A Stirling Engine From Minimal Parts

March 28, 2024 by Jenny List 5 Comments

The model Stirling engine is a staple of novelty catalogues, and we daresay that were it not for their high price there might be more than one Hackaday reader or writer who might own one. All is not lost though, because [jirka.luftner] has posted one on Instructables which eschews the fancy machined brass of the commercial models and achieves the same result with an array of salvaged parts.

The main cylinder is a former apple drops tin with a cardboard displacer, and the CD/DVD flywheel is mounted on either a 3D printed or cut out frame with the secondary cylinder cut into it. A diaphragm for the secondary cylinder is taken from a rubber glove, and the cranks come courtesy of bent wire.

A slight mystery of this design is that it appears not to have a regenerator, or heat store. This usually lies in the path between the two cylinders to improve efficiency by taking the heat from the air as it passes in-between the two, and returning it when it goes the other way. We’re guessing that on an engine this small it’s the tin itself which performs this function. Either way this is a neat little engine that shouldn’t break the bank.

If this has whetted your appetite, you’ll be pleased to hear it’s not the first Stirling engine we’ve seen made from what was lying around.

Home Made Stirling Engines From Expedient Materials

April 13, 2022 by Jenny List 28 Comments

Many of us have read about Stirling engines, engines which form mechanical heat pumps and derive motion from the expansion and contraction of a body of air. A very few readers may have built one, but for many they remain one of those projects we’d rather like to try but never quite have the inclination. The YouTube channel of [Geral Na Prática] should provide plenty of vicarious enjoyment then, with the construction of a range of Stirling engines from commonly available materials. We have Coke cans, PVC pipe, and nebuliser cartridges forming pistons and cylinders, with wire wool serving as a regenerative heat store. The latest video is below the break, an amazing 10-cylinder rotary device.

The Stirling engine is perhaps the quintessential example of a device whose time never came, never able to compete in power and efficiency with first steam engines and then internal combustion engines, it has over the years been subject to a variety of attempted revivals. Today it has appeared variously in solar power projects and in NASA’s hypothetical off-world power plants, and will no doubt continue to be promoted as an alternative energy conversion mechanism. We’ve featured many working model Stirling engines in our time and even done a longer investigation of them, but sadly we’ve yet to see a story involving a practical version.

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This Custom Dynamometer Is A Stirling Example Of Homebrewing

April 6, 2021 by Dan Maloney 25 Comments

[Leo Fernekes] has fallen down the Stirling engine rabbit hole. We mustn’t judge — things like this happen in the best of families, after all. And when they do happen to someone like [Leo], things can get interesting mighty quickly.

His current video, linked below, actually has precious little to do with his newfound Stirling engine habit per se. But when you build a Stirling engine, and you’re of a quantitative bent, having some way to measure its power output would be handy. That’s a job for a dynamometer, which [Leo] sets out to build in grand fashion. Dynos need to measure the torque and rotational speed of an engine while varying the load on it, and this one does it with style.

[Leo]’s torque transducer is completely DIY, consisting of hand-wound coils on the ends of a long lever arm that’s attached to the output shaft of the engine under test by a magnetic coupling. The coils are free to move within a strong magnetic field, with a PID loop controlling the current in the coils. Feedback on the arm’s position is provided by an optical sensor, also DIY, making the current necessary to keep the arm stationary proportional to the input torque. The video goes into great detail and has a lot of design and build tips.

We just love the whole vibe of this build. There may have been simpler or quicker ways to go about it, but [Leo] got this done with what he had on hand for a fraction of what buying in off-the-shelf parts would have cost. And the whole thing was a great learning experience, both for him and for us. It sort of reminds us of a dyno that [Jeremy Fielding] built a while back, albeit on a much different scale.

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Spinning Up A Water Cooled 3D Printed Stirling Engine

March 31, 2021 by Tom Nardi 7 Comments

The Stirling external combustion engine has fascinated gear heads since its inception, and while the technology has never enjoyed widespread commercialization, there’s a vibrant community of tinkerers who build and test their own takes on the idea. [Leo Fernekes] has been working on a small Stirling engine made from 3D printed parts and common hardware components, and in his latest video he walks viewers through the design and testing process.

We’ve seen Stirling engines with 3D printed parts before, but in most cases, they are just structural components. This time, [Leo] really wanted to push what could be done with plastic parts, so everything from the water jacket for the cold side of the cylinder to the gears and connecting rods of the rhombic drive has been printed. Beyond the bearings and rods, the most notable non-printed component is the stainless steel spice shaker that’s being used as the cylinder.

