Adjustable Strut Models

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.

The Adjustable Strut approach uses three different pieces which can make any shape: standard "connector" pieces with a hole punched through one end:

Straws of a slightly larger diameter so that the connector pieces can be slid inside them to provide the proper lengths for any model:

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".

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.
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:
 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:

Tetrahedron         Cube

Octahedron           Dodecahedron    Icosahedron


(Double click to enlarge)

Models on my work table

Stellated Dodecahedron

Rhombic Octahedron Cube

Stellated Icosahedron

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.

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.