An advanced robot that uses PID control on the motor speed, and an IMU for making accurate turns.
Dependencies: mbed Motor ITG3200 QEI ADXL345 IMUfilter PID
Diff: main.cpp
- Revision:
- 0:7440a03255a7
--- /dev/null Thu Jan 01 00:00:00 1970 +0000 +++ b/main.cpp Fri Sep 10 14:03:00 2010 +0000 @@ -0,0 +1,345 @@ +/** + * Includes. + */ +#include "Motor.h" +#include "QEI.h" +#include "PID.h" +#include "IMU.h" + +/** + * Defines. + */ +#define BUFFER_SIZE 1024 //Used for data logging arrays +#define RATE 0.01 //PID loop timing + +//PID tuning constants. +#define L_KC 0.4312 //Forward left motor Kc +#define L_TI 0.1 //Forward left motor Ti +#define L_TD 0.0 //Forward left motor Td +#define R_KC 0.4620 //Forward right motor Kc +#define R_TI 0.1 //Forward right motor Ti +#define R_TD 0.0 //Forward right motor Td + +//PID input/output limits. +#define L_INPUT_MIN 0 //Forward left motor minimum input +#define L_INPUT_MAX 3000 //Forward left motor maximum input +#define L_OUTPUT_MIN 0.0 //Forward left motor minimum output +#define L_OUTPUT_MAX 0.9 //Forward left motor maximum output + +#define R_INPUT_MIN 0 //Forward right motor input minimum +#define R_INPUT_MAX 3200 //Forward right motor input maximum +#define R_OUTPUT_MIN 0.0 //Forward right motor output minimum +#define R_OUTPUT_MAX 0.9 //Forward right motor output maximum + +//Physical dimensions. +#define PULSES_PER_REV 624 +#define WHEEL_DIAMETER 58.928 //mm +#define ROTATION_DISTANCE 220.0 //mm +#define REVS_PER_ROTATION (ROTATION_DISTANCE / WHEEL_DIAMETER) +#define PULSES_PER_ROTATION (REVS_PER_ROTATION * PULSES_PER_REV) +#define PULSES_PER_MM (PULSES_PER_REV / WHEEL_DIAMETER) +#define DISTANCE_PER_PULSE (WHEEL_DIAMETER / PULSES_PER_REV) +#define ENCODING 2 //Use X2 encoding +#define WHEEL_DISTANCE (ROTATION_DISTANCE / DISTANCE_PER_PULSE) + +/** + * Function Prototypes + */ +void initializeMotors(void); +void initializePid(void); +//cmd = "move", "turn" +//direction = "forward", "backward", "left", "right" +//length = distance in metres or angle in degrees +void processCommand(char* cmd, char* direction, float length); + +/** + * Globals + */ + +//Debug. +Serial pc(USBTX, USBRX); + +//Motor control. +Motor leftMotor(p21, p20, p19); //pwm, inB, inA +Motor rightMotor(p22, p17, p18); //pwm, inA, inB +QEI leftQei(p29, p30, NC, 624); //chanA, chanB, index, ppr +QEI rightQei(p27, p28, NC, 624); //chanB, chanA, index, ppr +PID leftPid(L_KC, L_TI, L_TD, RATE); //Kc, Ti, Td +PID rightPid(R_KC, R_TI, R_TD, RATE); //Kc, Ti, Td +//IMU and peripherals run at a different rate to the main PID loop. +IMU imu(IMU_RATE, GYRO_MEAS_ERROR, ACCELEROMETER_RATE, GYROSCOPE_RATE); + +//Filesystem. +LocalFileSystem local("local"); + +//Left motor working variables. +int leftPulses = 0; +int leftPrevPulses = 0; +float leftVelocity = 0.0; +float leftVelocityBuffer[BUFFER_SIZE]; + +//Right motor working variables. +int rightPulses = 0; +int rightPrevPulses = 0; +float rightVelocity = 0.0; +float rightVelocityBuffer[BUFFER_SIZE]; + +//General working variables. +float heading = 0.0; +float prevHeading = 0.0; +float degreesTurned = 0.0; +float positionSetPoint = 0.0; +float headingSetPoint = 0.0; + +//Store the initial and end heading during a straight line section +//in order to be able to correct turns. +float startHeading = 0.0; +float endHeading = 0.0; + +//Command Parser. +char cmd0[16]; //{"move", "turn"} +char