  Researchers have developed various cascaded controllers and non-cascaded
controllers for the navigation and control of quadrotors in recent years. It is
vital to ensure the safety of a quadrotor both in normal state and in abnormal
state if a controller tends to make the quadrotor unsafe. To this end, this
paper proposes a non-cascaded Control Barrier Function (CBF) for a quadrotor
controlled by either cascaded controllers or a non-cascaded controller.
Incorporated with a Quadratic Programming (QP), the non-cascaded CBF can
simultaneously regulate the magnitude of the total thrust and the torque of the
quadrotor determined a controller, so as to ensure the safety of the quadrotor
both in normal state and in abnormal state. The non-cascaded CBF establishes a
non-conservative forward invariant safe region, in which the controller of a
quadrotor is fully or partially effective in the navigation or the pose control
of the quadrotor. The non-cascaded CBF is applied to a quadrotor performing
trajectory tracking and a quadrotor performing aggressive roll maneuvers in
simulations to evaluate the effectiveness of the non-cascaded CBF.
