An epicyclic gear train (also referred to as planetary gear) includes two gears mounted so that the centre of one equipment revolves Conveyor Chain around the center of the other. A carrier links the centres of both gears and rotates to carry one gear, called the planet gear or planet pinion, around the additional, called the sun gear or sun wheel. The planet and sun gears mesh so that their pitch circles roll without slide. A point on the pitch circle of the earth equipment 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 teach can be assembled therefore the planet equipment rolls within the pitch circle of a fixed, outer gear band, or ring gear, sometimes called an annular gear. In cases like this, the curve traced by a spot on the pitch circle of the earth 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 instance, the ring gear is normally fixed and sunlight gear is driven.
Epicyclic gears obtain name from their earliest application, that was the modelling of the actions of the planets in the heavens. Believing the planets, as everything in the heavens, to end up being perfect, they could only travel in ideal circles, but their motions as seen from Earth cannot be reconciled with circular movement. At around 500 BC, the Greeks invented the idea of epicycles, of circles venturing on the circular orbits. With this theory Claudius Ptolemy in the Almagest in 148 AD was able to predict planetary orbital paths. The Antikythera System, circa 80 BC, got gearing which was in a position to approximate the 
moon’s elliptical path through the heavens, and actually to improve for the nine-season precession of that path.[3] (The Greeks could have seen it not as elliptical, but instead as epicyclic motion.)