This paper presents the modeling of a four rotor vertical take-off and landing (VTOL) unmanned air
vehicle known as the quad rotor aircraft. The paper presents a new model design method for the flight
control of an autonomous quad rotor. The paper describes the controller architecture for the quad rotor
as well. The dynamic model of the quad-rotor, which is an under actuated aircraft with fixed four pitch
angle rotors was described. The Modeling of a quad rotor vehicle is not an easy task because of its
complex structure. The aim is to develop a model of the vehicle as realistic as possible. The model is
used to design a stable and accurate controller. This paper explains the developments of a PID
(proportional-integral-derivative) control method to obtain stability in flying the Quad-rotor flying object.
The model has four input forces which are basically the thrust provided by each propeller connected to
each rotor with fixed angle. Forward (backward) motion is maintained by increasing (decreasing) speed
of front (rear) rotor speed while decreasing (increasing) rear (front) rotor speed simultaneously which
means changing the pitch angle. Left and right motion is accomplished by changing roll angle by the
same way. The front and rear motors rotate counter-clockwise while other motors rotate clockwise so
that the yaw command is derived by increasing (decreasing) counter-clockwise motors speed while
decreasing (increasing) clockwise motor speeds.