Quote:
Originally Posted by EricVanWyk
By definition, it is impossible to stably hit your set point with a P only control loop. You must have an I term.
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It is
possible to have an accurate feed-forward and achieve this. Not likely, for sure.
Also, for benefit of anyone reading this and not recognizing the distinction, you can stably hit a
position set point with a P-only control loop. (Well, actually you need some D, but this doesn't need to be in software - a bit of friction will often do the job nicely.)
As to a P-only loop only reaching 50% speed, that makes sense if you don't have a feed-forward. Thought experiment: what happens if you start at the setpoint speed, or equivalently read the current speed, and make it the setpoint? Answer: the difference is zero, so zero voltage is applied to the motor. It slows down. As it slows down, D increases and voltage is again applied, but never enough to get back up to the set point.