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Pulleys, Sprockets, and Gears

Pulleys, Sprockets & Gears

Pulleys, sprockets and gears are mechanisms used to transfer energy through rotary motion. These components can be used to:

– change the speed of rotation– change the direction of rotation– change the amount of torque available to do work

Following is a comparison of the components and the equations used to calculate speed and torque.

Applications

SprocketsPulleys

Pulleys & Sprockets

Pulley SprocketMethod of

Transmitting Force

Belt Chain

AdvantagesQuiet, no lubrication needed, inexpensive

No slip, greater strength

Disadvantages Can slipHigher cost,

needs lubrication, noisy

Pulleys & Sprockets

Speed Ratio = Input Rate

Output Rate

Angular velocity uses the symbol and has units of revolutions per minute (rpm).

In / out = D out / D in

Torque in = D in

Torque out D outDriver (in)

Driven (out)

D out

D in

Gears

A gear train is another mechanism for transmitting rotary motion and torque. Gears transmit rotary motion through interlocking teeth. A gear train is made when two or more gears are meshed.

Applications

Gears

Driven (out)Driver (in)

Driver (in) Driven (out)

Idler Gear

N = number of teeth

Gear Ratio = Input RateOutput Rate

Angular velocity in * N in = Angular Velocity out * N out

in * N in = out * N out

Gear Ratio = in = N out

out N in or

Gear Ratio = in = D out

out D in

and

Torque in = D in = N inTorque out D out N out

DriverDriven

24T36T

Example: Find gear ratio and find the input torque required so that the output torque is 100 ft-lb.

GR = N out / N in = 36/ 24 = 1.5T in = T out * N in / N out = 100 * 24 / 36 = 66.7 ft-lb

DriverDriven

12T24T

36T

Example: Find gear ratio and find the input torque required so that the output torque is 100 ft-lb.

GR = N B / N A * N C/ N B= N C / N A = 36/ 24 = 1.5T in = T out * N in / N out = 100 * 24 / 36 = 66.7 ft-lb

Gear Ratio is unchanged by the idler gear.

A BC

Compound Gear Trains

DriverDriven

15T

60T

15T

60T

GR = N B / N A * N D/ N C= 60/ 15 * 60/15 = 16

A

B

CD