[Aaron.Graeve]

PID is a general control loop for getting a physical action to a particular point. By using a sensor on the moving part, the code compares the current position of the part to where it is supposed to be (the error), how long the part is taking to get there (the cumulative sum of the error), and how quickly the part is moving (the derivative of the error with respect to time) and uses these to calculate a new value for the controlling motor to be powered. For an closed-loop autonomous drivetrain, you would almost certainly need to use an encoder on the wheels (two really, one for each side so the robot goes relatively straight). There are many papers published here on Chief Delphi and all over the net about this. Since the loop is updating many times a second, it can very quickly adjust to changing conditions or resistance. Control loops are, in my opinion, the biggest difference programming-wise between good and great teams. You may find them useful even in teleop if there is a mechanism that needs to be held at a particular angle.

Message me if you have any more questions.