cookie can and bike parts, drill only

[tomostre]

Hi, I found lots of info on soda can stirlings; my first one used a balloon as a membrane, with a large disk crazy-glued to it as a power piston. It runs well (turning a 160mm rotor from a pedal bike disk brake at about 200 rpm on a single tealight candle)
Wanting to make something useful (like a solar waterpump, or perhaps an air circulator for a wood-burning oven), I had to do away with balloon, as it desintegrates after awhile. The newer models have fingers from mechanics gloves as accordeon-type power piston.

I found that some plastic bottles (top part with cap) make excellent base for the power piston (accordeon) and I use the presta valve stem from an old bike tube to connect it to pressure vessel. The displacer gland is lined with teflon from gear cable housing, and the displacer rod is a 1.8 mm spoke. Due to friction and weight, this no longer runs as joyfully on a candle, it likes an alcohol burner better.

balloon membrane popcan stirling
glove finger membrane pop can stirling

I transferred this design to a cookie can (about 16cm in diameter, looking to make a lower temp version) and set it onto the stove. The can top and bottom flex a great deal, stealing power from the power piston, so it would run only when the oven is really hot (chimney thermometer says 150-200 C) and I hold down the top to prevent it from flexing.

So here are the questions:
1) has anyone considered using the expansion of the cookie can top (or bottom) as membrane to turn cranks? It seems quite powerful, although the stroke is small.

2) solidifying a cookie can to be a better pressure vessel?

[tomostre]

here is the pic of the cookie can experiment

cookie can stirling

Photo0418.jpg (143.58 KiB) Viewed 6675 times

[Ian S C]

Tomostre, you could stiffen the top by drilling some (say 6)holes to match holes in the brake disc for small bolts, push the bolts through from the inside, and solder them in place to seal them, and maybe 2 or 3 through the holes near the centre. A similar doubler could go on the bottom if need be.
The tin can motor that I built made quite a bit of noise, going click clack as it ran, It has been decommissioned, and some of the bits might be used on another motor. Ian S C

[tomostre]

Hey Ian,
I am considering hiting two birds with one stone, that is drilling two holes in both top and bottom, and using two spokes as inner guides for the displacer - and brace top with bottom. At which point I could replace displacer rod with fishing wire to reduce weight and friction (since there is little chance that I would run the thing upside down).Although I do wonder if these guide-rails spokes might also conduct some heat into the cold end - but probably not too much, since they have a very small surface.
Alternatively, I am really wondering if the top could be used as membrane. You know how you are supposed to toss your glass jar of pickles if you can press the centre of the lid? Do you know if similar design has been tried? Also, do you know if anyone attempted to use the membrane from a speaker for power piston - I wonder, mainly because it can be found of all sizes, it is supposed to air tight, and it has a coil/magnet group - perhaps for a free piston type of experiment?
Thanks for keeping up with all the posts.

[Ian S C]

I would not do it. The spokes used as guides are going to cause all sorts of trouble, heat conduction being the least, your main problem is allinement, and friction, the bush that the displacer rod passes through should be all you need.
Pickle jar, oil can, Yes, look up TMG, Thermo- Mechanical-generator, worth looking at. Ian S C

[tomostre]

Hey Ian, you would be glad to know I went against your advice. Alignment was not a big issue, as i made holes with enough clearance in the displacer, and welded the spokes when they were both in place through top and bottom. This one made a good practice; I added some styrofoam into the dead air space under the membrane. here it is turning over http://youtu.be/SB83k1KjvuA

[tomostre]

just to see if friction was a problem in the displacer shaft, replaced its crank rod with a string. Set the whole thing on a block of metal, to improve heat transfer.
The stove is relatively cold (100C on the chimney thermometer)
youtube video is here
cookie can stirling turning over

[tomostre]

an update:
smaller flywheel, and inside pics
http://youtu.be/blzU6eASNpw
video of the can in action

[Triangle.Stirling]

Nice! It's running, although not very fast.
Keep on building!