Motion Controlled RC Car
Contents
1. define MCP DIGITAL POT1 SLAVE SELECT PIN 10 arduino lt gt Chip Select gt CS Pin 01 on McpDigitalPot DIP define MCP DIGITAL POT2 SLAVE SELECT PIN 9 arduino lt gt Chip Select gt CS Pin 01 on McpDigitalPot DIP Its recommended to measure the rated end end resistance terminal A to terminal B Because this can vary by a large margin up to 20 And temperature variations float rAB_ohms 9700 00 10k Ohm Instantiate McpDigitalPot object with default rW 117 5 ohm its typical resistance McpDigitalPot digitalPot1 McpDigitalPot MCP_DIGITAL_POT1_SLAVE_SELECT_PIN rAB_ohms McpDigitalPot digitalPot2 McpDigitalPot MCP DIGITAL POT2 SLAVE SELECT PIN rAB ohms Instantiate McpDigitalPot object after measuring the real rW wiper resistance McpDigitalPot digitalPot McpDigitalPot MCP DIGITAL POT SLAVE SELECT PIN rAB_ohms rW_ohms Declaring x and y displacement of operator s center of mass on the board measured in from center of board double xDisplacement 0 double yDisplacement 0 Declaring helper variables double frontWeight double rearWeight double leftWeight double rightWeight double totalWeight double FL 0 double FR 0 double RL 0 double RR 0 double throttle double steering Total weight on the front Total weight on the rear Total weight on the left Total weight on the right Total weight Weight on the front left2. 0 250 500 250 pygame draw circle screen 255 0 xScreen yScreen 7 pygame display flip pygame event clear board disconnect print WiiBoard disconnected pygame quit main Modified WiiBoard library The library found at http code google com p wiiboard simple was modified slightly so that it prints out the right instructions import bluetooth import sys import thread import time import pygame base pygame USEREVENT WIIBOARD_BUTTON_PRESS base 1 WIIBOARD_BUTTON_RELEASE base 2 WIIBOARD_MASS base 3 WIIBOARD CONNECTED base 4 WIIBOARD DISCONNECTED base 5 CONTINUOUS REPORTING 94 COMMAND_LIGHT 11 COMMAND_REPORTING 12 COMMAND_REQUEST_STATUS 15 COMMAND_REGISTER 16 COMMAND_READ_REGISTER 17 INPUT STATUS 29 INPUT READ DATA 21 EXTENSION 8BYTES 32 18 BUTTON DOWN MASK 8 TOP RIGHT 9 BOTTOM RIGHT 1 TOP LEFT 2 BOTTOM LEFT 3 BLUETOOTH NAME Nintendo RVL WBC 1 class BoardEvent def _ init__ self topLeft topRight bottomLeft bottomRight buttonPressed buttonReleased self topLeft topLeft self topRight topRight self bottomLeft bottomLeft self bottomRight bottomRight self buttonPressed buttonPressed self buttonReleased buttonReleased self totalWeight topLeft topRight bottomLeft bottomRight class Wiiboard None None receivesocket controlsocket def _ init__ self self calibration self cal
3. Weight on the front right Weight on the rear left Weight on the rear right Throttle value Steering value double throttleResistance Resistance value for the throttle potentiometer double steeringResistance Resistance value for the steering potentiometer char FL_input 4 char FR_input 4 char RL_input 4 char RR input 4 char inChar 1 A char table to read front left input as a text string A char table to read front right input as a text string A char table to read rear left input as a text string A char table to read rear right input as a text string A char where each input char will be read byte index1 0 Index for going through the FL input string byte index2 0 Index for going through the FR input string byte index3 0 Index for going through the RL input string byte index4 0 Index for going through the RR input string Neutral resistance values for throttle and steering these will be applied when the user input is zero or within the deadzone double neutralThrottleResistance 3500 double neutralSteeringResistance 3300 10 void setup Serial begin 9600 Declaring output pins for the slave selection signal pinMode MCP_DIGITAL_POT1_SLAVE_SELECT_PIN OUTPUT pinMode MCP_DIGITAL_POT2_SLAVE_SELECT_PIN OUTPUT Setting both selection pins HIGH so they are both unselected at first digitalWrite MCP_DIGITAL_POT1_SLAVE_SELECT_PIN HIGH digitalWr
