[ATM] Re: Purpose of spring counterweights

[Mark Holm <mdholm@telerama.com>]

Martha,

You are right, the cg of the whole assembly will still move forward as 
you tilt the scope.

Three possibilities come to mind.

1. Arrange things so that the cg of the scope + rocker is somewhat aft 
when the scope is at the zenith.  Then, as it rotates forward, the cg 
may stay within the required limits.

2. Mounted to the rocker somehow, put a roller drawer slide with a 
weight affixed.  This weight moves toward the center as the scope tilts 
down via some system of cords & pulleys.  Whether this is better or 
worse than a fixed counterweight behind the mirror depends on your 
design and needs.  It might be possible to extend this system somehow so 
that the moving counterweight travels a relativly large distance.  that 
would increase it's leverage, reducing the required weight.

3. As a variant of idea 1, the center pivot does not have to be centered 
under the rocker.  if the pivot is somewhat forward of the rocker cg 
(scope pointing at zenith), then, when the scope tilts forward, the cg 
will move toward the pivot first, and only away from it later on.  It 
might be possible to accomodate a sufficient range of cg motion this way.

-- 
Mark Holm
mdholm@telerama.com
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