cmd1[16]; //{{"forward", "backward"}, {"left", "right"}} +float cmd2 = 0; //{distance in METRES, angle in DEGREES} + +void initializeMotors(void) { + + //Set motor PWM periods to 20KHz. + leftMotor.period(0.00005); + leftMotor.speed(0.0); + + rightMotor.period(0.00005); + rightMotor.speed(0.0); + +} + +void initializePid(void) { + + //Input and output limits have been determined + //empirically with the specific motors being used. + //Change appropriately for different motors. + //Input units: counts per second. + //Output units: PwmOut duty cycle as %. + //Default limits are for moving forward. + leftPid.setInputLimits(L_INPUT_MIN, L_INPUT_MAX); + leftPid.setOutputLimits(L_OUTPUT_MIN, L_OUTPUT_MAX); + leftPid.setMode(AUTO_MODE); + rightPid.setInputLimits(R_INPUT_MIN, R_INPUT_MAX); + rightPid.setOutputLimits(R_OUTPUT_MIN, R_OUTPUT_MAX); + rightPid.setMode(AUTO_MODE); + +} + +void processCommand(char* cmd, char* direction, float length) { + + //move command. + if (strcmp(cmd, "move") == 0) { + + int i = 0; //Data log array index. + + //The PID controller works in the % (unsigned) domain, so we'll + //need to multiply the output by -1 if our motors need + //to go "backwards". + int leftDirection = 1; + int rightDirection = 1; + + //Convert from metres into millimetres. + length *= 1000; + //Work out how many pulses are required to go that many millimetres. + length *= PULSES_PER_MM; + //Make sure we scale the number of pulses according to our encoding method. + length /= ENCODING; + + positionSetPoint = length; + + if (strcmp(direction, "forward") == 0) { + //Leave left and rightDirection as +ve. + } else if (strcmp(cmd1, "backward") == 0) { + //Change left and rightDirection to -ve. + leftDirection = -1; + rightDirection = -1; + } + + startHeading = imu.getYaw(); + + //With left set point == right set point, the rover veers off to the + //right - by slowing the right motor down slightly it goes relatively + //straight. + leftPid.setSetPoint(1000); + rightPid.setSetPoint(975); + + //Keep going until we've moved the correct distance defined by the + //position set point. Take the absolute value of the pulses as we might + //be moving backwards. + while ((abs(leftPulses) < positionSetPoint) && + (abs(rightPulses) < positionSetPoint)) { + + //Get the current pulse count and subtract the previous one to + //calculate the current velocity in counts per second. + leftPulses = leftQei.getPulses(); + leftVelocity = (leftPulses - leftPrevPulses) / RATE; + leftPrevPulses = leftPulses; + //Use the absolute value of velocity as the PID controller works + //in the % (unsigned) domain and will get confused with -ve values. + leftPid.setProcessValue(fabs(leftVelocity)); + leftMotor.speed(leftPid.compute() * leftDirection); + + rightPulses = rightQei.getPulses(); + rightVelocity = (rightPulses - rightPrevPulses) / RATE; + rightPrevPulses = rightPulses; + rightPid.setProcessValue(fabs(rightVelocity)); + rightMotor.speed(rightPid.compute() * rightDirection); + + i++; + + wait(RATE); + + } + + leftMotor.brake(); + rightMotor.brake(); + + endHeading = imu.getYaw(); + + } + //turn command. + else if (strcmp(cmd0, "turn") == 0) { + + //The PID controller works in the % (unsigned) domain, so we'll + //need to multiply the output by -1 for the motor which needs + //to go "backwards". + int leftDirection = 1; + int rightDirection = 1; + headingSetPoint = length + (endHeading - startHeading); + + //In case