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SWIVEL |
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Swivels
allow parts of the model to rotate. So you can use them as a base |
for legs,
arms, heads, etc. Or they can be used for rotating gadgets. The
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structure of a swivel consists of the hub,
the pivot, or hinge, and the rim. Note |
that this swivel is similar to the
one shown in the previous lesson as a |
polygon that should be stable according to
Euler's equation, M = 2 J - 3, but |
is not. As in that case, it is the proper
arrangement of the structural members |
that gives gizmos the proper balance between
rigidity and flexibility, not just |
the number of members used. The object is
to engineer the mechanism so |
that when the imbalance between the external and
internal forces occurs, |
the net force moves in the proper direction to
achieve the desired effect. In |
this case the desired effect is a swiveling
action. So when the hub is kept |
from moving and the pivots are moved, the rim
rotates thereby displacing the |
net force in a circular direction around the
central axis of the structure. Fig. |
click
images to enlarge |
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Fig. 308
Swivel structure and action (large sqocta swivel shown) |
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308 shows the pivots rotate, or swivel, in the opposite direction of the hub. |
Note also
the optional use of thin rubber bands (four shown here in red) that
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crisscross
the rectangular shaped openings of the swivel. These act as shock |
absorbers
and dampeners when the swivel rotates. They offer resistance to |
the rotation in the form
of tension forces which tend to return the swivel back |
to a state of equilibrium (in
this case the octagon shape). This allows the |
bodies of critters to stand
upright when swivels are used as hips/legs. But |
they are still able to bend forward
and backward at the waist. Note: don't use |
too many rubber bands. A few light weight
bands of identical size placed |
symmetrically usually
do the trick. |
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There are
six basic types of swivels: |
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Prismatic
swivels - swivels that have a prism shaped hub |
Dodecahex swivel |
Large sqocta swivel |
Small sqocta swivel |
Conic swivels
- swivels that have conic shaped hubs |
Octonic swivel |
Pentonic swivel |
Sqonic
swivel |
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PRISMATIC SWIVELS |
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Dodecahex
swivels - Dodecahex swivels are called that because their |
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shape
jitterbugs between a 12-sided dodecagon and a 6-sided hexagon as |
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they
swivel (like the one that is shown in the
GIZMO logo). |
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back |
Page 161 - Gizmo - Swivels |
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