The Elliptical Trap (also known as the Elliptical Trap or the Trammal of Archimedes) is a simple mechanism that can trace an exact elliptical path. It consists of two ferries that are confined (trapped) to channels or perpendicular rails and a rod that is attached to the shuttles by pivots in fixed positions along the bar.
As the ferries move forward and backward, each along their channel, the end of the bar moves in an elliptical path. The axes a and b of the ellipse are the distances between the end of the rod and the two pivots. An ellipsograph is an Archimedes trammel intended to extract, cut, or machine ellipses, eg. In wood or other materials in sheet. Usually the distances a and b are adjustable, so that the size and shape of the ellipse can vary.
The elliptical flap is an inversion of the double mechanism of the crankshaft chain. A double slider crank chain consists of four links forming two sliding pairs and two turning pairs. Frame and coupling.