Input: green shaft to which blue crank is fixed.
The blue crank traces an ellipse (in pink).
Angle between green and crank A = 0 deg. (in this video) or 180 deg.
For case A = 0 deg. the ellipse semi-axes are B and (B-G).
For case A = 180 deg. the ellipse semi-axes are B and (B+G)
B: radius of the blue crank.
G: radius of the green crank.
Disadvantage: the input shaft bearing is not stationary.