the rover tries to [pointlessly] turn >360 degrees. + if (headingSetPoint > 359.8) { + + headingSetPoint -= 359.8; + + } + + //Set up the right previous heading for the initial degreesTurned + //calculation. + prevHeading = fabs(imu.getYaw()); + + if (strcmp(cmd1, "left") == 0) { + + //When turning left, the left motor needs to go backwards + //while the right motor goes forwards. + leftDirection = -1; + + } else if (strcmp(cmd1, "right") == 0) { + + //When turning right, the right motor needs to go backwards + //while the left motor goes forwards. + rightDirection = -1; + + } + + //Turn slowly to ensure we don't overshoot the angle by missing + //the relatively slow readings [in comparison to the PID loop speed] + //from the IMU. + leftPid.setSetPoint(500); + rightPid.setSetPoint(500); + + //Keep turning until we've moved through the correct angle as defined + //by the heading set point. + while (degreesTurned < headingSetPoint) { + + //Get the new heading and subtract the previous heading to + //determine how many more degrees we've moved through. + //As we're only interested in the relative angle (as opposed to + //absolute) we'll take the absolute value of the heading to avoid + //any nastiness when trying to calculate angles as they jump from + //179.9 to -179.9 degrees. + heading = fabs(imu.getYaw()); + degreesTurned += fabs(heading - prevHeading); + prevHeading = heading; + + //Get the current pulse count and subtract the previous one to + //calculate the current velocity in counts per second. + leftPulses = leftQei.getPulses(); + leftVelocity = (leftPulses - leftPrevPulses) / RATE; + leftPrevPulses = leftPulses; + //Use the absolute value of velocity as the PID controller works + //in the % (unsigned) domain and will get confused with -ve values. + leftPid.setProcessValue(fabs(leftVelocity)); + leftMotor.speed(leftPid.compute() * leftDirection); + + rightPulses = rightQei.getPulses(); + rightVelocity = (rightPulses - rightPrevPulses) / RATE; + rightPrevPulses = rightPulses; + rightPid.setProcessValue(fabs(rightVelocity)); + rightMotor.speed(rightPid.compute() * rightDirection); + + wait(RATE); + + } + + leftMotor.brake(); + rightMotor.brake(); + + } + + //Reset working variables. + leftQei.reset(); + rightQei.reset(); + + leftPulses = 0; + leftPrevPulses = 0; + leftVelocity = 0.0; + leftMotor.speed(0.0); + + rightPulses = 0; + rightPrevPulses = 0; + rightVelocity = 0.0; + rightMotor.speed(0.0); + + leftPid.setSetPoint(0.0); + leftPid.setProcessValue(0.0); + rightPid.setSetPoint(0.0); + rightPid.setProcessValue(0.0); + + positionSetPoint = 0.0; + headingSetPoint = 0.0; + heading = 0.0; + prevHeading = 0.0; + degreesTurned = 0.0; + +} + +int main() { + + pc.printf("Starting mbed rover test...\n"); + + initializeMotors(); + initializePid(); + + //Some delay before we start moving. + wait(5); + + //Open the command script. + FILE* commands = fopen("/local/commands.txt", "r"); + + //Check if we were successful in opening the command script. + if (commands == NULL) { + pc.printf("Could not open command file...\n"); + exit(EXIT_FAILURE); + } else { + pc.printf("Succesfully opened command file!\n"); + } + + //While there's another line to read from the command script. + while (fscanf(commands, "%s%s%f", cmd0, cmd1, &cmd2) >= 0) { + + pc.printf("%s %s %f\n", cmd0, cmd1, cmd2); + + processCommand(cmd0, cmd1, cmd2); + + wait(1); + + } + + fclose(commands); + +}