What is a gear motor?

A gear motor is a combination of a gearbox and an electric motor. This combination of two systems is used for efficient usage of the motor. It makes a cost-effective solution for high torque, low-speed applications. These motors are used in our household as, garage door openers, alarm clocks. In commercial areas, hospital beds, cranes.


The gearbox is a mechanical device used to increase the output torque and for reducing RPM. The shaft of the motor is connected to one end of the gearbox, and the internal combinations of gears in the gearbox produce the required speed and output torque characteristics based on the gear tooth ratio set by the user.

A gearbox, that represents several gears interconnected to each other

CC BY-SA 3.0 | Image Credits: https://commons.wikimedia.org | StationNT5Bmedia

These gearboxes are available in various sizes, with various gear tooth ratios, to fulfill the wide range of torque requirements.

High torque is required for starting the motor and in transient states (accelerating, decelerating, pulling a load). The IC engine operates predominantly over low torque applications. So, the engine is responsible for the motion, if the speed falls below the required speed no motion is observed. The torque developed by the engine by increasing the speed becomes constant after reaching some maximum speed. If the motor shaft is directly connected to load, engine speed may reduce. Due to the variable nature of load or vehicle resistances, we need to operate the engine over a wide range of speeds. Hence the engine is connected to a gearbox system for operating in a wide range of speeds requirement.

Internal structure of a gear motor, showing the connection of the motor with the gears
CC BY-SA 4.0 | Image Credits: https://commons.wikimedia.org | Raimond Spekking

Working principle

A gear motor can work on alternating current (AC) or direct current (DC). AC for AC electric motors, DC for DC electric motors.

These gear motors generally have an output ranging from 1,200 to 3,600 revolutions per minute (RPM). These motors have two-speed specifications, they are normal speed and stall speed torque specifications/characteristics.

The engine motor shaft is not connected directly to the load shaft, it is connected through the gear train. The increase in torque is inversely proportional to the speed reduced in it. This reduction gear technique allows small electric motors to drive large loads (but slower than the large powered motors).

Gear train

A gear train is a mechanical system formed by placing several gears on a frame (generally made up of steel) so that the gears mounted on it can engage together (fit properly in their respective gear tooth) and rotate together smoothly. In other words, it is a series combination of two or more gears for transmitting power, by interlocking individual gears with other gears with the help of their gear teeth (for reducing slipping) for smooth transmission of power.

The ratio of pitch circles (or) gear tooth ratio defines the speed ratio of the two gears connected.

A compound gear train showing how the gears are connected internally

CC BY-SA 4.0 | Image Credits: https://commons.wikimedia.org/wiki | 100kWhr

The speed ratio is given by:


Where Z1, n1 is gear tooth, speed of the leftmost gear, Z2, n2 is gear tooth, speed of the middle gear and Z3, n3 is gear tooth, speed of the rightmost gear respectively.

So, by setting the correct gear tooth ratio we can control the speed at the required torque. It is used for reducing speed and high torque requirements.

Types of gear motors

Most of the gear motors used in industries are alternating current (AC) powered gear motors with fixed-speed devices. They have a fixed gear tooth ratio, but a variable gear tooth ratio provides greater control than the fixed one.

The general applications of direct current (DC) powered gear motors are mainly in the automotive industry, such as power winches on trucks, power window motors so on.

Other types of gear motors are:

  1. Helical gear motor
  2. Shaft mounted gear motor
  3. Bevel-geared motor
  4. Worm gear motor

Need of speed reduction

Whenever we require to reduce the speed of the rotating shaft of a motor, in the device being driven gear motors can be used for speed reduction by using gear trains. Like in an electric clock, we have three rotating hands (seconds, minute, and hour). These three hands have different revolutions per minute (RPMs) and each hand is connected to a different gearbox (with different gear ratios) for the correct operation of each hand. Speed reduction is used in this case with the help of a gear motor setup.

Use of gear motor

HouseHold Areas:

  1. Garage door openers
  2. Stairlifts
  3. Rotisserie motors
  4. Timer cycle knobs on washing machines
  5. Power drills
  6. Cake mixers
  7. Electromechanical clocks

Industrial Areas:

  1. Jacks
  2. Cranes
  3. Lifts
  4. Clamping
  5. Robotics
  6. Conveyance and mixing

Gear motors can also be used in coin changing equipment, redemption games, pinball machines, peristaltic pumps, food service equipment, value actuators, damper actuators, pitching machines, auger motors, oil skimmers, fan oscillators, vending equipment, and so on.

Context and Applications

This topic is significant in the professional exams for both undergraduate and graduate courses such as

  • Bachelors in Science (Physics)
  • Bachelor of Technology (Mechanical)
  • Masters in Science (Physics)
  • Masters in Technology (Mechanical)

Practice Problems

Q 1 What is the gear train present in an electric clock?

  1. Reverted gear train
  2. Simple gear train
  3. Sun and planet gear
  4. Metal gearbox gear

Answer: Option a

Explanation: Reverted Gear Train are those first and last gear is coaxial, in the clock, the second, minute, and hour hands must be moving coaxially.

Q 2 Which of the following types of the gearbox is used in a car?

  1. Compound train
  2. Parallel-shaft train
  3. Epicyclic train
  4. None

Answer: Option a

Explanation: Compound gear trains can be used for variable speed applications, these are found generally inside machines, used in a car (for various speeds).

Q 3 How does an auto-rickshaw take a sharp turn?

  1. It has a different mechanism.
  2. The tyres slip during turns.
  3. The power is transmitted to only one wheel.
  4. None of the above.

Answer: Option c

Explanation: When a rickshaw takes a sharp turn, power is transmitted to one wheel and the wheel slips across the road and takes a sharp turn.

Q 4 Two mating spur gears have 50 and 150 teeth respectively. The pinion(round gear) present in the system transmits a torque of 20 Nm or 177.02 lb-in rotating at 1200 rpm. What is the torque transmitted by the gear to the load?

  1. 20 Nm
  2. 6 Nm
  3. 60 Nm
  4. 40 Nm

Answer: Option c

Explanation: Gear ratio is 150/50 = 3, So torque is 3 times 20 = 60 Nm and speed will be 1200/3=400 rpm.

Q 5 Gear drive is_____________ than belt drive in power transmission

  1. More efficient
  2. Less efficient
  3. Equally efficient
  4. None of these

Answer: Option a

Explanation: Gear drive requires less space than belt drive. Low friction loss for gear drive than belt drive. So gear drive is more efficient than belt drive.

  • Gear box
  • Geared motor drives
  • Gear belt/trains

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