4. reverse Our first idea was to simply measure the voltage difference over the potentiometers in neutral and both end positions Next was to recreate the same voltage range with the Arduino using the Arduino s pulse width modulation based AnalogWrite function However this did not work By measuring the voltage difference over the potentiometer with an oscilloscope we found out that the voltage in the transmitter circuit was not constant but instead a 50 Hz pulse signal Turning the potentiometers then caused a change in pulse height so we could conclude that the transmitter was using pulse amplitude modulation This could not be handled with the Arduino alone We found out that the easiest way to get it working was to simulate the actual resistance of the analog potentiometers This could be done using digital potentiometers which behaves the same as an analog potentiometer but is controlled digitally instead of manually On the Arduino website we found the Mcp4261 code library which can be used to control digital potentiometers using SPI Serial Peripheral Interface However it was not compatible with the Arduino s standard SPI h library After a bit more searching we found an updated library called McpDigitalPot h available at https github com teabot McpDigitalPot which is compatible with the standard SPI library so we decided to use this library For digital pots we chose two MCP4161 10kohm single channel digital pots
5. same output pin on the Arduino but only the potentiometer with its selection pin currently set to LOW will receive the input data After the input data is sent the potentiometer is unselected At first we tried using the same resistance range as the analog potentiometers but the car did not respond to this Instead we had to test different resistance values to get the desired response The used resistance range ended up much bigger than the range of the analog pots The reason for this is unclear to us It should be noted that the Arduino code is long and ineffective since our experience in coding was very limited and parts of the code where quickly put together in the ending phases of the project when we were making the connection between the Arduino and PC As we got the whole system working in the ending phase there was no time for tuning and further development of the program and the control algorithm There is probably much room for improvements in the code Arduino AREF Ground GND Clock SPloutput 11 Chip 1 selection pin 10 Chip 2 selection pin 9 8 OKNUWUARUNN Selection pin Selection pin SPlinput MCP4161 MCP4161 Throttle Radio transmitter circuit Steering Final results In the end our results matched up with our goals After some long hours of programming and getting the arduino microcontroller hooked up with the car controller correctly the car works Once all componen
6. Displacement leftWeight totalWeight 0 5 200 Calculates a value of y displacement between 0 and 100 steeringResistance map yDisplacement 5 100 3500 9000 Maps steering input between 5 and 100 to resistance between 3500 ohms and 9000 ohms if yDisplacement lt 5 f y displacement is within 5 deadzone steering neutralSteeringResistance else f not within deadzone steering steeringResistance else f turning right 15 yDisplacement rightWeight totalWeight 0 5 200 Calculates a value of y displacement between 0 and 100 steeringResistance map yDisplacement 5 100 2800 440 Maps steering input between 5 and 100 to resistance between 2800 ohms and 440 ohms if yDisplacement lt 5 f y displacement is within 5 deadzone steering neutralSteeringResistance else f not within deadzone steering steeringResistance digitalWrite MCP_DIGITAL_POT2_SLAVE_SELECT_PIN LOW Sets the steering selection pin LOW selects the throttle chip so it can receive input digitalPot2 setResistance MCP_DIGITAL_POT2_SLAVE_SELECT_PIN steering Sets the resistance of the digital pot digitalWrite MCP_DIGITAL_POT2_SLAVE_SELECT_PIN HIGH Sets the throttle selection pin HIGH unselects the throttle chip Python code import wiiboard import pygame import time import serial def main print BalanceBoard controlled RC Car time sleep 1 print Connecting to Ardui
7. Motion Controlled RC Car Kon 41 3131 Mechatronics Exercises Presented April 18 2012 By Henri Helki Jacob Sindberg Fredrik Sj blom Tatu Pollari Table of contents Description Project goals Procedure Phase 1 Balance board and computer Phase 2 Arduino and transmitter Final Results Further development User s Manual Attachments List of components Arduino code Python code Modified WiiBoard library O O O OO S S P gt Q Q av Q 09 D e re O N Project Goals The goal of our project was to be able to control an RC car with a wii balance board We wanted the car to go forward when user was leaning forward and also we wanted the car to go backward when the user was