[amsat-bb] Alpha Spid Rotator

Sat Jun 6 01:27:47 UTC 2020

What's everyone using for rotor cable to feed the Alpha Spid?

Ryan, NF0T

On Wed, Jun 3, 2020 at 1:45 PM Leffke, Zachary via AMSAT-BB <
amsat-bb at amsat.org> wrote:

> Hi Dave,
> We use a lot of the RAS/HR and Big-RAS/HRs at VT in our ground station and
> on other projects.  My biggest recommendation is if you don't absolutely
> need the resolution, don't get the high resolution variants (0.2 deg
> resolution).  It uses a quadrature encoder feedback mechanism that is
> highly susceptible to EMI corruption leading to 'dropped counts' and a
> general slew of problems related to calibration and reliable pointing
> knowledge.  We have constantly battled this problem since day 1 of the VTGS
> and still don't have reliable resolution for the problem (but enough
> band-aid solutions to keep limping along and periodic trips out to the
> tracking station to recalibrate).  The smaller Ras/HRs seem to generally do
> better on the feedback front (still high resolution with the quadrature
> feedback) for some reason, but we typically use those in 'deployable'
> scenarios and the feedback cabling is much shorter (maybe 20ft or so)....so
> not necessarily an apples to apples comparison with the perm
>  anently installed Big-RAS/HRs that have longer feedback cables (roughly
> 100-200 ft depending on which antenna stack we're talking about) and
> generaly seem to be more prone to issues.  I also personally own a Ras/HR
> (smaller one) with the high res feedback and a 2.4m solid dish mounted on
> it.  It can handle the load just fine with proper counterweighting and so
> far I haven't had any feedback issues (roughly 50ft feedback
> cable)....knock on wood.
>
> The 'non high resolution' (low resolution?...its still accurate to about 1
> deg) variants use plain ol' potentiometer feedback.  I don't have direct
> experience with them, but have reports from some colleagues that they
> haven't had any serious or repetitive issues with pointing calibration
> (some radio astronomers in Physics dept are using one with a 2m dish).  (I
> think that one uses a different controller than the MD-01 that we use, but
> I think the MD-01 or MD-02 could handle either type of feedback).
>
> Other 'warnings' include realizing they have no mechanical stops in
> azimuth (they do in elevation, roughly at 180 deg limits).  That said, it
> isn't really a problem as most controllers work reliably with 'software
> limits' and the MD-01s at least have timeouts that help if things 'go
> wonky' with feedback.  There are some cases though that result in the
> perfect storm of corrupted feedback that goes undetected by the MD-01 that
> could lead to a bad azimuth situation; in our case we monitor antenna
> motion on a camera, so are able to mitigate that scenario with human
> intervention (and our custom control software looks for 'impossible speeds'
> as reported by the MD-01 positions that further helps mitigate that when
> the feedback goes awry).
>
> Mechanically, they have done very well for us with the double-worm gear
> design, imperceptible gear slip (if any).  I've heard of folks having
> mechanical failures, but I don't know the details, and that hasn't been my
> experience.  As an example, at the height of 'performance' I was able to
> reliably track multiple S-Band downlinks with a 3m mesh dish antenna with
> no discernible negative effects due to point errors or 'jiggle' in the
> system (part of that is the ramp up, also part the counterweighting).  In
> the 5 or so years we've been running them, we haven't had any major
> mechanical malfunctions (knock on wood), and part of that is probably due
> to periodic maintenance (re-greasing and such), which I've done at least
> once (can't remember exactly, maybe twice in that 5 year window).  Part of
> that is also the fact that we tend to use the yagi stacks with a lighter
> load a lot more than the larger dish systems, I might be singing a
> different tune if the dishes were used daily.
>
> The MD-01 controller (and MD-02s as well for non-rackmount variants) does
> have some nice ramp-up/ramp-down features, particularly useful for larger
> systems (like our 4.5m dish).  I do wish the API documentation for the
> MD-01 command interface was a little better...but we've been able to work
> through it (for example, they changed the protocol a bit in a relatively
> recent firmware update that broke compatibility with our software and
> presumably things like rotctl in hamlib, but I think that has all been
> fixed/updated).  The API issue might not be a problem for most folks not
> interested in writing their own software, or if you are using a different
> controller.  The overall documentation situation is a little 'meh' in
> general as there have been a lot of versions and such released and they are
> on different websites run by different folks.....but at least there is
> documentation at all and a little reading and experimentation is usually
> enough to get what you need, and the basics such as th
>  e wiring diagram hasn't really changed over the years.
>
> I can't directly speak to the SatPC32 question because we don't use it.
> Other than that firmware update hiccup, I'd be willing to bet it works fine.
>
> Bottom Line:  When they work, they seem to work well, at least in my
> experience.  If I were going to buy one today for personal use, I'd get one
> with the potentiometer feedback if the intended use is for something like a
> few Yagis and if I were planning a more permanent installation.  If I were
> going to buy something for VT/work with a better funding source than my
> 'hobby budget' I'd probably look for something better, like M2 products
> (pretty significant jump in price point though).
>
> I hope this helps.
> -Zach, KJ4QLP
>
> --
> Research Associate
> Aerospace & Ocean Systems Lab
> Ted & Karyn Hume Center for National Security & Technology
> Virginia Polytechnic Institute & State University
> Work Phone: 540-231-4174
> Cell Phone: 540-808-6305
>
> -----Original Message-----
> From: AMSAT-BB <amsat-bb-bounces at amsat.org> On Behalf Of Dave via AMSAT-BB
> Sent: Wednesday, June 3, 2020 1:20 PM
> To: AMSAT BB <amsat-bb at amsat.org>
> Subject: [amsat-bb] Alpha Spid Rotator
>
> Is anyone using an Alpha Spid az/el rotor? If so how do you like it? Would
> you recommend it over the Yaesu's and are there any issues using it with
> SatPC32?
>
> Thanks,
>
> Dave
> N2OA
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