Gears are toothed machine part and round in shape like a wheel or cylinder used to transmit power. The gears teeth are mesh with one another in order to transmit torque or to change speed.

Cycloidal gears is subcategory of gears used in mechanical clocks. Whenever the teeth make contact, an imaginary circle is drawn at the center of either gear.  The curve outside the pitch circle is called addenda, and the curve inside the pitch circle is called dedenda. The wheel teeth of addenda are convex epi-cycloidal and the dedenda are concave hypocycloidal curves.

To obtain conjugate action Cycloidal gears requires two different curves. Conjugate action is one in which at a constant angular velocity a gears rotates. Rolling gears is used to generate the tooth profile which helps the outer edge to roll one of the gear wheels. The gears ratio is same as the velocity ratio at a constant velocity.  

Whenever the teeth are in contact one gear drives another gear by putting pressure on it. When the gears rotates the teeth are disengage with one another.

Cycloidal gears are used in industrial applications as speed reducer, geroter pump and many more. It is also used in the design of foots blower rotors, mechanical clocks, automobile and so on. They are expensive. They are light in weight, have fewer breakdowns and fewer sliding friction. They are easy to use and perform efficient operation.