Picture of Tin Can Stirling Engine
How I built a hot air engine almost entirely from junk.  I've wanted to build one of these ever since discovering stirling engines in about 2003.  Spending the weekend making things in Steveastrouk's workshop gave me the opportunity to make the precision parts I'd need, and I knew most of the engine was going to be made of improvised materials, so decided to see if I could make the entire thing out of scrap or unwanted materials.

If you aren't familiar with how Stirling engines work, there are plenty of resources online- the Wikipedia page is a good place to start.

Step 1: Design

Picture of Design
The "core" of a gamma stirling engine of this design is a large cylinder that holds the displacer, connected to a smaller power cylinder providing the power strokes.  I decided to follow Darryl Boyd's "walking beam" design, where the power cylinder sticks out of the side of the dis[placer cylinder, because it suited the materials I had and it looks cool  :)

I found that an aluminium drinks can would fit neatly inside a steel soup can, so decided to use that for the displacer on the grounds of being cheap, light and easy to work with. The steel soup can provides a sturdy body for the engine and also meant I could ake the bottom removable to allow maintenance.

I found some decking to use as the base, some 1" x 1/2" pine to use as supports for the moving parts, and a piece of 3/4" aluminium strip to use as the beam.  The engine is a messy combination of metric and imperial units- that's what happens when you use scrap materials!
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T0BY2 months ago

This is a great project! You have done particularly well to make it mostly from scrap.

wmada2 months ago
Hey thanks for this instructable. I have a really cool idea which I dont want to reveal intil I build it and I will post it. I am curious if this can handle a load. Do you know or have you tested what this design can handle?
PKM (author)  wmada2 months ago

It can handle a load. Just not a very big one :) I connected the flywheel up to a DC motor running as a generator, and running the engine at full power it was just about able to light a red LED. That's an electrical output power of about 50mW, and if we assume a candle flame outputs 75 watts of heat the efficiency is 0.07%. For generating electricity you'd do better with a Peltier/Seebeck module over a tea light candle.

In terms of mechanical power, it's pretty bad as well :) a very small torque will make it stall, so you'd need lots of reduction gearing to get a usable torque out of it but I'd guess that (say) mounted on a model train carriage it could propel itself at a quarter of a mile per hour.

My setup was certainly not optimal and you could get more power out of a similar engine with more attention paid to impedance matching, having the right stroke length for the engine and so on. Plenty of people online have powered LED flashlights and radios from
tin can stirling engines, getting a few hundred milliwatts out of an engine with a similar (or simpler) design.

ShailP7 months ago

do u put anything inside the can??

and how much time does it take for the engine to start running??

Electrospark10 months ago

Well explained instructable! :-)

Thanks for the info!

AATHIS1 year ago

hey what is the difference between displacer cylinder and displacer,?
thnx for your help in advance

LOL!!! Put down your handbags guys.

As far as I am aware Sterlings are used today in pretty much all modern nuclear submarines to help generate power from the heat of the reactor. Think of the heat differential between a nuclear reactor and the depths of the sea!

I think a big factor behind the lack of practical sterling engines is that they are largely unheard of by the general public something which the internet and youtube is now helping along. I also know that some manufacturers have tried and failed to install them into cars as early as the 1940s, probably due to the problem with ramping up the power you get from them. Mainly caused by the fact they will run at a steady rate and accelerating / decelerating can be tricky.

Now a sterling vs a solar panel is an interesting match and I wouldn't be surprised if over the next 10 years or so we start to see some really nice green generators based on Stirlings coming out. Especially when petrol and diesel start to become so expensive that they become no longer feasible for the general population.

eyesee2 years ago
Piston seal problem
jeveda122 years ago
can you explain a little more about this engine, like how to build the piston and why there is to pistons.how this works please
PKM (author)  jeveda122 years ago
Step 3 links to some ways of making pistons- you can make one out of glue, or a balloon, or (the way I did) machining it out of metal. I'm not good enough at machining to write a guide on how to do that, so I skipped over that part.

