Re: [amsat-bb] More Kansas City Tracker Questions

[Joe Leikhim <jleikhim@xxxxxxxxxxxx>]

Thanks for the suggestions. The reduction pully and bridge idea sounds good.

Dave Metz wrote:

>
> Dear Joe,
>
> I faced this same set of problems when I put my antenna system together.
> For the elevation pot, I used a 10K carbon linear pot.  The trick here is how
> you move the pots shaft.  Forget about the pendulum, it just does not work very
> well.  Unless you have a 10 pound wieght on a three foot arm, it will always be
> sticking and giving you an incorrect reading.
>
> My solution was to use two metal bell cranks.  One on the cross mast, the other
> on the pot shaft.  A metal bar linked the two.  By offsetting the links downward
> about 30 degrees when the antennas are in the horizontal position, you can swing
> the beams the full 90 degrees.  The mechanical
> linkage moves the pot shaft perfectly.
>
> By using the pot in a bridge circuit, you can obtain a full scale deflection on
> a meter.  By scaling the values of the resistors in the circuit, just about any
> value of meter (within reason) and pot can be used.  I ended up using 0-100uA
> meters and 10K pots.  0 on the meter scale equals 0 degrees. Full scale equals
> 100 degrees.
>
> Yes, the voltage to the bridge circuit must be regulated.  I ran mine on plus
> five volts.
>
> For my azimuth drive I used a old Ham-M rotator and I built my own control box.
> This rotator uses a 200 ohm pot for direction indication.
> The wiper on the pot is grounded and one side goes to the control box.  To drive
> the meter, I feed the pot with a constant current source.
> As the resistance changes, there is a linear change in voltage that is displayed
> on the meter.  I changed the meter scale to read 0-360 degrees.
>
> In your case for the mechanical linkage between the mast and the pot shaft, I
> would use "O" ring as a belt.  By using a pulley larger in diameter then the
> mast (your other pulley), you can translate 360 degrees of rotation into 270 or
> less.
>
> To recap:
>
> Ordinary 270 degree rotation pots will work perfectly
> Pendulums don't work Do your metering with a Wheatstone bridge circuit
>
> >
> --73-- Dave WA0AUQ

--
Joe Leikhim K4SAT
Jleikhim@nettally.com

"Jazz is not dead.  It just smells funny." -F.Z.


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