When we were making new year’s resolutions last month, mine was to, y’know, build some of the cool kits and kit-like part collections I’ve acquired over the years.
First up: Solarbotics marble machine. Cute, simple, less than an hour build time if you don’t count waiting for the glue to dry. Laser-cut frame, less than a dozen solder joints. I only managed to assemble two of the sections backwards, and just broke/lost one piece taking them apart, so I think it was a success. (And thanks, Solarbotics, for making some of the waste pieces from the gear-wheel supports exactly the same width as the tab that aligns the wheel layers.)
It’s a mostly glue-optional kit, because all of the tolerances on the laser-cut pieces are close enough that you have to hammer lightly on the bits to get them to go together, or somehow put all of your weight on one thumb. Which bodes well for it holding together longterm.
If I had been smarter, I would have done a test fit of the electronics and the structural bits before soldering, because some of the placements are not what they seem from looking at the instructions. The spacing of the pads on the circuit board (which is cleverly made part of the back of the solar cell) looks as if you can just tack down the component leads after trimming them to length, but no. The leads also need to be a bit longer than the nominal 3/8″ for some of the components to comfortably clear the body of the gearmotor, and the leads on the big capacitor need to be shorter to clear the marble race. But it all worked out.
The other thing I learned is just how pitifully weak northern sunlight is in the winter. I brought the completed marble machine to our front window to see how it moved; the instructions say it should pulse every 2-5 seconds, but nope. More like every 15-20. Maybe I’ll rethink that rooftop solar-panel installation I’ve been yearning for.