[amsat-bb] Re: inquiry about homebrew az-el systems

Lizeth Norman normanlizeth at gmail.com
Thu Feb 28 22:17:46 PST 2013

Gus and all:
Had a bad experience with a stepper motor based 3 axis mill project.
That thing had a mind of it's own. Definitely needed the big red kill
switch every once in a while.

The choice of a position sensor is as much as what you can get locally
that meets the need as what will work.

Three turn pots are necessary unless we want to limit rotation to 360
degrees. Easy enough to in satpc32.
 Also, not all pots rotate 360. Some only 320, some less. The more
expensive pots have much greater possible feature set. The Arduino
does not care what we use..
What sort of position encoders are available in your local surplus
store? How about available as salvage from other gear??

Am going to Peru towards the end of April. What's available here and
what's available there are two different things.
Last time I visited, a few OT's and I had a conversation regarding
exactly what we have been discussing, namely an inexpensive full
featured satellite station using  mostly homebrew for super cheep.


On Fri, Mar 1, 2013 at 12:29 AM, Gus <8p6sm at anjo.com> wrote:
> On 02/28/2013 11:24 PM, Lizeth Norman wrote:
>> A stepper still needs some sort of position feedback..
> Not really.
> Steppers rotate a predictable amount with each step.  To calibrate, the
> software only needs to count steps from one limit switch to the other.
> Then, by keeping track of step count (+/-), it will always know exactly how
> far round the turn it is.  It can store last position in NV RAM or EEPROM,
> so as to avoid the need to recalibrate on every startup.
> Unfortunately, I can't think of a common source for surplus steppers of
> useful size.  And driving them is slightly more complicated than firing a
> relay to a DC motor.
> OK, why do we have to use A multi-turn pot?  Why not just an ordinary linear
> pot?
> -- 73, de Gus 8P6SM
> Barbados, the easternmost isle.
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