[ATM] Re: Second Thoughts on Mirror Support

[sho at surfnetUSA.com (Steve Houlihan)]

I started this thread last week and am fascinated at how it has progressed.
Many people that have responded have been rather dogmatic in their beliefs,
but only a few seem to understand the problem or are willing to listen.
Such is the nature of a mailing list I guess.  Never the less, I am really
enjoying the discussion.

I have used the actual sizes of my cell and mirror and done a few simple
calcs.  The worst case for uneven forces being applied to the back of the
mirror would be when one of the triangles was oriented horizontally and the
mirror was vertical.  The moment arm from the ball joint to the center of
the mirror is 1.75 inches and the mirror weighs about 12 pounds.  1/3 of the
weight is carried by each triangle so the moment applied to the mirror would
be 12/3 or 4 pounds times 1.75 inches which is 7 in-lbs.  This is resisted
by the two RTV pads that in the worst case are only 2 inches apart.  This
puts a 3.5 pound force into the mirror and another 3.5 pound force just 2
inches away in the opposite direction.  That seems like a lot of bending to
me.

Steve Houlihan
Santa Cruz, California

sho@SurfnetUSA.com
http://sho.mystarband.net/
http://www.surfnetusa.com/sho
----- Original Message -----
From: "Jeff Anderson-Lee" <jonah@eecs.berkeley.edu>
To: <atm@atmlist.net>
Cc: "Mark Holm" <mdholm@telerama.com>
Sent: Friday, February 06, 2004 9:35 AM
Subject: Re: [ATM] Second Thoughts on Mirror Support


> Stuart Hutchins wrote:
>
> >How did Nils Olof Carlin get the sling force (when the sling pulling at a
> >slight up-angle) into Plop?
> >
> Beats me. Nils?
>
> >Just for rough numbers, could the pivot points be offset to produce
uneven
> >supports forces similar to what would be produced by the sideways
component
> >of mirror weight?  The resulting pattern would not be rotationally
> >symmetric.  But I see on your pages of 12 point patterns some systems
that
> >are not symmetric. Number 12j, in particular, has two short vertical bars
at
> >the top and bottom.  Can the pivots of those bars be moved from 50% up to
67
> >or 75% ?  That would produce the "S" bending forces.
> >
> >The goal would not be an exact deformation plot for Steve's cell, but a
> >general idea of how bad the "S" shape becomes.
> >
> Plop tells you where the pivots go, rather than the other way around.
> (You specify the parts relationships, and it places the pivots.)
>
> It will accept uneven force definitions, but only in a symmetrical
> fashion, not differently at the top and bottom.
>
> Jeff
>
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