Pantograph for drawing straight lines 1a

Blue, orange, green and yellow bars create a pantograph. Two red pins and blue one are in line. The blue pin traces a straight line (in green). Condition for tracing a straight line: R1/R2 = AE/EF R1: radius of pink crank R2: radius of violet crank Its length L = 2R2 2 (R1 R2)(FE/AF) The direction of the line depends on angular position between pink and violet cranks at starting position of the mechanism. For the starting position in this video, the line is vertical.