Mechanical power systems are composed of pulleys, sprockets, gears, bearings, shafts, and numerous other components that are used to deliver power to the individual components of a machine and to change it to meet each component's requirement. Changes in speed, direction of rotation, or torque may be needed. The next sections illustrate some of the principles of mechanical power trains and provide examples of how these principles are used.
V-pulleys or sheaves are used in conjunction with V-belts because the V shape of the belt wedges in the V shape of the pulley. This increases friction between the belt and the pulley, which results in greater allowable power transmission. A belt drive will always have at least two pulleys, the driver and the driven. Consider Figure 6.1, which represents two pulleys mounted on shafts and connected by a belt.
When we apply torque to the driver shaft and cause it to turn or rotate as indicated by the arrow on the driver pulley in Figure 6.1, a tension or force will be created in the belt. If the tension exceeds the load (torque) of the driven pulley and the friction of the drive train, it will cause the driven pulley and shaft to turn. Drive trains using belts and pulleys may contain more than two pulleys. If more than two are used, one will be the driver and the others will be driven.
If the driver pulley in Figure 6.1 has a diameter of 10.0 in and rotates at 100.0 revolutions per minute (rpm), and the driven pulley has a diameter of 5.0 in, we can determine the speed of the driven pulley (and the shaft it is attached to) because
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