Re: Tensegrity Blocks

["J & D Goldman" <jmgoldma at dwx dot com>]

Very interesting work.  I just wondered if any structural analysis (I
think the engineers use finite element analysis) had been done on
this, helps show where the failure might come if overloaded.
- Dan G.

-----Original Message-----
From: Spencer W Hunter <shunter at u dot arizona dot edu>
To: domesteading at sculptors dot com <domesteading at sculptors dot com>
Date: Saturday, February 19, 2005 4:30 PM
Subject: Tensegrity Blocks


>Tensegrity Blocks
>
>Spencer Hunter, 2005
>
>(I hope to have accompanying public-domain images under a new
>"Tensegrity Blocks" directory in the next couple of weeks at
>http://www.u.arizona.edu/~shunter/cads.html .  I'll post an
>announcement when they're ready.)
>
>A series of self-deployable tensegrity building blocks or components
>are outlined.  These blocks may be deployed on-site and assembled
into
>complete structures; or, alternatively, they may be factory-assembled
>into complete structures that are more-or-less self-deployable.
>
>I do not claim the idea is novel, only that I have developed it
>independently.  Unique features, if any, not covered by [1]current
>patents are hereby placed into the public domain.
>
>Working on [2]zigzag-strut tensegrities, my intention was to overlap
>tetrahedra and dual tetrahedra to form a truss.  In the process of
>doing so, I discovered that most of the tendons in the truss interior
>were basically unneeded, and the shape that emerged as the basic
>building component is what most researchers refer to as the
triangular
>prism simplex, or what I used to refer to as a "pseudo-octahedron."
>The triangular prism simplex is the simplest possible tensegrity,
>consisting of three struts that comprise the diagonals of the
>rectangular sides of a prism of tendons.  In my [3]self-deployable
>parabolic zigzag-strut tensegrity dome, each simplex has three
>vertical elastic tendons that enable it to be collapsed and stowed,
>which is joined end-to-end with other simplexes in a [4]network.
>
>Heavily influenced by the work of [5]BinBing Wang, I came to realize
>that this kind of truss was not necessarily the most efficient, and
>was led to design a new configuration with the following
>specifications:
>
>a)  Truss depth is maximized
>b)  Strut length is minimized
>c)  Simplex construction is as simple as possible
>d)  Simplexes are collapsible and self-deployable
>
>Returning to my [6]basic tetrahedron, it seemed that whereas the
>zigzag-strut tensegrity pulled the
>straw-pairs-connected-by-paper-rolls apart, it might be better to
>force them back together again at the center.  My problem with the
>truss described by Wang made of such "crystal-cell pyramids" was that
>it would only be able to resist loads effectively in one direction,
>and I wanted it to be bi-directional as zigzag-strut was.
>
>After some unsuccessful experimentation, I came across a simplex
>design that does meet all the specifications.  Unlike the basic
>triangular prism simplex, my new triangular prism consists of three
>tube strut pairs (six struts) with each strut connected by a rolled
>connector to another in the pair.  The rolled connectors are lashed
>together at the center, and the struts bend out from the center where
>they are connected to inelastic ribbon tendons that form triangles at
>the top and bottom.  Finally, three elastics comprise the vertical
>tensioning side tendons that force the simplex into rigidity.  This
>center-node simplex or block is heavier than the three-strut simplex,
>but the struts are shorter and the overall strength is greater.  One
>problem I came across is that the center node was too flexible, so
>that during collapse it would pop outside of the prism and defeat
>re-deployability.  Taping toothpicks to the straw struts that pass
>through the center node of the model stiffens and stabilizes the node
>during collapse.  A similar kind of hinge locking mechanism should
>work for blocks of similar configuration.
>
>This same idea of struts radiating from a center node of lashed
>flexible hinges works for prisms of greater than three sides as well.
>I've built a cubic block that should work for trusses, furniture,
>walls, and other structures of the box-obsessed world.  Prisms of
five
>and six sides could be used for hex-pent geodesic domes.
>
>Of course, collapsibility becomes much more of a liability than an
>asset in completed structures.  At that point, adjustable non-elastic
>tendons could be swapped for or augment the elastic tendons.  A much
>better solution, I think, would be to develop a small
>independently-powered winch for ratcheting individual pull-wires to
>their desired length and tension.  A system of such winches could be
>used to self-deploy antennae in space or domes on Earth or other
>worlds.
>
>References
>
>   1. The 1996 U.S. patent #5,505,035 seems to cover single-node
>      configurations of irregular polyhedra.
>   2. http://www.u.arizona.edu/~shunter/zigzag.html
>   3. http://www.u.arizona.edu/~shunter/zdome.html
>   4. http://www.u.arizona.edu/~shunter/zfiligree.jpg
>   5. Wang, "From Tensegrity Grids to Cable-strut Grids,"
>      International Journal of Space Structures, v.16(n.4):279-314
>      2001
>   6. http://www.u.arizona.edu/~shunter/tetra.jpg
>
>Spencer Hunter, Tucson, AZ
>gopher://www.u.arizona.edu:80/hGET%20/%7Eshunter