stirling engine made from a pringles box


youtube movie

The first stage of converting a pringles box into a stirling engine is to make a pinhole in the middle of the lid



Because the plastic is quite springy the hole will shrink to less than the diameter of the pin used to make it.
A short length of nylon is threaded through the hole, it needs to be only a bit narrower than the hole to minimise air leakage



This shows the components of the bellows, which is made from a finger cut from a latex glove. An additional hole is made in the lid & the air pipe inserted. Incidentally the air pipe can be any length because it only transmits enough air to inflate & deflate the bellows. And it doesn't have to be mounted on the lid: this is a movie of a stirling engine where the bellows is mounted on the side of the pringle box.



this shows the assembled bellows



and this shows it inserted into the lid



the next stage is to attach some bent garden wire to the air pipe with a zip tie; this will eventually form the crank support structure & bearings



leakage is the bête noire of homemade stirling engines: I have tried to design this one in such a way that the chances of leakage are minimal but it almost certainly will leak (this one did) round the lid. This shows how you can make a seal from the wrist of a latex glove



now fold it back to make a double thickness



I cut this too short, eventually I replaced it with a much longer one that didn't leak.
This shows the lid fitted, I've also put some hot glue round the air pipe









The next stage is to make a former for making the the displacer; I've made this one by wrapping some paper round a beer can



Now wrap some paper round the former & glue it with pritt stick. I used quite thin paper but I don't think it really makes much difference. Using lined paper helps a lot with the marking out



Having formed the basic paper cylinder you make the base







You can now withdraw the former & complete the displacer just by glueing a strip of paper across the open end. This is simply to attach the thread which passes through the lid of the pringle box.



The displacer doesn't need a covered top, this is because as it moves up & down the column of air inside moves up & down too. Making the displacer topless greatly simplifies the making because you can remove the former through the open end. Previously I used to fit a closed top after having removed the former which was very fiddley & time-consuming.
This shows the displacer inside the box, I have used a small slip of card to attach the thread, this prevents accidentally tearing the thread off.



And here you can see it through the transparent top near its top dead centre position, its total travel is about 4cm









The next step is to make the crank, I have used a large paper clip & two plastic beads to act as spacers. The first bend is about 2cm, it moves the displacer up & down



the second bend should be no more than about 4mm, at right angles to the first. It gets pushed & pulled by the connecting rod from the bellows. It's shown here mounted in the bearings which I've bent into the supporting wire.



Only one of the bearings goes right round the crank, the one on the right hand side is simply a 'V' that the crank rests in. This makes assembling & disassembling the bearing far easier.



The right hand end of the paperclip is bent in a double right-angle to which the cardboard flywheel is glued; bits of drinking straw are used to attach the displacer thread & the connecting rod (no connecting rod in this picture)



The engine is finished by sliding folded sheets of paper onto the flywheel card to increase its inertia without greatly increasing its weight. You can balance the weight of the displacer at this stage by sliding one of the folded sheets of paper out along the card, this makes the engine run more evenly but it should work anyway without doing this



this is how you're supposed to do it. Notice he starts modifying it with tat near the end
car made from pringles box motor
same thing but more compact, uses scotch yoke to work displacer

Link to my original stirling engine page






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my email is davidvwilliamson@hotmail.com