[ScottWalls]

I'll scour around for some of the old encoder modules, although I don't recommend you use them just yet.

You intend to use potentiometers to figure out velocity? I would recommend that you use encoders to control velocity, as potentiometers deal more with position. However, if you would still like to use potentiometers, Post again and I can walk you through code to do so.

Also, for reference, that application of PID is not terribly useful in any real application, although it is fine to test that PID functions. This is because to use a PID loop here is to match joystick output to voltage, which is already perfectly responsive. To add a PID loop only lowers this responsiveness. A more appropriate use of PID would be to match joystick input to velocity output on the motors given by encoders. In this way, you could move the joystick to a position to attain a given velocity, meaning even if there is some resistance against your robot, the PID loop would compensate for it (less driver control).