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

Gus 8p6sm at anjo.com
Thu Feb 28 21:29:51 PST 2013

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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