> >We used microstepped steppers plus gearing and have similar OTT numbers
for
> >pulses/degree.
> Are you counting the pulses to the stepper motors or have you got
separate
> encoders?

I'm counting pulses. The steppers are micro-stepped 128x and a full speed
slew is just over 1MHz input pulse rate. I was expecting to have problems
with mechanical slippage and/or possibly stepper/translator errors, but it
seems to work well. I'm using simple opto interrupters for reference points
and getting repeatability of around an arc-second on a limit to limit slew.

All of this is being done by an 8 bit micro, including environmental
monitoring, opening/closing the observatory, measurement scheduling,
positioning, filter selection, photon counting from the PMT, simple error
checking for clouds etc and then emailing the results to the appropriate
people after a night observing. Excluding the stepper translators and the
modem, the whole controller cost <$1000 for 5 units.

Now they want to use area CCDs (which we technical types wanted in the
first place), so the whole exercise was a bit of a waste of time. The CCD
needs a hard disk to save piles of data and has a huge field of view
(compared to a PMT) so a commercial controller, CCD and PC probably would
have done the job.
Aarghh ! Bloody astronomers. :-)

Steve.

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  Very funny Scotty.  Now beam down my clothes.
======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680                email: steveb@kcbbs.gen.nz
New Lynn, Auckland           ph  +64 9 820-2221
New Zealand                  fax +64 9 820-1929
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