  This paper develops an adaptive digital autopilot for quadcopters and
presents experimental results. The adaptive digital autopilot is constructed by
augmenting the PX4 autopilot control system architecture with adaptive digital
control laws based on retrospective cost adaptive control (RCAC). In order to
investigate the performance of the adaptive digital autopilot, the default
gains of the fixed-gain autopilot are scaled by a small factor, which severely
degrades its performance. This scenario thus provides a venue for determining
the ability of the adaptive digital autopilot to compensate for the detuned
fixed-gain autopilot. The adaptive digital autopilot is tested in simulation
and physical flight tests, and the resulting performance improvements are
examined.
