Guide

Idler Gear
Driving
Gear
Driven
Gear
Idler Gear
Driving
Gear
Driven
Gear
Idler Gears
Driving
Gear
Driven
Gear
G.3
cont.
Gear Trains and Idler Gears (Grades 4-8)
A simple Gear Train is a connected set of rotating gears that transmits power from an input (like
a Driving Gear connected to a motor) to an output (like a Driven Gear connected to a wheel or
mechanism). Simple Gear Trains can have any number of gears in a single row. All gears in between
the Driving Gear and the Driven Gear that only transmit power are known as Idler Gears. Idler Gears
have NO EFFECT on Gear Ratio or Gear Reduction, regardless of the number of teeth they have.
Example Gear Trains:
In all three of these example Gear Trains, the Driving Gear is 12-teeth and the Driven Gear
is 36-teeth, thus the Gear Ratio for all three examples is the exact same - 12:36 . Size and number of
Idler Gears have no eect on Gear Ratio or Gear Reduction, they just transmit power!