[Mark McLeod]

I've found it pretty easy to use a rotational mechanism to demonstrate PID tuning.

Just add a weighted moment arm and have them stop on a dime-a marked target. You can exchange lighter/heavier weights or slide a weight out further along an arm you're rotating in a circle. You can also shift it from horizontal to vertical to add the experience of the deceleration of gravity on the up swing and the acceleration on the down swing. I just use a 10-turn pot and a slip coupler so overshoots (and you should allow overshoots) don't damage it. Rotational is nice when the pot does slip, because there isn't a chance of mechanical damage. You can substitute an absolute encoder for the pot or use a continuous pot too.

The method applies to moving an arm joint both with and without holding the extra weight of a game piece, or the motion of a turret.

Switching the pot out for a relative encoder lets you practice PID position control and speed control.