Healthcare and Medicine Reference
In-Depth Information
Building a tensegrity model
Although a clothesline, a balloon, Denver airport, or a
'Skwish!' toy (invented by the designer of the tensegrity
models on display in this topic, Tom Flemons, www.inten-
siondesigns.com) are commonly seen structures employing
tensegrity principles, you can build a more 'pelvis-like'
model, a tensegrity icosahedron, on a very simple scale. It
is a potent tool for showing clients how a body works
(Fig. 1.55).
You will need 6 equal dowels, ideally a foot or less in
length, 12 thumbtacks or pushpins, and 24 equally-sized
rubber bands. Push a thumbtack into each end of all
the dowels, leaving a little of the shaft showing so that
four rubber bands can be slipped under the head of each
tack.
You may need a friend to help hold dowels for this project,
especially your first time out and especially in the latter
stages of building.
Take two dowels and hold them vertically parallel to each
other, and place another dowel horizontally between them at
the top, to form a letter T, Connect rubber bands from each
of the two upper ends of the verticals to each of the ends of
the one horizontal dowel - four bands in all. Turn the vertical
dowels over 180° so that the horizontal dowel lies on the
table, and do the same operation at the other end: four
rubber bands from these ends of the uprights to both ends
of a new horizontal dowel. You will now have a capital letter
T (Fig. 1.56A).
Now turn the structure 90° so that the two horizontal
dowels are upright, turning it into an 'H' with a double cross-
bar. Place the fifth dowel horizontally between the two
uprights, at 90° to both other sets, pointing toward and
away from you, and again connect the two uprights to the
two ends of the new horizontal dowel. This is where it gets
difficult to do with only two hands, because as you place
these bands, the lower ends of the uprights want to spread
into a letter 'A', and in early attempts the structure
may spring apart. Persevere! Turn the structure over
and repeat the same operation with the sixth and last dowel
(Fig. 1.56B).
To finish the structure, add the remaining rubber bands in
the same pattern, connecting each dowel end to all the four
adjacent ends except the obvious one - the ends of each
dowel's parallel 'brother'. In the end, the structure should
stand alone, balanced and symmetrical, with three sets of
parallel pairs of dowels. Each dowel end should have four
rubber bands going out to all the ends near it, save that of
its parallel partner. You can take extra turns around the tacks
with some of the rubber bands to even out the tension and
thus the position of the dowels.
The sturdiness of your structure will depend on the
relative length of the dowels and rubber bands. If the
bands are too long, the structure will have 'lax ligaments'
and may collapse under its own weight. If the bands are too
tight, the structure will bounce well but will not demonstrate
a lot of responsiveness in the following experiments. So add
rubber bands or take more turns around the ends until you
achieve the middle ground in which these moves make
sense:
Try pushing a dowel out of place, and see the whole
structure respond to the deformation. Try tightening one
rubber band, and see how this tightness can produce a
change in the shape of the 'bones' at some distance
from where you are putting the strain. Push two parallel
dowels together and watch the whole structure
(counter-intuitively) compress together. Pull two parallel
dowels apart (gently) and see the structure expand in every
direction.
Push on any side to see the structure bend to accom-
modate the strain. Where will it break? At its weakest point,
since no matter where the strain is introduced, it is trans-
ferred to the structure as a whole. All these attributes are
properties that your little tensegrity structure shares with
human bodies.
Notice how the rubber bands form a continuous outer
net - you can travel anywhere around the whole structure on
the rubber bands, but each dowel is isolated. Continuous
tension, discontinuous compression. In this model, the
Anatomy Trains are commonly used pathways for distribut-
ing strain, via the groups of rubber bands that run more or
less in straight lines.
Bodies are strain distributors, not strain focusers, when-
ever they can be. A whiplash, for example, is a problem of
the neck for only a few weeks before it becomes more dis-
tributed throughout the spine. Through this phenomenon of
tensegrity, within a few months this is a 'whole-body' pattern,
not just a localized injury.
Fig. 1.55 A simple tensegrity
tetrahedron gets not-so-simple
when you try to make one.
(Reproduced with kind
permission from Oschman
2000.)
Fig. 1.56 Assemble the model through these stages to make it
easier. In the end, each dowel end will be connected to all the
other four nearest dowel ends - excepting its parallel brother.
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