The Planetary Reduction Drive was a project for a class used to demonstrate the simplicity of gear reductions in situations such as vehicles. The part uses the planet gears as the driving gears so you can rotate the part using your fingers. It's fun and durable, and will have you mindlessly moving for hours. (Trust me!)SCALE COMPONENTS DOWN Once printed, bond the connector to the base (using glue) and insert planet gears into assembly. Then insert sun gear into base assembly and attach using the nut. Threads may be tight at first, but keep using them and they'll loosen. Works with up to five planet gears.