Came up with this idea after seeing a couple of cheap plastic toys that used gears. Like every other woodworker I said I can build one better out of wood and less cost. Baltic birch ply for the gears and base. Each set has one gear with a handle and when you turn one they all turn. The hard part was tuning them so there wasn’t any high points on the teeth that would stop rotation. Turn the crank and when I felt resistance remove the gears one by one until I found the offending gear. Sandpaper and rasp until they turned smoothly. They sit loose on dowels for the axles so they can be taken off and put in any configuration the child wants. I was thinking of painting them different colors but in the end I thought that natural finish looked better. For the impossibly cute grandchildren.