degrees every time While this can be combined with a Set Distance or Set Position command the motion of the robot may not be what you expect It is better to use this with a zero distance change so that the robot rotates in place In the hypothetical robot in the Set Velocity command description angle changes of less than 10 20 degrees may not be especially well controlled Name Get Relative Angle Code Z Ox5A Params none Returns mnop the current measured angle 0 359 degrees through which the platform has rotated available in any Axis Control mode Description Currently the firmware returns the same value for this command as for the Get Angle command In the WheelCommander WC 132 Product Manual 26 future it could return the angle subtended from the start of the last Set Relative Angle or Set Angle command This can be used during either velocity or position control
43. ill 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 KdV 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 KfV scale is good it should continue to match the goal velocity up to Vmax If not you may need to increase KfV a little If this results in the low speed not being stable again reduce KfV back to the good position then reduce b by 10 or so and increase m by one to slightly increase the slope resulting in larger WheelCommander WC 132 Product Manual 36 outputs on the high end but not much or any change on the low end Rotation Rate Steering Control Loop Left Velocity Error Left Correction ees snp sat 1 s gt KdiV Steering Command iat i p eering Correction c s j gt KDdV EERTE EEAO eee eterna eee h E Right Velocity Error Right Correction Nubotics WheelCommander c 2009 Noetic Design Inc Figure 9 Velocity Steering Tuning Differential Drive Steering Parameters Constants KdpV steering velocity proportional constant KdiV steering velocity integral constant and KDdV steering velocity differential constant are used to tune the ability of your robot to drive in a straight line Often KdpV can be zero KdiV shoul
44. irst make sure velocity control works well Most typical servos cannot spin the wheels faster than 100 RPM usually more like 60 to 80 Assuming 60 RPM calculate the maximum possible velocity Vmax 60 RPM 1 minute 60 seconds WheelCircumference e g for 1 units and a standard injection molded wheel Vmax 100 60 82 82 tenths of an inch per second This value is automatically measured during the calibration procedure and can be queried by reading MxSpd a 16 bit constant stored at addresses 29 and 30 It is also displayed in WCWizard on the Calibration dialog 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 Issue a velocity command for Vmax followed by the Go command V 00 52 n G n WheelCommander WC 132 Product Manual 35 Now query the velocity a few times and see what the current velocity is vy n If the velocity is too low you need to increase KfV if it is too high decrease it It might not be stable yet though At this point you are just trying to set the overall scale Now try running it at the lowest velocity you expect to require in your application A value of 5 20 of Vmax are common 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 KpV KIV KdV and KfV
45. it is time to tune position control KpP KiP KdP and KfP are the constants for tuning the position loop KpP specifies the proportional term KiP specifies the integral term and KdP specifies the differential term KfP specifies a velocity feedforward term normally 16 is the correct value 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 If it overshoots reduce KpP and or KiP If it oscillates increase KdP but not too much or it will oscillate even more If the cruising speed is incorrect too high or too low adjust the KfP value Firmware revisions 37 39 do not work properly if Trapezoidal mode is not set this is fixed in firmware 40 and above Trapezoidal mode enables smooth acceleration cruising and deceleration using either the default of 12 of the maximum velocity as measured during calibration or the value specified before Go using the Velocity and or Acceleration commands WheelCommander WC 132 Product Manual 38 Steering Angle Control Loop Left Position Error Left Correction i k 1 s gt KdiP Steering Command ae r eering Correction Sc er I Kop 9 normally 0
