I was continuously spitting out the raw A/D value from the control and=20
feedback pots and can see that I have the resolution, and there there is=20
some discrepancy between those two.  Range is ~113 to ~870 (raw A/D=20
values), and the difference is sometimes around 30 when the motor=20
"stalls" for a bit . It seems like it wants to correct it, but can't,=20
then every so often it gets enough oomph (I expect from the Integral=20
component building up) to move, overshoots a bit and then repeats in the=20
other direction.

I am seeing (on the continuous serial dump) the LSB (in decimal)=20
toggling by one digit, so I don't think it's noise (since the=20
discrepancy is ~30).  But I can add some IIR filtering easily anyway.

Cheers,
-Neil.



On 1/1/2015 4:42 PM, Ruben J=F6nsson wrote:
>> *Basic* tuning (ie: no oscillation, chatter and getting pretty close to
>> setpoint) with the Ziegler-Nichols method was relatively easy, but it
>> seems a bit "sticky" -- ie: very small changes to my control pot don't
>> immediately take effect, and continuing to change the pot a bit more
>> suddenly makes it "jump" to the correct position.
> Could it be that you have too low resolution so very small changes to the=
 pot
> isn't registered? When you move it a bit more, you will get a step change=
..
>
>
>> Also, just sitting
>> with a fixed setpoint, it will move a bit every once in a while (like
>> 5-10 seconds).
> Could be noise in the signal from the motor position and/or pot. You norm=
ally
> will get one to a couple of bits jitter from the A/D converter if your an=
alog
> circuit isn't well filtered and separated from the digital circuit. Perha=
ps
> digital filtering could help.
>
> /Ruben

--=20
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