slow rpm dc motor

The speed of the DC Motor may not be as important as the speed of
gearbox output. Typically the motor run at thousands of revs per minute
and the gearbox steps this speed down and torque up to something useful
for your application.

regards,
colin

--

www.minisumo.org.uk

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It also depends on how quickly you want to turn the dish, the mass and
orientation of the dish ect.
There are some motor and gearbox combinations that are useful for
small projects
Also i believe you can often purchase dedicated satellite tracking
systems or motorised mounts that are probably cheaper than you could
make them

I hope that can help a little if not can you give us more information
on what you need?

    If you want to track the sun, build a sun tracker.  Edmund Scientific
has a little one here:

    http://scientificsonline.com/product.asp?pn081628&bhcd2 80419926

    All you need are two solar cells arranged in a wedge as shown.  Use
comparators to drive relays to run the motor in one direction
or the other.

    You can build this out of op amps and relays, or use a microprocessor.
I'd be inclined to use op amps, because you can power the tracker off the
solar panel without worrying too much about what
happens during low power conditions.  After all, when it's dark,
it doesn't matter where the collector is pointed.  Allow for a dead
band, so when the outputs from both halves of the wedge are nearly
equal, the motor doesn't run.

    The Art of Electronics by Horowitz and Hill covers op amps
and comparators quite well.

    Read this manual for a commercial solar panel tracker:

http://www.wattsun.com/PDF/Wattsun_TR-55_Installation_Guide.pdf

                    John Nagle

You might want to look into motorized telescope mounts.  Some have geared
bases that track night sky objects for timed exposer photography.  The sun
is a star right?