46. les that come with the WheelCommander are too short for my application How can I get longer ones We can sell 6 or 8 cables to you Please contact info at nubotics dot com Or you can buy the precrimped wires for a variety of lengths as well as the connectors at Digikey Here are the part numbers H2019 ND 4pos 2mm dual row crimp sockets H2022 ND 8pos 2mm dual row crimp sockets H3BBT 1010x A8 ND x orange 28 gauge wire with precrimped socket terminals on each end H3BBT 1010x RS ND x red H3BBT 1010x V8 ND x violet H3BBT 1010x BS ND x black Replace the x with a number for the length in inches for example H3BBT 10106 B8 ND is for a 6 black wire e I can t seem to code the ability of a command to delay until the present command has stopped executing I am reading the status word and checking the flags but I can t find a flag or set of flags that gives me this effect Sequences work if I introduce appropriate delays but I don t want to use this approach Reading the status word seems to be fine What am I doing wrong Which command is presently executing Is it an Angle Relative Angle Position or Delta Distance command If so then Motion Goal Reached Status bit 4 will be set when the motion concludes However if the position loop PID constants are such that the unit either overshoots and oscillates over the goal or that it never quite reaches the goal because of static friction because KdiP is too
47. mmandCode if short mode is off plus the returned parameters Be sure to compare the CommandCode to that which you originally issued to make sure the parameters are what you expect WheelCommander WC 132 Product Manual 7 NOTE This non standard method of reading parameters was added to support access from Via MiniITX boards and others under Linux In that environment the I2C sensor library can be used to communicate with 12C peripherals such as Devantech SRFO8 sonar rangers as well as the WheelCommander Most WheelCommander commands can be issued with a single library call except for commands which require parameters to be written and also read in the same command In that case you must issue separate write and read requests Parameters are specified in binary format with the least significant byte first in order to be compatible with SMBus standards For example one could set a relative position change of 500 500 decimal 1F4 hexadecimal units by issuing the following command START SlaveAddr Write Ack X Ack F4 Ack 01 Ack STOP START Addr Write x OxF4 0x01 STOP ZA e o 0 0 X is the 8 bit ASCII value for the capital letter ex 0x58 which represents the Set Delta Distance command In this case Ack represents the I2C notion of acknowledgement not the WheelCommander Ack character Certain commands C B R G and K can take a relatively long time to execute As a result the read phase of the command
48. n to a PC s true serial port requires either an RS 232 serial level shifter available separately or a USB to serial converter Connection to I2C is via J12 on the left edge of the board External 4 7K ohm pull up resistors on both SDA and SCL are required for proper I2C operation The WheelCommander command set has the same high level structure command codes parameters and return values regardless of physical interface used to transport them The encoding of parameter and return values does change to be appropriate for each interface as does the method of specifying the length of a command Each WheelCommander command has the following structure CommandCode param1 param2 EndOfLine CommandCode is an 8 bit value between 0x41 ASCII A and 0x5A ASCII Z or the special value 0x2E ASCII the Sync command Commands can be set commands action commands or get commands Parameters and return values can be 8 16 or 32 bits in length The method of indicating EndOfLine is indicated differently depending on transport method The byte order for multibyte parameters also depends on transport method Each WheelCommander command returns one of the following results Sync EndOfLine Ack EndOfLine Nack EndOfLine CommandCode param1 param2 EndOfLine Sync is the 8 bit value 0x2E ASCII It indicates that the WheelCommander confirms receipt of a Sync command Ack is the 8 bit value 0x61 ASCII
49. nabled these pullups are located inside the microcontroller on the WC 132 and are normally between 20K and 50K ohms Example Your robot has a font bumper switch connected to D1 The switch is wired so that it grounds the pin relying on the internal pullup to pull D1 to a logic high level when the bumper is not depressed actuated You wish to see an interrupt in your main robot controller by connecting one of its input pins to another digital output pin already enabled as the interrupt output see below whenever the bumper is pressed You would set the digital input interrupt flags byte so that Digital Input Monitor and Watch Lo are Is To do so issue the following command Host sends Y 01 2E WC 132 returns a Name Interrupt Control Code I 0x49 Params xy 8 bit interrupt system control flags Returns a or n Description This command allows you to specify details about the interrupt system A single digital output pin if set using the Pin field of the interrupt system control flags and enabled with the Int Enable flag will be generated when any specified condition occurs These conditions include when a motion command completes the Motion Complete flag below or when any of the analog input or digital input interrupt conditions are met These multiple interrupt sources are logically OR d together to generate the single interrupt output Note that the WC 132 interrupt system is a softwar
