Cc: Dale Eason , atm{at}shore.net
To: Michael Lindner 
From: Fabio Pettinati 
Reply-To: Fabio Pettinati 


The main concern I have about non-uniform truss designs (i.e. different
tube diameters, absence of some members) is that the overall structure
might be more prone to vibrations and also torsional deformations that
might move shift the upper cage from collimation. I don't have a FEM
program handy to confirm these suspicions, so take this point with a couple
of grains of salt.

On the other hand, what about a double truss design, where you have an
intermediate ring between the mirror cell and the upper cage and two
trusses connecting these three elements. By increasing the size of this
intermediate ring (which doesn't have to be round) you can effectively
reduce the diameter of the tubes used for the two trusses. About 2 years
ago I did run some tests with an evaluation copy of a FEM program and I did
find that increasing the intermediate ring's size made the compound
structure must stiffer: which would allow me to reduce the diameter of the
tubes used in the trusses. I didn't play long enough to come up with a way
to minimize overall weight. Maybe someone else might want to continue these
tests.

Fabio
San Jose, CA

On Tuesday, July 15, 2003, at 04:35  PM, Michael Lindner wrote:

>
> On Monday 14 July 2003 10:23 pm, Dale Eason wrote:
>> I know that some have gone to a 6 tube truss but I'm
>> not really ready to do that yet because I can't figure
>> out how to attach it to the square mirror box.
>
> Make an 8 tube truss, and leave off the bottom two truss tubes. You
> will not
> miss them, unless you have a shroud that gets into the light path
> without
> them. Advantages are a 25% reduction in wieght and you don't have to
> deal
> with 2 different size tubes.
>
> --
> Michael Lindner
> http://www.starastronomy.org
> http://home.att.net/~mikel http://www.atmsite.org
> http://home.attbi.com/~dcass/atmfaq/atm-faq.htm
>
>

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