Quadcopters (Figure 1) are aerial vehicles with 4 propellers that produce a vertical thrust similar to a helicopter, but unlike a helicopter, no tail rotor is required for stability. The Quadrotor’s attitude (aircraft orientation relative to the vehicle’s center of gravity) is completely controlled by four propellers and a control system programmed on a microcontroller. Figure 2 shows the three axes of rotation on which the aircraft’s attitude is defined.

Roll, pitch, and yaw are controlled by increasing and decreasing the thrust produced by sets of motors. Figure 3 shows the top view of AirWolf II along with the rotational direction of the propellers and the associated motor numbers (motor numbers are used for the AeroQuad Shield v1.9).

A right side roll of the aircraft is performed, for example, by increasing the thrust produced by motor set 1 and 4 while decreasing the thrust produced by set 2 and 3. Similar logic is applied to explain the control of pitch. While the explanation of roll and pitch are fairly straight forward, the explanation of how yaw is controlled is more interesting. The control of yaw is explained by the resulting torque produced by a motor. When the motor applies a torque to a propeller, a counter torque is applied to the aircraft. This counter torque phenomenon is the reason why a standard helicopter must have a tail rotor to compensate for the torque produced by the main engine. Quadcopters, on the other hand, use the torque produced by sets of propellers/motors to control yaw. For example, increasing the torque produced by motor set 1 and 2 while decreasing the torque produced by set 3 and 4 will cause a counter-clockwise rotation about the yaw axis.

Now that a rudimentary understanding of quadrotor helicopters has been established (the complexity of flight dynamics and microcontrollers will not be covered in this report), an analysis of the aircraft can be performed. The next section of this report covers static thrust and its relevance to quadcopters.


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