[amsat-bb] Optical shaft encoders (Alfa Spid RAS-HR & BIG RAS-HR)

Clayton W5PFG w5pfg at amsat.org
Sat Mar 19 22:11:11 UTC 2016

Since my Alfa Spid RAS-HR after Christmas was installed, it requires 
calibration to 0 azimuth and 0 elevations weekly.  In a given week, 
elevation and azimuth both tend to drift 10-15 degrees. It varies based 
on the number of tracked satellites in the given period.

Not only is this issue annoying to a manned station, it makes remote 
operation of my station especially annoying.

Finally, as others have mentioned, there is a potentially dangerous 
situation that has occurred more than once.  While I have feed line and 
rotor loops for approximately 720 degrees of rotation, it is not a 
parameter I would like to utilize.  I would prefer to stay somewhere in 
the range of 540 degrees to be safe and not stretch any cabling.  On 
more than one occasion, the MD-01 controller decided it lost its mind 
and was continuing to turn far past the command that had been sent to 
it.  Fortunately on these occasions, I was watching the rotor interface 
closely and was able to manually send a stop command.  Thanks to Zach 
Leffke, I will now refer to this Alfa Spid RAS-HR & MD-01 feature as 
undocumented "runaway feedback" mode.

I'm using shielded #18 wire running approximately 50' from the rotor 
sensor output to the controller.  There are 6 conductors in the same 
bundle which I'm breaking out for the 2 rotors (az & el.)  Had there 
been better documentation (any,) I might have used two separate, 
shielded 3 conductor cables.

As others have stated, the Alfa Spid RAS-HR (or it's big brother) have 
been very reliable minus this strange anomaly.

One course of action in my shack recently has been to bypass SatPC32's 
spid.exe and utilize PstRotator.  It has some added benefit to allow me 
to use greater than 450 degrees of azimuth rotation.  It also allows me 
to set fixed limits on az and el rotation capabilities of the Alfa Spid. 
  However, it will not prevent the runaway feedback.


On 3/16/2016 13:10, Robert McGwier wrote:
> I would like to consider adding optical shaft encoders to augment or
> replace the hall effect sensors in use on an Alfa Spid az/el installation.
> We have the high resolution sensors and are experiencing some annoying
> anomalies that have been very difficult to trace and are detrimental to
> autonomous operation at our ground station at Virginia Tech.
> Any information or help would be appreciated.
> 73s
> Bob
> N4HY
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