[amsat-bb] Re: TV antenna rotators

[Robert Bruninga]

> After running it to a hard stop, disconnecting one wire and 
> running the controller to 360, it now works properly..

>From a random plug in of power, all these cheap rotators need a
calibration to get the POINTER motor and the outside motor in
sync.  You have to rotate the knob to the right stop for over a
minute, and then back to the left stop for over a minute.  The
outside motor will hit the stop and sit there until the insider
motor catches up.  Then you go the other way, incase the inside
was already too far to the right.

Once this is done, they remain in sync.  (but only because they
assume the two motors will run at the same speed.  Periodically
you need to re-clibrate to be sure.

But this is how my APRSdos cheap satellite tracking program
works.  It uses no pots or any feedback.  It just runs the motor
based on time and then every now and then when it finds itself
near South stop, it runs the thing about 45 degrees past the
south stop, then recalibrates its "known position to 180".  Most
of the time, it doesn teven need to do this, because many passes
a day go through south, and the mechanicl stops automatically
assure it gets calibrated.  This is perfectly fine for LEO's and
small beams.

It is NOT adequate for OSCAR arrays and HEO's (of which there
are none operational now anyway)...

Hence a $70 satellite tracking antenna that only needs a $10
opto-sisolator to a serial port for tracking.

See http://www.ew.usna.edu/~bruninga/rotator1.html

I have a prototype PIC version running that I hope to make
avaialble.

Bob, Wb4APR