An unmanned aerial vehicle (UAV) is an aircraft that does not carry a human operator. It is normally a powered aircraft that relies on aerodynamic forces to provide motion. This motion is controlled either by onboard computer (autonomous) or by remote control. Accurate methods of detecting and reacting to the UAVs environment are being developed; making some modern UAVs are virtually crash-proof (Merz & Kendoul 2013).
Quad rotors are symmetrical vehicles with four equally sized rotors at the end of four equal length rods. Early designs of quad rotors were completed in the 1920‟s by Etienne Omichen, Dr. George de Bothezat and Ivan Jerome. These designs, however, never truly grasped the attention of the public or the in case of Dr Bothezat and Jerome the military. Therefore, neither Omichen’s or Bothezat and Jerome’s were mass produced. This fact, however, does not discredit the advantages of quad rotors. Unlike their counter parts, quad rotors make use of multiple rotors allowing for a greater amount of thrust and consequently a greater amount of maneuverability. Also, the quad rotors symmetrical design allows for easier control of the overall stability of the aircraft. Each of the rotors on the quad-rotor helicopter produces both thrust and torque. Given that the front and rear motors both rotate counter-clockwise and the other two rotate clockwise, the net aerodynamic torque will be zero, as seen in Figure 1.0