Re: [APML] Declination Drive problem

[Chuck Vaughn <aa6g@aa6g.org>]

Bill,

I don't know who told you 'tangent-arm Dec systems have "no backlash" '
because that is not my experience. Backlash can come the motor, as you
have seen, the interface between the arm and the worm gear, and even
poor balance can enhance the problem.

I don't worry about a little backlash in my Dec drive because most of
the Dec corrections are trying to follow seeing and are therefore
unnecessary. All of my experiences with trailed stars have come from
RA drive problems or flexure.

Are you saying you have trailed stars and the direction is 100% in
declination?

Chuck <aa6g@aa6g.org>

------------------------------------------

> Gentlemen,
> 
> While probably Off-Topic I have a problem when guiding photographs that
> has me stumped. Situation is this, mount is a 1.5 inch shaft GEM with
> conventional RA drive and tangent-arm Dec driven by a Hurst 1 rpm motor.
> After being inspired by what I am seeing by lurking here I am trying to
> refine my guiding and have run into this. By definition I was told that
> tangent-arm Dec systems have "no backlash" and this seems plausable. But
> what I am experiencing seems to be just that. Backlash. When reversing
> directions there is a definent delay before the Dec reverses direction.
> After disassembling the Dec assembly and drive I have come to the
> conclusion that the "backlash" is present in the motor itself. Not the
> drive assembly itself. So I pondered this and cannot fathom a solution.
> I have three of these motors and they all exhibit the exact same
> behavior. I would imagine that constructing a new motor assembly would
> bear no fruit either since after adding the gears to reduce the speed to
> 1 rpm the backlash is introduced. That and the motor coasting. Can
> anyone point me in the right direction here ? I can guide in RA with
> *no* trouble at all, but this Dec thing is giving me fits.
> 
> Perhaps superflouous information would be:
> 
> 10" f/6 Newt. Guidescope is 90mm f/11 refractor. I am guiding at ~303x
> 9mm EP and 3X barlow. Flexure is *not* a problem.
> 
> Trying desperately to get pin point stars .....
> 
> Regards
> 
> Bill


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