Picture of Build a Better Stirling Engine

Following my experiments with the first LTD Stirling, I decided to try and make a better one. The main problems with the first had been the glued joint leaking air, and excessive requirements for machining. This one would have soldered joints to prevent the leaks and would have far less machining and could be made with just a drill press..

The main difference between this one and the first one I made was the diffuser cylinder. This one would use a longer, thinner cylinder with an aluminium piston. I also decided to use metal where possible on this one and have roller bearings. The diffuser cylinder would be bolted on allowing strip down of the machine and a rubber gasket to hold the seal.

Step 1: Materials

Picture of Materials

For this engine I used the following materials:

1 length of 22mm (1") copper pipe
1 length of 15mm (1/2") copper pipe
1 22mm copper end cap (not shown)
3 aluminium heatsinks from an old TV (scrapyard)
1 piece of resin stock
Paxolin copper clad PCB board
HDD actuating head arm with bearings and shaft
2.5mm brass tube
1.5mm brass rod (sliding fit)
One marker pen with an aluminium body (not shown)
Part of a plastic 3" pipe or similar (not shown)
The brass centre boss from a defunct CD drive
A short length of 10mm aluminium bar from a scrap printer
A short length of aluminium channel (not shown)
Various nuts and bolts rescued from scrap items (not shown)
A small piece of high density rubber (a piece of bicycle inner-tube)
4 15mm brass disks (not shown)

The reason for the not shown items is ..... at this point I haven't acquired them yet!

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T0BY2 months ago

My goodness! You have really done a beautiful job here!

NeilRG3 months ago
I was inspired by the way you fabbed the crankshaft. Very clever. I was aso inspired by your use of the hdd bearing. Very nice presentation. Thank you for the post. Neil R
fdiaz91 year ago
approximately how much power can you get from your engines?
conopodium2 years ago
Re: "I then cast the tube using the resin process in my other instructable."
Is this the process with the car filler?
rimar20002 years ago
WOW, this is a very good instructable! Congratulations.

I don't know why I did not see it when published.
Greyfox953 years ago
looks very steampunk
cgc1234 years ago
does the small piston size matter?
marshon (author)  cgc1234 years ago
Only relative to the larger one. Generally it seems that there is great debate about the relative merits and drawbacks. Experimentation is the key here.

The displacer cylinders function is simply to help move the air from the 'hot' side to the 'cold' side and vice versa. There are versions of the Stirling that require no displacer cylinder at all.

To run, the displacer cylinder must be at least 1.5 times the volume of the power cylinder, but I have run engines that had 10 times the volume. You see the displacer piston is not a gas tight seal fit to the cylinder whereas the power piston is.
winn24 years ago
Oh..and one more thing- are you experienced with this sort of technology? If so, would I have to be skilled in order to construct one of these engines as well? I'm probably driving you nuts with all of my questions, but if you could answer these questions it would be great.
marshon (author)  winn24 years ago
Well. I'm no engineer that much I can tell you.
I have only my own experiences to draw on, no formal taining whatsoever.
I have simply aquired skills here and there, done a LOT of reading and watching the right TV programs.
winn24 years ago
How much did it cost for all these items and where did you get them? ......You must be a genius to make all this stuff! Are you a skilled engineer?
marshon (author)  winn24 years ago
Nothing, they were all hanging around the workshop. It pays never to throw anything away.....
I have no idea what they would cost to buy.
winn24 years ago
How long did it take you to make this sterling engine?
marshon (author)  winn24 years ago
I did it over a weekend.
Chowmix124 years ago
Oooh pretty... 0_o me like.
Makes you wonder why computer fans can't be powered by the heat of the processor? Or am I going made here? ;) :P
Hello Rocket man MSI did develop one but I have searvched all over and never found a n example of it.


is this http://www.excitris.com/2008/03/01/fan-that-runs-off-heat/ it that you were searching?
Brilliant, although it looks like the offspring of a toilet and a swamp boat. Mmm efficiency.
Because electric fans are smaller, and given the cost of copper these days, probably cheaper. It's all about how cheap components are these days. Ever wonder why the fans in computers are so noisy? Its cos they've got cheap bearings causing the fan to vibrate more.
Fair point, I wasn't looking from a manufacturers POV just considering the possibilities for a mad inventor.
kcbford14 years ago
nicely done, i will working on this soon!! Thanks
Egoritz4 years ago
Great Build, I liked your use of the brass blanks on your crankshaft.
texhon35 years ago
how can you use the power? I almost see a sterling attached to something to do real work..
LinearB texhon35 years ago
Hi. http://www.whispertech.co.nz/main/PRODUCTS/ I was asked to help design a dam / hydroelectric thing, but the fall was insufficient. It flows into a pond with about a 40 degree temp differential, so i looked at stirling engines. This company claims they've got one that will both power a house and heat the water. Haven't seen one yet, but it will apparently run off propane.
marshon (author)  texhon35 years ago
The two engines I have made so far are purely experimental. Ultimately I intend to make one to run a squirrel cage blower for an aluminium forge, driven by a heat tap from the forge itself.
savaSS5 years ago
Where did you buy the copper clad paxolin. I'm having a very hard time finding it
marshon (author)  savaSS5 years ago
I had mine in the scrap box. Just use single or double clad PCB board instead. You can get that from RS, Farnell or Maplin.
6raleyh5 years ago
Hi Would you be able to post a video of this model working? Thanks
marshon (author)  6raleyh5 years ago
There's a link at he top of the page
Nerdz5 years ago
For those who want some mathematics involved (ie formula) here is a great reference on a forum: http://stirlingengineforum.com/viewtopic.php?f=1&t=48

