Page 50 - Electromechanical Devices and Components Illustrated Sourcebook

12 Electromechanical Devices & Components Illustrated Sourcebook

left. Study the illustration carefully and follow the motion of Pulleys
the linkage. Also notice that return springs are applied at both
the solenoid and at the far end of the linkage. The pulley is a variation of the wheel. The pulley is a wheel
with a circular groove, which provides a guide for a rope
draped over the outside diameter. If one end of the rope is pulled
The Wheel with 1 pound of force, then the other end generates 1 pound
of lift. Figure 2-13 illustrates a simple pulley.
The wheel is a variation of a first class lever. Consider the
lever in Figure 2-3 and instead of a beam, imagine a circular
disk with the fulcrum at the center. If the disk is allowed to Fixed Axle
Pulley
rotate freely, then you have a wheel. The basic wheel is
Bearing
encountered in two versions, those with a rotating axle, as
shown in Figure 2-10, and those with a fixed axle, as shown
in Figure 2-11. Both variations have broad applications. Rope
Figure 2-12 shows an example of a gear train. The gear on
the motor carries a rotating axle, which allows the rotation of
the motor to be transferred to the gear. The rotation of the
drive gear is transferred to the idler gear, which has a fixed Pull
axle. The rotation of the idler gear is transferred to the driven
gears, which have rotating axles and are used to conduct some
Lift
sort of work.
Figure 2-13 Pulley

Rotating Axle
Wheel Fixed Overhead
Mount

Pulleys

Figure 2-10 Wheel and Rotating Axle Fixed Block Rope

6 to 1 Ratio (R)
Fixed Axle
Wheel
12" of Motion
Bearing Moving Block Applied (MA)
30 Pounds of
Force Applied
(FA)
Figure 2-11 Wheel and Fixed Axle
2" of Motion
Generated (MG)

Driven Gears 180 Pound of Force
Generated (FG)
Rotating Axles
Figure 2-14 Block and Tackle
By arranging pulleys in a progressive manner, significant
mechanical advantage can be realized. Figure 2-14 shows a
typical block and tackle intended to provide higher lifting
force. To determine the lifting force for a block and tackle,
divide one by the number of vertical ropes between the pul-
Fixed Axle
leys. The illustration shows a block and tackle arrangement
Idler Gear Drive Gear with a 6-to-1 ratio. To calculate the force generated (FG),
Rotating Axle multiply the applied force (AF) by the ratio.
Motor

Figure 2-12 Gear Train 30 pounds (AF) 6 180 pounds of force generated (FG)