[amsat-bb] Rotator design question

[Phil <phil@xxxxxxxxxxxxxxxx>]

Hello All,

I have a home-built rotator that uses a DC motor and is coupled to a 
home-build controller. The controller is similar to the Fodtrack design and 
from the comparators on, is almost identical.

The problem is that the rotator overshoots the required stop point fairly 
often. The output transistors of the controller drive relays that don't 
always open long enough for the motor to stop.

The rotator turns at roughly 360 degrees per minute so I don't think it is 
too fast. The controlling pot is a standard 4k7 carbon pot and this may be 
where the problem lays. I considered a ten-turn pot but I have had difficulty 
in locating gears to turn the pot and perhaps that is not the answer anyway. 
The ten-turn pot will still output the same voltage for the same amount of 
degree change. I have reduced the one Meg resistors in the comparator circuit 
without any noticeable change, in fact the overshooting may have been worse.

What type of pot is normally used in a rotator? Can anyone offer a suggestion 
on how I might broaden the dead point of the comparator? Maybe I should 
consider a solid state device instead of the relays.

-- 
Regards,
Phil
phil@spiderweb.com.au
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