[Joe Johnson]

With regard to the I part of PID, be very careful.

There is a phenomon called "integral wind up" that is not a theoretical problem but a practical implementation problem.

Essentially, you need to "turn off" the integration when the controller output is saturated or limited (for example when your robot is disabled).

We had a nasty bug that we had fits trying to kill. Our robot would come out of a disabled state and do a major twitch that hurt our robot and almost hurt some workers on a number of occassions. We finally killed the bug, but it was very sutble and was quite difficult to discover. It turned out to be a case of integral wind up.

Joe J.