The Tamiya double gearbox is a compact unit with two independent motors and gear trains. The kit includes two motors and all gears and parts to build any of the four possible gear ratio configurations (12.7:1, 38:1, 115:1, and 344:1). Although it is not typical, it is possible to assemble each side with different gear ratios. There are two possible output axle locations (for any given gear ratio, only one output location is possible).
The output shafts included in this kit are 3 mm hexagonal axles that are 10 cm (about four inches) from tip to tip. The axles work with any of the Tamiya wheels we carry, giving you many options for your robot speed. The low-voltage motors run on 3-6 volts and draw up to a few amps, making them perfect candidates for the Dual DRV8833 motor driver carrier. Motor overheating can be caused by excessive stalling, even at very low voltages. We recommend that you use stall-detection sensors, or just watch your robot, to make sure that it doesn’t stall for more than a few seconds at a time.
The double gearbox is very similar to the Tamiya 70097 twin-motor gearbox. The gear ratio options of the two products complement each other well, but the mounting holes and overall dimensions vary slightly. The double gearbox is shorter and wider than the twin-motor gearbox, and the gears are a bit smaller and wider. This should make the double gearbox a bit more robust, though we have not heard any reports of the twin-motor gearbox gears breaking.