PID without the D

[Joohoo]

Originally Posted by JonathanLKS

Well if you have a full PID loop up and running,

on that note, the PID loop, how fast do I really need it. Is the normal 26ms loop fast enough? or does this need to be faster?

[ay2b]

Originally Posted by Joohoo

on that note, the PID loop, how fast do I really need it. Is the normal 26ms loop fast enough? or does this need to be faster?

a) We've always done the PID loop in the 26ms loop, and it's worked for us.
b) Since you can't update the PWM outputs any faster[*] than every 26ms, I don't see how running your PID calculations any faster would be of help to you.

Why do you want to do just a PI loop? I've heard of people using just P, or PD, but never PI.

[*] Actually, you can update your PWM outputs faster, if you use PWMs 13-16 and your own pwm generation functions (or one from a non-IFI library)

[Alex.Norton]

I would think that doing a PI would be really unstable. The D part has the effect usually of dampening the I since the I will always overshoot the goal. Of course the instability will dampen itself over time because of friction in the system but I would agree that I have never seen a PI loop. Plenty of P+D and P-D and just P loops but never a PI loop.

What exactly is your reason for not using the derivative part of the loop?

[billbo911]

Originally Posted by Alex.Norton

Plenty of P+D and P-D and ......

Not meaning to side track here, but that is what I'm going to do.

P+D and P-D, which is correct? Or should I ask, how do I determine which to use?