Pulleys, Sprockets, and Gears Principles of EngineeringTM Unit 4 - Lesson 4.1 - Mechanisms Forging new generations of engineers Project Lead The Way, Inc. Copyright 2007

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 Sprockets Pulleys

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

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

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

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

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

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.

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