50. nd can be used during either velocity or position control modes Name Set Distance Code X 0x58 Params mnopgrst a 32 bit distance to move the platform Axis Control 2 or the selected wheel relative to the current position Returns a or n Description This command is similar to the Set Position command except that it specifies a distance to move relative to the current position A series of Set Distance commands with a parameter of 100 moves the robot forward 100 units each time a series of Set Position commands with a parameter of 100 results in no motion once position 100 is reached Units and reference frame information are the same as the Set Position command Name Get Distance Code X 0x58 Params mnopgrst a 32 bit absolute position Returns Description Currently the firmware returns the same value for this command as for the Get Position command This can be used during either velocity or position control modes Name Set Angle Code W 0x57 Params mnop a 16 bit absolute angle in degrees to rotate the platform Axis Control 2 ignored for Axis Control 0 or 1 Returns Description This command sets a goal angle in degrees through which the robot platform should be rotated in a controlled manner This is relative to the robot s frame of reference where the origin is an angle of zero degrees when the robot was last powered on or when the last Reset Motion Parameters
51. nector installed at J12 facing left in figure 8 It is best to go by the wire color not the WC 132 silkscreen pin numbers nor the connector housing pin numbers as pins 1 and 4 differ between the two Signal Name Color of Wire WC 132 Silk Screen Pin Numbering vad 5v Red SCL 2 SDA 3 4 Vss Ground J7 left servo J7 1 servo control white yellow orange 37 2 Vservo Cred J7 3 servo Vss black brown to right in figure 8 J9 right servo 39 1 servo control white yellow orange 39 2 Vservo Cred 39 3 servo Vss black brown to left in figure 8 WheelCommander WC 132 Product Manual 41 J6 left encoder black and red are topmost in figure 8 violet and orange will be closest to the board 36 1 Clock or Channel A violet 36 2 Vdd red 36 3 Direction or Channel B orange 36 4 digital vss black J8 right encoder black and red are topmost in figure 8 violet and orange will be closest to the board 38 1 Clock or Channel A violet 38 2 Vdd red 38 3 Direction or Channel B orange 38 4 digital vss black J3 analog inputs signal is topmost row ground is bottom row NOTE supply is analog power and ground isolated from rest of board A3 A2 Al AO Signal 33 12 13 9 33 6 33 3 Power Vdd 33 11 33 7 33 5 33 2 Ground vss 33 10 33 7 33 4 33 1 Other analog inputs A4 left H bridge current sense when using optional H bridge to drive a DC ge
52. ng 7 bits are the binary whole part this constant is new for firmware revision 37 and above this constant has been widened from 8 to 16 bits to provide more precision in firmware revision 37 and above this constant s address has moved compared to firmware older than revision 37 Mode Constant Bit Assignments stored in constant address 2 Default Meaning Slow Comms insert a 40ms intercharacter delay for compatibility with the BasicStamp 0 instant ack motion commands 1 current position velocity on goal reached turn off echoing of command code when returning data for OOPIC for commands that take an address field such as Get Const Analog Input and Digital Input the address field will also not be returned in short mode only the requested value is Polarity 0 1 flip dont flip forward vs backward direction of platform 0 RC servo mode 1 PWM h bridge mode LockedAntiphase if PWM 1 0 sign magnitude control 1 locked antiphase control Short Mode hal WheelCommander WC 132 Product Manual 12 6 DualDirLines PWM 1 LockedAntiphase 0 0 single 1 dual inverted direction line PWM HighEnable 1 LockedAntiphase 1 0 active low 1 active high motor enable 7 CounterAxis motor shafts point in 0 same 1 opposite directions Baud Rate Selection stored in constant address 3 Value Baud Rate Value Baud Rate 0 1200 5 57600 1 4800 6 115200 2 96
