Bill Powers writes:
... the artificial insect's physics isn't TOO odd. It corresponds to
that for a highly damped system, which probably isn't too bad an
approximation for legged systems)
Well, you have to admit it's a LITTLE odd, in that the whole bug is
damped rather than the individual legs!
But that's just my point! Muscle has damping characteristics.
Insects almost always have several legs on the ground at once, and
experiments have shown that certain legs generate forces which
actually OPPOSE the forward motion of the body (in the American
cockroach, the front legs have this property). Thus one could
consider a walking insect as always being connected to the ground
through one or more dashpots, which WOULD damp the motion of the
whole bug.
Greg Williams, thanks very much for the articles by Cruse . . .
I noticed the similarity between the walking stick work and your model
too and I'm glad that Greg sent you some of Holk's papers. Recently,
we successfully implemented his leg coordination rules for stick
insects (see "What mechanisms coordinate leg movement in walking
arthropods?", Trends in Neurosciences 13:15-21 for a recent review) in
our hexapod robot, robustly generating a range of gaits similar to our
original model.
I continue to encourage your interest in models of insect locomotion.
However, it seems that you prefer to make everything purely
sensory-driven. This is, of course, a perfectly legitimate approach,
but I must repeat that it does not appear to be the way biology does
it. A number of experiments have demonstrated that the neural circuits
underlying many rhythmic behaviors (e.g. walking, swimming, chewing,
breathing) can generate the basic oscillatory pattern IN THE COMPLETE
ABSENCE OF SENSORY FEEDBACK. Of course, this central rhythm must be
reinforced and fine-tuned by sensory feedback in order to exhibit
completely normal output patterns. In addition, work on cockroach
locomotion by Sasha Zill has suggested that even when sensory feedback
is intact, it may come in too slowly to play any role in fast walking
insects (the cockroach is capable of stepping frequencies in excess of
24 Hz!).
Best Regards,
Randy Beer