The animated figure shows two possibilities for generating an epitrochoid (or epicycloid) with three cusps. This curve can be generated by the rolling of two circles, where the ratio of the radii equals 3:1 (red and blue circle), or 3:4 (red and green circle). The evolute is again a curve of the same type. It is enveloped by the normals (cyan) of the original curve. Note that the normals intersect the red circles in the corresponding points of contact of the two rolling circles.