PID control loops - closed loop feedback

[10intheCrunch]

The PI loop on the wrist was immensely successful for us (I ran the arms at the Sacramento regional this weekend). The only problem it has, other than the bounciness on the way down Jay described (in actuallity that is a small problem, we only *fold* the arm once or twice in a match, to stow a ball or to stow when hanging), is that it can be slow to react when holding a ball. The integral has to get pretty high to move the arm up from extended to vertical (say, when we pick up a ball from a goal), and until I learned to correct, it would overshoot vertical (if thats when I moved the joystick to neutral) and fly down the other side. After about four rounds on Friday, though, I got that worked out and it worked really well for the rest of the tournament.

We had tried to build a PID loop earlier in the year, and didn't really end up with a workable solution. The important thing, it seems, was the engineer who came down and helped us map out the logic of the process. Once we knew what we wanted to do, it was actually only took about a half hour to write the function (and update as needed later).

By the way, you can see the pictures of the arm straight out on our website, in my signature =).

edit: The Reposition functions for the arms came from our old code for the arm, before we implemented the PI loop. It takes the distance from the desired position to generate a velocity. Pretty much, we only use it for the preset buttons on our control box and autonomous mode.