Quote:
Originally Posted by flameout
Also, with full PID, having a feedforward on the velocity target will cause overshoot, just FYI. If you're doing PID for position control, then having an acceleration feedforward should be fine; a velocity feedforward would be beneficial if you're doing PD.
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I disagree with this statement. I'll give you a fuzzy explanation now, and try to find time to prove it for real with the math later. I'll probably cheat and give you the continuous time proof...
You can model the velocity feed forward as a disturbance. It adds a power to the motors that the control loop is not expecting. This power is constant (at least at constant velocity), so, since the loop is stable, it will stabilize out and converge. This is very similar from the loop's perspective to changing the goal, and since both of them are happening at the same time, it shouldn't have much effect.
Differentiating the goal signal will also introduce delay into it. This won't have a huge effect on the system since the time constant of a robot is very slow compared to a good loop frequency, but this can become more and more pronounced as your system's time constant gets closer to the period of your loop.