[Note: This was the first Gakken I ever built, and is mostly responsible for my wanting to get a few more of the older ones to play with. Ultimately, it’s the DC motor car that got me started on writing this blog series.]
Kit 21: DC motor car. Here, we have a DC motor that uses an electromagnetic coil to attract one of 6 magnets on a drive wheel. As a different magnet on the wheel approaches a normally-closed reed switch, the switch opens and the coil turns off. Inertia causes the wheel to keep spinning so that the reed switch closes again and the coil turns on to attract the next magnet. Kind of like how the propulsion on maglev (magnetic levitation) trains work. The motor uses a single AA battery, and it goes through batteries fast, plus the gearing on the drive pulley results in the car moving fairly slowly forward (you can swivel the front axle to make the car go in a circle). But again, the point is to show you how to make such a motor. You even have to hand-wrap the wire on the coil. This also took about 2 hours to build the full kit (not including the time for unwinding and rewinding the coil because I got it wrong the first time).
When you’re done, you still have the mook to read. The first part of the mook talks about the practical applications and long history of motors (in Japanese of course). Then, the rest of the mook covers other DIY projects (like making a small wind generator, or a really complicated paper airplane).
There’s a higher-end series of kits for building your own steam engine or dirigible, but they run well over $500 apiece. The steam engine kit (now out of print) outputs 3 watts at 12 volts, and costs roughly $1600.
I like this lower-end gakken series of kits, because they’re fun, inexpensive and just a little challenging to build.