A special case of the 4-bar linkage.
Input: pink conrod.
Output: oscillating green and yellow cranks.
The unusualness: a working cycle of the mechanism corresponds 2 revolutions of the driving crank (in pink) Output oscillating angles are larger than 180 deg., a thing that is hard to get by using an ordinary 4-bar linkage. It happens because:
1. The sum of the lengths of the two adjacent links is equal to the sum of the lengths of the other two links.
A + B = C + D
A: length of green crank (=40)
B: length of pink conrod (=10)
C: length of yellow crank (=36)
D: distance between fixed axes of cranks (=14)
2. There are measures to overcome dead positions (when cranks are in line with pink conrod). For example, inertia of the cranks must be big enough.