Re: Infantry Walkers

At 10:29 AM 8/24/98 -0600, you wrote:
>On Mon, 24 Aug 1998 10:51:24 -0400, Jerry Han writes:
>>I remember reading somewhere of materials that contracted when
electric
>>current ran through them, and relaxed when the current was shut off.	
>>I also remember that they weren't very reliable or strong, but it is
>>conceivable that these are 'merely' problems of engineering, and not
>>of the actual physics.
>
>I forget what its called, but I've actually built some robots with
>this stuff.
[snip]

Well, Jerry's description could be pizeoelectric materials, but your
description (especially the wire part) makes it pretty obvious you're
both
talking about a shape/phase memory alloy, most likely Nitinol.	(Or
NiTiNOL, but whatever.)  I studied the stuff in a lab at school; pretty
incredible.  It's not the electricity that causes the change (aka a
hysteresis loop), though, it's the residual heat.  The wire also doesn't
fully stretch back on it's own, but requires an applied force.	I don't
remember the numbers that we got exactly, but we were working with 100
micron wire, which needed a mass of about 150-200 grams on the end to
force
it to stretch back to it's full length.  (That's not the maximum weight
the
wire held; I don't remember what that is.)  Using a bundle of the things
would do a very good simulation of a muscle while also providing
redundancy
in case a few snap.  The counter force could, as in the human body, be
provided by a second bundle on the other side of the joint.  If anyone
wants my lab report on the topic I could probably dig it up and send it
to
you... not sure how enlightening it would be, but you could look. ^_^;

Later,
					Aaron Teske
					ateske@HICom.net