Figure 6-11.-Cable winch.GEARS USED TO INCREASEMECHANICAL ADVANTAGEWe use gear trains to increase mechanicaladvantage. In fact, wherever there is a speed reduction,you multiply the effect of the effort. Look at the cablewinch in figure 6-11. The crank arm is 30 inches long,and the drum on which the cable is wound has a 15-inchradius. The small pinion gear has 10 teeth, which meshwith the 60 teeth on the internal spur gear. You will findit easier to figure the mechanical advantage of thismachine if you think of it as two machines.First, figure out what the gear and pinion do for you.You find the theoretical mechanical advantage (T.M.A.)of any arrangement of two meshed gears by using thefollowing formula:In which,T.= number of teeth on driven gear;To = number of teeth on driver gear.In this case,T. = 60 and T. = 10.Then,Now, figure the mechanical advantage for the otherpart of the machine-a simple wheel-and-axle arrange-ment consisting of the crank arm and the drum. Dividethe distance the effort moves (2nR) in making onecomplete revolution by the distance the cable is drawnup in one revolution of the drum (2nr).Figure 6-12.-Camdriven valve.6-6
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