53. oduct Manual 9 Set Accel A 41 mnop Set goal acceleration for use in position or angle commands Get Accel returns current acceleration goal not measured Set Velocity Vv 56 mnop set goal velocity to mnop signed value in distance units per second Get Velocity Vv 56 none Returns currently measured velocity signed value Set Position 44 mnopqrst set absolute goal position in terms of distance units see below signed Get Position fo a none f mnopqrst returns current absolute position Set Delta X 58 mnopqrst set relative distance goal signed Distance Get Delta X 58 mnopqrst mnopqrst same as Get Position Distance Set Angle w 57 mnop set angle to rotate the platform in degrees signed gt 0 is counter clockwise when robot viewed from above Get Angle distance the platform has rotated since reset Set Relative Zr 5A mnop set relative angle change from current position Angle in degrees signed Get Relative Z 5A none same as Get Angle Angle Set Rotation sY 59 mnop set rate of rotation of platform in degrees per Rate second signed Get Rotation y 59 none returns currently measured rate of rotation Rate Go G 47 none start executing current velocity rotation rate distance and or angle movements Maintenance Commands Upgrade UF 55 mnop none if mnop is correct password jump to the bootloader to perform firmware upgrade other n 6E not acknowledge r
54. one particular speed thats pre configured as per the WheelCommander WC 132 Product Manual 52 PID constants The speed as well as rate of rotation can be commanded modified on the fly at run time That is one of its main purposes The PID constants adjust how the feedback provided by the encoders together with the commanded speeds of each wheel result in motor control signals that seek to minimize the error between the feedback and the commands They do not by themselves set the speeds of the wheels There may be some confusion due to the MxSpd constant It stored in EEPROM like the PID constants are is determined automatically by the calibration routine and is later used to convert PID equation outputs to PWM values appropriate for your robot It is not meant to be changed at run time e Are internal pullups enabled for the encoder input pins No they are not The encoder inputs need to be driven high and low by your encoder within the DC Input High and Low ranges mentioned in the Specifications section 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 2011 Noetic Design Inc All rights reserved November 23 2011 WheelCommander WC 132 Product Manual 53
55. rameter for indicating simple values of 0 and 1 in other words a single bit in this case only one ASCII numeral 0 or 1 are sent byte an 8 bit value between 00 decimal 0 and FF decimal 255 both nibbles must be transmitted each consisting of one 8 bit ASCII character signed byte an 8 bit 2s complement value between 80 decimal 128 and 7F decimal 127 Both nibbles required word a 16 bit value between 0000 and FFFF decimal 65535 all 4 nibbles must be transmitted signed word a 16 bit 2s complement value from 8000 decimal 32768 to 7FFF decimal 32767 all 4 nibbles required WheelCommander WC 132 Product Manual 6 dword a 32 bit value between 00000000 and FFFFFFFF all 8 nibbles must be transmitted signed dword a 32 bit 2s complement value between 80000000 decimal 2147483648 and 7FFFFFFF decimal 2147483647 all 8 nibbles required I2C Transport The factory default I2C Slave Address for the WheelCommander is 0010000 0x10 this is the upper 7 bits of the 8 bit I2C address byte where the least significant bit indicates the direction of transfer 1 read 0 write per the I2C standard The complete 8 bit I2C address byte would then be 0x20 or 0x21 7 6 5 3 2 oe 0 0 joo 0 0 NOTE A common source of error when first using any I2C device results from using the wrong slave address Some I2C APIs want the 7 bit value and oth
56. rams none Returns L c where c is defined as in the Set Axis Control command Description This returns the current state of Axis Control The default value is 2 which means the two wheels are controlled simultaneously Name Set Acceleration Code A 0x41 Params mnop a 16 bit acceleration goal for position or distance moves Returns a or n Description This command lets you set the maximum rate of change of velocity during a position distance and or angle command It has no effect on simple velocity or rate of rotation motions The unit of measurement is in terms of distance per second squared where distance is in the same units used for wheel circumference and wheel base WheelCommander WC 132 Product Manual 22 NOTE the Reset Motion Parameters R command will reset the acceleration for position distance and or angle commands to max speed firmware 37 or max speed 2 firmware 38 and above over one second Name Get Acceleration Code A 0x41 Params none Returns mnop the current actual setting used for position or distance moves Description Unlike the other query commands this does not return the actual measured value it instead returns the actual value used by the firmware based on the value set in a previous Set Acceleration command The value is adjusted automatically by the firmware to conform to numeric limitations in the firmware so the value read back may not be the val
