On Sat, 19 Oct 2002, Roman Black wrote:

*>* when the friction surface has a uneven friction
*>system, like the angled plastic "carpet" fibres
*>shown on the web page for that commercial system.
*>Horizontal vibration is all that is required.

More exactly one of the vibrations, or the contact friction must be
non-linear, resp. asymmetrical.

There was a model 'robot' demo that used two toothbrush heads glued under
a vibrator unit, both inclined at about 15 degrees in the same direction.
I built it once, it works. If you couple two such vibrators loosely with
an axle then you could have the equivalent of a two-wheel desktop robot.
No gears, moves slowly, high mass is not a problem, noise is, won't go
backwards (I have ideas on this using two vibrators, one x one y, and
control the phase between them, with straight brushes). Travel could
be measured by a free coasting wheel and encoder, or better, build an
optical mouse into the axle between the drive units, and slightly behind
them so it tends to run straight. Maybe this is the future of desktop
robots. Sunday I'll build one to see (note to self:  buy 4 hard bristled
toothbrushes).

Peter

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