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Dome2
7/28/2006 4:21 PMLast year I built an icosahedral shade structure for Burning Man '05. It had some successes and failings. It didn't withstand the very heavy winds at all, it wasn't as opaque as I wanted and it was kind of small. So I've decided to make a larger and sturdier one: dome2.
I again have chosen to go with schedule 40 PVC because it's light, cheap and very easy to work with. And instead of a n-frequency polyhedron I have decided to implement a bent strut design incorporating a number of great circles connected together. I ended up using this guy's 2f design, slightly modified.
I reused the 6'8" struts from the icosahedron (I had only to make ten additional ones) and made twenty connectors out of 12" long pieces of 1/2" EMT drilled with a bazillion 1/4" and 3/16" holes (for connecting bolts). The dome structure this creates has a radius of 11.14 feet and, therefore, has 390 square feet of floor space and about 780 square feet of surface area. Since I had to cut several lengths of 1/2" EMT into many shorter lengths I was able to justify purchasing a 14" cutoff saw.
After setting it up the first time I realized it had quite a lot of wobble. Matt M was over the
other day and he analzyed
the wobble factor and suggested a good technique to make it more stable. Each of the six pentagons (five
along the sides, one at the top)  | | A simple test to see how everything is fitting together so far. Pretty good! |
now have a five pointed star made of nylon mason line. When I simulate a large gust of winding pushing in one of
the sides of the dome and then release it there is now only a minimal
shimmer throughout the structure rather than the lengthy oscillation it
used to have. Huzzah!
Initially I was hoping to make a bunch of hexagons and pentagons out of fabric and stitch them together in the shape of a truncated icosahedron. After doing the math I discovered the hexes and pentas would be too large to be easy to manufacture.  | | Little a tracing out segments onto the large pattern diagram. |
So I decided on a different covering design. The hemisphere will be divided into ten vertical strips. Each strip, when transposed to two dimensions, ends up looking like a long puffy isosceles triangle. I was able to calculate the ideal shape they should take by using some simple trigonometry and, using low-tack blue mask tape, have marked out the shape on my living room floor. Now it's just a matter of cutting and sewing this random assortment of fabrics that Andy has into ten identical "triangles".
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