Tamiya 72001 Planetary Gearbox Kit The first in Tamiyas high efficiency series the planetary gearbox features two 4:1 and two 5:1 stages that can be combined in any way you likeyou can even combine two kits to get really huge gear ratios. The output is always conveniently on the same axis as the motor shaft. Available gear ratios are 4:1 5:1 16:1 20:1 25:1 80:1 100:1 and 400:1. Getting its name from the way the gears rotate like the planets around the sun the Planetary Gear Box is a precise high quality gearbox with a RC260 motor built into the gear box itself to add to its compactness. A wide range of gear ratios can be attained and two kinds of crank arms are supplied for a wider range of functions. This gearbox has a 4 mm diameter round output shaft which works with the wheels that are compatible with Tamiya 4 mm round shafts or 3 mm universal mounting hub also fits on the smaller threaded end of the shaft although it is not specifically intended to work with this type of shaft (the hubs set screw could damage the thread on the shaft). For motor specs see the Mabuchi motor RC260 (#2295) data sheet (60k pdf). To compare all Tamiya gear box kits see the Tamiya Gearbox Gear Ratio Comparison. Note: The planetary gearbox is a kit; assembly is required. To use the kit in robotics projects you need to connect the motors to your own robot controller. 3 Volt Motor requires 2 Batteries and holder (available separately)