The BEAM Bestiary is a BEAM
So called, because they're
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):
it on a flat surface, and our Symet scoots along
it contacts an obstacle, the Symet (if you built it
correctly) starts to tip:
it has tipped onto another set of "outriggers," the
Symet will now be moving away from the
For more information...
Solarbotics published plans for a Trimet here.
F.J. Tragauer (SunBEAM) has a "step by step"
tutorial on Symets here.