[amsat-bb] Re: inquiry about homebrew az-el systems
tomdoyle1948 at gmail.com
Fri Mar 1 06:52:07 PST 2013
Stepper motors work. You can actually see it turning two real sat antennas
on a 4 foot cross boom and it is not as big as a bike. No obscure parts
W9KE Tom Doyle
On Fri, Mar 1, 2013 at 1:17 AM, Lizeth Norman <normanlizeth at gmail.com>wrote:
> 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
> > far round the turn it is. It can store last position in NV RAM or
> > 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
> > pot?
> > -- 73, de Gus 8P6SM
> > Barbados, the easternmost isle.
> > _______________________________________________
> > Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> > Not an AMSAT-NA member? Join now to support the amateur satellite
> > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
> Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
> Not an AMSAT-NA member? Join now to support the amateur satellite program!
> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
Sent from my computer.
More information about the AMSAT-BB