Mechanism for reversing rotation direction.
i = n1/nc = 1 - ((Z2.Z4)/(Z1.Z3)
nc: velocity of the blue crank.
n1: velocity of the orange gear, its tooth number: Z1 = 20.
Z2 = 40 (yellow gear); Z3 = 30 (pink gear); Z4 = 30 (fixed green gear)
Z1 + Z2 = Z3 + Z4
i = - 1
The blue crank and the orange gear have equal velocity but rotate in opposite directions.