I was preparing an exhibit of crank-operated kitchen appliances and toys, when I thought it might be interesting to display how gears work. I had collected a whole bag of plastic gears from various toys that had broken when my kids were young. It turned out to be more challenging than I anticipated to find ones that meshed correctly, and to locate them accurately on a plexiglass base. I happened to notice that two of the gears incorporated ramped cams, so I hooked them up to brass contact strips which would operate both a flashlight bulb and an old electric bicycle horn using 3 AA batteries. It ended up working like gang busters! Turn the crank and gears turn in all directions and the light flashes and the horn honks!