PID control help

[gpetilli]

Originally Posted by cstelter

I'll play :-).

Would this work? I don't know.

Is there a better way? I don't know.

This seems to be taking me back to one or two courses I had in college regarding stability and Laplace transforms I think-- but I'm not sure about that. That work was all based on electrical circuits, but I think the math translates to any system of differential equations. Either that or I'm way off in the weeds. I've had no need to revisit that part of my education in the past 25 years, so it's not just rusty, it's frozen/locked up.

The part I find curious is using different error terms for P and I on the 'slave' motor. I have absolutely no idea what effect that might have, nor how to solve for it. Thus proving my inability to claim any guru status whatsoever. But I am finding the discussion fascinating, so I really appreciate it.

Intuitively it seems it could work, but whether or not in practice the system could keep up with it, or if another formulation would be more effective, I don't know.

This is a bit more complicated than even most college courses (although the concepts are all there). Most courses only deal with one system of equations at a time, not two slaved systems. Don't feel bad about being lost in the weeds.

Basically any servo control loop "attenuates" the error. Three things about this statement -
1) it needs error to work
2) the error is never zero
3) far better reduce the systematic error before entering the loop

By sending the same command to both motors simultaneously, you reduce the error before it even develops. The servo has less work to do, is easier to tune and responds faster.