PID Question

[Codec]

@The_To

On Auton settings does int desired value need to be 0

int desiredValue = 200;

It represents the target value so how far you want the robot to drive. Set it to the desired distance (in your case measured in motor degrees since that is what you use).

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@The_To

And in the end if I were to use a tracking wheel for no wheel slippage. Could I just switch the, for example, left motor or right motor with that?

PID simply takes in sensor values and translates them to motor power. If you add tracking wheels in the same general orientation, then it is as simple as using those values instead (you will have to adjust the PID constants).

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One error I did notice was…

LeftMotor.spin(forward, lateralMotorPower + turnMotorPower, voltageUnits::volt);
RightMotor.spin(forward, lateralMotorPower + turnMotorPower, voltageUnits::volt);

You have to add turnMotorPower to one of the motors and subtract it from the other. Also make sure you apply it correctly as doing it backwards would multiply any small turn. (You can test this by setting lateralMotorPower to zero, running you program, and seeing how it responds when you try to turn it.)

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Also if you want to make you PID more precises, I would recommend applying proper time units to the timed variables, I and D. Here is a great example of how to do that from another post I made…

@Codec

How program PID

Remember it doesn’t always have to be PID. Just using the P part is sometimes all you need.
Anyways, here is an example I wrote…

Declarations…

double kP = 1.0, kI = 0.01, kD = 0.1;
long preUpdate = 0, timeout = 50;
double prePosition = actualPosition;
double error, speed, integral = 0;

In the loop…

error = target - actualPosition;

long elapsedTime = vex::timer::system - preUpdate;
if(elapsedTime >= timeout)
{
	double preSec = (1000.0 / elapsedTime);

	speed = (actualPosition - prePosition) * preSec;
	integral += error * preSec;
	prePosition = actualPosition;
	preUpdate = vex::timer::system();
}

motorVoltage = error * kP - speed * kD + integral * kI;

Here it calculates error and speed. Then it update the integral, the I component. For speed ( D ) and integral ( I ) they are time based to they are in an if statement that run at set a interval. Then all the values get add up, which is what you want the voltage to be set to. The kP, kI, kD variable are what you want to change to tune your PID.

Also, since you would probably need to use this code numerous time, it would make sense to make this a class. I encourage you to do that part yourself to get better at coding (I don’t know you skill level though, you might be a pro). If you need any help though feel free to ask.

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Another slight note, probably useful for a judges interview, the P in PID stand for Proportional, not Potential.