57. roduct Manual 29 Mounting mounting holes are 118 diameter 4 40 screw size spaced 1 89 x 1 40 the WC 132 fits between the standoffs on Junun org MarkIII style chassis under the main robot controller though you may have to extend the standoffs a bit to clear the analog and digital I O connectors On MarkIII style chassis the mounting holes cannot be used as they are above the servos use double stick foam tape instead Setup In your own software or using the optional Windows based WCWizard utility establish communications with the WheelCommander set the following parameters as needed oo N DU RWNE asynchronous serial baud rate I2C slave address wheel circumference wheel base mode default is servo mode counter rotating axes invoke the built in motor calibration command with the robot raised off the ground so that its wheels freely rotate check the result of calibration tune the velocity and position PID loops WheelCommander WC 132 Product Manual 30 WheelCommander elocity PID Loop Tuning Oj x Go Max Go Step Max Velocity 53 Min Velocity E Step Cycle Time p Max Rotation jo sich ca atl Min Rotation jo Output Gain 35 Velocity Parameters Proportional Integral Differential Feed Forward m Differential Drive Steering Parameters Velocity vs Time 60 ne 7 RA Rotation Rate vs Time 3 Proportional Integral E aval
58. 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 Motor Calibration 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 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 an
59. rrent units of measurement e g millimeters or tenths of an inch 21 22 82 wheel circumference in current units e g millimeters or tenths of an inch 23 24 F 375 left servo zero calibration constant 25 26 375 right servo zero calibration constant 27 28 te 80 maximum useful speed measured during motor calibration 29 30 EFE 0 motor vs encoder direction control bit 0 right motor bit 1 left motor 0 is 31 normal 1 means the direction of motor rotation is inverted EF 200 left motor output slope 32 33 WheelCommander WC 132 Product Manual 11 left motor output intercept 34 35 when in H bridge mode the current PWM frequency see table 36 ModeExt extended mode bit 0 quadrature encoder not clk dir bit 1 trapezoidal move 37 enable encoder ticks per wheel rotation 38 39 steering position control D differential gain 40 steering velocity control D differential gain 41 axis position velocity feedforward gain 42 difference in wheel circumference between left and right used to correct slight differences in wheel size which cause long term curvature of a straight movement E 43 44 right motor output slope 45 46 right motor output intercept 47 48 binary point for fixed point arithmetic associated with m and b motor output constants 49 9 means the 9 least significant bits represent the binary fractional part and the remaini
60. s a goal distance for the platform or a specific wheel relative to the robot s frame of reference where the origin is where the robot was last powered on or when the last Reset Motion Parameters command R was executed Units are in distance the same as used for wheel circumference and wheel base In the hypothetical robot mentioned in the Set Velocity command above motions of less than 10 15 less than 1 0 1 5 may not be able to be accomplished due to low encoder resolution coupled with wheel and motor gear train friction Name Get Position Code D 0x44 Params none WheelCommander WC 132 Product Manual 24 Returns mnopgqrst a 32 bit position of the platform Axis Control 2 or of the selected wheel Description This command returns the current measured position in the robot s frame of reference relative to the origin and in the units of measurement as defined in the Set Position command The position can be of either the platform or an individual wheel NOTE the robot s frame of reference changes as it rotates so the distance is really a line integral of the actual distance the robot has travelled It is not trivial to estimate the robot s position in the room s frame of reference although executing a series of simple stationary rotations and simple forward and reverse motions will make it easier if one also ignores wheel slippage Wheel slippage can be reduced by using low acceleration values This comma
