> *Basic* tuning (ie: no oscillation, chatter and getting pretty close to=20
> setpoint) with the Ziegler-Nichols method was relatively easy, but it=20
> seems a bit "sticky" -- ie: very small changes to my control pot don't=20
> immediately take effect, and continuing to change the pot a bit more=20
> suddenly makes it "jump" to the correct position.

Could it be that you have too low resolution so very small changes to the p=
ot=20
isn't registered? When you move it a bit more, you will get a step change.


> Also, just sitting=20
> with a fixed setpoint, it will move a bit every once in a while (like=20
> 5-10 seconds).

Could be noise in the signal from the motor position and/or pot. You normal=
ly=20
will get one to a couple of bits jitter from the A/D converter if your anal=
og=20
circuit isn't well filtered and separated from the digital circuit. Perhaps=
=20
digital filtering could help.

/Ruben
--=20
http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist
.