From: Clive Milne 
To: atm{at}shore.net
Reply-To: Clive Milne 



"John Sherman"  wrote:
    Thus I think
> that the upper and lower trusses can be made out of
> much smaller diameter tubing saving a lot of weight.
> Anybody have any thought about reducing the left and
> right truss diameters?

   Tom K has done some interesting research on various different
truss configurations and has posted real performance data on his web page
(absolutely worth reading).  One comment I will pass though, and this is
not to be implied as criticism of Tom's work, is that asside from any
conclusions that you might draw from the _RELATIVE_ performance of any
given truss, be mindful of the _ABSOLUTE_ deflection values given (even in
the worst case). From this data and the experimental work of myself and
others, we can conclude that a (properly designed) truss made from tubes of
a diameter sufficient to resist buckling, will be plenty strong enough to
make a supremely rigid telescope.   ie) For a 20" telescope,
anything larger than 3/4" (19mm) is just a waste of materials.
   So to answer your question. Yes, by all means reduce the
diameter of ALL the truss tubes. (3/4" will be fine) If your scope
still vibrates, I'd wager it's not the truss tubes at fault. It might be
time to take a good hard analytical look at the whole design from the
ground up.  Just because everyone has built them basically the same way for
for the last 15 years doesn't make it right. It's high time we moved on.
   ~Clive.

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