Input: pink shaft.
Two blue cranks are driven thanks to bevel gear drives.
The yellow platform is translated horizontally along an absolutely straight line (no need of a runway).
Its stroke length L = 4R.
R: length of the cranks (in blue) and bars (in green).Grey chain wheels of Z2 teeth are stationary.
Green sprockets of Z1 teeth are fixed to the green bars.
Z2 = 2.Z1