Re: [ATM] PLOP Calculations

[Mark Holm <mdholm@telerama.com>]

Jake,

I tried a few cells last night, using Plop, with Pyrex, 46 inch diameter 
and 2.125 inch thickness, assuming f/5 and about 220 mm secondary.

27 points came up iffy.  The RMS wasn't too bad, but the P-V was pretty 
high.  It might make the mirror look a bit "dog biscuit" like.

36 points gives reasonable results, but the parts layout is crazy!

54 points, if you pull out all the stops,using both variable angle and 
variable force, gets down to 2 nM RMS and 12 nM P-V.  This is really 
good support.  No need to look any farther.

Even with variable angles on, the 54 point design looked symmetrical.  I 
suspect that one could fix the angles near where it ended up, in order 
to get a fully symmetric design, and still have excellent support.  
Using variable force did move some of the triangle pivots away from 
their centroids, but not extremely so.  Also, the proportions of the 
triangles are not too extreme.  If the triangles are cut with a milling 
machine, there should be no issues.

If you send me the dimensions for your mirror, I will rerun this cell to 
adjust.

Mark Holm
mdholm@telerama.com
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