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dowel-and-fishing-line augmented tensegrity five-fold prism restudy
(VRML Model)

After some thought, I realized it isn't necessary that the outer girdle of the Concentric Five-fold Prisms be arranged so a sequence of three connected side tendons connect adjacent struts to one another as in most non-girdled prisms. Here the girdle is connected to the inner prism so that a sequence of three connected side tendons goes from one end to the other end of the same strut of the inner prism. For now I think I'll leave this structure completely conceptual, but if you're interested in building it, the data is below. If you do build it, send me a photo and I'll put it here. This design was completed March 2, 2004.

Member
Name
End Points LengthMember
Force
strut1p2'p1 2.35548-1.51332
strut2p4p5' 2.35548-2.35548
side1p4'p2' 1.000001.97053
side2p4p4' 1.000002.84656
side3p1p4 1.000001.97053
end1p2p1 1.000001.16261
end2p2'p1' 1.000001.16261
Average tendon force = 1.82257

This tensegrity reminds me of nothing so much as the witchs' cauldron in William Shakespeare's Macbeth:

1. Witch.   Thrice the brinded cat hath mew'd.
2. Witch.   Thrice, and once the hedge-pig whin'd.
3. Witch.   Harpier cries, "'Tis time, 'tis time."
1. Witch.   Round about the cauldron go;
In the poison'd entrails throw;
Toad, that under cold stone
Days and nights has thirty-one
Swelt'red venom sleeping got,
Boil thou first i' th' charmed pot.
All.   Double, double, toil and trouble;
Fire burn, and cauldron bubble.
...
 
from Macbeth, Act IV Scene I

I received the first rendition from the audience from Eric Phillips, an undergraduate at the School of the Art Institute of Chicago, on March 22, 2004:
Eric Phillips' prism
Eric states: I used components left over from another project, but my sculpture class actually liked this one better. This was my first attempt at a tensional integrity structure (it probably shows) and I have to admit, once I got the hang of it wasn't as difficult as I thought it would be. I used twisted nylon twine, so it took a while to get the knotting down. I didn't have screw eyes, so I used bent hooks, but it worked. I left excess twine on for effect, and I let it lean heavily to one side. I thought it more interesting that way.

I imagine it could use more tension. I usually decrease all the tendon lengths 2% relative to what they will be when they are prestressed. The tighter tendons I decrease more and the looser tendons less, but I make sure it averages out to 2% and I do all right, with fishing line anyway. I never have things lean like that. But wow, I never expected to get anything so quickly!


Two-fold Prism Girdled by Four-fold Prism Index Modified Orthogonal Girdled Six-fold Prism