Theory of Machine
To obviate axial thrust, following gear drive is used

Double helical gears having identical teeth
Mutter gears
Single helical gear in which one of the teeth of helix angle a is more
Double helical gears having opposite teeth

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Theory of Machine
Crowning on pulleys helps

For automatic adjustment of belt position so that belt runs centrally
In decreasing the slip of the belt
Increase belt and pulley life
In increasing velocity ratio

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Theory of Machine
The secondary unbalanced force due to inertia of reciprocating parts in a reciprocating engine is given by (where m = Mass of reciprocating parts, ω = Angular speed of crank, r = Radius of crank, θ = Angle of inclination of crank with the line of stroke, and n = Ratio of the length of connecting rod to radius of crank)

m.ω².r (cos 2θ/n)
m.ω².r sinθ
m.ω².r cosθ
m.ω².r (sin 2θ/n)

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Theory of Machine
The inversion of a mechanism is

Obtained by fixing different links in a kinematic chain
Turning its upside down
Obtained by reversing the input and output motion
Changing of a higher pair to a lower pair

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