I got a little birthday mad money, and donated half of it to the ACLU and spent the other half on some AstroMedia kits. I bought their golden ratio calipers, a Ferris wheel, a steam engine and a Sterling engine. (I still haven't built the Sterling engine.) AstroMedia is a German company, but I bought the kits from an English distributor, because it my high-school German isn't good enough to figure out shipping charges. Here's a link to AstroMedia UK.
I guess I spent about 15 or 20 hours building the steam engine. It's a very well-engineered kit, and it goes together smoothly. Most of the pieces are constructed by laminating the very heavy cardstock. Some of these stacks of paper receive a metal rod along the length of them, while others get a nylon bearing sandwiched inside. There are quite a few non-paper pieces involved, including sheet aluminum, wire mesh, the metal boiler, the crankshaft and other rods, syringes, rubber O-rings, and eight Euro pennies which are glued into the outer edge of the flywheel. It's certainly not 100% paper, but you can either be a purist or you can have a mostly paper steam engine.
It runs on five tea lights. (It will run on as few as two tea lights, but very slowly.) The flames of the tea lights heat a circular tin boiler, which rests in a wire mesh cage. A silicone (?) hose connects to the boiler with a magnet. (The magnet functions as the safety valve. If the pressure gets too high, it will separate from the tin to let off excess steam.) The hose conveys the steam to the finger of a disposable glove, which inflates and pushes the piston up. This makes the rocker arm see-saw upwards, which turns the crankshaft. The crankshaft conveys the power to the flywheel, which keeps the momentum going, and drives the rocker arm up and down. The crankshaft also provides power to another arm which presses a valve, which clamps and unclamps the far end of the disposable glove's finger. When the valve is closed, the finger fills with steam, and when open, it releases the steam into the stack.
All the pieces that come into contact with steam must be lined with aluminum foil. At the bottom of the steam stack, there's an empty aluminum tea light holder, into which you insert an aluminum cone to funnel the steam upward. The stack is removable, so you can remove the condensed water as needed.
MODIFICATIONS: I made a couple of the pieces from aluminum baking pans I got at the dollar store, because it was easier to cut and fold than the stiff aluminum sheet provided in the kit. I plan to re-make the bearing spacers for a more precise fit in order to cut down on the side-to-side rattle of some of the moving parts. I'm also going to put a little silicone plumbers' grease between the magnet and the boiler to get a better seal.
While the included instructions are generally very clear, I'd recommend you go to the AstroMedia UK "Construction in Pictures" page, where they've done an excellent build log. (That link is to the Google translated page; the original is in German.)
I've run it four times now, each time for about a half hour to forty minutes, with a ten-minute warmup.
Here's my steam engine running the Ferris Wheel.
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