I've been looking at ideas for electrically raising and lowering a
vertical antenna (like a 6BTV or R7000 style... basically 20-30 ft of
aluminum tubing). One idea is to use a garage door opener (or a
similar chain/track or leadscrew arrangement from some other source,
but a garage door opener is probably the cheapest way to get a 8 foot
long linear drive, 1/2 HP motor, etc.).
The other way would be to find some inexpensive gear box that runs
at, say, 1 RPM (it would take 15 seconds to go 90 degrees) and has
the torque capability to handle the wind load on a 30 ft mast. Any
ideas on consumer products with this sort of capability (I don't
think electric window drives are quite in the ballpark, but maybe?)
The moment load is about 700 ft lb for a 30 foot, 2" diameter mast in
a 60 mi/hr wind. I suspect you could get away with a lot less as the
drive, accepting the fact that the drive might slip if you try and
actuate during a windstorm. You could have mechanical stops to take
the load once all the way up. Of course, some drives (worm gear
window motors come to mind) can't backdrive, and will break if
overloaded on the output shaft.
700 ft lb @ 1 RPM is a pretty small mechanical load (550 ft lb/sec is
1 HP, so we're down in the 1/5th of HP or smaller... a pretty small
motor, with suitable gearing.. on 12V, something like 10-15 Amps.. a
couple amps for a 110V motor). probably a bit much for an
inexpensive TV antenna rotator..
The overall idea is to hide a vertical antenna on a rooftop by laying
it down when not in use.
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