The way I understand control sampling is:
sampling frequency (Ws) is 2xmax system frequency (Wm) (Nyquist) and
usually more than this but not too much (say 4 x Wm). Suppose that the
sampling interval is 500 us => Fs=1/.0005=2000 Hz. That gives the Fm of 500
Hz (WOW that is fast! ) giving a Wm=2xpi*Fs=3141.6 rad/s. I work with some
high performance small motors from Maxon that are very fast and very
powerful. I sample at 1 ms intervals for the control and have a sizable
delay for calculations (that I am in the midst of reducing). I do not have
problems due to jitter in the timing. I guess what I am saying is that you
may wish to look at the dynamics of your system. If you sample too fast you
actually induce extra poles and depending on the over-sampling the poles
induced may not be stable. If you do not account for them WHAM-WHAM-WHAM
(that is upside the head). If people have motors and applications that are
in this range I would love to hear about them! I have yet to encounter this
but then I am not 64.5 years old and ready to retire :-). I would look to
the sampling period first, then to the state values (estimated and
measured) check for missing interrupts, then noise in the analog channel to
your amplifier, then back off on the aggressiveness of your control ... I
would be interested in hearing more about this so we can fix or at least
document the limitations.
-John
On Monday, August 09, 1999 3:51 PM, Stuart Warren
[SMTP:[EMAIL PROTECTED]] wrote:
>
>
> -------- Original Message --------
> Subject: Re: [rtl] Reply to ancient post: servo control.
> Date: Tue, 10 Aug 1999 08:18:50 +1000
> From: Stuart Warren <[EMAIL PROTECTED]>
> To: SteenbeckDigital <[EMAIL PROTECTED]>
> References: <[EMAIL PROTECTED]>
>
> > - Where did you get the P123 from???
> Oops - that should have been P120.
>
> > - What kind of RC-servo did you use??
> The cheapest one I could find. I can't remember the model number but it
> was a Futaba brand. Cost me the equivalent of US $12.
>
> > Only the slow servos didn't show the symthom to me.
> Maybe cheapest = slow, and hence why I didn't have any problems.
>
> > - Is there a patch to RtLinuX where the jitter has been reduced??
> I used stock V1.0 RTL.
>
> Regards
> Stuart Warren
>
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