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Design, Modeling and Control for a Tilt-rotor VTOL UAV in the Presence of Actuator Failure
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Abstract and Figures
Providing both the vertical take-off and landing capabilities and the ability to fly long distances to aircraft opens the door to a wide range of new real-world aircraft applications while improving many existing applications. Tiltrotor vertical take-off and landing (VTOL) unmanned aerial vehicles (UAVs) are a better choice than fixed-wing and multirotor aircraft for such applications. Prior work on these aircraft has addressed the aerodynamic performance, design, modeling, and control. However, a less explored area is the study of their potential fault tolerance due to their inherent redundancy, which allows them to sustain some degree of actuator failure. This work introduces tolerance to several types of actuator failures in a tiltrotor VTOL aircraft. We discuss the design and model of a custom tiltrotor VTOL UAV, which is a combination of a fixed-wing aircraft and a quadrotor with tilting rotors, where the four propellers can be rotated individually. Then, we analyze the feasible wrench space the vehicle can generate and design the dynamic control allocation so that the system can adapt to actuator failure, benefiting from the configuration redundancy. The proposed approach is lightweight and is implemented as an extension to an already existing flight control stack. Extensive experiments are performed to validate that the system can maintain the controlled flight under different actuator failures. To the best of our knowledge, this work is the first study of the tiltrotor VTOL's fault-tolerance that exploits the configuration redundancy.
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This paper presents a novel open source design of the Y-shaped hexarotor Unammend Aerial Vehicle (UAV), and proves both in theory and real experiments its robustness to the failure of any of its propellers. An intuitive geometrical interpretation of UAV static hovering ability is presented, through which the robustness of different coplanar/collinear hexarotor designs is analyzed. Following the presented geometrical interpretation, we also show he conditions that allow the Star-shaped hexarotor to be robust to the failure of some of its propellers, while showing its incapability to static hover in the case of the failure of any of its propellers. Finally, the efficiency of the Y-shaped and Star-shaped hexarotors are tested experimentally, and conclusions on the advantages and disadvantages of the two designs are drawn.
Urban Air Mobility (UAM) vertical takeoff and landing (VTOL) aircraft designs frequently include multiple distributed propulsors, complex wing-propulsor aerodynamics, significant airframe configuration changes during normal flight operations, and no historical database regarding the best ways to transition between vertical and horizontal flight. This paper describes the methodology used for wind tunnel testing of the Langley Aerodrome No. 8 (LA-8) in the NASA Langley 12-Foot Low-Speed Tunnel during multiple test entries in 2019 and 2020. The LA-8 is a tandem tilt-wing aircraft with 4 motor-propeller units and 4 control surfaces distributed across each wing, plus an inverted V-tail with 2 ruddervators on the fuselage. An initial tunnel entry used one-factor-at-a-time (OFAT) testing to (1) define candidate trimmed transition corridors between vertical and horizontal flight, (2) assess whether there was adequate control authority, and (3) define appropriate test factor ranges for subsequent design of experiment (DOE) wind tunnel testing. The total number of independent variables for these wind tunnel tests (23) made DOE testing an efficient option for assessing the large number of potential interactions associated with the LA-8. The general advantages and disadvantages of OFAT and DOE wind tunnel testing techniques are also discussed – along with the benefits of a combined approach.
span>The development of fully autonomous Unmanned Aerial Vehicles (UAV) plays a major contribution towards reducing the risk to human life in various applications including rescue teams, border patrol, police and inspection of buildings, pipelines, coasts, and terrains. Tiltrotor hybrid UAV exhibit special application value due to its unique rotor structure. The variation in the model dynamics and aerodynamics due to the tilting rotors are the major key issues and challenges which attracted the attention of many researchers. This vehicle combines the hovering capabilities of a helicopter along with the high-speed cruise capabilities of a conventional airplane by tilting its four rotors. In the present research work, the authors attempt to model a quad tilt rotor UAV using Newton-Euler formulation. A dynamic model of the vehicle is derived mathematically for horizontal, vertical and transition flight modes. A robust H-infinity control strategy is proposed, evaluated and analyzed through simulation to control the flight dynamics of the different modes of the UAV. Simulation results shows that the tiltrotor UAV achieves transition successfully.</span
A system for cooperative transport of a slung load by a team of autonomous rotorcraft is described. The method described here is hierarchical and centralized, with the payload defined as the leader (here denoted as load-leading control): the payload uses knowledge of its current state and its desired trajectory to determine the net force and moment acting upon its center of gravity required to follow the desired trajectory. Using knowledge of the cable attachment geometry, the required cable forces are computed and transmitted to the rotorcraft. The cable force optimization problem is defined and shown to be nonconvex; constraints that make the problem convex are introduced. Cable forces computed using both the convex and nonconvex formulations are compared. Controllers for both payload and rotorcraft trajectory tracking are designed. Hardware implementation that uses small single-board computers carried onboard the payload and rotorcraft is described. Flight demonstrations conducted in an indoor motion capture studio using preplanned trajectories as well as human-in-the-loop control of the payload are described to show trajectory following and rejection of impulse disturbances. An outdoor flight test showing coordinated transport in the presence of light winds is described. All calculations are hosted on the computers carried on the payload and rotorcraft, and the system is shown to be capable of real-time control and path following both for fixed and in-flight changing formations.
This article presents a model predictive control (MPC) controller and its novel application to a hybrid tilt-quadrotor fixed-wing aircraft, which combines vertical takeoff and landing (VTOL) capabilities with high-speed forward flight. The developed MPC controller takes a velocity command from the pilot and then computes optimal attitude setpoints and propeller-tilt angles that are supplied to a fast inner attitude controller. A control allocation algorithm then maps the output of the inner attitude loop to actuator commands. The proposed MPC and control allocation of this article constitute a unified nonlinear control approach for tilt-rotor VTOL aircraft, valid in all flight modes and transitions in between. The whole approach is verified both in simulations and in real-world outdoor experiments with a remote controlled VTOL aircraft transitioning from hover to high speed and vice versa in a stable and controlled manner. Results show superior performance compared to the common binary-switch transition strategy between multicopter flight mode and the fixed-wing flight mode. The MPC controller also consistently performs better than a previously developed fused-PID control architecture in our tests.
Aerial cinematography is revolutionizing industries that require live and dynamic camera viewpoints such as entertainment, sports, and security. However, safely piloting a drone while filming a moving target in the presence of obstacles is immensely taxing, often requiring multiple expert human operators. Hence, there is a demand for an autonomous cinematographer that can reason about both geometry and scene context in real‐time. Existing approaches do not address all aspects of this problem; they either require high‐precision motion‐capture systems or global positioning system tags to localize targets, rely on prior maps of the environment, plan for short time horizons, or only follow fixed artistic guidelines specified before the flight. In this study, we address the problem in its entirety and propose a complete system for real‐time aerial cinematography that for the first time combines: (a) vision‐based target estimation; (b) 3D signed‐distance mapping for occlusion estimation; (c) efficient trajectory optimization for long time‐horizon camera motion; and (d) learning‐based artistic shot selection. We extensively evaluate our system both in simulation and in field experiments by filming dynamic targets moving through unstructured environments. Our results indicate that our system can operate reliably in the real world without restrictive assumptions. We also provide in‐depth analysis and discussions for each module, with the hope that our design tradeoffs can generalize to other related applications. Videos of the complete system can be found at https://youtu.be/ookhHnqmlaU.
