# Gear Reducers

A gear reducer, also known as a speed reducer or a gearbox, is a mechanical transmission device consisting of a gear or a series of gears placed between machinery and its motor to reduce the output rotational speed and increase the torque created by the motor.

The motor provides a very high rotation speed but minimal torque. A speed reducer is required to reduce the speed and increase the load capacity. Multiplying the torque produced by the motor leads to increased serviceable power to the machine connected. Gear reducers are used to improve the efficiency of any operation.

## Principle of gear reducers

As mentioned above, a gear reducer consists of one or more pairs of gears, and each pair consists of a larger driven gear and a smaller driver gear. The gear ratio is a way of measuring how different sizes of gears interact to transfer energy. The ratio of the number of teeth on the driven gear to the number of teeth on the driver gear decides the reduction ratio of the pair.

For example, there’s a driven gear with 75 teeth and a driver gear with 25 teeth. In this case, the single reduction gearbox has a ratio of 75/25, which is 3:1. This concludes that the input shaft must rotate four times to fully rotate the output shaft once.

If the electric motor speed is 3,000 rpm, the gearbox reduces this speed by three times to 1000 rpm. If the motor torque is 15 lb-in, the gearbox increases this torque by three times to 45 lb-in (before subtracting out gearbox efficiency losses).

Other gearboxes may have multiple gear sets, thereby increasing the gear reduction. For example, a gearbox consists of two gear sets, each having its gear ratio; the total gear reduction ratio is calculated by multiplying the first gear set ratio by the second. If the first gear set had a reduction ratio of 4 and the second gear set had a reduction ratio equal to 6, the total gear reduction ratio would be 4×6=24.

Gear reducers are available in more complex reduction stages (worm gearboxes) that can reach reduction ratios of more than 100:1. In addition, it is possible to reach a reduction ratio of 10000:1 if two highly efficient gear reducers are combined.

Sometimes, an idler gear is placed between the driven and driver gears. In normal conditions, the driven and driver gear move in opposite directions, but the addition of the idler gear causes the two gears to rotate in the same direction. The idler gear does not affect the reduction ratio and is not part of the calculation; it just changes the direction of rotation of the gears and rotates in the opposite direction of them.