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

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

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

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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