Gear units are necessary for converting the speed and torque of an electric motor into a force that drives a given application. Depending upon the size, design and stages of a gear unit, the motor's speed is transformed into steps – either up or down. They are categorised by what kind of force flow they transmit and come in three basic designs: planetary, parallel shaft and right-angled.
Planetary and parallel shaft gear units both transmit linear power, with input and output shafts sited in the same direction. Parallel shaft gear units are sometimes also called helical gear units, when the shafts are mounted on the same level. In some parallel shaft/helical gear units the shafts are mounted with the output shaft positioned below the input shaft.
Planetary or epicyclic gear train units are somewhat more complex, with power transmitted by a rotating system of gears like planets round a sun. The input and output shafts still move in the same direction, but the torque and speed transmit power to a coaxial ring on the output shaft containing rotating planetary gears. This kind of gear unit offers great stability and power density, with torque increasing according to the number of planetary gears in the unit.
Right-angle gear units are largely self-explanatory, with the two drive shafts mounted at right angles to each other, resulting in a flow of force also diverted at 90°. They come in three main versions, including those using worm gears, bevel and spiral tooth gears.