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R5914 Pages: 2

(a) What are the advantages and disadvantages of involute gears over cycloidal (6)
gears?

(b) List the advantages of helical gears over spur gears? (4)

Two gear wheels mesh externally and are to give a velocity ratio of 3 to 1. The (10) teeth
are of involute form, module is 6 mm, addendum is one module, and pressure angle is
20°. The pinion rotates at 90 rpm. Determine ( i) The number of teeth on the pinion to
avoid interference and the corresponding number of teeth on the wheel (ii) The length of
path of contact and arc of contact (iii) The number of pairs of teeth in contact, and (iv)
The maximum velocity of sliding.

PART ^
Answer any four full questions, each carries 10 marks.
What is a gear train? Explain with neat sketches the different types of gear (10)
trains.

An internal wheel B with 80 teeth is keyed to a shaft F. A fixed internal wheel C (10 )
with 82 teeth is concentric with B. A compound wheel D-E gears with the two internal
wheels; D has 28 teeth and gears with C while E gears with B. The compound wheels
revolve freely on a pin which projects from a disc keyed to a shaft A, co-axial with F. If
the wheels have the same pitch and the shaft A makes 800 r.p.m., what is the speed of the
shaft F?

a) Explain the different tasks involved in the kinematic synthesis of mechanisms.
(6) b) Explain Chebyshev’s precision points. (4)

a) Explain the different types of kinematic synthesis with examples. (6) b)
Explain the overlay method of synthesis. (4)

Derive a relation for Freudenstein’s equation for the synthesis of mechanisms.
(10)

Synthesize a four bar mechanism by using three precision points to generate y = (10) ‏أ‎ 5,

where ‘x’ varies between 1 and 4. Assume 0, = 30; 00,.00000°O0OO,= 90°:

OOOOOOOO[DOTake the length of the fixed link as 25 ൩൩.

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