Questions about Encoders and PIDControllers

[Ether]

Originally Posted by BradAMiller

Maybe that was a little confusing...
I meant that as the actual speed reaches the setpoint speed, the error term goes to zero.

Much better :-)

Suppose there was only a proportional term, then the output value from the PID controller would go towards zero (proportional constant times zero is zero, similar for the other terms).

It's not similar for the other terms. The I term can be non-zero at the setpoint. In fact, that's one of the purposes for the I term, to provide a non-zero output at the setpoint (if required).

That's what the feedforward term attempts to fix.

Yes, feedforward is one way to address that issue.

Another is to use the I term, when controlling speed, like you would use the P term when controlling position.

Yet another is to integrate the output of the PID.