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.
The mechanism is set so as when the blue cranks are horizontal, the green cranks are horizontal 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 horizontally along an absolute straight line (no need of a runway). Its stroke length L = 4R.
R is radius of the green crank.It is possible to set the mechanism for translation along a slanting straight line.