Design Update #2 to Tensegrity Blocks

[Spencer W Hunter]

ref.: http://www.u.arizona.edu/~shunter/tblock.html

I am placing any unique features mentioned here into the public
domain, and I will announce when pictures of my self-deployable
octahedra are available (though the way things are going, don't hold
your breath).

One of the most intriguing structures I have ever seen was a
cable-strut octet truss built by the great structural morphologist,
Robert Le Ricolais.  Each octahedron in his truss consists of six
struts radiating from a central node and twelve cable tendons forming
the edges of the octa.  The struts are joined end-to-end with struts
in other octahedra to form a cubic lattice.

Using Wang's taxonomy in his book, _Free-Standing Tension
Structures_[1], Le Ricolais' octahedron--and his truss built from many
copies of it--may be thought of in two ways that make it
self-deployable: as an anti-prism and as a di-pyramid.

As an anti-prism, the octa is nearly identical to my triangular
tensegrity block, only the top and bottom triangles of inelastic
tendons are skewed (depolarized) relative to each other, and there are
now six elastic tensioning tendons at an angle instead of three
vertical tensioning tendons that enable it to be collapsed and stowed.
Although heavier and more complex than my triangular block, it is
possible that the structure may redeem itself when efficiently coupled
with other octahedra in a truss.

As a di-pyramid, Wang suggests that two of the struts are fused into
one central pole that runs down the middle of the octa.  The remaining
four struts are attached to a runner on the pole that enables them to
fold up.  Using a powerful spring mechanism, it can self-deploy in a
manner much like many of today's self-deployable umbrellas.

Curiously, the deployable or self-deployable octet truss does *not*
appear in Wang's book, which is even more remarkable considering that
the solid-bar version is the most efficient truss configuration
possible.

References:
   1. Wang Bin Bing, _Free-standing tension structures : from
      tensegrity systems to cable-strut systems_, London ; New York :
      Spon Press, 2004  ISBN 0415335957

I previously mentioned that a high-tensile rod can ride along with
each elatistic tendon in my blocks to secure them in their deployed
state using an attached cone and cylindrical trap.  It may be better
to replace the cone with a butterfly flange that locks into a wire
framework once that framework is penetrated.  This would make
collapsing the structure easier: one would only have to pinch the
flange together to release the rod.
--
Spencer Hunter, Tucson, AZ
gopher://www.u.arizona.edu:80/hGET%20/%7Eshunter