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Re: Home Brew Auto Rotor Control?



Jeremy,
The main homebrew automatic rotor controller is FODTRACK which is available 
for download from www.amsat.org.  It's information is in the downloadable 
files/software section.  You may have to make your own board or just wire 
wrap it or use some other "one off" method.  I heard about PCBs being 
available at one time, but I don't recall from whom or if they're still 
available.  I suppose it couldn't hurt to check with FAR circuits 
(www.farcircuits.com).

The biggest problem with automating those rotors is that neither of them have 
position sensing potentiometers.  All automatic circuits I know of require 
them.  In addition to the inherent lack of precision and potential for losing 
their alignment, these "clacker" style controllers can't be directly read by 
the controller.

The elevation axis is relatively easy, requiring only 90 or 180 degrees 
rotation.  A standard linear pot could be attached to the crossboom and use a 
weight attached to the shaft to sense position.  The ARRL antenna handbook 
has a good example of this (at least the 14th and 15th editions - I don't 
have the new one).  It also has a nice schematic of how to homebrew a 
controller for the U-100 using parts salvaged from the old controller box.  
Obviously you'd use the U-100 for elevation as it can pass the crossboom 
through the rotor.  

The az rotor (your radio shack one) is more troublesome.  Since the shaft 
does not pass through the rotor, there's no easy way to couple to the end of 
it.  In addition, most pots won't go a full 360 degrees without hitting their 
physical stops.  If you're willing to do a little more fabrication work, you 
could hook a gear or pully to the mast and use a reduction drive to move the 
pot.  Concerns about slippage would make me consider a gear or toothed belt 
approach rather than the pully set-up sometimes seen.  A 10 turn 
potentiometer may be useful to overcome the 360 degree rotation problem, but 
using one tenth of the range limits resolution somewhat.  Perhaps you could 
arrange the gear/pulley ratio to use more of the pot's range.  If you could 
find an AZ rotor with a built in pot (like the HAM X series), you'd simplify 
the task considerably.

W5UN has a nice little schematic for a digital rotor positon readout on his 
website.  Search for W5UN, moonbounce and EME and you should hit it.  The 
bridge circuit should be of interest for both manual and autamated set-ups.  
He also has a crude sketch of a pulley driven potentiometer.

Unless your goal is unattended operation, I would encourage you to first make 
a manually controlled set-up with these rotors and then try to upgrade.  With 
wide beamwidth antennas, they shouldn't require as frequent adjustment and 
should reduce operator workload.  For AO-10, even if you use longer antennas, 
the pass is much slower and should offset the decreased beamwidth.

One more concern I'd mention is that these are realtively light duty rotors.  
Use of small antennas is a very good idea, both to limit the weight and wind 
load, but also the lower gain will result in wider, more forgiving beam 
widths.  It may be advisable to mount the rotors close together or use a 
second bearing set to reduce the mechanical stress of the EL rotor and 
antennas on the AZ rotor bearings.  The RS rotor won't withstand too much 
abuse.  I've split the case on one with a heavy 6M beam.  The Alliance seems 
to be well suited to elevation use since many sat ops have been using them 
for years.  Just make sure you balance the antenna array since the rotor 
doesn't have a brake or an excess of torque.

73 and good luck,
John Oppen, KJ6HZ


Original Message:
_____________________________________________________________
Does anyone have plans on how to make an automated rotor control system? I
have an Alliance U-110 and just a simple radio shack rotor that I am hoping
to simply put up a 70cm and 2m beam for AO-10 work, and then maybe go ahead
and try to use them on the LEO's, if I can get an automated rotor control
system.

I would appricate any information,

Jeremy - KB8LFA@amsat.org
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