leaning backward And the same procedure with steering right and left We wanted to have a proportional steering in all four directions Procedure None of us have had much experience with these kinds of projects therefore we started the project by gathering information and figuring out what needed to be done We found out that we needed a computer between the balance board and the RC transmitter The balance board cannot connect to Arduino directly even if the Arduino would have had a Bluetooth module because neither one of them can operate as a host they are both additional devices Bluetooth connection always needs a host so we needed a computer for that An Arduino microcontroller was needed to be able to control the transmitter and some program
8. button address None bluetoothdevices bluetooth discover devices duration 6 lookup names True for bluetoothdevice in bluetoothdevices if bluetoothdevice 1 BLUETOOTH NAME address bluetoothdevice if address None print No Wiiboards discovered return address def createBoardEvent self bytes buttonBytes bytes 2 bytes bytes 2 12 buttonPressed False buttonReleased False 20 state int buttonBytes encode hex 16 lt lt 8 int buttonBytes 1 encode hex 16 if state BUTTON DOWN MASK buttonPressed True if not self buttonDown pygame event post pygame event Event WIIBOARD BUTTON PRESS self buttonDown True if buttonPressed False if self lastEvent buttonPressed True buttonReleased True self buttonDown False pygame event post pygame event Event WIIBOARD BUTTON RELEASE rawTR int bytes encode hex 16 lt lt 8 int bytes 1 encode hex 16 rawBR int bytes 2 encode hex 16 lt lt 8 int bytes 3 encode hex 16 rawTL int bytes 4 encode hex 16 lt lt 8 int bytes 5 encode hex 16 rawBL int bytes 6 encode hex 16 lt lt 8 int bytes 7 encode hex 16 topLeft self calcMass rawTL TOP LEFT topRight self calcMass rawTR TOP RIGHT bottomLeft self calcMass rawBL BOTTOM LEFT bottomRight self calcMass rawBR BOTTOM RIGHT boardEvent BoardEvent topLeft topRight bottomLeft bottomRi
9. e coding with the device in order to make it compatible with the existing code and the existing code would most likely need to be manipulated as well Another solution would be to start all over with a bigger microcontroller Our current microcontroller is quite small and general as we did not need the more expensive one using a PC If the controller were bigger Bluetooth accessible and could act as a host the PC host could be replaced and the project would be improved User s manual 1 Connect arduino to computer with USB cord 2 Turn power on in all devices 3 Start eclipse 4 Run the main program 5 Follow instructions on screen Note If the program fails after the board has been connected to the PC you will need to restart the PC Attachments List of components Name Units Price Description LRP S10 Twister Buggy 1 135 00 RC Car Snakebyte balance board 1 29 90 Balance board Arduino UNO Atmega 328 SMD 1 23 90 Microcontroller PC 1 Bluetooth host MCP4161 2 20 00 Digital potentiometer Logic NX85E Vector 1 36 40 Battery charger Orion sport power 3300mAh 1 26 90 Extra battery Arduino code SPI library for communicating with digital potentiometers through SPI protocol Hinclude lt SPI h gt McpDigitalPot library available from https github com dreamcat4 McpDigitalPot Hinclude lt McpDigitalPot h gt Then choose any other free pin as the Slave Select pin 10 if the default but doesnt have to be
10. ght buttonPressed buttonReleased return boardEvent def calcMass self raw pos val 0 0 if raw lt self calibration 0 pos return val elif raw lt self calibration 1 pos val 17 raw self calibration pos float self calibration 1 pos self calibration 0 pos elif raw gt self calibration 1 pos val 17 17 raw self calibration 1 pos float self calibration 2 pos self calibration 1 pos return val def getEvent self return self lastEvent def getLED self return self LED 21 def receivethread self while self status Connected if True data self receivesocket recv 25 intype int data encode hex 2 4 if intype INPUT STATUS self setReportingType elif intype INPUT READ DATA if self calibrationRequested True packetLength int str data 4 encode hex 16 16 1 self parseCalibrationResponse data 7 7 packetLength if packetLength lt 16 self calibrationRequested False elif intype EXTENSION 8BYTES self lastEvent self createBoardEvent data 2 12 try pygame event post pygame event Event WIIBOARD MASS mass self lastEvent except self disconnect else pass self status Disconnected self disconnect pygame event post pygame event Event WIIBOARD_ DISCONNECTED def parseCalibrationResponse self bytes index if len bytes 16 for i in xrange 2 for j in xrange 4 self calibra
