Mechanism relates to plane hinged (lever) mechanisms and can be used for cranes design
Balanced hinge-lever mechanism
The lever is balanced if the vector sum of moments of forces acting on it equals zero.
Pa - Qb = 0,
If two forces P and Q are applied to the lever on one side from fulcrum then they must be directed to different sides for their balance (see Fig. 1b).
Fig. 1a Fig. 1b
Fig. 4 Fig. 5