One of the comments mentions a book:


I might look into getting this book. Ive been working on my own version of yours for a while, Ive spent 14 bucks so far (since my last comment anyway).

Hagar1 Nerdz5 years ago
Hagar15 years ago
I have know the formula to calculate the power for an engine like this. I don't know how it went exacly but it must have been something like this. Anybody that does know the formula? I know the power ~ ΔTemperature³ x volume² x 10^-8 x Cte x ... (or 1/ volume(²)) The power depends on the temp difference, a little on the volume (altough it could be it was 1/ volume² and then some constants depending on the density of the gas and it's heatcapacity, the stroke and bore of the engine, how closse the components resemble the perfect adiabatic components of a perfect engine... So does this ring a bell with anywone?
Blackice5045 years ago
i have been interested in this type of engine since i have seen them however most of the time i have never been able to contact its owner so i ask you what sort of torque or rpm do you get from this device. Thanks for the great info on how to build and i now understand more on how this type of engine works.
marshon (author)  Blackice5045 years ago
I'm no engineer, and certainly didn't work anything out using gas flow thermal dynamics. You'd need to ask someone who knows about these things. However, over the two first experimental engines I have found that (testing them to destruction) the limiting factors are mechanical design, and temperature (differential). The LTD ran between about 50 RPM and 300 RPM before the temperature started to soften and deform the walls of the diffuser cylinder (made from a plastic tub). I am working on a glass cylinder to improve this. The metal engine shown here runs between about 200 and 700 RPM but the bearing for the diffuser decided to bind and this bent the crankshaft and the con-rod, so I'm working on improvements here too. The torque and therefore the power is more dependant on the temperature and the speed at which the air can be heated and cooled effectively. I have no idea as to the Newton Lbs Ft figure, but for these small engines it would be quite low. Theoretically, these engines could be nearly as powerful as a steam engine, but that would depend on materials and design. Eventually I'm aiming to build one to drive a squirrel cage fan for a forge.
Bubbler5 years ago
This is a great looking Stirling engine, and you have done a great job. A video would be much appreciated, and perhaps you can enter it onto Boyd's Tin Can Stirling web site?
Very cool! I'm thinkin about it. Perhaps have power one or two leds.. Nice Job!!
Wesley6665 years ago
Very nice! For the piston, I have one I made awhile back, I used Epoxy Putty and it woked fine. I had to make two cause I didn't grease the pipe enough to get it out on the first try, but the second one is amazing. I also had the idea of using copper pipe, but I used some high strength epoxy instead of soldering mostly cause I had alot of it anyhow, and it can withstand 2000C heat. Cool Instructible! :D
marshon (author)  Wesley6665 years ago
Yes I have seen some nice examples using epoxy putty. I did try using white Milliput but I broke it trying to get it out of the pipe and internally cast resin shrank too much. I may try it again sometime though.
I used Perma Poxy (TM) Multi - Metal 4 min. Epoxy. I found it didn't shrink, and it has a breaking strength of 3500 PSi, and a temp. range from -40C to 176C (-40F to 350F) The only thing is since its the metal bond stuff, it bonds to the copper pipe I was using for the cylinder and to cast it like S*$t to a wool blanket, so it requires alot of oil or Pam cook spray to get it out. I formed it and after about a min started pushing it out, cause it will still bond to the pipe if you let it cure in the pipe, which is annoying because you have to be careful not to deform it while pressing it out, but I got it on the first try (Well the second, cause it cured inside the tube on the first). Work fast cause it does harden up in 4 mins! Wait 10mins (For good measure, and because it can get quite warm), then drill a big hole in it for the connecting rod and another hole in the side for the pin to hold the connecting rod on, works AMAZINGLY! One thing though is make it longer then it needs to be, because when I pushed it out, the side I was pushing on was a little deformed, but it was long enough I just cut the weird part off. Hope this helps! BTW, its super cheap! Its like $5 for a stick 10cm long and about an inch in diameter! Better then anything else I saw at Canadian Tire! Also added a picture of mine...I don't really like the grey color...but its a piston, color doesn't affect performance! :D
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