Re: [ATM] Focuser speed reducer

["Eric S. Johansson" <esj@harvee.org>]

Michael Lindner wrote:
> I've seen lots of great focuser plans out there, but I've never seen 
> plans or even a commercial source for a speed reducer like the ones used 
> on feathertouch and moonlite focusers to get dual speed focusing. 
> Anybody have plans or a source for such a beast?
> 
> Thanks, and clear skies!

it seems to me that the dual speed focusers are using very small planetary 
reduction drives similar to those used in radio applications for decades.  see 
http://en.wikipedia.org/wiki/Reduction_drive.

If you're not married to one knob focusing, you can combine a racket and pinion 
design with a sled focuser.  the sled focuser should use a fine thread bolt for 
its position control.  One problem with this model is that you need to pay 
attention to limits of travel and reverse direction.

I think it might be possible to reduce this problem if you use one of the 
classic rotation to reciprocating motion designs for coupling the focus adjust 
to the sled travel.  The reciprocating motion option could make motor driven 
focusing easier because the motor would only need to turn in one direction.

I had one of these designs mostly built out of a 1960s rack and pinion focuser 
and wood from a Clementine box.  Unfortunately, I realized that I needed to fix 
my mount first so that my six" f11 Newtonian could be used.  I really need to 
figure out what I can use for a mount design out of parts from Home Depot, 
motors from hard drives or some other salvage, and brute force, bloody ignorance 
  drive control so I can track planets long enough to take webcam photos.

It's further complicated by my tree horizon profile.  I need to observe from 
three or four places in the yard depending on whether or not I'm looking east, 
west, south 1, or south 2.  Royal pain in the butt.

--- eric

-- 
Speech-recognition in use.  It makes mistakes, I correct some.
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