Figure 13.11 shows the schematic diagram of single purchase winch crab. There are two axles: effort axle and load axle. On the effort axle, a small toothed wheel of small diameter known as pinion is mounted. The pinion is a driving gear and is meshed with a large gear known as spur gear. Spur gear is a driven gear. Both the axles are mounted on a rigid frame. Weight W is attached to the string wound on the load axle while the effort is applied on the lever arm of the effort axle. Hence by rotating the lever, the pinion is rotated, which rotate the spur gear and in this way load W gets lifted.
Figure 13.11 Single Purchase Winch Crab
Let W = Load lifted by the load axle
P = Effort applied at the effort axle
D = Diameter of the load axle
T1 = Number of teeth on pinion
T2 = Number of teeth on gear wheel
L = Length of lever arm
When the lever arm rotates by one revolution, the effort axle and pinion also moves by one revolution = 2πL
As we know,
Example 13.11: The pinion of a single purchase winch crab has 32 teeth while the spur wheel has 320 teeth. The diameter of the drum is 180 mm. If the handle of the winch is 300 mm long and the effort required to lift a load of 400 N is 25 N, find velocity ratio, mechanical advantage.
Solution:
Given: T1 = 32, T2 = 320, L = 300 mm, D = 180 mm, W = 400 N, P = 25 N
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