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

[Steven Kalmar]

I don't own a Alfa Spid, or any other rotator at the moment.  I started
building a custom rotator and writing my own controller, using quadrature
encoders, pots, and 9DOF sensors to determine position.  While researching
my options, I discovered that rotary encoders don't like long lengths of
wire.  They work best with short runs of low capacitance wire.  I2C is even
more picky.  I had all kinds of issues when I was using cheap patch cables
for the i2c interface on the 9DOF board.  I decided early on to locate the
controller in the rotator and keep the wire runs short, with final control
via ethernet.

I can't imagine that 50' wire runs are noise free.  Is there any way to
locate the controller closer to the rotators?  Perhaps interface to the
controller via ethernet?  Ethernet can handle long runs quite well.  I'm
surprised that so much of the ham equipment still requires serial ports.

Steve
KD8QWT

On Sat, Mar 19, 2016 at 6:11 PM, Clayton W5PFG <w5pfg at amsat.org> wrote:

> 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.
>
> 73
> Clayton
> W5PFG
>
>
>
> 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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> to all interested persons worldwide without requiring membership. Opinions
> expressed
> are solely those of the author, and do not reflect the official views of
> AMSAT-NA.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
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