UCLA

Multirotor aerial platforms have obtained growing attentions in industry and academia, for its simplicity in mechanical structure, agility in maneuverability and ability for vertical take-off and landing (VTOL). Conventional multirotor has underactuated dynamics, and can not be fully controlled in 6 Degree-of-Freedom (DoF). In fact, only its three-dimensional position and yaw angle, called the flat outputs, can be controlled independently. However, for certain applications, such as perching on a vertical vertical wall or flying in a narrow space, the the non-flat outputs, the roll and pitch angles, are independently specified from the position requirements at some particular time. These tasks require the independent control of position and attitude at least partially for certain instants, and are generally challenging for multirotor platforms.

This dissertation addresses this issue in two aspects. Firstly, an algorithm is designed for the conventional quadcopter platforms to generate trajectories for tasks with requirements on both position and attitude. It is formulated as an optimization, and converted into a series of convex problems to solve. Constraints on dynamics, space limitations, inputs and states are explicitly included. The algorithm is verified numerically on the task of quadcopter perching at the specified location on a vertical wall.

Secondly, a fully actuated multirotor aerial platform is proposed. Commercial quadcopters and passive hinges are used to generate tiltable thrust vectors during flight. This platform has a salient feature for mechanical simplicity, as it does not require additional actuators to control the directions of thrust vectors. A controller for the proposed multirotor platform is designed to enable independent control of position and attitude.

The proposed multirotor platform has overactuation in dynamics, which renders a redundancy of 2 DoF for inputs. A new controller is proposed, under which the input allocation scheme searches within this redundancy for smaller thrust forces required to hover at different attitudes. The range of achievable attitudes is enlarged under this new scheme compared with the previously proposed controller, under the same thrust saturation limit for the platform actuators.

These controllers are validated with both simulation and experiments and demonstrated by the proposed multirotor aerial platform hovering at non-horizontal attitudes, or tracking independent trajectories for position and attitude simultaneously.