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Conn-Rod Mechanism

The connecting rod mechanism

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The connection rod (conn-rod) mechanism

A connecting rod - conn-rod - mechanism converts rotating motion to reciprocating motion - or vice versa.

The position of the rod can be expressed as

s = r (1 - cos φ) + (λ / 2) r sin2φ                                (1)


s = position of the rod (m)

r = radius of crank (m)

φ = ω t

   = 2 π ns t

   = angular position of crank (rad)

ω = crank angular velocity (rad/s)

t = time (s)

ns = revolution per second (1/s)

λ = r / l

   = crank ratio

l = length of rod (m)

The velocity of the rod can be expressed as

v = ω r sin φ (1 + λ cos φ)                               (2)


v = velocity of rod (m/s)

The acceleration of the rod can be expressed as

  a = ω2 r (cos φ + λ cos 2φ)                                (3)


a = acceleration of rod (m/s2)

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