61. small then it may take a long time or may never actually terminate Of course too large of an integral constant will make a PID loop unstable as well WheelCommander WC 132 Product Manual 50 Other constants that affects this are KdH angle hysteresis KpH position hysteresis and KpvTh position velocity threshold KpH sets the maximum error in position or angle allowed to declare Motion Goal Reached Likewise KpvTh sets the maximum absolute velocity allowed to declare Motion Goal Reached Using an H bridge in PWM mode we ve noticed that these constants may need to be adjusted somewhat larger Note that the Velocity or Rotation Rate commands will be declared Motion Goal Reached when the required velocity or rotation rate is within some tolerance of the goal KvTh If the velocity PID loop is not properly tuned it may never quite reach the goal due to static or dynamic friction The KiV velocity integral gain will ensure that such friction is overcome though too large of a value will make the loop unstable So better tuning will ensure it reaches the goal in a timely manner As a problem solving tool you can query the current position velocity rotation rate and or angle and display that to yourself to see how much error there is You could add your own acceptable limits on this so that you can issue a Coast command before moving on to the next motion e What is the difference between non trapezoidal position control vs trapezoid
62. sulting in active braking NOTE this can consume considerable power so do not leave you robot in this state for long periods or you will drain your WheelCommander WC 132 Product Manual 21 batteries Issue Coast instead to ensure motors and servos are turned off Name Coast Code Cc 0x43 Params none Returns a or n Description This command stops the velocity and position control loops When using servos no more control pulses are sent which results in your robot coasting to a stop When using h bridges the motors are unpowered This is the lowest power consumption setting Name Set Axis Control Code L Ox4C Params c a single character asynchronous serial mode or byte I2C mode where 0 specify settings for the left wheel 1 right wheel and 2 both wheels the default Returns a or n Description This command allows you to individually control the motion of each wheel The default is to coordinate each wheel together Currently the firmware is limited in that you must set acceleration velocity and or position or distance values for a given wheel then issue a Go command before you can change any settings for the other wheel Velocity position and distance queries will be of the currently selected wheel or whatever mechanism is attached to that motor or servo angle and rotation rate queries are always of the platform Name Get Axis Control Code L Ox4C Pa
63. te world coordinates Both of these systems have their own sets of PID constants for the wheels and for steering of them The following two figures outline the kinematics performed by the WheelCommander using either control system First for velocity and rotation rate control the figure shows you what measurements are needed of your robot how the robot will move for arbitrary combinations of velocity and rotation rate and the assumed world coordinate system within which the robot operates Second for position and angle control we show similar diagrams indicating how the robot will move along an arc based on the distance and angle movements specified Note that straight line motion and rotation in place are both special cases of the general problem of moving in an arc Straight line motion corresponds with a rotation rate of 0 degrees sec or angle change of 0 degrees resulting in an arc with an infinite radius of curvature Spinning in place corresponds with velocity of 0 distance units sec or a distance change of 0 units resulting in a radius of 0 Finally spinning around one wheel occurs when the arc radius equals 1 2 of the wheel base WheelCommander WC 132 Product Manual 3 Kinematics of Velocity and Rotation Rate Motion Inputs R goal rotation rate about center V goal velocity of center Wb wheel base We wheel circumference Outputs Velocity of each wheel VI V Wb R 1 360 Vr V Wb W tr
64. tor turns continuously in the correct direction but does not stop the other motor runs for 3 seconds in the correct direction then stops then reverses after 3 seconds it reverses again Is it possible that this is caused by incorrect direction or PWM signals It sounds like you have not tuned the PID loops Tuning is very important especially for DC motor operation as every plant motor driver motor gearbox encoder is different We highly recommend using our WCWizard to make this easier It sounds like the position loop constants KpP KiP KdP are too large and also probably the steering constants KdpP KdiP If you can t use WC Wizard then please WheelCommander WC 132 Product Manual 49 follow pages 25 28 of the manual This is a common procedure needed for all kinds of closed loop motion controllers especially those used in industrial applications but of course also robots Tuning of PID loops is a bit of an art but if you follow the process as described in the manual you should have a good chance of getting it to behave well e Can Iuse the motion control active flag to verify that the Wheelcommander is busy idle or do I have to check the relevant in progress flags Status bit 5 motion control active is the master flag for all motion types and is TRUE whenever moving to a position rotating to an angle moving at a specified velocity or rotating at a specified rotation rate e The WheelWatcher cab
