An epicyclic gear teach (also referred to as planetary gear) consists of two gears mounted to ensure that the centre of 1 equipment revolves around the centre of the various other. A carrier connects the centres of the two gears and rotates to transport one gear, called the earth gear or planet pinion, around the additional, called the sun gear or sunlight wheel. The earth and sunlight gears mesh to ensure that their pitch circles roll without slide. A point on the pitch Transmission Chain circle of the earth gear traces an epicycloid curve. In this simplified case, the sun gear is set and the planetary equipment(s) roll around sunlight gear.
An epicyclic gear train can be assembled so the planet gear 
rolls within the pitch circle of a set, outer gear ring, or ring gear, sometimes named an annular gear. In this instance, the curve traced by a point on the pitch circle of the planet is a hypocycloid.
The mixture of epicycle gear trains with a planet engaging both a sun gear and a ring gear is called a planetary gear train.[1][2] In this case, the ring equipment is usually fixed and sunlight gear is driven.
Epicyclic gears obtain name from their earliest app, which was the modelling of the motions of the planets in the heavens. Believing the planets, as everything in the heavens, to become perfect, they could just travel in perfect circles, but their motions as viewed from Earth cannot become reconciled with circular movement. At around 500 BC, the Greeks developed the idea of epicycles, of circles venturing on the circular orbits. With this theory Claudius Ptolemy in the Almagest in 148 AD could predict planetary orbital paths. The Antikythera Mechanism, circa 80 BC, acquired gearing which was in a position to approximate the moon’s elliptical path through the heavens, and actually to improve for the nine-year precession of that route.[3] (The Greeks could have seen it not as elliptical, but instead as epicyclic motion.)