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Re: [TowerTalk] Tower mast..

To: "Merlin-7 KI4ILB" <>,"Mike Rhodes" <>, <>
Subject: Re: [TowerTalk] Tower mast..
From: Jim Lux <>
Date: Mon, 18 Sep 2006 20:37:30 -0700
List-post: <>
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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