The piston is made of constrained steel wool.

Mating the hot metal cylinder to the 3D printed parts naturally introduced some problems. The solution [Leo] came up with was to design a toothed collar to hold the cylinder, which reduces the surface area that’s in direct contact. He then used a piece of empty SMD component feed tape as a insulator between the two components, and covered the whole joint in high-temperature silicone.

Like many homebrew Stirling engines, this one isn’t perfect. It vibrates too much, some of the internal components have a tendency to melt during extended runs, and in general, it needs some fine tuning. But it runs, and in the end, that’s really the most important thing with a project like this. Improvements will come with time, especially once [Leo] finishes building the dynamometer he hopes will give him some solid data on how the engine’s overall performance is impacted as he makes changes.

If you’ve got a glass test tube laying around, putting together a basic Stirling engine demonstration is probably a lot easier than you might think. Commercial kits are also available if you’re looking for something more substantial, but even those can benefit from some aftermarket modifications. With a little effort, you’ll have a power plant ready for the surface of Mars in no time.

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Hackaday Podcast 033: Decompressing From Camp, Nuclear Stirling Engines, Carphone Or Phonecar, And ArduMower

August 30, 2019 by Mike Szczys 4 Comments

Hackaday Editors Mike Szczys and Elliot Williams are back from Chaos Communication Camp, and obviously had way too much fun. We cover all there was to see and do, and dig into the best hacks from the past week. NASA has a cute little nuclear reactor they want to send to the moon, you’ve never seen a car phone quite like this little robot, and Ardupilot (Ardurover?) is going to be the lawn mowing solution of the future. Plus you need to get serious about debugging embedded projects, and brush up on your knowledge of the data being used to train facial recognition neural networks.

Take a look at the links below if you want to follow along, and as always tell us what you think about this episode in the comments!

Take a look at the links below if you want to follow along, and as always, tell us what you think about this episode in the comments!

Direct download (60 MB or so.)

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When Stirling Engines Meet 3D Printers

April 14, 2018 by Mike Szczys 17 Comments

Let’s face it, everybody wants to build a Stirling engine. They’re refined, and generally awesome. They’re also a rather involved fabrication project which is why you don’t see a lot of them around.

This doesn’t remove all of the complexity, but by following this example 3D printing a Sterling engine is just about half possible. This one uses 3D printing for the frame, mounting brackets, and flywheel. That wheel gets most of its mass from a set of metal nuts placed around the wheel. This simple proof-of-concept using a candle is shown off in the video after the break, where it also gets an upgrade to an integrated butane flame.

Stirling engines operate on heat, making printed plastic parts a no-go for some aspects of the build. But the non-printed parts in this design are some of the simplest we’ve seen, comprising a glass syringe, a glass cylinder, and silicone tubing to connect them both. The push-pull of the cylinder and syringe are alternating movements caused by heat of air from a candle flame, and natural cooling of the air as it moves away via the tubing.

We’d say this one falls just above mid-way on the excellence scale of these engines (and that’s great considering how approachable it is). On the elite side of things, here’s a 16-cylinder work of art. The other end of the scale may not look as beautiful, but there’s nothing that puts a bigger smile on our faces than clever builds using nothing but junk.

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16-Cylinder Stirling Engine Gets A Tune Up

December 20, 2017 by Dan Maloney 33 Comments

Tiny catapults, kinetic sculptures, a Newton’s Cradle — all kinds of nifty toys can adorn the desk of the executive in your life. On the high end of the scale, a 16-cylinder butane-powered Stirling engine makes a nice statement, but when it comes equipped with a propeller that looks ready for finger-chopping, some mods might be in order before bestowing the gift.

We don’t knock [JohnnyQ90] for buying a rotary Stirling engine from one of the usual sources rather than building, of course. With his micro Tesla turbine and various nitro-powered tools, he’s proven that he has the machining chops to scratch-build one of these engines. And it wasn’t just the digit dicing potential of the OEM engine that inspired him. There was a little too much slop in the bearings for his liking, so he machined a new bearing block and shaft extension. With a 3D-printed shroud, a small computer fan, and snappy brass nose cone, the engine started looking more like a small jet engine. And the addition of a pulley and a small generator gave the engine something interesting to do. What’s more, the increased airflow over the cold end of the engine boosted performance.

Need the basics of Stirling engines? Here’s a quick look at the 200-year history of these remarkable devices.

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