Robust Control of Vectored Thrust Aerial Vehicles via Variable Structure Control Methods

The popularity of Unmanned Aerial Vehicles (UAVs) has grown rapidly in many civil and military applications in the last few decades. Recent UAV applications include crop monitoring, terrain mapping and aerial photography, where one or several image sensors attached to the UAV provide important terrain information. A thrust vectoring aerial vehicle, a vehicle with the ability to change the direction of thrust generated while keeping the UAV body at a zero roll and pitch orientation, can serve well in such applications by allowing the sensors to capture stable image data without additional gimbals, reducing the payload and cost while increasing the flight endurance. Furthermore, thrust vectoring UAVs can perform fast forward flight as well as hover operations with non-zero pitch: features which can serve well in military applications. The first part of this research focuses on developing a comprehensive dynamic model and a low level attitude and position control structure for a tri-rotor UAV with thrust vectoring capability, namely the Vectored Thrust Aerial Vehicle. Nonlinear dynamics of UAVs require robust control methods to realize stable flight. Special attention needs to be given to wind gust disturbances, and parametric uncertainties. Sliding Mode Control , a type of Variable Structure Controller, has served well over the years in controlling UAVs and other dynamic systems. However, conventional Sliding Mode Control results in a high frequency switching behavior of the control signal. Furthermore, Sliding Mode Control does not focus on fast set-point regulation or tracking, which can be advantageous for UAVs and many other robotic systems. Taking these research gaps into account, this work presents an Adaptive Variable Structure Control method, which can acquire fast set-point regulation while maintaining robustness against external disturbances and uncertainties. The adaptive algorithm developed in this work is fundamentally different from current Adaptive Sliding Mode Control and other Variable Structure methods. Simulation and experimental results are provided to demonstrate the superiority of the proposed approach compared to Sliding Mode Control. The novel adaptive algorithm is applicable to many nonlinear dynamic systems including UAVs, robot arm manipulators and space robots. The same adaptive concept is then utilized to develop an Adaptive Second Order Sliding Mode Controller. Compared to existing Second Order Sliding Mode Control methods, the proposed methodology is able to produce reduced sliding manifold reach times and consume less amount of control resources: features which are particularly advantageous for systems with limited control resources. Simulations are conducted to evaluate the performance of the proposed Adaptive Second Order Sliding Mode Control algorithm

The aerodynamics of micro air vehicles: technical challenges and scientific issues

Micro air vehicles raise numerous design problems associated to the size reduction: lower aerodynamic and propulsion efficiencies, higher sensitivity to atmospheric turbulence, low-density energy of electric propulsion, etc. The paper discusses some of the most important design issues and analyses the aerodynamic challenges encountered in the field of MAVs. A number of novel aerodynamic configurations combining rotors and fixed-wing are proposed and discussed in order to recover efficiency and maneuverability at low speeds

Conceptual design and control of twin-propeller tail-sitter mini-UAV: Conceptual study of V-TS mini-UAV

This paper describes progress made on the design and analysis of a twin-propeller tail-sitter mini-UAV (named V-TS). Since the V-TS mini-UAV is a combination of airplanes and copters, high energy efficiency during the forward flight and VTOL capability in the hover flight are achieved. However, this configuration also brings new challenges and difficulties, especially in the case of control. Free software which was used in the design process is presented and described. AVIGLE Demonstrator is analyzed in SU2 to verify correct settings of the aerodynamic analysis. Furthermore, 3D model of the V-TS mini-UAV with the Y-tail configuration and its basic geometrical parameters are shown. The results prove that it is aerodynamically efficient for our purpose. In addition, probably all control modes, transitional flight phases, and difficulties which appear in the control of the twin-propeller tail-sitter mini-UAV are defined and solutions are proposed. The transitional flight phases are determined as a combination of the control modes and sub-modes. © 2019, Deutsches Zentrum für Luft- und Raumfahrt e.V

Experimental Investigation of Shrouded Rotor Micro Air Vehicle in Hover and in Edgewise Gusts

Due to the hover capability of rotary wing Micro Air Vehicles (MAVs), it is of interest to improve their aerodynamic performance, and hence hover endurance (or payload capability). In this research, a shrouded rotor conguration is studied and implemented, that has the potential to oer two key operational benets: enhanced system thrust for a given input power, and improved structural rigidity and crashworthiness of an MAV platform. The main challenges involved in realising such a system for a lightweight craft are: design of a lightweight and stiff shroud, and increased sensitivity to external flow disturbances that can affect flight stability. These key aspects are addressed and studied in order to assess the capability of the shrouded rotor as a platform of choice for MAV applications. A fully functional shrouded rotor vehicle (disk loading 60 N/m2) was designed and constructed with key shroud design variables derived from previous studies on micro shrouded rotors. The vehicle weighed about 280 g (244 mm rotor diameter). The shrouded rotor had a 30% increase in power loading in hover compared to an unshrouded rotor. Due to the stiff, lightweight shroud construction, a net payload benefit of 20-30 g was achieved. The different components such as the rotor, stabilizer bar, yaw control vanes and the shroud were systematically studied for system efficiency and overall aerodynamic improvements. Analysis of the data showed that the chosen shroud dimensions was close to optimum for a design payload of 250 g. Risk reduction prototypes were built to sequentially arrive at the nal conguration. In order to prevent periodic oscillations in flight, a hingeless rotor was incorporated in the shroud. The vehicle was successfully flight tested in hover with a proportional-integral-derivative feedback controller. A flybarless rotor was incorporated for efficiency and control moment improvements. Time domain system identification of the attitude dynamics of the flybar and flybarless rotor vehicle was conducted about hover. Controllability metrics were extracted based on controllability gramian treatment for the flybar and flybarless rotor. In edgewise gusts, the shrouded rotor generated up to 3 times greater pitching moment and 80% greater drag than an equivalent unshrouded rotor. In order to improve gust tolerance and control moments, rotor design optimizations were made by varying solidity, collective, operating RPM and planform. A rectangular planform rotor at a collective of 18 deg was seen to offer the highest control moments. The shrouded rotor produced 100% higher control moments due to pressure asymmetry arising from cyclic control of the rotor. It was seen that the control margin of the shrouded rotor increased as the disk loading increased, which is however deleterious in terms of hover performance. This is an important trade-off that needs to be considered. The flight performance of the vehicle in terms of edgewise gust disturbance rejection was tested in a series of bench top and free flight tests. A standard table fan and an open jet wind tunnel setup was used for bench top setup. The shrouded rotor had an edgewise gust tolerance of about 3 m/s while the unshrouded rotor could tolerate edgewise gusts greater than 5 m/s. Free flight tests on the vehicle, using VICON for position feedback control, indicated the capability of the vehicle to recover from gust impulse inputs from a pedestal fan at low gust values (up to 3 m/s)

