On Tue, 6 Oct 2009, Eric H. Johnson wrote:
> Date: Tue, 6 Oct 2009 11:19:11 -0400
> From: Eric H. Johnson <ejohn...@camalytics.com>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <emc-users@lists.sourceforge.net>
> To: "'Enhanced Machine Controller (EMC)'" <emc-users@lists.sourceforge.net>
> Subject: Re: [Emc-users] Scaling angular axis
>
> John,
>
> Ok, got it. Fractional values for PID values just didn't seem right, but
> after closer inspection I see how it would work out that way. It wasn't that
> close to a divide by 360 however, more like divide by 60, at least for P. I
> and D were already too small to establish a meaningful proportionality.
>
> I had not really thought through the consequences of giving scaled, real
> world positions to the pid component's command and feedback pins, as opposed
> to raw encoder positions, as is the case with most other types of motion
> systems I have used.
>
> ISTM there are advantages to using raw encoder values rather than real world
> positions for PID tuning, in that it eliminates the effects of a number of
> variables such as gear ratio and acceleration (real world, as opposed to
> encoder counts per sec^2). It also means that the same motor / encoder pair
> should have the same, or very close to the same pid values, regardless of
> gearing or other scaling (linear vs. angular for example).
>
> Regards,
> Eric
Maybe there's a way to use the PWM scale to compensate for input scale so you
end up with commensurate PID values...
Peter Wallace
Mesa Electronics
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