Table of Contents

Animation Of Double Crank-Locomotive Mechanism

Introduction :

When one of the links is fixed in a kinematic chain, it is called a mechanism. So we can obtain as many mechanisms as the number of links in a kinematic chain by fixing, in turn, different links in a kinematic chain.

This method of obtaining different mechanisms by fixing different links in a kinematics chain is known as inversion of the mechanism.

Types of inversion

1. Four bar chain or quadric cycle chain

Beam engine
Coupling rod of locomotive
Watt’s indicator mechanism

2. Single slider crank chain

Bull engine or pendulum engine
Oscillating cylinder engine
Rotary engine
Crank & slotted quick return mechanism
Whitworth quick return mechanism

3. Double slider crank

Elliptical trammels
Scotch yoke mechanism
Old-ham’s coupling

Coupling rod of locomotive

Coupling rod of a locomotive (Double crank mechanism). The mechanism of a coupling rod of a locomotive (also known as double crank mechanism) which consists of four links, is shown in Fig.

In this mechanism, the links AD and BC (having equal length) act as cranks and are connected to the respective wheels. The link CD acts as a coupling rod and the link AB is fixed in order to maintain a constant centre to centre distance between them. This mechanism is meant for transmitting rotary motion from one wheel to the other wheel.