Presented in this paper are the design and experiments for a transformable Vertical Take Off and Landing (VTOL) UAV. This work demonstrates shape-shifting transformation, building upon the conceptual designs put forth in [1] and [2], along with hardware prototyping and component testing from [3]. A deterministic model is presented to characterize the flight of the MIST-UAV in simulation. Experimental results from the platform demonstrate for the first time successful in-air transformation from multi-rotor, tail-sitter, and fixed-wing operation. Experiments also validated transformation repeatability, successfully testing multiple sequential transformations.

Aerial robotic platforms are an increasingly sought-after solution for a variety of sensing, monitoring, and transportation challenges. However, as invaluable as unmanned aerial vehicles (UAVs) have been for these applications, fixed-wing and multi-rotor systems each have individual limitations. Fixed-wing UAVs are generally capable of high-altitude surveillance and long flight times, while quad-rotors are most effective when used for their maneuverability and close-quarters surveying. This paper improves upon the prototypes discussed in [1] by creating a series of three next-generation prototypes to isolate the aspects of solar powered fixed-wing flight, quad-rotor flight, and transformation modes of the SUAV:Q platform. Improvements to the transformation mechanism, airframe design, variable pitch propulsion system, and custom-designed power electronics are presented along with validation of the designs through empirical testing.

Given the wide variety of flight conditions typically encountered by fixed-wing aerial vehicles, the flight performance of a solar-powered unmanned aerial vehicle (SUAV) depends on many factors. Predicting the performance for a given application requires characterization of both system and environmental components. Furthermore, a SUAV with a transformable airframe increases the number of characterizable states, where each state features a unique set of capabilities. This results in significant differences with respect to power consumption, solar panel orientation, and increases the design limitations on system components. This paper characterizes the energy collection, propulsion, and power electronics subsystems of a transformable SUAV developed at the University of Minnesota. Clear-sky and solar panel models are used to predict the power available for a given location and time. Propulsion system design is validated with flight data, and a proposed model correlates propulsion limits with available energy. Power electronics are modeled and simulated to determine hardware and tracking algorithm efficiencies. Finally, a pulsed battery charging methodology is implemented in hardware and evaluated against conventional charging techniques.

Selecting an aerial platform for an application typically requires compromise. A choice must be made between the flight time and long-range capabilities of a fixed-wing aircraft or the maneuverability and stationary characteristics of a multi-rotor platform. Recent developments of small-scale solar-powered UAVs have leveraged the advances in solar cell, energy storage, and propulsion system technology to reach extended flight times capable of all-day and multi-day flight. This paper presents the concept of a small-scale hybrid unmanned aerial vehicle capable of augmenting the maneuverability of a quad-rotor with the energy collection and supply of a solar-powered fixed-wing aircraft. An investigation into the aircraft design, transforming mechanism, and energy management of the multi-state system is presented. A proof-of-concept prototype has been constructed to demonstrate the airframe operating in a quad-rotor configuration. Power electronics capable of simultaneous battery charging and power loading from a solar array have been validated. Additional work in optimization of the propulsion system and airframe needs to be completed to maximize the performance of the hybrid system.

Throughout the wide range of aerial robot related applications, selecting a particular airframe is often a trade-off. Fixed-wing small-scale unmanned aerial vehicles (UAVs) typically have difficulty surveying at low altitudes while quadrotor UAVs, having more maneuverability, suffer from limited flight time. Recent prior work [1] proposes a solar-powered small-scale aerial vehicle designed to transform between fixed-wing and quad-rotor configurations. Surplus energy collected and stored while in a fixed-wing configuration is utilized while in a quad-rotor configuration. This paper presents an improvement to the robot's design in [1] by pursuing a modular airframe, an optimization of the hybrid propulsion system, and solar power electronics. Two prototypes of the robot have been fabricated for independent testing of the airframe in fixed-wing and quad-rotor states. Validation of the solar power electronics and hybrid propulsion system designs were demonstrated through a combination of simulation and empirical data from prototype hardware.

Unmanned solar powered aircraft offer a unique set of advanced capabilities and have set general aviation records for longest continuous flight and greatest sustained altitude. However, the application of solar powered flight to small scale solar powered unmanned aerial vehicles (UAVs) has seen sparse research activity and is only partially explored. The use of solar power as an energy resource allows small scale UAVs to carry heavier, more powerful sensor payloads, and can extend flight times to over 24 hours, thereby achieving multi-day flight. This work focuses on recent developments by the Center for Distributed Robotics on a four meter wingspan solar UAV designed for low altitude aerial sensing applications. Highlighted in this paper are aspects of airframe, propulsion, and electronics hardware design as well as experiments that quantify the solar power system and airframe performance.

Small ground robots remain limited in their locomotion capabilities, often prevented from accessing areas restricted by tall obstacles or rough terrain. This paper presents the improved design of a hybrid-locomotion robot made to address this issue. It uses wheels for ground travel and rotary-wing flight for scaling obstacles and flying over rough terrain. The robot's initial design suffered from a number of issues that prevented it from functioning fully, such as overheating motors, inadequate control electronics, and insufficient landing gear. Several improvements have been made to the robot's design to correct these problems. These obstacles, and the solutions implemented in the improved design, have enabled several design principles to be formulated for miniature hybrid-locomotion robots. It is found that hybrid-locomotion vehicles utilizing rotary-wing flight are most useful when the design is optimized for ground mode performance. Collapsibility is necessary in such vehicles to reduce the impact of the helicopter rotor on the size of the ground mode. Finally, since a large number of actions are necessary to propel and transform the robot, integrating multiple functions into each mechanism can reduce the mass of the robot.