Quad Copters or multi rotor models utilise three, four or more independent motors to provide control flight, acting as a lift mechanism rather than a propulsion source. controlling the individual speed of each motor allows for controlled bank, yaw, and pitch control as well as height ans speed.
Skyartec have produced the Butterfly Quad Copter with 4 rotors. This Quadcopter features 3 axis gyro and three axis accelerometer and three axis Angluar Rate Sensor. This provides excellent stability of flight whilst retaining control and performance.