This Tamiya gearbox is a good compromise between speed and power. Build for either 41.7:1 or 64.8:1 ratios this motor features quality polyacetal gears. Each kit includes a disc with holes around its circumference that can be used with a photo-interrupter to provide feedback to a controller on motor speed (and distance travelled when using wheels). Motor included. Runs on 3 - 4.5 VDC. Assembly required.