It is a homemade rock tumbler, made entirely from stuff from my junk pile. Specifically, I used a 1/8 HP 90v DC Dayton gearmotor, a 10v power supply (since the voltage is 9x below the rating of the gearmotor, it turns a lot slower and with lower, but still completely sufficient, torque. The container for rocks is made from a "refrigerant accumulator" , from which I cut off one end.
The gearmotor and the bucket are coupled with a custom made coupling, 1/2"-13 NC on one end and 1/2"-20 NF on other end, to accommodate the arbor adapter on the motor and the accumulator's mounting bolt.
It is meant to be positioned with some incline, so that the water does not pour out. The bucket is supported by two steel casters.
This contraption is almost completely quiet (when run without rocks), meaning that I cannot hear it run unless I get my ear close to it. I lubricated the casters, their axles and their running surface.