2.3 Power Train Formulas and Shaft Speed

Shaft Speed

The size of the sprockets in a chain drive system determines the speed relationship between the drive and driven sprockets. For example, if the drive sprocket has the same size sprocket as the driven, then the speed will be equal. 

If we change the size of the driven sprocket, then the speed of the shaft will also change. If we know what the speed of the electric motor is, and the size of the sprockets, we can calculate the speed of the driven shaft by using the following formula: 

Here is an example: 

The Driven Shaft rpm = (6 x 1800) / 12 = 900

Now, we understand how changing the size of a sprocket will also change the shaft speed. Knowing this, we could also assume that to change the shaft rpm, we must change the sprocket size. The problem is how do we know the exact size sprocket that we need to reach the desired speed? 

Use the same formula that was used to calculate shaft speed, only switch the location of the driven shaft speed and the driven sprocket size:

Let’s say that we have a problem similar to the ones that we just did, but we want to change the shaft speed of the driven unit. If we know the speed we are looking for, we can use the formula above to calculate the sprocket size required. 

Driven Shaft rpm = (6 x 1800) / 900 = 12