myCopter: Enabling Technologies for Personal Air Transport Systems - an Early Progress Report

This paper describes the European Commission (EC) Framework 7 funded project myCopter (2011-2014). The project is still at an early stage so the paper starts with the current transportation issues faced by developed countries and describes a means to solve them through the use of personal aerial transportation. The concept of personal air vehicles (PAV) is briefly reviewed and how this project intends to tackle the problem from a different perspective described. It is argued that the key reason that many PAV concepts have failed is because the operational infrastructure and socio-economic issues have not been properly addressed; rather, the start point has been the design of the vehicle itself. Some of the key aspects that would make a personal aerial transport system (PATS) viable include the required infrastructure and associated technologies, the skill levels and machine interfaces needed by the occupant or pilot and the views of society as a whole on the acceptability of such a proposition. The myCopter project will use these areas to explore the viability of PAVs within a PATS. The paper reports upon the early progress made within the project. An initial reference set of PAV requirements has been collated. A non-physical flight simulation model capable of providing a wide range of handling qualities characteristics has been developed and its function has undergone limited verification. Results from this exercise show that the model behaves as intended and that it can deliver a predictable range of vehicle dynamics. The future direction of the themes of work described within the paper are then described

A survey of free software for the design, analysis, modelling, and simulation of an unmanned aerial vehicle

The objective of this paper is to analyze free software for the design, analysis, modelling, and simulation of an unmanned aerial vehicle (UAV). Free software is the best choice when the reduction of production costs is necessary; nevertheless, the quality of free software may vary. This paper probably does not include all of the free software, but tries to describe or mention at least the most interesting programs. The first part of this paper summarizes the essential knowledge about UAVs, including the fundamentals of flight mechanics and aerodynamics, and the structure of a UAV system. The second section generally explains the modelling and simulation of a UAV. In the main section, more than 50 free programs for the design, analysis, modelling, and simulation of a UAV are described. Although the selection of the free software has been focused on small subsonic UAVs, the software can also be used for other categories of aircraft in some cases; e.g. for MAVs and large gliders. The applications with an historical importance are also included. Finally, the results of the analysis are evaluated and discussed—a block diagram of the free software is presented, possible connections between the programs are outlined, and future improvements of the free software are suggested. © 2015, CIMNE, Barcelona, Spain.Internal Grant Agency of Tomas Bata University in Zlin [IGA/FAI/2015/001, IGA/FAI/2014/006

Validation of Quad Tail-sitter VTOL UAV Model in Fixed Wing Mode

Vertical take-off and landing (VTOL) is a type of unmanned aerial vehicle (UAV) that is growing rapidly because its ability to take off and land anywhere in tight spaces. One type of VTOL UAV, the tail-sitter, has the best efficiency. However, besides the efficiency offered, some challenges must still be overcome, including the complexity of combining the ability to hover like a helicopter and fly horizontally like a fixed-wing aircraft. This research has two contributions: in the form of how the analytical model is generated and the tools used (specifically for the small VTOL quad tail-sitter UAV) and how to utilize off-the-shelf components for UAV empirical modeling. This research focuses on increasing the speed and accuracy of the UAV VTOL control design in fixed-wing mode. The first step is to carry out analysis and simulation. The model is analytically obtained using OpenVSP in longitudinal and lateral modes. The next step is to realize this analytical model for both the aircraft and the controls. The third step is to measure the flight characteristics of the aircraft. Based on the data recorded during flights, an empirical model is made using system identification technique. The final step is to vali-date the analytical model with the empirical model. The results show that the characteristics of the analytical mode fulfill the specified requirements and are close to the empirical model. Thus, it can be concluded that the analytical model can be implemented directly, and consequently, the VTOL UAV design and development process has been shortened

Aerial Robotics for Inspection and Maintenance

Aerial robots with perception, navigation, and manipulation capabilities are extending the range of applications of drones, allowing the integration of different sensor devices and robotic manipulators to perform inspection and maintenance operations on infrastructures such as power lines, bridges, viaducts, or walls, involving typically physical interactions on flight. New research and technological challenges arise from applications demanding the benefits of aerial robots, particularly in outdoor environments. This book collects eleven papers from different research groups from Spain, Croatia, Italy, Japan, the USA, the Netherlands, and Denmark, focused on the design, development, and experimental validation of methods and technologies for inspection and maintenance using aerial robots