Design of a Transformable Unmanned Aerial Vehicle

Abstract

The development of spatially capable and energy efficient unmanned aerial vehicles (UAVs) has long been a necessity for applications ranging from sensing and inspection to search and rescue and package delivery. Recently, the commercial availability of high performance actuators, energy dense batteries, and efficient embedded systems have enabled tremendous growth in the use of small-scale aerial vehicles. Aerial vehicles typically come in the form of either fixed-wing or multi-rotor platforms. Although fixed-wing platforms offer greater efficiency and range, they lack the maneuverability and hovering capabilities of a multi-rotor platform which can be critical to satisfying mission objectives. Due to the physics of traditional energy strategies, both types of platforms suffer from a limited flight time, making them unfit for supporting many applications to their greatest fruition. The work presented in this thesis solves these challenges through the introduction of a first-of-a-kind class of UAVs called the Transformer UAV. Platforms that fall under the Transformer UAV class are capable of vertically taking off in the configuration of a multi- rotor and once in air, transforming into the shape of a fixed-wing aircraft. The Transformer UAV class can transform between flight states while in the air, supporting both the higher efficiency of a fixed-wing UAV, and also being able to operate with the precise maneuver- ability and hovering capability of a multi-rotor UAV. Air-to-air transformation is made possible through a cascaded control approach to manage several control surfaces, propellers, and servo driven hinges across the system. Initially, an overview and background information on UAVs is presented. An introduction to the aerodynamics of UAVs is also made. The intent of this section is to cover key principles that guide the design of multi-rotor and fixed-wing flight. Details covering the existing classes of UAVs is presented and a discussion of hybrid-VTOL platforms is made. A case is made for the introduction of a first-of-a-kind Transformer UAV class which is then introduced. Details regarding the design approach and considerations for the Transformer UAV class are made. This design process is divided into sections describing the energetics, aerodynamics, airframe design, mechanism design, electrical hardware design, propulsion system selection, and power measurement. Given the particularly unique flight modality of the Transformer UAV class, a flexible approach to the control architecture of the platform is presented. This control architecture distributes the actuation effort for attitude and position control over the four control surfaces and four propulsion systems as a function of airframe geometry. An open-source multi-degree-of-freedom flight simulator is developed and presented. The purpose of this simulator is to provide an experimental environment to rapidly develop and iterate sophisticated multi-body aircraft. These multi-body aircraft are often beyond the scope of most traditional flight simulators. The software architecture for the simulator is outlined, illustrating the generalization and ease of implementation. The control architecture of the Transformer UAV class is implemented in the simulator and several tests characterizing system operation are performed. Finally, prototypes developed to achieve full transformation are described. Several instantiations of the Transformer UAV class are presented. These systems range in size and hardware complexity in order to balance system validation with the large scope nature of air-to-air transformation. Results from simulation are compared and validated with experimental prototype performance. Several indoor and outdoor experiments are performed, validating the robustness of the Transformer UAV class of prototypes.