Recently I saw a video of a remote controlled boat powered by a miniature steam engine and was instantly hooked on the idea. After doing a bit of research I found miniature steam engines cost hundreds of dollars or require some very advanced skills and tools to build. Yet looking at the actual mechanism which allows them to run they are really quite simple so I decided to try and make one on the cheap.
The point of this project was really to see how cheaply and easily a miniature steam engine could be built. I built this engine in one day and for under $10 in materials so I think it's safe to call it a success.
This engine is 7.2cm (2.8") tall.
Some Things to Note:
First off I should state that this steam engine is only a steam engine. This instructable does not include instructions on how to build a boiler to produce steam. Instead I run the steam engine on compressed air. If you don't have a compressor a bicycle pump works well too, it's just a lot more work for you. ; )
I should also note that even if you did build a boiler this engine probably wouldn't work well because many of it's major components are wood. In the presence of steam the wood would swell and warp causing problems. A simple solution to this problem would be to replace the wood parts with aluminum ones.
I am a very visual teacher so be sure to read the 'Image Notes' (hover your mouse over the yellow boxes on the images), it will likely make my instructions clearer.
How it Works:
You could read my lengthy description below or you could check out the totally awesome animation by the guys over at www.animatedengines.com, find it here! I should note that this animation is of a "double acting" engine, in that is has ports on both the bottom and the top of the cylinder where mine is a "single acting" engine with ports just on the top. This just means that the engine relies more heavily on the momentum of the flywheel to keep it running but is a lot simpler to build.
This type of engine is called an Oscillating Steam Engine. If you watch the video below you will see that the cylinder on this engine actually moves back and forth as the flywheel turns (it oscillates!), this action is what opens and closes the ports which let compressed air enter the engine and exhaust air leave.
The cylinder has one port at it's top which is pressed up against the main body of the engine. The main body on the other hand has two ports, one for the compressed air and one for exhaust. As the cylinder tilts to the right it aligns with the compressed air port allowing air to flow into the cylinder and push down the piston. This causes the crankshaft to turn, thus tilting the cylinder over to the left and allowing the air to exit the cylinder though the exhaust port as the piston comes back up. Then the process repeats.