Quadrotor

A quadrotor is a rotary wing aircraft similar to a helicopter but with four rotors, all
providing vertical lift. The Aeryon Scout is a type of quadrotor. It uses four separate electric motors, each directly drives one rotor. Varying each motor's speed controls the generated thrust and thereby the orientation of the vehicle.

A quadrotor is mechanically simple, compared to a helicopter; however, stabilizing a quadrotor requires numerous sensors and a complex control system.

Theory of operation

Two of the rotors rotate clockwise (front and back). The other two rotate counter clockwise (left and right). This counter rotation provides torque balance so that, unlike a helicopter, no tail rotor is required. All rotors are fixed pitch, making the design mechanically simple compared to a conventional helicopter. During steady state flight all rotors turn at approximately the same speed, producing the same lift and torque.

Pitch and roll are controlled by varying the speed of opposing pairs of rotors. For example, to pitch the aircraft forward, the front rotor speed is decreased while the rear increased by the same amount. Total lift is kept constant and since the front and rear rotors turn the same direction, the total torque around the yaw axis is constant. Similarly to roll right, the right rotor speed would be decreased and the left rotor increased.

Yaw is controlled by adjusting the relative speed of the clockwise and counter-clockwise rotors. For example, to yaw right, the left and right rotor speed would be increased and the front and back decreased, all by the same amount. Vertical speed is controlled by adjusting the total lift from all four rotors. To climb or increase rate of climb, all four rotor speeds are increased equally. Horizontal flight is controlled in the same manner as a helicopter. The quadrotor is pitched or rolled to accelerate in a desired direction. For example, it is pitched forward to accelerate into forward flight.