Browsing by Subject "VTOL"

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Open Access
Design, fabrication, and soft impact modeling and simulation of a collision-resilient foldable micro quadcopter
(2022-09) Abazari, Amirali
Despite the appreciable advancements in mobile robot navigation and obstacle avoidance algorithms using an abundance of sensors and sensor fusion methods, the navigation of moving robots through confined and cluttered spaces is still a great challenge. The physical interaction and collision between mobile robots and surrounding obstacles in these environments are unavoidable. This becomes more concerning for the case of Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicles (UAV) that the system is naturally unstable, and a minor fault or disturbance may result in severe crashes. In this thesis, a Collision-Resilient Quad-rotor Micro Aerial Vehicle (MAV) is designed using the Origami-inspired design fabrication techniques. The quadcopter is lightweight (220g max) and is designed for outdoor inspection and surveillance missions. This compliant drone provides an stable flight for a duration of 5 - 10 min, depends on the flight condition. A dynamic model is derived for the quadcopter to represent the realistic features designed for this specific UAV. In addition to that, the impact of the compliant body to surrounding obstacles is modeled as visco-elastic contact force and is added to the quadcopter’s dynamic model. The contact dynamic friction force between the protective soft bumpers and the surface is also modeled. The developed dynamic model is then used to simulate the impact of the collisionresilient quadcopter in two different simulation environments; MATLAB Simulink and ROS Gazebo. A cascaded PID control scheme is suggested for low-level (attitude) and high-level (global position) control of the drone in experiments and simulation. The result of these soft impact simulations closely imitate the collision-resilient properties of the actual quadcopter in experiments. Coefficient of Restitution (CoR) for the compliant drone impact, both in simulations and experiments, is in the interval [0.5 0.6]. This shows a great capacity for the drone to dampen the collisions.
Open Access
Nonlinear hierarchical control of a quad tilt-wing UAV: An adaptive control approach
(John Wiley and Sons Ltd, 2017) Yildiz, Y.; Unel, M.; Demirel, A.E.
In this paper, a nonlinear hierarchical adaptive control framework is proposed for the control of a quad tilt-wing unmanned aerial vehicle (UAV). An outer loop model reference adaptive controller with robustifying terms creates required forces to be able to move the UAV on a reference trajectory, and an inner loop nonlinear adaptive controller realizes the required attitude angles to achieve these forces. A rigorous stability analysis is provided showing the boundedness of all the signals in this cascaded controller structure. The development and the stability analysis of the controller do not use any linearizations and use the full nonlinear UAV dynamics. The controller is implemented on a high-fidelity nonlinear tilt-wing quadrotor model in the presence of uncertainties, wind disturbances, and measurement noise as well as actuator and structural failures. In this work, in addition to earlier modeling studies, the effect of wing-angle variations, actuator failures, and structural failures and their effect on the center of gravity of the UAV are rigorously and systematically investigated and reflected in the model. Simulation results showing the performance of the proposed controller and a comparison with the fixed controller used in earlier studies are presented in the paper. Copyright © 2017 John Wiley & Sons, Ltd.