Any means of speed reduction common industry may be used in robotics as well. This includes fixed axis and planetary gear trains called Harmonic Drive and Orbidrive as well as a novel design with nutating gears may be used. The following sections describe the Harmonic Drive concept as well as the nutating gears concept.
In planetary gear trains, there are normally four basic elements: the sun gear , the ring gear, the arm , and the planets. For calculation purposes, the sun and the ring gears are called first and last gears. Although we will not develop the following equation here, it can be stated that for a gear train, with corresponding angular velocities and number of teeth for the first and last gears, the following is true.