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Unread 30-03-2004, 10:40
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Re: PID control loops - closed loop feedback

Wow, great post!

A few questions, though: first, how high a resolution encoder are you using? You spoke about sampling at 100hz, which is *much* higher than our sample rate (5 and 10hz)--we found that anything higher didn't allow for much change at all during one tick and as a result operated inproperly. We use a potentiometer on the motor with 1024 ticks on it (10 turns), using about 900 in the actual arm scope.

Two, just as general practice, make sure to use 254 instead of 255 (and -127 instead of -128, or you're adding too much); you can get into trouble with the speed controllers with 255.

Three, what circumstances are you dealing with integer overflow? We've never had anything close to that high an integral, much less wanted it (it would cause the motor to swing all the way over and jam the arm into the robot...). Perhaps we have radically different output systems, but our integral never really gets higher than 30-50 (and that can be dangerous).

Hey but thanks for this! Now I gotta sit down and try to understand the part about linearizing it...
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Last edited by 10intheCrunch : 30-03-2004 at 12:20.
 


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