PID: what is it exactly?

[nathan_hui]

Actually, PID for shooting is a little more than keeping wheels at a constant speed. The one problem we had was the repeatability of shots. Each time we chucked a ball out, the wheels would slow down because of the amount of energy released into the ball. One thing PID would have to do was compensate for that loss in speed fast enough to maintain a reasonable rate of fire, which I believe required some hacking (almost similar to a motion profiler). But to do distance aiming, we used a lookup table, with input from a camera or joystick. For lateral aiming, we did use PID. The thing about setting distance is that there's no immediate feedback - you need the shot to land before you get feedback, so you can't correct the flight path in the middle, thereby defeating the purpose of PID.