11. ghtWeight FR RR totalWeight FL FR RL RR THROTTLE if frontWeight gt rearWeight FORWARD xDisplacement frontWeight totalWeight 0 5 200 Calculates a value of x displacement between 0 and 100 throttleResistance map xDisplacement 10 100 6500 8000 Maps throttle input between 10 and 100 to resistance between 6500 ohms and 8000 ohms if xDisplacement gt 0 f x displacement is within 10 deadzone throttle throttleResistance else f not within deadzone throttle neutralThrottleResistance else REVERSE xDisplacement rearWeight totalWeight 0 5 200 Calculates a value of x displacement between 0 and 100 throttleResistance map xDisplacement 5 100 2500 800 Maps throttle input between 5 and 100 to resistance between 2500 ohms and 800 ohms 14 if xDisplacement gt 0 f x displacement is within 5 deadzone throttle throttleResistance else f not within deadzone throttle neutralThrottleResistance digitalWrite MCP_DIGITAL_POT1_SLAVE_SELECT_PIN LOW Sets the throttle selection pin LOW selects the throttle chip so it can receive input digitalPot1 setResistance MCP_DIGITAL_POT1_SLAVE_SELECT_PIN throttle Sets the resistance of the digital pot digitalWrite MCP_DIGITAL_POT1_SLAVE_SELECT_PIN HIGH Sets the throttle selection pin HIGH unselects the throttle chip STEERING if leftWeight gt rightWeight f turning left y
12. ibrationRequested False self LED False self address None self buttonDown False for i in xrange 3 self calibration append for j in xrange 4 self calibration i append 10099 self status Disconnected self lastEvent BoardEvent 0 0 0 0 False False try self receivesocket bluetooth BluetoothSocket bluetooth L2CAP self controlsocket bluetooth BluetoothSocket bluetooth L2CAP except ValueError raise Exception Error Bluetooth not found def isConnected self if self status Connected return True else 19 return False def connect self address if address None print Non existant address return self receivesocket connect address x13 self controlsocket connect address x11 if self receivesocket and self controlsocket print Connected to Wiiboard at address self status Connected self address address thread start_new_thread self receivethread self calibrate useExt COMMAND REGISTER 04 A4 00 40 00 self send useExt self setReportingType pygame event post pygame event Event WIIBOARD CONNECTED address else print Could not connect to Wiiboard at address address def disconnect self if self status Connected self status Disconnecting while self status Disconnecting self wait 1 try self receivesocket close self controlsocket close except pass def discover self print Press the sync
13. ite MCP_DIGITAL_POT2_SLAVE_SELECT_PIN HIGH initialize SPI SPI begin void loop index1 0 index2 0 index3 0 index4 0 byte readChar 1 Avariable keeping track of which input is currently being read while Serial available gt 0 if readChar 1 f reading input 1 FL inChar Serial read Read 1 char to inChar delay 1 if inChar As long as the input text is not save the input to FL input increasing the index every time 11 FL input index1 inChar index1 else If input is that is the end of the current input put end of string to FL input and start reading the next input by increasing readChar by 1 FL_input index1 0 readChar if readChar 2 inChar Serial read delay 1 if inChar FR_input index2 inChar index2 else FR_input index2 NO readChar if readChar 3 12 inChar Serial read delay 1 if inChar RL_input index3 inChar index3 else RL_input index3 0 readChar if readChar 4 inChar Serial read delay 1 if inChar RR_input index4 inChar index4 else RR_input index4 NO readChar 13 FL atoi FL input FR atoi FR input RL atoi RL input RR atoi RR input frontWeight FL FR rearWeight RL RR leftWeight FL RL ri
