Gear Trains

A simple gear train is used to transmit rotary motion

A simple gear can change both the magnitude and the line of action of an effort force.

gear trains

The effort force is applied to the "driver" and the load is applied to the "follower".

Transmission Ratio

Transmission or movement ratio can be expressed as

μM = nD / nF = tF / tD         (1)

where

μM = movement ratio

nD = revolutions of driver (rpm)

nF = revolutions of follower (rpm)

tF  = number of teeth on follower

tD = number of teeth on driver

 

When the same direction of rotation is required for both the driver and the follower, an idler wheel is used.

gear trains idler

The movement ratio for a gear with an idler wheel can be expressed as

μM = nD / nF = (tI / tD) (tF / tI) = tF / tD         (2)

where

tI  = number of teeth on idler

 

Make 3D models of spurs and gears with the Engineering ToolBox Sketchup plugin

Spurs and Gears Spurs and Gears

Typical Gear Ratios

Typical gear ratios for different types of gearsets are indicated below.

Type of Gearset Typical Gear Ratios
Min Max
Spur gear, external 1 : 1 5 : 1
Spur gear, internal 1.5 : 1 7 : 1
Helical gear, external 1 : 1 10 : 1
Helical gear, internal 1.5 : 1 10 : 1
Straight bevel gear 1 : 1 8 : 1
Spiral bevel gear 1 : 1 8 : 1
Epicyclic planetary gear 3 : 1 12 : 1
Epicyclic star gear 2 : 1 11 : 1

Related Topics

  • Mechanics - Kinematics, forces, vectors, motion, momentum, energy and the dynamics of objects

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