PID target value problem

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#1

Hello,
this is my first coding on my robotics and I’ve been struggling with my PID, for some reason my int target that is used to set the target value in inches in the void just sets itself to zero regardless of what I set it to. plz, help me if you can. (also I have my encoders set to 0 at the start of auton)

my pid:
``void moveFwd(double target, double maxVoltage) {// scale 0 to 12 mvolt

//chassis_Set PIDControl;

// MACHINE STATE WHEN ENTERING FUNCTION, MACHINE STATE AFTER
double enterAngle = Gyro.rotation();

// CONVERSION FROM INCHES TO ENCODER TICKS
target = ((target * 360) / (4 * M_PI)) * (36 / 84);

double output = 0, Dt = 0, encoderAvrg = 0;
double prevError = 0, prevTime = t.time(msec);

// SLEW COMPONENTS
double volCapMax = 12, volCap = 0;

// SLEW TUNABLE
double acceleration = .07;

// PID COMPONENTS
double error = 6, integral = 0.01, derivetive = 0.1;

// CONSTATNTS
double Kp = .11, Ki = 0.009, Kd = .007, kt = 0;

// BOUNDS
double errorMargin = 4, integralBound = 20;

// CORECTION VARIABLES
double targetAngle = 0, correctionOutput = 0;

double enterVal = ((end1.position(rotationUnits::deg) + end2.position(rotationUnits::deg)) /2);

int sign = 1;
double sensorVal = ((end1.position(rotationUnits::deg) + end2.position(rotationUnits::deg)));

// CALCULATES ERROR FOR FUNCTION TO RUN
error = target - encoderAvrg;
 std::cout << "error: " << error << std::endl;
while (fabs(error) > errorMargin || error == 0) {
  std::cout << "power: " << output << std::endl;
  std::cout << "error: " << error << std::endl;
  std::cout << "target: " << target << std::endl;
  sensorVal = ((end1.position(rotationUnits::deg) + end2.position(rotationUnits::deg)));

  // AVERAGE BETWEEN ENCODER VALUES
  if (sensorVal == 0){
    encoderAvrg = sensorVal;
  }
  else {
    encoderAvrg = sensorVal / 2;
  }
  // FINDS THE DIFFRENCE BETWEEN THE TARGET AND ROBOT
  error = (target - sensorVal);

  // CALCULATES DELTA TIME IN MSEC
  Dt = (t.time(msec) - prevTime) / 1000;

  // FINDS  INTEGRAL WITH CONSTANT MULTIPLIER, AND ERROR
  integral += error * Dt;


  // FINDS DRVITIVE USING ERROR, AND PREVIOUS
  // DIVIDES BY TIME
  derivetive = (error - prevError) / Dt;

  // UPDATES THE PREVIOUS ERROR
  prevError = error;

  if (fabs(error) > integralBound) {
    integral = 0;
  }

  // CALCULATES THE VOLTS TO BE SENT TO THE MOTORS
  output = error * Kp + integral * Ki + derivetive * Kd;

  // FINDS IF POS OR NEG
  sign = fabs(output) / output;

  if (fabs(output) > maxVoltage) {
    output = maxVoltage * sign;
  }

  // Slew rate
  if (fabs(output) > volCapMax)
    output = volCapMax * sign;

  volCap += acceleration * sign;
  if (fabs(volCap) > fabs(volCapMax)) {
    volCap = volCapMax * sign;
  }

  if (fabs(output) > fabs(volCap)) {
    output = volCap;
  }

  // DIFFRENCE IN MACHINE STATE
  correctionOutput = targetAngle - (enterAngle - Gyro.rotation())*kt;

  // CHECKS MACHINE STATE
  if (fabs(enterAngle - Gyro.rotation()) > targetAngle) {
   leftDrive.spin(directionType::fwd, output + correctionOutput, voltageUnits::volt);
   rightDrive.spin(directionType::fwd, output - correctionOutput, voltageUnits::volt);
    // UPDATES MACHINE STATE TO BE DESIRABLE
    //PIDControl.move(output + correctionOutput, output - correctionOutput);

  }
  else if (fabs(enterAngle + Gyro.rotation()) < targetAngle) {
   leftDrive.spin(directionType::fwd, output - correctionOutput, voltageUnits::volt);
   rightDrive.spin(directionType::fwd, output + correctionOutput, voltageUnits::volt);
    // UPDATES MACHINE STATE TO BE DESIRABLE
    //PIDControl.move(output + correctionOutput, output - correctionOutput);

  }

  // IF MACHINE STATE DESIRABLE CONTINUE PID
  else {
    leftDrive.spin(directionType::fwd, output, voltageUnits::volt);
    rightDrive.spin(directionType::fwd, output, voltageUnits::volt);
  }

  // DEBUGGING
  

  // UPDATES PREVIOUS TIME
  prevTime = t.time(msec);

  // ALLOWS FOR UDATES TO VALUES
  wait(15, msec);
}

// STOPS THE ROBOT PREVENTS FURTHER MOVEMENT
//PIDControl.rest();
leftDrive.stop(hold);
rightDrive.stop(hold);

}``

how I call it in the auton function:
moveFwd(50, 10);

1 Like
#2

Try double type for variable target.

#3

I think the problem with this line

is that 36 and 84 are recognized as integers and expression (36/84) evaluates to 0 because of the way integer arithmetic in C++ works.

You could fix that by telling C++ compiler to recognize all those numbers as doubles like this:

5 Likes