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Q.10.Explain the coupled wheels of locomotive mechanism.



Links -

link AD frame (Fixed)

link AB (Crank)

link BC (Coupling Rod)

link CD (Crank)

Pairs -

Turning Pair = AD (Frame) & AB (Crank)

Turning Pair = AD (Frame) & CD (Crank)

Turning Pair = AB (Crank) & BC (Connecting Rod)

Turning Pair = CD (Crank) & BC (Connecting Rod)


This mechanism is an inversion four bar kinematic chain . This has four turning pairs.

It is consists of frame AD which is fixed, on which two cranks AC & BD are fitted on it .The cranks are free to rotate about points A and D. Both the cranks have same lengths. Two cranks are connected to each other by means of coupling rod, which connects the other ends B and C of both cranks. At the connections B and C there is turning pair.

Working –

When link AB starts rotating about fixed point A. The rotary motion of wheel is transmitted to next wheel by means of coupling rod BC. As a result the other wheel also starts rotating in same direction and same speed, because both cranks have same radius of rotation.

Application –

The mechanism is used to connect driving & driven shaft of locomotive. Here both driving & driven wheels always rotate in same direction.