14. ming was also needed We decided to split this project into two pieces The first task was to have a connection between the balance board and the computer and to be able to read signals received from balance board The other task was to send those signals through the Arduino to the RC car A sketch of our project can be seen in figure 1 PC Arduino Bluetooth Host Transmitter Bluetooth Signal Wii Balance Board Figure 1 Phase 1 Balance board and computer We started this phase by gathering more information about how to able to read those signals sent by balance board with the computer We were able to find some projects that had done this by using program called GlovePie To be able to use GlovePie we also needed a program called BlueSoleil which is a program that creates a Bluetooth connection to the computer with the device desired BlueSoleil was needed because the GlovePie was not able to find balance board with the standard Bluetooth connection created by computer With these two programs we were able to read the x and y values from balance board but we were not able to send those values to Arduino For the sending we would have needed a program called Processing and for that program a library called oscP5 which stands for open sound control However it wasn t that easy to use this program and we realized that this whole project was getting too complex and heavy so we decided to use
15. no ser serial Serial COM7 time sleep 2 print Connected to Arduino time sleep 1 16 print Connecting to WiiBoard pygame init board wiiboard Wiiboard address board discover if address None pygame quit exit else print Found Wiiboard at address address board connect address time sleep 5 print WiiBoard ready Hold the power button to disconnect screen pygame display set_mode 50 500 done False while not done x 0 y 0 if board buttonDown True print Power button pressed done True else pass event pygame event wait if event type wiiboard WIIBOARD_MASS if event mass totalWeight gt 10 sensor1 int event mass topLeft event mass totalWeight 100 sensor2 int event mass topRight event mass totalWeight 100 sensor3 int event mass bottomLeft event mass totalWeight 100 sensor4 int event mass bottomRight event mass totalWeight 100 toArduino str sensor1 str sensor2 str sensor3 str sensor4 ser write toArduino time sleep 5 x y sensor1 sensor3 sensor2 sensor4 sensor1 sensor2 sensor3 sensor4 else ser write 25 25 25 25 time sleep 9 1 else pass xScreen int x 2 5 250 17 yScreen int y 2 5 250 screen fill 9 pygame draw line screen 255 255 255 250 09 250 500 pygame draw line screen 255 255 255
16. nt for the Mechatronics Circus so this task never occurred However it would not take too much time and the PCB seminar taught earlier in the course would help A second task that could be done is to refine our computer code Both the python and arduino code potentially have minor flaws in them This is because every once in a while the program will freeze up particularly when the car would go in reverse suddenly or for an extended period of time None of the four group members have had substantial work with programming so consulting a computer engineer or electrical engineer with more experience would help our situation Also we could add more code to the programs in order to make the driving of the car more precise This can always be improved since it is our first time conducting such a project Steering could be made sharper and acceleration faster or slower depending on one s weight on the balance board None the less the car still operates properly and the overall programming is successful To make our project even more sophisticated we could remove the computer all together Not having the PC act as a host between the balance board and controller would require much more time and could maybe be carried on in a future project One way to directly improve our car is to use an expansion shield with the arduino microcontroller This little component could replace the computer itself and connect the two main components It would require much mor
17. our plan B We decided to write our own code for reading the signals from balance board We decided to write this program with Python because we found a good library for Python that was used in a similar project We also found some examples of similar projects that were made with Python The library was called wiiboard simple and it used another library called pygame The advantages of using these libraries were that they made the Bluetooth connection and also read the data from balance board So all we needed to do was to write the main program which used these libraries and transformed the data so that it could be sent to Arduino These programs were written by studying how those two libraries function We also added a xy coordinate system to computer so that we were able to see graphically what values the balance board was sending Phase 2 Arduino and transmitter The idea of the project was to use the Arduino controller to take inputs from the PC and then control the throttle and steering channels on the radio transmitter The Arduino controller used was an Arduino Uno connected with a USB cable to the computer For programming we used the Arduino software for the PC The first step was to disassemble the transmitter and take out the circuit boards battery box and antenna The steering and throttle inputs were controlled with 2 analog potentiometers in the transmitter casing connected to a steering wheel and a trigger for throttle
