The lengths of the links comply with the conditions: A͞B=C͞D and B͞D=A͞C. Thus, links 1, 2, 3 and 4 form crossed-crank linkage ABDC. When link 1 is turned about fixed axis O, link 4 is turned in the opposite direction about fixed axis O₁. The whole wagon turns about point P which is the instantaneous centre of rotation.
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