[ATM] Pyramid shaped, 3 tube open truss

[artbianconi@blast.net]

I've been looking at what a friend wrote about the light weight 
of the secondary end of a Schiefspiegler. I did some mass 
property experimenting with the engineering software. He's right 
and it's even lighter than I thought!

Given this revelation, I found myself wondering "Why fabricate a 
long cylinder, composite or otherwise, just to hold a 3" diameter 
piece of glass? The cylinder will weigh many, many  times more 
than the glass!" 

So I dug a little bit into the application of trusses. 

The OTA trusses I've seen are typically built on the use of two 
tubes per truss. The number of trusses per scope is predominantly 
4 and, to a lesser degree, 3. But, as Gordon Waite was quick to 
point out, that's the "evil end" of your typical Newtonian and 
has all sorts of heavy stuff out there: crayfords, cameras, 
spiders, etc. so there is some justification for a rigid and 
robust structure to hold all that paraphernalia accurately in 
place.

Not so with a Schief! Six tubes forming 3 trusses looks a Hell of 
a lot like overkill. More so when I realized how little mass 
there is hanging out in the breeze. I got to thinking: "why not a 
three tube, pyramid shaped "truss" with the secondary mirror 
snuggled up inside the nested tubes, up near the apex?" 

The new design software hasn't arrived yet so my ability to test 
it's rigidity is limited to hand calculations (something I hate!)

There is nothing in this geometry to suggest it would anywhere 
else but in a Schief. I can't see it working on a Newtonian or on 
a Cass.

Have any of you ever seen a pyramid shaped, open truss 
successfully supporting optical geometry on a telescope or 
anything else?  I'm aware of the need for the light shielding 
that an open truss design would demand. 

Can anyone think of a reason why this would not work structurally 
in such a featherweight application? 

Thanks 

Art Bianconi


This post and any attachments were tested before being sent and 
found to be virus free.
Our Norton-Symantic virus list is updated daily.



_______________________________________________
ATM mailing list http://www.atmlist.net/