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Pantograph for drawing ellipses

Blue, orange, green and yellow bars create a pantograph.

Two red pins and blue one are in line.

R1/R2 ≠ AE/EF

R1: radius of pink crank

R2: radius of violet crank

The blue pin traces an ellipse (in green).

Its size depends on radii of pink and violet cranks.

The direction of the ellipse depends on angular position between pink and violet cranks at starting position of the mechanism.

For the starting position in this video, the ellipse is horizontal.

Its semi axes:

d = R2 + (R2 + R1)(EF/AF)

c = R2 + (R2 - R1)(AE/AF)

Its center O lays on O1O2:

OO2 = O1O2(EF/AF)

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