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So called, because they're SYMmETrical

Symets are the ultimate in producing elegant behaviors from simple mechanical and electrical designs -- they make use of their symmetry to produce obstacle-avoiding behavior with a single motor and no sensors.

The basic idea is that a Symet scoots along a flat surface (table, etc.) on the tip of its motor shaft, and on 2 "outriggers" (remember that it only takes 3 points to define a plane, so a motor shaft and 2 "outriggers" will be stable on a flat surface). In most Symet designs, the "outriggers" are capacitors that are part of the Symet's electronics, although other structural elements can also do the job. Symets avoid obstacles by having 3 or more "outriggers" -- when the Symet butts up against a wall or other obstacle, it tips onto different "outriggers," thus altering its subsequent path away from (or at least parallel to) the obstacle.

This is easier to see with an example. Let's look at a Trimet (trilateral Symet):

Symet example

Symet, step 1Set it on a flat surface, and our Symet scoots along comfortably:

Symet, step 2When it contacts an obstacle, the Symet (if you built it correctly) starts to tip:

Symet, step 3Once it has tipped onto another set of "outriggers," the Symet will now be moving away from the obstacle:

For more information...

Solarbotics published plans for a Trimet here.

F.J. Tragauer (SunBEAM) has a "step by step" tutorial on Symets here.

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Page author: Eric Seale
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