Newsgroups: comp.robotics
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From: av574@FreeNet.Carleton.CA (Tim Sallans)
Subject: Re: Artifical Muscles
Message-ID: <D2q97L.Jy7@freenet.carleton.ca>
Sender: av574@freenet3.carleton.ca (Tim Sallans)
Reply-To: av574@FreeNet.Carleton.CA (Tim Sallans)
Organization: The National Capital FreeNet
References: <3fp4h7$lmg@crl6.crl.com> <D2oEvu.Bw7@cunews.carleton.ca> <3fot77$q6l@newsbf02.news.aol.com>
Date: Fri, 20 Jan 1995 23:28:32 GMT
Lines: 57


In a previous posting, Darin L. Reed (dreed@crl.com) writes:
> Centauri7 (centauri7@aol.com) wrote:
> : jpaulson@chat.carleton.ca (Jess Paulson) wrote:
> : >from WIRED magazine, Feb.'94:
> : > A small electric current causes Muscle Wires to heat and shrink. 
> : > Turn off the current and they expand.
> :    Not quite true.  The wires must be streched after they have cooled. 
> : They don't expand on their own.  This is part of the design problem of
> : using them.  You have to control precisely how much you strech them.
> 
> One more design problem is how do you connect them to anything? Do you
> just tie the ends of the wires to whatever you want to move, and apply
> current to the portion of wire in between the knots? Also, how do you
> connect to these wires? I'd like something better than alligator clips,
> but I don't think you could solder onto them. I'll probably buy one of 
> their kits pretty soon just to see what the stuff looks like, but until 
> then I have been doing some thinking about my own designs and these are 
> unanswered questions.
> 
> 
> -- 
> Tracy Reed
> treed@ucssun1.sdsu.ed
> dreed@crl.com
> 


As I understand it, the nitinol contraction is caused by the
*thermal* change in the wire...a rather inefficient conversion
of thermal to mechanical energy, after the electrical energy
has been converted to thermal by an inefficient resistance
conversion.  For anything larger than a miniscule power contraction,
the wire must be heated even further (requiring higher current
and lower efficiency).  For mobile projects, I would think the size
and weight of a decent power supply would outweigh (sorry for the pun)
any gain from using the nitinol in the first place.  The only place
I could see it being useful would be for space critical uses (perhaps
fine end effectors), however I think tendon systems could be used
even there.

The original thread, I believe, did not refer to nitinol.  I think
it may have been more in the spirit of a recent Scientific American
article talking about contractile organic polymers, which could be
made to convert thermal, electrical or chemical energy to mechanical 
through an efficient molecular folding similar to that found in some 
natural elastin tissue.  I had heard vague references to other work
done with contractile polymers of varying compositions (not biologically
inspired) and would be interested in hearing any comments, references,
or thoughts on that subject as well.

					--Tim

--
Tim Sallans                        "I've a plan so cunning, you
Ottawa, Ontario, Canada             could stick a tail on it and  
av574@freenet.carleton.ca           call it a weasel." -- Black Adder
