A special case of the 4-bar linkage.
Input: pink conrod.
Output: oscillating cranks.
The unusualness: a working cycle of the mechanism corresponds 2 revolutions of the input. Oscillating angle of the yellow crank is 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 opposite links is equal to the sum of the lengths of the other two links.
A + B = C + D
A: length of pink conrod (=10)
B: length of green crank (=35)
C: length of yellow crank (=15)
D: distance between fixed axes of cranks (=40)
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.