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Unread 21-03-2004, 23:51
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Re: PID control loops - closed loop feedback

Before we limited the integral, we found that it could wind itself up into the thousands if we weren't *very* careful. That could happen if the OI was off, the robot was on, and the arm moved, or if a velocity went in and the arm was held down. An integral that high means that when the arm is allowed to move, it will smash all the way over and ram into itself, or do other nasty things to itself.

We found that the integral never actually gets higher than 30-50, and thats very rare too. Usually it is under 20.

We run the elbow loop at 10hz, and the wrist loop at 5hz. That leaves enough time to create a speed error we can actually work with...too much faster and we get mostly 0 speed with intermittant high speed as it actually moves. Very bad.

edit: To the above poster: You're right. The proportional is supposed to be the major factor when the speed error is large, and the integral builds up to balance it out and hold steady as the speed error decreases (ie the integral maintains the speed the proportional generates). It just so happened that the arm worked best for us when the proportional and integral were both 1/8. It took a lot of testing and frustration to find the right values.
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Last edited by 10intheCrunch : 21-03-2004 at 23:54.
 


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