An Stainless Steel Chain Epicyclic gear teach (also called planetary gear) contains two gears mounted to ensure that the 
centre of one equipment revolves around the centre of the other. A carrier connects the centres of the two gears and rotates to carry one equipment, called the planet gear or planet pinion, around the other, called the sun gear or sun wheel. The earth and sun gears mesh to ensure that their pitch circles roll without slide. A point on the pitch circle of the planet gear traces an epicycloid curve. In this simplified case, sunlight equipment is set and the planetary equipment(s) roll around sunlight gear.
An epicyclic gear teach can be assembled so the planet equipment rolls on the inside of the pitch circle of a fixed, outer gear ring, or ring equipment, sometimes named an annular equipment. In cases like this, the curve traced by a point on the pitch circle of the planet is a hypocycloid.
The combination 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 cases like this, the ring equipment is usually fixed and sunlight gear is driven.
Epicyclic gears obtain name from their earliest application, which was the modelling of the motions of the planets in the heavens. Believing the planets, as everything in the heavens, to end up being perfect, they could just travel in perfect circles, but their motions as seen from Earth could not be reconciled with circular movement. At around 500 BC, the Greeks developed the thought of epicycles, of circles traveling 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, got gearing which was in a position to approximate the moon’s elliptical route through the heavens, and even to correct for the nine-yr precession of that route.[3] (The Greeks would have seen it not as elliptical, but rather as epicyclic motion.)