1. Pulleys, Sprockets & Gears

2. 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.

3. Applications
Sprockets
Pulleys

4. Pulleys & Sprockets Pulley Sprocket Method of Transmitting Force Belt
Chain
Advantages
Quiet, no lubrication needed, inexpensive
No slip, greater strength
Disadvantages
Can slip
Higher cost, needs lubrication, noisy

5. Speed Ratio = Input Rate
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 out
Driven (out)
D out
Driver (in)
D in

6. 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.

7. Applications

8. Gears N = number of teeth Driver (in) Driven (out) Driver (in)
Idler Gear

9. Angular velocity in * N in = Angular Velocity out * N out
Gear Ratio = Input Rate
Output 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 in
Torque out D out N out

10. Example: Find gear ratio and find the input torque required so that the output torque is 100 ft-lb.
Driven
Driver
24T
36T
GR = N out / N in = 36/ 24 = 1.5
T in = T out * N in / N out = 100 * 24 / 36 = 66.7 ft-lb

11. Example: Find gear ratio and find the input torque required so that the output torque is 100 ft-lb.
Driver
Driven
12T
24T
36T A B C
GR = N B / N A * N C/ N B= N C / N A = 36/ 24 = 1.5
T in = T out * N in / N out = 100 * 24 / 36 = 66.7 ft-lb
Gear Ratio is unchanged by the idler gear.

12. Compound Gear Trains 60T 60T Driven Driver C A D 15T B 15T
GR = N B / N A * N D/ N C= 60/ 15 * 60/15 = 16