  Nonlinear PID control systems for a quadrotor UAV are proposed to follow an
attitude tracking command and a position tracking command. The control systems
are developed directly on the special Euclidean group to avoid singularities of
minimal attitude representations or ambiguity of quaternions. A new form of
integral control terms is proposed to guarantee almost global asymptotic
stability when there exist uncertainties in the quadrotor dynamics. A rigorous
mathematical proof is given. Numerical example illustrating a complex maneuver,
and a preliminary experimental result are provided.
