Gear Train

What is a Gear Train?

Before we can define a gear train, we need to know what a individual gear is and what it does for a mechanical system. A gear is a spinning wheel with teeth that can “connected” with other toothed devices in order to transmit power and are widely used in many different mechanical devices [1]. In a gear train, two or more gears are used together to transmit power from shaft to shaft that each gear is connected to and there are many different types of gear trains that can be used depending on the mechanical system it will be used in. By using a gear train, the end goal is to increase or decrease the speed or torque of the final shaft in the sequence, which determines the final power output, and you can use something called the Gear Ratio in order to calculate those values [2]. 

The formula to calculate the Gear Ratio is the number of output teeth divided by the number of input teeth, and you do this step for each gear as you move from one to the other if you have more than two gears.

Gear Ratio Calculation (A-B)

The Gear Ratio is important when calculating a gear’s speed and torque. To calculate a following gear’s speed (rpm), you use your known input gear’s speed and divide by your gear ratio. 

Speed Calculation (Gear B)

And finally, to calculate the next gear’s torque, you multiply the input gear’s torque by the gear ratio to find the output gear’s torque. 

Torque Calculation (Gear B)

So as we can see through this example with gears A and B, gear B rotates slower and has a higher torque in comparison to gear A. 

In order to find the speed and torque of sequential gears past just a gear train with two, you would repeat these steps, however using values found from gear B to calculate gear C, as shown below [3]. 

Animation going through the steps of adding an extra gear to the gear train

Why do we need one? What is its importance?

A well-designed gear train transmission allows the system to modify the input load into an output that meets the design requirement.