At 03:50 PM 9/18/2006, Merlin-7 KI4ILB wrote:
>OK I'm busted...
> My budget is going to be very tight for a while after I move to the new
>qth. I kinda put my foot down with the wife so that I can get the funds for
>the tower but there is not much left over after that (unless the home I am
>in now sells for a bit more than I think it will)
> Most of you might know where I am going with this by now...
>
> For a while I can see me turning the beams by hand.
The time honored "Armstrong rotator"..
> That should not be a
>problem (just a pain in !$$) as the tower will be right next to my shack.
> I could keep that set up and build a chain or gear driven rotor myself and
Ropes are your friend.
But really, once you rig up a shaft all the way to the bottom,
improvising a rotator is actually pretty easy. Keep your eyes open
for suitable DC gear motors surplus. You can get things like car
window motors very inexpensively (who cares if it breaks, at
<$10each, you just junk it and install a new one)). You can also get
10:1 or so reduction pretty easily with toothed belt
technology. Bicycle chain works up to around 5:1 gear ratios. Check
out the surplus stuff aimed at robotics people. A Vbelt pulley the
motor and rope or steel cable wrapped a couple times around the shaft
also works.
While you're doing the rigging, put some sort of shaft encoder up at
the top of the tower. Nothing says the motor and the encoder have to
be in the same place.
>add it later. I know its better just to buy one but like most hams, I like
>building stuff.
You bet. I've built more than one positioning system using the
parallel port outputs of a PC to drive the motor one way or the other
(through a relay), and using the status bits to read an
encoder. Given the usual 30 degreeish beamwidth, the encoder can be
as simple as a bunch of magnets glued to the shaft and a reed switch.
Say it takes 60 seconds to make an entire circle, and you have
magnets every 30 degrees (12 magnets).. If you want to position to
halfway between a magnet, you just keep running 2.5 seconds after
passing the magnet before your desired position.
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