[amsat-bb] Re: inquiry about homebrew az-el systems

Daniel Schultz n8fgv at usa.net
Sun Feb 24 19:43:05 PST 2013


Most of us could probably cobble together some sort of one-of-a-kind design
using surplus motors and gears from Skycraft or other sources. Making a design
that is reproducible and publishable, made from parts and components that will
be available in quantity a year or two or three from now is another matter.

I have experience making various antenna kludges for use on field day, with
door hinges as elevation bearings, and ropes, pulleys and threaded rod as
actuators. Everything but the motors came from Home Depot (but the small
electric screwdrivers that they sell there could make great gear motors...) I
never had any intention of leaving it up all year long or operating it
unattended on a roof top. My design worked OK when the air was calm but the
slightest breeze would back-drive the motors and blow it all over the place.
When antennas start acting as sails in the wind, you need strong motors and
big gear ratios, probably with brakes. You might perhaps take a look at the
AlfaSpid design, which uses automobile windshield wiper motors to drive really
big worm gears.

Practically speaking, you will need a better workshop than just a grinder, a
drill, a saw and a few hand tools. A lathe and a small bench-top milling
machine are essential to any serious metal worker. You might be able to find
these at a local "maker" shop in your town if there is one, or look at
www.littlemachineshop.com, $1500 should get you a basic bench top machine
shop, about the cost of an all mode satellite radio.

Finally, Samudra, as a graduate student working on your PhD, is this really
the best use of your time? In the end, that is the reason why most hams end up
writing a check and buying a ready made rotor system, so they can get on to
doing other things in their hobby and their life.

Dan Schultz, N8FGV

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