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I have been considering using Nitinol wire for some experimentation as a component in an autonomous system. My understanding is that it will return to its original, contracted state when it reaches ~70°C, which seems to be capable of some pretty neat applications by passing current across it. I assume that if I were to buy some, I should purchase the stuff with the thinnest diameter for maximum resistance in relatively short (<20cm) lengths.

So, for those of you who have been able to play with the stuff, is Nitinol the nerdy engineer-candy it appears to be?

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I've been told two things:

  1. It gets very hot, which imposes some limitations (the person who told me this was using it in clothing).
  2. It contracts and expands disappointingly slowly.

However, I recently came across a device developed at the (late) Haptics Laboratory at McGill University called a "high strain shape memory allow actuator":

They consist of thin NiTi fibers woven in a counter-rotating helical pattern around supporting disks. This structure accomplishes a highly efficient transformation between force and displacement overcoming the main mechanical drawback of shape memory alloys, that of limited strain. They are as fast as the fibers are thin, while preserving the humph due to the many fibers in parallel. Because fibers can be made very thin indeed, they can twitch and relax in milliseconds. Various variable structure controllers were successful at controlling position, force and acceleration for vibration control. Thus we have high strain, high speed, high precision Shape Memory Actuators amazingly simple to build and to control.

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  • \$\begingroup\$ Awesome, so maybe in a couple years we can expect to see high-speed/precision actuators on the market. I suppose the contraction does not increase [significantly] with the increase in temperature? I'll still have to get some and piddle around to see what its characteristics really are for hobbyist potential. Perhaps I'll log the data I collect to post on the net for others with the same curiosity to read. \$\endgroup\$
    – iklln6
    Dec 24 '09 at 19:28
  • \$\begingroup\$ If you end up buying some, please do post your results -- I would be curious to see. \$\endgroup\$
    – terrace
    Dec 26 '09 at 6:07
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here's a video of it being used as an inch worm bot Youtube Video

I think the fact that it's an inch worm says something about the effectiveness of Nitinol, it's still pretty cool in my opinion

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  • \$\begingroup\$ That video was incredibly helpful! Gives me an idea of what to expect with responsiveness and insight to what may or may not be realistic with applications. Thank you very much for that! \$\endgroup\$
    – iklln6
    Dec 24 '09 at 19:25
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It's certainly used in medical applications for expanding stents in the body. enter image description here

It's also used for coupling hydraulic tubes in military applications. However, it's not a lot of good for the use we normally, imagine, that of an actuator. For me, the killer is that I don't know of any applications that use Nitinol for repeated contractions under load. The problem is that it stretches over time, making it essentially useless.

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