A special case of the 4-bar linkage.
Input: pink crank.
Output: oscillating green crank.
The unusualness: a working cycle of the mechanism corresponds 2 revolutions of the input. 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 opposite links is equal to the sum of the lengths of the other two links.
A + B = C + D
A: length of pink crank (=10)
B: length of green crank (=40)
C: length of yellow conrod (=35)
D: distance between fixed axes of cranks (=15)
2. There are measures to overcome dead positions (when green crank is in line with yellow conrod). For example, inertia of the green crank must be big enough.