Dual gearbox from Tamiya. This is an excellent way to get started quickly with robotics! You may have read many websites about servos, gear head motors, DC motors, stepper motors, and the pit-falls associated with each. We swear by these gearboxes because of their price, their ease in assembly, and the ability to be controlled by low-cost motor driver ICs. This gear box can drive two wheels independently in either forward or reverse. The twin-motor gearbox can also be configured for two different gear ratios (fast and faster). Gearbox comes unassembled as shown.  Includes gears, housing, motors, lube, and allen wrench.   58:1 and 203:1 gear ratios possible.  Motors operate from 3-6V.  Can be controlled by L293DNE, SN754410, and other low-cost motor drivers.  Mounting holes and hardware included.