They are usually mechanical devices (simple machine) gear manufacturers , but can also be based on hydraulic, pneumatic, electromagnetic principles. They consist of at least three members, one of which forms the frame.

* General primary function of any transmission is the adaptation of a given input speed, such as the speed of electric motors, to a required output speed, for example, for a tool. Examples: engine speed of the shaver to the circular knife or car engine speed (6000 rpm) should have input on the transmission output gear at 1000 rpm. In the 4th or 5 Response is common in gasoline engines, 1:1, ie, "direct" response.
* Up gear. Pulleys for example: The speed of the input wheel is on the output by a factor greater n2/n1. The desired (larger) output speed is achieved by the ratio of the diameter of the entrance (D1) to output (D2); 100/min at D1 = 42 cm and with n = D2 = 14 cm is the output speed n2: D1/D2 = n2/n1. n2 = 42/14 × 100 = 300 bpm. This is no formula to solve, due to simple reasoning. Has three times the diameter of the big wheel i. See, for small, it also has 3 times as much volume. Turns one time this extent, must turn the small wheel 3 times, so it also has three times the speed. This ratio can be loaded or unloaded not change.

Direct drives, ie working without a gears manufacturers drives have, but in some cases benefits - there is no game and account for the losses of the transmission. As an example, the spindle motor may be mentioned.

As always above or below a gear ratio i, the speed ratio of input speed to output speed is understood. In addition to i are the efficiency, the maximum torque at the output, the game, the maximum speed and maximum axial and radial shaft load (force) are important parameters of a gear motor.

Gear types (one or more stages), which are mainly geared motors are used in:

* Worm gear: the axis perpendicular to the engine output shaft rotational axis
* Spur: axis of the output shaft is parallel, but offset to the motor axis of rotation
* Planetary gear: axis of the output shaft of the motor-like rotating axis
* Bevel: the axis perpendicular to the engine output shaft rotational axis

Continue to differ are rotary actuators and rotary actuators. In a rotary drive, the shaft turns as often, with a pivot drive less than a full rotation.

A feature of gear motors is whether they are irreversible or reversible, that is, whether the rotation is the drive shaft at no motor current possible. Epicyclical gears and spur gears at low speed reduction that is often the case, are self-locking worm gear in the rule.