UC Berkeley

Aerial vehicles for physical interactions as a form of a freely-floating manipulator are ofgrowing interest in recent times. Aerial vehicles like quadrotors enable us to address issues such as last-mile delivery and search & rescue. Using multiple such vehicles collaboratively increases the scope of manipulation beyond what a single vehicle can achieve. This dissertation presents theoretical and experimental contributions toward using multiple quadrotors for collaborative tasks, with an emphasis on cable-suspended payloads.

The dissertation studies the problem of collaborative aerial manipulation from two overarchingviews. The first half of the dissertation has an “individualistic view” and presents methods and algorithms for a single quadrotor/quadrotor with a cable-suspended payload. An L1 adaptation scheme is implemented on a geometric attitude control for the quadrotor on SO(3) in the presence of model uncertainties and disturbances. Next, the extended Kalman filter is modified to estimate states on S2. The concept of variation on manifolds is employed to linearize the system states and compute the variations in the state. Optimal and obstacle-free trajectories for a quadrotor with a suspended payload are generated using direct collocation. The planning method exploits the differential flatness for generating the trajectories in the flat space and converts non-differentiable obstacle avoidance constraints into smooth constraints using dual variables.

The second part of the dissertation has a “collaborative view” and presents results for twotypes of aerial manipulation, multiple quadrotors carrying a payload using suspended cables (parallel-aerial-manipulator) and a series of quadrotors connected using a flexible cable (serial-aerial-manipulator). The dissertation presents experimental results for grasping and controlling payload using a cable-suspended gripper using more than one quadrotor. Finally, the dissertation models and computes coordinate-free geometric dynamics for multiple quadrotors connected in series using a single flexible cable and shows that the system is differentially-flat.