Sunday, March 22, 2009

Soft Robotics - The Right And Wrong

"Soft robotics" being something like this article.  Watch the video, then see if you spot three things I spotted right away.  I thought of all three in the space of the last 20 seconds of the movie.

Maybe that's because I've already used this method in an experiment I carried out, 25 years ago.  Yep, quarter of a century ago...

See, I got hold of an experimenter's kit of that Nitinol memory wire.  Nitinol, for anyone that never heard of it, was the original "memory metal" that you heated, bent into a shape, then allowed to cool in that shape.  Now you could bend it or stretch it to another shape, and when you heated it again, it resumed the first shape it had "remembered."  In the case of the experimenter kit, the wire just shrank in length when it was heated.  Looking at the "tentacle" that thet were demonstrating, you can see where this was going can't you?

First point, and a major point of difference between their clumsy thing and mine - why use four "muscles" ?  Unless your aim was to exactly mimic and octopus' tentacle, in which case they were still short of the central sheath muscle.  My "gripper" used three "muscles" made of Nitinol, which pretty much used up my precious stock of the stuff.

Second point: Using "draw wire" technology is not going to be the same as using this stuff I wrote about in the previous article.  The "muscle" fibers can be embedded in the structure of the flexible limb, meaning more precision about where the force is applied

Last point.  They are only worrying about a cable-like muscle in tractive mode.  But big advances have also been made in tubular fibres which inflate and shorten through the use of compressed air or liquid.  I'm betting it's just a matter of aligning or "weaving" these new carbon fibre muscles and you can mimic the compressive/shortening mode that biological muscles use.

So - if they thought about embedding three bundles of traction-mode fibres with three bundles of compression mode fibres alternating, they could pretty much mimic the octopus' tentacle.  If you include with this a central "core muscle" filled with liquid, and tapered the "muscle" ends and the arm body, you would have something that would be considerably better than a tentacle.

Oh - and the reason I didn't try doing more with my Nitinol "gripper?"  Because the wire got hot, it would tend to cut into the plastics I had access to after a while.  Silicon rubber tubing was too expensive for me to use, and very soft so the wire would have cut into it too, anyway.  I gave it away as an idea too far ahead of the technology at the time.  Now I wish I had access to some of the new materials that these guys have...

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