[ATM] Re: Purpose of spring counterweights

[fabio@voreas.com]

Martha L. Gay writes: 

> The design phase of my 6" travel dob is progressing. I had thought I would
> use spring counterweights, which just sound so elegant.  I do have one
> question.  What exactly do they do?  I still have to put the center of
> gravity inside the feet, or the whole thing will tip over.  So are spring
> counterweights for use with just a slightly nose-heavy scope? When I'm using
> a heavy eyepiece? When one side of the secondary cage is heavier than the
> other? 
> 

Martha, 

The center of gravity must be within the polygon that the feet define 
(triangle for 3 feet, quadrilateral for 4 feet, etc). If this doesn't 
happen, the telescope will tip over. The spring counterweight is just that: 
a spring that pulls the telescope tube the right way exactly like a real 
counterweight would do. When you change eyepieces the balance changes as 
well, so with real counterweights you would move them to the new balance 
position. With a spring counterweight you could do the same, provided you 
have the means to change the configuration of the spring/string and fixation 
point to account for the new weight. Spring counterweights are meant for 
"slight" unbalancing. Don't expect to have a foolproof solution if the scope 
is too unbalanced to begin with. 

Fabio 
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