Input: green crank of length L1.
Blue pulley of radius R1 is stationary.
Yellow pulley of radius R2 is fixed to yellow bar of length L2.
R1 = 2.R2
L1 = L2
A point on revolution joint of the yellow bar traces a straight line. Its length is 4.L1.
This mechanism has a relation with Cardano cycles.
If L1 ≠ L2, condition to get the said straight line: R1/R2 = 1 + (L1/L2)
The belt should be toothed.
It is possible to use chain drive instead of belt one.