GRIP WITH PID and 1 Target Tracking

[mlyhoops]

Originally Posted by ThomasClark

This should help:

http://wpilib.screenstepslive.com/s/...rs-pid-control

So in this example the PIDController constructor only has 1 output source. What happens if I am trying to use 6 motors? (Since it is the drive train)

[AMendenhall]

If you're doing this in a Command (I'd recommend this), you can change it to a PIDCommand. This will require the methods returnPIDInput() and usePIDOutput() and a new constructor. In returnPIDInput(), you can return the heading from the gyro. In the usePIDOutput, you can write code that runs each side based on the output. Ex:

protected void usePIDOutput(double output) {
	//limit output
	output = Math.min(1, output);
	output = Math.max(-1, output);
	//use output
	driveTrain.setLeft(output);
	driveTrain.setRight(-output);
}

If your PID constants are positive, and your gyro isn't reversed, the sign of the outputs should be as is (if the bot needs to turn left, the error is negative, so left should drive back, so left output should be negative). It's easy enough to check for that and reverse though.

As far as tuning goes, start with a P around 0.1. Get it as good as you can just by tuning P, then move on to D. You probably won't need I. There are lots of articles on this though.

[ThomasClark]

Originally Posted by mlyhoops

So in this example the PIDController constructor only has 1 output source. What happens if I am trying to use 6 motors? (Since it is the drive train)

So these are all separate speed controllers? In that case, you could use a lambda to set all of them.

PIDController pid = new PIDController(0.8, 0.01, 0.2, gyro, speed -> {
	frontLeft.set(speed);
	centerLeft.set(speed);
	backLeft.set(speed);
	
	frontRight.set(-speed);
	centerRight.set(-speed);
	backRight.set(-speed);
});

double setpoint = calculateSetpoint();
pid.setSetpoint(setpoint);