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Nitinol Engines (1992) (free-energy.ws)
70 points by blacksqr 57 days ago | hide | past | web | favorite | 31 comments

Application of the subject aside, Nitinol is fun to play arround with. If you want to tinker, this book comes with a coil of Nitnol wire to use in the demos contained in the book:


In my experience, challenges of Nitinol (a.k.a. 'muscle wire') for use as a electoactive linear actuator is that if you're not careful you can over heat (or apply too much tensile load to) the wire and it will permanently deform (lose it's memory). Still, and interesting material to toy around with.

There is also a deluxe kit that comes with more wire. 1 meter of each kinds instead of 20cm & 40cm wires.


(Disclaimer: I work at RobotShop in their Web & IT team -- I have nothing to do with marketing though and I'm just a fan of Hacker News.)

One problem with Nitinol is that it has a limited number of cycles before the material becomes weak and then breaks or no longer returns to its proper state.

This is a major limitation on "muscle wires" when using them for products that require a high number of cycles of greater than 100k.

Banks reported no weakness nor degradation in his Nitinol engine after 20,000,000 revolutions. Any idea why there's such a big difference between the numbers reported in each paper?

Where are you getting this? The credible sources I find say they improve with use.

Here is a good article showing thermal and mechanical fatigue. You can see under moderate mechanical stress, it fails between 1e5 and 1e7 cycles. While that sounds like a lot, consider that there are 3e7 seconds in a year.

So if you had a mechanical device that operated at 1HZ, it would fail in less than a year.


How difficult/expensive is it to recycle the material? i.e. if one had some sort of wonder-generator based on it, would it make sense to use a model where once per year, the owner sends the nitinol pieces back to the manufacturer (who recycles them) in exchange for a discount on replacements?

I assume since titanium is part of the alloy, just discarding it after use is probably not great from a cost perspective.

I balked at first glance because "free energy," but here we have a unique method for turning thermal into kinetic energy. Slightly outside the bounding box of this energy system, of course, lies the expending of more energy than what's produced to keep the hot water hot and the cold water cold.

But using natural low-grade temperature differentials as the author suggests, what might this arrangement achieve that a Stirling engine doesn't? More torque? Advantage of fewer moving parts? Novelty only?

Wikipedia claims that one of the problems of Stirling engines is that they depend on the rate at which heat can be transferred to a gas. A Nitinol engine has a metal as its working object (functionally like a working fluid, just not actually fluid), so the thermal conductivity could be considerably better. The result could plausibly be higher power for a given amount of metal in use.

We already have this unique method via Nichrome wire. You can see a really neat application of this in a common toaster here: https://www.youtube.com/watch?v=1OfxlSG6q5Y

Technology Connections is my favorite YouTube channel. He's just so good in explaining the technological intricacies of everyday things, and his humor is so wonderfully snarky. I highly recommend turning on the subtitles as well, he puts a lot of effort in them.

"oh, god... he has a third one"

excellent writing and delivery, and yes, usually an easter egg or two in the CC ;)

Yes, I wonder why "free energy". It is not free energy, it is a respectable, thermodynamic law abiding machine.

According to what I've seen here, it is good for making tiny engines but the efficiency is low.

Nitinol is also used in the smallest & lightest servos you can buy: https://www.micronwings.com/Products/Servo%20Biometal/BioMet...

Seems like you could make a fan out of this stuff that could be used to vent the heat from air conditioning units instead of using electric fans.

I guess you could... but that would be complicated and expensive and electric fans are pretty efficient anyway.

The omnipod insulin pump, by insulet, uses this in a clever way.


The attached CNN video is fascinating. It seems a shame that the research seemingly abated.

Can anyone else speak to whether more work is being done into the metal or its applications?

I recently went to a talk at my university on microcombusters but the professor (I cant remember his name off the top of my head) was also working on small insect like drones. There were videos of nitonol powered beetle crawling and a non flying prototype of a bee drone with nitinol wing flappers. Rather cool but he said they are incredibly inefficient compared to traditional electric motors.

You can make very tiny motors with nitinol, but it is a real waste of the capability of the material.

Those work by using electrical resistance to heat a sample, which moves, and then cools off and can be moved back again, such as by a spring. Turning high-grade electrical energy to low-grade heat, thence to motion, wastes most of it (probably ~70%) vs. a magnetic motor that wastes normally less than 10%.

But nitinol can extract high-grade mechanical energy (kinetic energy of motion, or potential spring tension) from existing low-grade heat by conducting the heat from a higher temperature source to a lower temperature sink. I don't know why the other commenter claimed they wear out; the reported experience from labs was that after 20M cycles they were (a little) stronger than they began.

Yea thats how it tied in with the over all microcombusters talk, they were using tiny swiss roll burners to power the nitinol motors. Due to liquid fuels having higher energy densities than batteries apparently they could go for much longer than their electrical counterparts even though they weren't as efficient.

What sort of orders of magnitude are we talking about here? Could you wind a watch with body heat?

You have to find a way of applying and removing the heat in order to make that happen - for watches I would have thought the normal "self winding" kinetic mechanism was best.

They usually say you need 40 degrees of difference. So, probably not.

Any advice on where to get started on nitinol alloys/engines as a layman tinkerer?


The "Earth Engine" is also similar?

eeZah7Ux 57 days ago [flagged]

"Free Energy" wackos? facepalm

Even though you can't win against thermodynamics, Nitinol wire seems fairly neat.

Please don't do this here.

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