A micro scale steam engine rendered in LEGO form.
I've always thought the Technic Competition Cannon looked like the boiler from a steam engine. In 2005 I decided to make it happen and this was the result.
PDF instructions, parts list and LDraw file can be found at truedimensions.com.
There are quite a few friction based connections, but they are all pretty solid with the old version of the cannon. Unfortunately the piece was redesigned a few years ago, and although the connections still mostly work with the new version, the main wheels are quite loose and there are some odd looking gaps in a couple of places.
15 x 3 x 5 studs