There is only one piston, which has to be a very close fit in the small cylinder but slide freely, and the displacer inside the engine which needs a small gap around the sides. To understand how the engine works I'd suggest reading the Wikipedia page about them. Briefly, the displacer is there to move air around inside the engine, and the piston is pushed in and out by air pressure.  This explains why the parts need to fit the way they do, but to understand the entire cycle you should read more about Stirling engines- there is plenty of information on the internet about them.
lonely1642 years ago
asdasd2 years ago
Cool, but I'm not sure is it stirling.
PKM (author)  asdasd2 years ago
Well, as I understand it this engine uses the Stirling cycle (heat, expand, cool, contract), so I think it is. What part are you unsure about?
deep923 years ago
I get that for the power piston to be able to move, it has to be smaller in diameter than the power cylinder, but the thing that i don't understand is that if the piston is smaller than the cylinder won't it cause air leakage??
thanks for ur response! This is the only thing thats bothering me, otherwise i'm really looking forward to making this!!!
PKM (author)  deep923 years ago
That is the biggest problem with building solid power pistons, they have to move freely but fit very closely. Mine, thanks to a very big lathe, is smaller than the inside of the cylinder by something like a quarter of the thickness of a human hair...!

Unless you can make the cylinder and piston perfectly smooth you are aiming for the best compromise between it being too loose (and leaking air) and too tight (and friction taking power away from the engine).  I believe loose is generally better for a hand-made first engine. How you do this is entirely up to you, there are a number of possible approaches- check out the many other Instructables on stirling engines.
yokozuna3 years ago
Nicely done sir, 5 stars.
Very cool little project. Thanks. Oh, and Sterling engines have enormous real world application without any further development. They already work so they aren't just "curiosities". These engines are highly efficient (and they are also typically used with free or very cheap energy sources anyway) and very low maintenance & cheap to operate. Without any further development whatsoever, these engines are already available for purchase from numerous sources, especially relating to electricity producing solar concentrators and co-generation applications where new or existing heating furnaces & incinerators are fitted to also produce electricity. Co-generation engines are not only available for large commercial applications, but also for residential and small commercial applications, requiring as little as 500 degree Celsius to operate. Comparing petroleum diesel engine applications to sterling engine applications is utter nonsense. Diesel has absolutely no application where sterling engines are designed to be used. These applications are specific to producing very cheap electricity, so implying that diesel generators could somehow be used is ridiculous. I strongly suspect the poster makes his living from either petroleum or combustion engines and is making a feeble attempt to misinform. Now to be fair, algae generated diesel may be something to show enormous promise in the relatively near future with some further technological development, but petroleum based diesel is a non-argument. And even having given a nod to algae generated diesel, it doesn't appear that it will be cost effective enough to produce anytime soon to render sterling engines obsolete. Note: Hebinho posted some relevant links above in regards to this argument for anyone who missed them and would like to see just how advanced sterling engine technology already is and what it has to offer.
it's hard to make a sterling really work but when it works it shouldn't stop working
Barfight764 years ago
Excellent work! I want to build one using clear materials (i.e. glass, pvc, etc.), but I can't seem to find what kind of hot temperatures that are dealt with. The pvc specs I'm looking at have a max temp of around 150 deg F. My question really is, what kind of temperatures are you getting from your hot air portion?
charris74 years ago
can someone please explain the power piston and cylinder to me? what do I need, and how do i position it to make it work???
PKM (author)  charris74 years ago
Someone else has probably explained the cycle more concisely than I have, but in essence:

The displacer pushes the air in the engine to the hot end, where it heats up and expands. This expansion pushes the power piston outwards, because it's the only part of the engine that can move to let the air inside expand. The power piston moving outwards turns the rotating parts around, which moves the displacer and so moves the air inside the engine to the cold end. The air cools down and contracts, and so sucks the power piston back inwards.

