Integrated solution to quadrotor stabilization and attitude estimation using a pan and tilt camera

This work proposes a cascaded architecture comprising a nonlinear attitude observer and a nonlinear controller for position and attitude stabilization of a quadrotor. The attitude estimates are obtained from rate gyros measurements, corrupted by bias, and image coordinates from a set of landmarks on the terrain, obtained by a controllable pan and tilt camera. Lateral-longitudinal stabilization is achieved with a nested saturation control law by feedback of the image measurements, estimated body attitude, and corrected rate gyros measurements. The vehicle is stabilized vertically using an additional vertical position sensor. Due to the input-to-state stability property of controller, the quadrotor position and attitude are shown to converge to the desired equilibrium point and the convergence is robust to the estimation errors. Additionally, the pan and tilt camera is actively actuated to keep the landmarks visible in the image sensor for most operating conditions. The performance of the proposed ensemble is illustrated with some simulation results.