Perching Using a Quadrotor with Onboard Sensing

This thesis presents an implementation of autonomous indoor perching using only onboard sensors on a low-cost, custom-built quadrotor. The perching aggressive maneuver is representative of a class of control problems for aerobatics that requires an agile and robust control system for maneuvering accurately at high speeds. Such research extends the typical functionality of micro air vehicles (MAV) from low speed and stationary observation to dynamic aerobatic transitions for broader operational capabilities including confined landings and evasive maneuvering. To achieve this, three major challenges are overcome: precise and real-time positioning, sensing of the perch and path to the perch, and control methods for robust and accurate tracking at high speeds. Navigation in unstructured, global positioning system (GPS)-denied environments is achieved using a visual Simultaneous Localization and Mapping (SLAM) algorithm that relies on an onboard monocular camera. A secondary camera, capable of detecting infrared light sources, is used to locate the pathway for the maneuver and the perch, simulating sensing of the actual perch, for perching without prior knowledge of the location of the perch. The full physical system architecture is covered in detail, indicating the components and integration necessary to obtain effective aggressive control of an inexpensive quadrotor. The difficulties of attitude stabilization on noisy and lower-quality sensors are successfully addressed so that the air vehicle can be treated as a simple second-order system for the purposes of navigation and response to dynamic maneuvering commands. The system utilizes nested controllers for attitude stabilization, vision-based navigation, and perching guidance, with the navigation controller implemented using novel nonlinear saturation control within a Proportional-Integral-Derivative (PID) structure. The quadrotor is therefore able to autonomously sense the perch, reach initial high speeds for obtaining rapid deceleration from aerodynamic effects, dynamically transition to a high angle of attack post-stall configuration, and make a low-speed accurate landing on an inclined surface, using only onboard sensors.