18. tion i j int bytes index encode hex 16 lt lt 8 int bytes index 1 encode hex 16 index 2 elif len bytes lt 16 for i in xrange 4 self calibration 2 i int bytes index encode hex 16 lt lt 8 int bytes index 1 encode hex 16 index 2 22 def send self data if self status Connected return data 52 senddata for byte in data byte str byte senddata byte decode hex self controlsocket send senddata def setLight self light val ag if light True val 19 message 90 COMMAND LIGHT val self send message self LED light def calibrate self message 20 COMMAND READ REGISTER 04 A4 00 24 00 er self send message self calibrationRequested True def setReportingType self bytearr COMMAND REPORTING CONTINUOUS REPORTING EXTENSION 8BYTES self send bytearr def wait self millis time sleep millis 1000 0 23
19. ts are turned on the code updated if a person were to stand perfectly balanced on the board the car would not move Leaning forward on the board then allows the car to move forward In this direction speed can even be controlled on how far the person leans When going in reverse it is a little bit trickier as there is mostly one speed but the function still works Finally the person can steer the car properly left or right simply be shifting his or her weight on the board In conclusion we created a functioning RC car controlled by using a balance board We tested the system outside and it worked fine although it was quite hard to be able to drive straight There are also some problems that occur every once and a while there is some contact issues with the wiring the program freezes sometimes and sometimes the car starts going backwards when user is leaning forward and the opposite However the steering works fine all the time F Further development In further developing our motion controlled RC car there are several things that can be done The first thing to consider is taking the current bread board and making a printed circuit board PCB As of now the bread board has two chips and wires running everywhere between the original controller and the arduino microcontroller Therefore two small PCB s could be constructed for the chips with the proper configuration for the wires Time was tight when it came to getting ready to prese
20. which were easily available and seemed to suit our needs The digital pots were put on a breadboard and connected by wires to the Arduino and the transmitter circuit The wires were soldered to the holes in the transmitter circuit where the analog pots originally were connected Unlike dual channel potentiometers which have different input and output pins the MCP4161 have input and output multiplexed onto one pin We found out that since we will not be reading any data from the pot we could ignore the output of the potentiometer and only connect the input output pin on the potentiometer to its input an output pin on the Arduino The code for the Arduino works in the following way A text string of 4 numbers weight on every corner of the balance board in the form 50 20 20 10 separated by is sent to the Arduino The Arduino saves each number as a variable Then the sums of the weight on the front rear left and right halves of the board are calculated Using the calculated sums and the sum of all the weight of the board the displacement of the center of mass on the board is calculated in x and y directions If the displacement is greater than a certain dead zone value the displacement value is mapped to a resistance value between the neutral value and the end value Finally each of the potentiometers is selected in turn and the resistance value is sent to the currently selected potentiometer The potentiometers are connected to the
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