Abstract: An irregular-motion mechanism comprising two series-connected double cranks each comprising a driving link and a driven link connected thereto by a connecting rod, the driving link of the first double crank and the driven link of the second double crank being mounted for rotation about a common axis, the driven link of the first double crank being rigidly joined to the driving link of the second double crank, the driven link of the first double crank forming an obtuse angle with the driving link of the second double crank the ratio of their lengths being about 2:3 with a length-ratio range of about 3:2 to 5:4 for the driving link of the first double crank and the driven link of the second double crank, and with a length ratio of about 1:1 for the connecting rods of the first and second double cranks. The device provides a considerable increase in power in the extreme positions of irregularity because of the obtuse angle.