The pitch and roll motion is the rotation of the quadcopter about its horizontal axis. In this case, the opposite pairs of propellers produce unequal forces, which cause net non-zero moments.

Condition for linear motion:

Equation of motion:

These cause the rotation of the quadcopter about its horizontal axis. For linear motion in the horizontal plane, the pitch (Φ) and roll (ϴ) angles must be non-zero. This causes non-zero components of Thrust in a horizontal direction. This force causes resultant Moments in the horizontal plane.