Ep'i-cy-cloid'al, a.

a. Pertaining to the epicycloid, or having its properties.

Epicycloidal wheel, a contrivance for securing parallel motion in converting reciprocating motion into circular, depending on the principle that an inner epicycloidal curve becomes a straight line when the diameter of the fixed circle is just twice that of the rolling one. It consists of a fixed ring with teeth on the inside, into which is geared a wheel of half its diameter; to a pin in the circumference of this wheel the reciprocating motion is communicated, while the center of the wheel describes a circle, and may receive the pin of a crank whose shaft is concentric with the ring.