65. ue opqr contain the A D value of A D converter mn Description Analog inputs 0 3 are available on J3 located on the front left side of the PCB and are labeled AO A3 Analog inputs 4 and 5 are connected to left and right current sense pins for future use with the WheelDriver dual H bridge board Otherwise you may use these for your own purposes See the connector pinout section below for A4 and A5 locations Analog inputs 6 and 7 read the digital and servo supplies respectively They use resistor divider networks to ensure that the maximum allowable input voltage to the A D converters is not violated See the connector pinout section for divider values Name Set Analog Interrupt Control Code H 0x48 Params xy mn op qr see below Returns a or n Description This command new to firmware revision 37 allows one to specify how the user programmable interrupt output pin is affected by a given analog input xy specifies the pin number mn specifies the analog input interrupt control flags for this pin op specifies the lower limit value and qr specifies the upper limit value The interrupt control flags are specified as follows Analog and Digital Input Interrupt Control Flags Default Meaning Analog not used digital output value to set it to Digital 0 if an analog pin 1 if a digital pin 1 0 if an output digital only 1 if an input Monitor 0 0 ignore 1 watch this pin
66. ue written Name Set Velocity Code V 0x56 Params mnop a 16 bit velocity goal value for the platform if Axis Control 2 or the selected wheel if Axis Control 0 or 1 Returns a or n Description This command lets you specify a goal velocity for either a simple velocity control motion or as a maximum goal velocity for use during a controlled position or distance motion NOTE the Reset command will set the velocity to max speed firmware 37 or max speed divided by 2 firmware 38 or above for subsequent motion commands unless overridden with this command Max speed is determined during calibration and is stored as the Max Speed constant at addresses 29 and 30 The units are in terms of distance per second where the units of distance are the same as you used for specifying the wheel circumference and wheel base For example a robot with a wheel circumference of 8 2 inches specified as 82 might have a maximum useful velocity of 82 8 2 inches per second if the motors can rotate at 60 RPM which is the same as 1 rotation per second NOTE most robots cannot move at velocities below approximately 10 to 15 1 0 to 1 5 inches per second in a controlled manner due to the very low encoder click rate Name Get Velocity Code V 0x56 Params none Returns mnop the current measured velocity of the platform if Axis Control 2 or the selected wheel if Axis Control 0 or 1 Description This ret
67. urns the actual measured velocity of either the platform or a specific wheel in units of distance per second This can be used during either velocity or position control modes When returning the velocity of the platform the value returned is the average of each wheel WheelCommander WC 132 Product Manual 23 Position and Angle Movements Relative vs Absolute Command Sequence 1 Angle 0 distance 100 2 Angle 90 distance 0 3 Angle 0 distance 100 Using relative angle Using absolute angle and distance commands and distance commands Y 2 3 Y 100 100 gt gt S 0 0 0 100 100 O 100 K la ec va i pene P robot s local coordinate system established at reset at 0 0 3 Errors do not accumulate as long as there is no Starts at 0 0 ends at 100 100 wheel slippage 4 Movements are with respect to robot s 1 local coordinate system established at start of each move Errors accumulate CJ 71 28 actual position depends on Wb rel x 0 0 30 fOr x 100 Nubotics WheelCommander c 2009 Noetic Design Inc Figure 3 Note relative angle and distance commands are performed with the X and Z commands absolute angle and distance commands are performed with the D and W commands Name Set Position Code D 0x44 Params mnopgrst a 32 bit position to which to move the platform Axis Control 2 or the selected wheel Returns a or n Description This command set

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