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Each dome model requires specific length struts. The 8-frequency sphere on the
"About Megadome" page of this site requires 12 different lengths. The Megadome
system was conceived as a way to explore various structures. To make the
countless shapes that are possible with the Megadome system, more and more
specific lengths are required. |
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The Adjustable Strut approach uses three different pieces which can make any
shape: standard "connector" pieces with a hole punched through one end: |
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Straws of a slightly larger diameter so that the connector pieces can be slid
inside them to provide the proper lengths for any model: |
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And the folded locking hub: The straw sizes are "super Jumbo" which has an O.D.
of about 0.25" and the "giant" which has an I.D. of about 0.27". |
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| The outer sleeve "Giant" straws are
usually manufactured in about 8.5" lengths. If they are cut in approximate
quarters or thirds or halves, they can be used with the standard connector
pieces (Super Jumbo size) to make any number of lengths. |
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The adjustable strut length is set using a standard stapler and 1/4" staples. A
block about 1/4" thick forms a back-stop so the straw gets stapled in the
middle, and this block also keeps the stapler from squashing the staple or the
straw: |
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| The staple only goes through
one side of the straw, does not bend over, and can be easily removed if you
want to take the model apart, or use the pieces to make another model: |
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  Tetrahedron
Cube |
  
Octahedron
Dodecahedron Icosahedron |
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 (Double click
to enlarge) Models on my work table |
Stellated Dodecahedron |
 Rhombic Octahedron Cube |
Stellated Icosahedron |
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In keeping with the math-challenged approach, many of these models were made
using trial and error, and several began with mathematically derived chord
factors but then part way through the construction it became evident that
something was too long or too short, and the model would be re-started with a
different fudge-factor. Fudge factors are required with any mathematically
derived lengths, since the strut length is set by setting the distance between
the holes in the locking straw pieces: |
(double click to enlarge) This hole is 1/2 inch from the end of the straw, and the end
of the straw is, in turn, some distance from the locus of the vertex. |
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This fudge factor distance is slightly different depending on the number of
struts coming together at a given hub, and the angles at which they are joined.
It would be useful to establish a rule of thumb for determining the proper fudge
factor, so that models could be made from mathematically exact sets of
dimensions. |