epitrochoid

A curve traced out by a point that is a distance c from the center of a circle of radius b, where c < b, that is rolling around the outside of another circle of radius a. It is described by the parametric equations

x = (a + b) cos(t) - c cos[(a/b + 1)t],
y = (a + b) sin(t) - c sin[(a/b + 1)t].

Closely related to the epitrochoid are the epicycloid, hypocycloid, and the hypotrochoid. An example of an epitrochoid appears in Albrecht Dürer's work Instruction in Measurement with Compasses and Straightedge (1525).

Related category

• PLANE CURVES

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