As Unmanned Aerial Vehicles (UAVs) become more commonly used in industry, their performance will continue to be challenged. A performance bottleneck that is crucial to overcome is the design of electric propulsion systems for UAVs that operate in disparate flight modes (e.g., hovering and forward-moving flight). While flight mode dissimilarity presents a fundamental design challenge for fixed-geometry propulsion systems, variable-geometry systems such as the Variable Pitch Propeller (VPP) ones are able to provide superior propulsion performance across a wide range of flight modes. This work builds on previous work by the authors and presents a VPP system control and estimation framework for safe, near-minimum-electrical-effort propulsion system behavior across the whole operation state space of any UAV. Multiple simulated validations are presented to support the feasibility of the approach.

In response to an abundance of applications, Unmanned Aerial Vehicles are being called upon to perform missions of high difficulty for increasingly long periods of time. Traditional paradigms of propeller design and actuation are reaching a design ceiling, motivating creative approaches to the design of propeller-based propulsion mechanisms. Within the last decade, one particular kind of mechanism, the variable-pitch propeller, has been studied by researchers for its applications to the class of small UAVs. This paper pushes for new results in this area by exploring the use of Variable Pitch Propulsion (VPP) to minimize power consumption for small, versatile UAVs. A control algorithm is presented to minimize the consumed electrical power during a quasi-steady propulsive state. In particular, the algorithm is not confined to operation in limited regions of the state space, but it seeks to minimize power at whatever point in the state space a steady state is reached. Several experimental results are presented to validate the approach.

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.

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.