Please Help with my PID template i found

[Max_Waldman]

For learning how PID works in general, I highly recommend An Introduction to PID Controllers by George Gillard (download it from here).

If you want an explanation of the code you have, here is a brief one (assuming you have read the above document):

@ssierakowski

typedef struct { // init a reusable list of variables
  float current;
  float kP;
  float kI;
  float kD;
  float target;
  float error;
  float integral;
  float derivative;
  float lastError;
  float threshold;
  float totalError;

} pid;

This just is a placeholder for all of your PID-related variables.

@ssierakowski

pid turnPID;
pid leftDrive;
pid rightDrive;

These are different PID settings for turning and driving (I am not sure why leftDrive and rightDrive are separated; normally there is just a drivePID).

@ssierakowski

float turningPID(float iDes, int deg, float kP, float kI, float kD,
                 float kILimit) {

Turning PID function (iDes is desired angle in degrees, deg is current angle in degrees, and the rest are just constants)

@ssierakowski

turnPID.error = iDes - turnPID.current;

Calculates error

@ssierakowski

if (fabs(turnPID.error) > 180) {
    turnPID.error -= copysign(1.0, turnPID.error) * 360;
  }

This is just to get the turnPID error within the right range.

@ssierakowski

turnPID.integral += turnPID.error;

Accumulate the total error

@ssierakowski

if (fabs(turnPID.error) < kILimit)
      turnPID.integral = turnPID.integral + turnPID.error;
    else
      turnPID.integral = 0;

I am not sure why the total error is accumulated twice, and I don’t think the previously mentioned line (turnPID.integral += turnPID.error;) should be there.

@ssierakowski

turnPID.lastError = turnPID.error;

Set the previous error

@ssierakowski

float thePower = (turnPID.error * kP) + (turnPID.integral * kI) +
                   (turnPID.derivative * kD);

Calculate power

That was just the PID; if you are confused about the other code I can help you. If you are having trouble with integral windup (explained in the George Gillard document), it might help to look at the part about integral windup in this post. You probably don’t really need it (you don’t really need the I term itself either), but it is nice to have.