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From: modbob@netcom.com (Robert Emery Smith)
Subject: Re: nitinol underwater? (followup)
Message-ID: <modbobCoztAF.584@netcom.com>
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References: <2p2l3k$dd9@birdie-blue.cis.pitt.edu>
Date: Thu, 28 Apr 1994 23:30:15 GMT
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: 	IF you don't mind insulating the wires well (with sacrafice
: 	in speed), if might be doable. I wired up a small "shark"
: 	in my bathtub and it _did_ "swim" forwards... slowly (I
: 	had a wire for power and used by toggle switches for 
: 	brains :-) In fact, I kind of wonder why people don't use
: 	nitinol in toy/competition projects... I'd like to see a
: 	submarine with seal flippers powered by nitinol ;-)

Several years ago some friends of mine had a toy company called 
Greybridge (eventually bought out by Worlds of Wonder, the Teddy 
Ruxpin/Laser Tag folks), and one toy they had a prototype of was called 
an Ice Freighter, or some such: a little toy boat, intended for warm 
bathtub use, with a little pilot house which had room for an ice cube or 
two.  It had a paddle wheel on the rear of the boat (like a river 
steamer) which had a pulley on it; another pulley was located in the 
pilot house.  A nitinol wire loop was wrapped around the pulleys; cooled 
by the ice, it would "relax" into its alpha phase (floppy) and wrap 
happily around the pulley in the ice house.  Warmed by the bath water, it 
would stiffen in its beta phase and try to reassume its straight drawn 
shape, leading it to roll off the paddle wheel pulley towards the ice house.

That little toy boat jammed!  I'm sorry it never made it to market: would 
have been great for races in the hot tub!

As for getting only 10% deformation, the usual approach to that problem 
is the same as that used for employing steel's elastic capabilities: you 
wind it into a spring, which employs its torsional stiffness (and bending 
to a lesser degree).  You can get all kinds of motion out of a system 
like that (I have a couple of nitinol springs with a phase transition 
temperature right around the temperature of a hot cup of coffee...great 
toys).

Have you seen the new eyeglass frames that take advantage of some of the 
alloys superelastic properties?  Wild stuff: metal frames that you can 
bend like spaghetti that just spring back to their original shape, no 
heating required.

					Bob

