And on the subject of PID, this ridiculous video makes the concept so=20
much [sarcasm]easier[/sarcasm] to understand...
https://www.youtube.com/watch?v=3DrFBlcS2Sg0k

Cheers,
-Neil


On 1/26/2015 10:52 AM, Neil wrote:
> So I finally got around to implementing this and it works.  I initially
> used the Arduino PID library, got it working/tuned and then wrote my own
> PID code for a PIC18F.  I used integer math, then scaled down to get the
> appropriate range.  In my final tuning, I used (what I believe is
> feed-forward) an offset -- I experimentally determined what constant
> output value would just counteract the spring pulling on the servo and
> added that to my PID output result. Works pretty nicely.
>
> Much thanks,
> -Neil.
>
>
> On 1/1/2015 7:36 PM, Neil wrote:
>> I was continuously spitting out the raw A/D value from the control and
>> feedback pots and can see that I have the resolution, and there there is
>> some discrepancy between those two.  Range is ~113 to ~870 (raw A/D
>> values), and the difference is sometimes around 30 when the motor
>> "stalls" for a bit . It seems like it wants to correct it, but can't,
>> then every so often it gets enough oomph (I expect from the Integral
>> component building up) to move, overshoots a bit and then repeats in the
>> other direction.
>>
>> I am seeing (on the continuous serial dump) the LSB (in decimal)
>> toggling by one digit, so I don't think it's noise (since the
>> 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 t=
o
>>>> 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 t=
he pot
>>> isn't registered? When you move it a bit more, you will get a step chan=
ge.
>>>
>>>
>>>> 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 no=
rmally
>>> will get one to a couple of bits jitter from the A/D converter if your =
analog
>>> circuit isn't well filtered and separated from the digital circuit. Per=
haps
>>> 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
.