It's raining here again so I pulled out some toys I made last year and played with them
. I like to dabble in metal work and have my own lathe and mill and a real soft spot for heat engines (stirling engines). I have chucked a few pics of a couple my engines up here to see if anyone else likes to make these. One is powered by ethanol and the other by a cup of hot water or a block of ice. The trick to making these engines is to keep the friction down as much as possible and get the timing right. When I first started making them I had to use exotic materials to get them to work but now have it down to a fine art and can get away with more readily available stuff. The ethanol powered engine will rotate at around 750RPM but if I use an gas torch will reach as much as 1500RPM before the hot cylinder melts
. It will also spin up to about 500RPM using the sun and a fresnel lens. The low temperature version spins up to about 200RPM on a cup of coffee
. This engine was great fun to make as my students had a large input in getting the design right (vectors, forces, gas expansion and contraction etc). Should have seen their faces when the engine ran for the first time on a block of ice
. We also designed a hot water tank using cotton wool, polystyrene and an old milo tin. When placed on this the engine will run for about 8 hours.
Mark