What is a speed reducer?

Speed reducers are mechanical devices generally used for two purposes. The primary use is to multiply the amount of torque generated by an input power source to increase the amount of usable work. They also reduce the input power source speed to achieve desired output speeds. A speed reducer is simply a gear train between the motor and the machinery that is used to reduce the speed with which power is transmitted.

Elements that compose a speed reducer

  • The concept of torque

It is a rotational force expressed in units of kilogram per metre, Newton per metre or pound per feet. When torque is combined with an execution time, it turns into a “power”.

  • Electric motor

An electric motor has a specific force specified in HP, and has an operational speed for the output shaft. Both characteristics, power and speed, define the torque the motor can provide. The torque will determine whether a load will turn or not.

  • Gearbox

It is a transmission mechanism. It is composed of a set of mechanical components that enable the proper speed reduction and increase in torque transmission. All of its items are just as important, and they need a perfect geometry and composition for the proper operation of the system.

What do Speed Reducers Do?

Speed reducers primarily serve two functions. First, they take the torque created by the power source (the input) and multiply it. Second, speed reducers, much as the name implies, reduce the speed of the input so that the output is the correct speed.

Speed reducer from torque

How does a speed reducer increase the torque while decreasing the speed? The output gear of a speed reducer has more teeth than the input gear. So, while the output gear might rotate more slowly, reducing the speed of the input, the torque is increased.

So, to sum up, they take an input power source and increase the torque while decreasing the speed.

Speed reducers come in many shapes and sizes, but some of the most commonly found speed reducers are gearboxes.

Types of speed reducers-

  • Planetary speed reducer

Due to its great precision and reliability, many automatic transmissions nowadays use this type of speed reducer.

Which elements compose a planetary speed reducer?

Sun: The central gear. It is larger and rotates around the central shaft.
Carrier: Its purpose is to hold up to 3 satellite gears of the same size which engage with the central gear, a.k.a. sun.
Ring gear: An external ring (with teeth on its inner side) engages with the satellites and encloses the entire epicyclic gear train. Additionally, the central shaft may also become the rotational centre for the outer ring, which makes it easy to change directions.

  • Gear reducers Spur

It is the most common type of gear, and its main feature is that its teeth are set up on parallel axes. This type of spur gear is used when motion has to be transferred from one shaft to another one that is close and parallel. It is used for transferring a great amount of power (around 500 KW) and provides a constant and stable speed ratio.


They run smoother and more silently when compared to spur gears; this is because of the oblique manner in which their teeth interact in relation to the rotation axis. They can be set up parallel to each other or, generally, at 90 degrees. If this is the case, and helical gears are crossed, they are combined with a worm gear.

Points to keep in mind while choosing a speed reducer-

  • Torque
  • Speed
  • Horsepower
  • Reducer efficiency
  • Service factor
  • Mounting position
  • Connection variable
  • Life required

We hope you find this article useful and now you are completely out of the confusion box regarding electric motor speed reducers.

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