One of the most amazing things for me is being able to build one of the Gakken kits and have it work right away. The kits aren’t really practical, being intended more as art pieces than anything else, but they do work, and generally the construction of the parts is really good for the price.
A case in point is kit #10, the Stirling Engine ($20). The original engine was designed by Robert Stirling, a Scottish clergyman who was trying to find a way to prevent the workers in his parish from getting injured or killed by exploding steam engines. He obtained a patent for his design in 1816, and built his first working model in 1818 to pump water from a quarry.
The Gakken version consists of a clear plastic drum with aluminum top and bottom plates. A piston made of light-weight foam is driven by temperature differences between the two plates, and the piston in turn causes a plastic disk to spin. The idea is to decorate the disk as you see fit, and watch it as the engine runs. The “fuel” is a heat source underneath the engine, and/or something cold on top (you can reverse the positions of hot and cold and the kit will run backwards, but not as fast). My first attempt was to have a couple ice cubes on the top plate, and to place the engine on top of a cup of hot tea. Amazingly, the wheel began spinning really fast right away, and kept spinning for a couple hours. I was surprised that it worked because some of the parts are kind of delicate, and the entire thing depends on having a mostly-airtight seal. The odds of my building it right were fairly low. But, the entire mechanism turns freely and it’s almost magical the way the piston moves up and down in the chamber on its own. Now, it’s fun to just heat up a cup of water and watch it spin for a while. (I don’t use ice anymore because it melts and drips all over everything.) (Gakken has a $100 version of the engine that can act like a car, run a fan, or light an LED. And, the German company, Boehm, has $400 brass kit versions that do nothing but run, while looking really cool on the desk of an executive).
(No review of the mook this time.)
Of the kits that I have now, the one I keep playing with is the stirling engine.