The yaw motion is the rotation of the quadcopter in the horizontal plane. As stated earlier, two propellers rotate in a clockwise direction and the other two propellers rotate in a counter-clockwise direction. These pairs of propellers produce the reaction Moments in opposite directions. If the reaction Moments produced by each of propeller pairs is equal and opposite, then there is no yaw motion. If the rotation Moment produced by one pair of propellers is more than the Moment produced by the other pair of propellers, then there is a net resultant Moment produced, which causes the rotation of the quadcopter about its vertical axis.
The condition for rotation motion is:
The equation of motion is: