Obtain the following parts:
1) Gear Motor - "6VDC 45 RPM Pinky Finger Sized Gear Motor 1" Long x 15/32" x 3/8"" from either amazon.com or directly from http://sciplus.com/p/MICROMOTOR_47952. Other sources are available, I've not tested them though.
2) Coaxial Power Jack - Radio Shack part number 274-1583.
3) 1.5 Vdc Power Supply - Radio Shack part number 273-315 with the "N" style plug (273-345, you get one free with the power supply).
Print emmett's "CubeGears2-3.stl". If you can edit the file, you can delete one of the large corners, the center hub, and one pin before printing as these parts are not used. Clean up any stray filament in the gear holes. See Geared Heart, Motorized Edition for the steps I performed in loosening up the geared cube as the it must spin freely.
Print all parts. While printing "Top.stl", I paused the printer at 4.2mm and changed filament from black to silver.
Test fit, file, sand, etc. for smooth operation. Lubricate the gears and any surface contact between rotating components
Solder a wire between the motor plus terminal and the coaxial power jack center pin. Solder a wire between the motor minus terminal and the coaxial power jack shell pin.
Plug in the power supply, and test. I run mine at 6VDC for an hour or so for break in, then switch to 1.5VDC for actual running. If yours doesn't run at 1.5VDC, then disassemble the cube gear, and re-tune the pins in the gear holes.
Hope you like it.