The lengths of the links of a 4-bar linkage with revolute

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The lengths of the links of a 4-bar linkage with revolute pairs only are p, q, r and s units. Given that p < q< r< s. Which of these links should be the fixed one, for obtaining a "double crank" mechanism?

1. links of length p
2. links of length q
3. link of length r
4. link of length s

Correct Option: A

To obtain a “DOUBLE CRANK MECHANISM” shortest link is always fixed. While obtaining a “DOUBLE LEVER MECHANISM”, the link opposite to the “SHORTEST LINK” is fixed.