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.
The effort force is applied to the "driver" and the load is applied to the "follower".
Transmission or movement ratio can be expressed as
μM = nD / nF = tF / tD (1)
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.
The movement ratio for a gear with an idler wheel can be expressed as
μM = nD / nF = (tI / tD) (tF / tI) = tF / tD (2)
tI = number of teeth on idler
Make 3D models of spurs and gears with the Engineering ToolBox Sketchup plugin
Typical Gear Ratios
Typical gear ratios for different types of gearsets are indicated below.
|Type of Gearset||Typical Gear Ratios|
|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|