Input: pink gear that makes two blue cranks of two identical planetary mechanisms rotate at the same velocity and direction.
Z2 = 2.Z1
Z2 and Z1 are tooth numbers of grey and green gears, respectively.
Radius of cranks (blue and green) R = 1/2 Pitch diameter of the green gear.
The mechanism is set so as when the blue cranks are vertical, the green cranks are vertical too.
Yellow platform has revolution joints with the green cranks. Center distance of platform joints is equal to center distance of two grey gears.
The platform is translated vertically along an absolute straight line (no need of a runway).
Its stroke length L = 4R.