Seems like automated telescopes are all the rage. Our one is small compared
to yours (11" SCT), but is fully automated and (will) live on its own on a
hill measuring variable stars with a PMT.
We used microstepped steppers plus gearing and have similar OTT numbers for
pulses/degree.

If you assume 2 minutes for a 180 degree slew in RA (which would seem
reasonable for flinging a ton of steel and glass around with arc-second
resolution)  that works out to 130 microseconds between pulses, which I
would have thought would be easy for a PIC to handle. It depends on what
else it was doing. If you have to do both encoders and convert between
coordinate systems at the same time, you might be pushing it.

Steve.


>     I am building a computer control system for a large astronomical
optical
> telescope. The telescope weighs about a ton (1000kg) and is driven by a
pair
> of synchro motors. These are currently controlled by some analogue
> electronics from a small joystick.
>     The first step is to provide the computer with position information
from
> the telescope.
>     The telescope has two axis of rotation, R.A. and Dec. The encoder on
> R.A. axis is attached to a large ring on the telescope mount, by a
toothed
> belt, giving a ratio of 300:1.... thus the encoder produces 1749600
> pulses/revolution... or 4860 pulse/deg.
>     The encoder on Dec. axis is attached to a smaller ring on the
telescope
> mount, by a toothed belt, giving a ratio of 100:1.... thus the encoder
> produces 583200 pulses/revolution... or 1620 pulse/deg.
>
>     The accuracy of the encoders may seem a bit OTT, but I really do need
> it!

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  Very funny Scotty.  Now beam down my clothes.
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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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