The power piston itself needs to be able to move in the cylinder freely, but also to move in the cylinder with a change of air pressure. The simple way to do this is to just glue a cut-out circle of balloon rubber over a hole in the engine, so it will move in and out with changing air pressure. I did it by making a smooth brass tube and a piston to fit very closely in that tube.  That way is more fun and can make a more powerful/efficient engine but needs workshop tools whereas the balloon method might only need a knife and some pliers.  Check out reukpower's instructables for more on how you can build stirling engines without precision engineering tools.
furyy4 years ago
That is soo cool!
wiinick4 years ago
What is that metal thing holding the cd, i see them in many of these projects and i cant seem to find one, help me.
steve-lane4 years ago
you could use one of those sterno cans.
I picked up some at a camping store
tzq33tdq4 years ago
i want one!!!
fail4 years ago
Ive got 2 soup cans and there is a gap of half a centimetre between the middle can and the outer one, all of the way around. Is that too much?
PKM (author)  fail4 years ago
No, that sounds about right. The gap should be wide enough to allow air to flow around without restricting it, so less than a millimetre or so would be too close, but not so wide that it creates "dead space" which doesn't contribute to the power cycle. Having a slightly wider gap does give you more leeway if not everything aligns perfectly (which I was glad of!)

Ideally the displacer should be light, so if you can find one an aluminium drinks can might be better than a thicker steel soup can, but I don't see any reason the soup can wouldn't work.
fail PKM4 years ago
I can't seem to find any drink cans around, so I'm going to use these cans instead, now that I know that it should work. I shall inform you on how well it runs.
wiinick4 years ago
Video pleeeeaaaassseeeee
Biotele4 years ago
video please. Can you calculate power and efficiency?
PKM (author)  Biotele4 years ago
I'll post a few more videos when I have time to take them. I'm not sure of the power, but I hooked up the flywheel pulley to a motor running as a generator and it would just about light up one LED :(

I think it was overheating at the time- with better cooling and a more suitable generator I figure I could get perhaps one or two hundred milliwatts out of it.

Efficiency is pretty poor, I think an average candle puts out something like a hundred watts of heat so we are talking about something like 0.1%. Not great!
that thing runs hecka fast
PKM (author)  arronsparrow4 years ago
The video doesn't show it running that fast- what you don't see is it stalling just after the end of the video because that's about as slowly as it will run :)

That was only running on one candle, though. Heating it with a small cup of meths, it will run at several revolutions per second- it might go faster but I'm afraid to let it run that fast in case something gets damaged in the process. I'll take a video of it running fast and post it in the comments when I have time.
you should put some oil on joints and on the pistons! you can minimise the friction in this way ;)
PKM (author)  Timofte Andrei4 years ago
I did actually consider that, but the piston is machined with such a smooth surface and such a tight fit that oil actually increases the friction. The forces involved are small and the piston has quite a large area, so the drag of the film of oil tends to slow the engine down.

I do oil the crank bearings and the sliding displacer rod- it's possible I hadn't done that when I recorded the video, but it doesn't squeak as much now.
komodoboyx54 years ago

Just realize that this power source it a very viable power source.

After all, it's simplicity provides a very simple source of power and makes it very efficient.

Hobby to you or not, theres great possibilities in this machine.

I'm sure the wheel was just pushed around for giggles and grins before someone realized they could use that thing.
PKM (author)  komodoboyx54 years ago
It is beautifully simple, yes, but (in this scale) not really efficient or viable.

The temperature a stirling engine runs at determines how much of the heat you put in gets converted to work output- its efficiency.  For a commercial solar-powered engine, that might be 25%, but for the low temperature engines that run from the heat of someone's hand it's below 1%. 

The useful output of an engine like this might be enough to run a few LEDs or a radio but it's never going to power your house.  There are more efficient, less junky engines around which can produce useful amounts of power but they need a machine shop to build and a wood stove or large solar dish to power them, not a few candles.
try using some silicon caulking instead of the epoxy- let me know how it turns out
Biotele4 years ago
harddisks make excellent flywheels.
79spitfire4 years ago
That is soo cool!
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