Quad-Copter

A quad-copter, also called a quad-rotor helicopter or quad-rotor is a multi-rotor helicopter that is lifted and propelled by four rotors. Quad-copters are classified as rotor-craft, as opposed to fixed-wing aircraft, because their lift is generated by a set of rotors. Quad-copters generally use two pairs of identical fixed pitch propellers; two clockwise (CW) and two counterclockwise (CCW). These use independent variation of the speed of each rotor to achieve control. By changing the speed of each rotor it is possible to specifically generate a desired total thrust; to locate for the center of thrust both laterally and longitudinally; and to create a desired total torque, or turning force.