WPILib PID controller object

[sircedric4]

Originally Posted by Mike Soukup

The PIDController constructor takes floats for P, I, & D, a PIDSource pointer for the 4th argument, and a PIDOutput for the 5th argument. So assuming P, I, D are just placeholders for your constants, the first three look good. I'm also assuming that in your example, turretPot is an AnalogChannel pointer. Look at AnalogChannel.h and you'll see that it derives from PIDSource. You should just pass in your turretPot object, the way you wrote it should cause a compiler error. Again assuming turretMotor is a Jaguar or Victor pointer, the 5th argument looks good.

If you still don't understand exactly how the PIDController class works, here's a rundown of the methods that get called when it runs:

• The PIDController hooks itself to an interrupt via the Notifier class and the Calculate() method gets called periodically
• Calculate() calls m_pidInput->PIDGet(), where m_pidInput is the source that was passed into the constructor, so look at PIDGet() in the AnalogChannel class. That method is a single line that returns GetAverageValue().
• After a bunch of fancy PID math, Calculate() calls m_pidOutput->PIDWrite(), where m_pidOutput is the output that was passed into the constructor, so look at PIDWrite() in the Jaguar or Victor classes. Those methods are just wrappers for Set().

Hopefully that clears up any misunderstandings about the PIDController.

It does clear things up. The GetAverageValue() is what was blowing my mind till I could output what the code was doing and see it was looking for a 0-1024 value. The nice example that was posted previously in the thread indicated that the value to set the SetSetPoint needed to be between 0-5 because the potentiometer reads 0-5 volts. Your explanation shows that is not the case.

Once I just sent the information in terms of the 10 bit "raw" data the potentiometer outputs my robot started to converge. I am still trying to figure out what values of P,I, & D to send so that the turret doesn't jitter, but I understand that is mostly empirical depending on your system.

Edited to Ask:
How did you look at the source code of the WPILib to find what the PIDGet() call was doing? I can only find the .h files for the different classes. Needless to say it would be easier to figure out my problems if I could see what each of the library classes was actually supposed to be doing.