Free Piston Stirling Engine | Assembly and Technical Explanation

Watch a free-piston Stirling engine being assembled and running on a cup of hot water. Technical explanations are included in the clip.
This unusual Stirling-cycle engine was allegedly designed by JAXA (Japan Aerospace eXploration Agency) and demonstrates a simple concept for generating power in outer space with only a heat source and a heat exchanger and a bare minimum number of moving parts.
The Stirling engine's working piston (made of graphite) is hidden inside the middle part of this contraption, and the dark sponge that can be seen in the bottom (jumping up and down) acts as the displacer piston, and causes the air to move between the hot and the cold surfaces.
Compared with other Stirling engines, the Stirling cycle is implemented in an interesting way in this engine: when the piston drops, a small rod pushes down a springy piece of plastic foil that momentarily lifts the sponge upwards towards the top of the chamber. The sponge there displaces the cool air at the top, forces it downwards toward the hot bottom of the chamber, raising the air temperature and pressure, thus lifting the worker piston once again. Then the sponge drops again due to gravity, displacing the hot air at the bottom, forcing it towards the top where it is cooled down again, lowering the air pressure. The reduction in air pressure causes the worker piston to drop, and the cycle stars over again.
This model does no useful work, but more useful designs include a strong magnet fixed on the moving rod, which moves through a wire coil, generating electricity through magnetic induction.
The term "free piston" refers to the fact that the working piston in this engine (unlike typical Stirling engines) is moving freely, and is not connected to a crank shaft by a piston rod.
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[@johnfuhrman1352]

Nice work, I could watch it run all day!

[@znerol1]

it's a thing of beauty

[@X197ToPlay]

Came for the Motor stayed for the Music :D

[@christomold3142]

Great job! ❤ Seen many of free piston, but only Yours is working on such a low temp difference.

[@GoingtoHecq]

That displacer spring is a very creative bit of design. This is a fairly novel miniaturized Stirling engine. Extremely impressive. Also it looks good. Very shiny. Well done.

[@RetroTechyNerdyStuff]

I am glad you liked the clip. Yes the plastic spring is a novel solution, and I find its use quite funny in the light of the fact that the engine is designed by JAXA, the Japanese space agency; It's ironic that a model engine designed by a space agency employs a creative spring solution which depends on _gravity_ when space technology is usually required to be able to operate in a zero-gravity environment.

[@eliottc5371]

Amazing. Thank you.

[@behrouzmovahed7525]

Great job 👌

[@nikbivation]

very cool! amazing!

[@zhitaburnurli9631]

Really cool

[@riveraricojoseangelgabriel5152]

Alv jaja, ya presente mi motor stirling en la universidad, fue el único que funcionó completamente.

[@RetroTechyNerdyStuff]

Well done. Stirling motors can be tricky to get working because they don't have much pressure to overcome mechanical friction and leaks.

[@PrismaDimensional]

Eres de México? Tengo una idea para construir un Stirling pero no sé por dónde empezar de la firma correcta Haha mándame msj

[@riveraricojoseangelgabriel5152]

@@PrismaDimensional smn soy de México, pero no estoy muy adentrado en los motores stirling

[@benjaminfoley919]

Where can I get one of these??

[@RetroTechyNerdyStuff]

I’m afraid I haven’t seen these models offered for sale for some years. I got mine from gyroscope.com many years ago, but they don’t carry them anymore.

[@sierraecho884]

This design with the cross shaped plastic spring is a great idea, was this your idea ?

[@RetroTechyNerdyStuff]

The engine was designed by JAXA, the Japanese space agency. I bought it as a kit several years ago. You can find more information in the video's description. Thanks for watching.

[@eifionjones559]

faCINATING

[@lunarrn]

Is there a practical use for this?

[@RetroTechyNerdyStuff]

It is merely demonstration model that demonstrates how a minimal Stirling engine can be constructed. It was designed by JAXA, Japan's equivalent of NASA, and illustrates how to convert heat into motion. This motion might be converted to electricity by adding a magnet and a coil. So no, there is strictly no practical purpose of this engine other than serving as an illustration of the concept which might be implemented in larger scale to generate power. An interesting benefit of the simple design is low weight and a low number of parts that may wear out, which is a factor when needing to run for very extended time periods during lengthy space exploration missions.

[@zhitaburnurli9631]

I think it will be used for future nuclear reactor in spaceship. Using radioactive as an heat source.

[@sierraecho884]

@@RetroTechyNerdyStuff This is probably the most minimalistic and cleanest free piston stirling engine design I have ever seen. I want to build a small demonstrator myself, ohne which can run off of a candle light and charge a phone very very slowly. This is a great general design which can be improved (better insulation, higher temp delta, helium as working fluid maybe even pressurized) and upscaled of course. Thank you

[@sierraecho884]

@@zhitaburnurli9631 Free Piston Stirling Engines are already used for combined heating and power units and for submarines to charge their batteries while under water. This design does have practical applications.

[@rmarbertin8131]

One could use it to extract excess heat from soup.

[@MrFactotum]

Hi RTNS Thanks for sharing this Ive tried in vain to make this from your detailed video, but after many different combinations of trial i still cannot get it going, would it be possible for you to detail me the critical dimensions of the parts please. I've even tried buying one but they are nowhere to be found, I want to make one for my brother in law who is bed bound from a severe stroke and want it for his amusement which he has very limited scope with. Regards Kev

[@RetroTechyNerdyStuff]

I've taken some measurements: power piston diameter is 8.0 mm, and is made of graphite. Displacer cylinder inner diameter is 25.9 mm, inner height is ~20 mm. The displacer piston (foam) diameter is 24.5 mm and 11 mm in height. I wish you the best of luck making your own. I believe the critical part is the spring mechanism on top which balances out the forces against gravity.

[@MrFactotum]

@@RetroTechyNerdyStuff Thank you very much, i really appreciate you taking the time to do that for me,👍👍👍👍 It should be a tremendous help. Just one more thing if i may, when the brass rod on the power piston comes to contact with the lower plastic spring, where abouts in the bore does the actual graphite piston come to in the bore, is it protruding or is it level with the edge of the bore or is it still inside the cylinder by a certain amount. kind regards Kev

[@RetroTechyNerdyStuff]

No problem; I would estimate the bottom of the power piston is above 3 or 4 mm above the lower edge when it hits the plastic spring at the bottom.

[@MrFactotum]

@@RetroTechyNerdyStuff great thats very helpful, thankyou very much. as soon as i get back off holiday i will be in the workshop using your dimensions. again thankyou for your time and help.👍👍👍👍

[@shahid3520]

@@MrFactotum Hi, please let us know if it is working now? I think the graphite piston must have made all the difference ? Hope your brother in law's health is better now.

[@shahid3520]

Beautiful !

[@PrismaDimensional]

Wooow