Gear Ratio and Speed – JSS2 Basic Technology Lesson Note (Third Term)

Gears II

CONTENT 

•     Gear Ratio

•    Gear Speed

GEAR RATIO

Gear ratio is defined as the ratio of several teeth of output to input gear or input speed relative to output speed. It is calculated by dividing the number of teeth on the driven gear by the number of teeth on the driver gear.

 Gear ratio Number of teeth on the driven gear 

Example: Calculate the gear ratio if a gear with 15 teeth is used to drive a gear with 30 teeth.

Gear ratio= Number of teeth on the driven gear= 30/15= 2/1 

Gear ratio= 2:1

Ratio of a Series of Gears

When power flows through a series of gears, the ratio can be calculated similarly. For example, if a 20-tooth driver gear drives a 24-tooth cluster gear, and the second-speed cluster gear has 16 teeth driving a 20-tooth second-speed driven gear, this could be calculated as follows:

Driven/Driver x Driven/Driver= 24/20 x 20/16= 1:5:1

Gear speed

Gear speed is a measurement of how quickly a gear spins, often about the rotations of other gears. The speed of rotation of a gear is directly proportional to the number of teeth of the gear. For example, the speed of a 5-tooth gear will be twice the speed of a 10-tooth gear.

Example: A gear has 20 teeth. Its speed of rotation is 10 rpm. The gear drives another gear with 10 teeth. Determine the speed of the 10-tooth gear.

Solution

20 teeth x 10 rpm= 10 teeth x X rpm 

X rpm= 20 teeth x 10 rpm/10 teeth

X rpm= 20 rpm 

Evaluation questions

1.          What is the gear ratio?

2.          Explain gear speed