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Unformatted text preview: The motor shaft is connected to gear A and rotates
at 975 r.p.m . The gear wheels B, C, D and E are fixed to parallel
shafts rotating together. The final gear F is fixed on the output
shaft. What is the speed of gear F ? The number of teeth on
each gear are as given below : Fig. 13.3 Gear A B C D E F No. of teeth 20 50 25 75 26 65 Solution. G iven : N A = 9 75 r.p.m. ;
T A = 20 ; T B = 50 ; T C = 25 ; T D = 75 ; T E = 26 ;
T F = 65
From Fig. 13.3, we see that gears A , C
and E are drivers while the gears B , D and F are
driven or followers. Let the gear A rotates in
clockwise direction. Since the gears B and C are
mounted on the same shaft, therefore it is a
compound gear and the direction or rotation of
both these gears is same (i.e. anticlockwise).
Similarly, the gears D and E are mounted on the
same shaft, therefore it is also a compound gear
and the direction of rotation of both these gears
is same (i.e. clockwise). The gear F will rotate in
Let Battery Car: Even though it is run by batteries,
the power transmission, gears, clutches,
brakes, etc. remain mechanical in nature.
Note : This picture is given as additional information
and is not a direct example of the current chapter. N F = Speed of gear F, i.e. last driven or follower. We know that Speed of the first driver Product of no. of teeth on drivens
Speed of the last driven
Product of no. of teeth on drivers Chapter 13 : Gear Trains l 433 50 × 75 × 65
N A TB × TD × TF
20 × 25 × 26
N F TA × TC × TE or
∴ NF = NA
= 52 r. p. m. Ans.
18.75 18.75 13.5. Design of Spur Gears
Sometimes, the spur gears (i.e. driver and driven) are to be designed for the given velocity
ratio and distance between the centres of their shafts.
Let x = Distance between the centres of two shafts,
N 1 = Speed of the driver,
T 1 = Number of teeth on the driver,
d1 = Pitch circle diameter of the driver,
N 2 , T 2 and d2 = Corresponding values for the driven or follower, and
pc = Circular pitch.
We know that the distance between the centres of two shafts,
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- Fall '08