Geometric Controls for a Tethered Quadrotor UAV

This paper deals with the dynamics and controls of a quadrotor unmanned aerial vehicle that is connected to a fixed point on the ground via a tether. Tethered quadrotors have been envisaged for long-term aerial surveillance with high-speed communications. This paper presents an intrinsic form of the dynamic model of a tethered quadrotor including the coupling between deformations of the tether and the motion of the quadrotor, and it constructs geometric control systems to asymptotically stabilize the coupled dynamics of the quadrotor and the tether. The proposed global formulation of dynamics and control also avoids complexities and singularities associated with local coordinates. These are illustrated by numerical examples

Attitude and Tension Control of a Tethered Formation of Aerial Vehicles

In this thesis we deal with the problem of formation control exploiting external constraints. In particular, we want to tether two quadrotors to each other and to a fixed point by ropes. Then, we want to control the quadrotors in order to drive the orientation of the formation, keeping the cables tautopenEmbargo per motivi di segretezza e/o di proprietà dei risultati e/o informazioni sensibil

Takeoff and landing on slopes via inclined hovering with a tethered aerial robot

In this paper we face the challenging problem of takeoff and landing on sloped surfaces for a VTOL aerial vehicle. We define the general conditions for a safe and robust maneuver and we analyze and compare two classes of methods to fulfill these conditions: free-flight vs. passivelytethered. Focusing on the less studied tethered method, we show its advantages w.r.t. the free-flight method thanks to the possibility of inclined hovering equilibria. We prove that the tether configuration and the inclination of the aerial vehicle w.r.t. the slope are flat outputs of the system and we design a hierarchical nonlinear controller based on this property. We then show how this controller can be used to land and takeoff in a robust way without the need of either a planner or a perfect tracking. The validity and applicability of the method in the real world is shown by experiments with a quadrotor that is able to perform a safe landing and takeoff on a sloped surface

Systems of Tethered Multicopters: Modeling and Control Design

A class of tethered unmanned aerial vehicles is considered, featuring a chain of multicopter drones tethered one to the other. Differently from previous contributions in the literature, here the tethers are assumed to be elastic and to transfer traction loads only. Moreover, their length can be adjusted through controlled winches installed in the ground station and on each drone. Named systems of tethered multicopters, these devices can be used for a range of applications where both long runtime and good flexibility are required. The paper describes a model of the system, and presents a hierarchical control approach for this class of drones. The proposed control approach is tested through numerical simulations

LiDAR-Based Navigation of Tethered Drone Formations in an Unknown Environment

The problem of navigating a formation of interconnected tethered drones, named STEM (System of TEthered Multicopters), in an unknown environment is considered. The tethers feed electrical power from a ground station to the drones and also serve as communication links. The presence of more than one interconnected drone provides enough degrees of freedom to navigate in a cluttered area. The leader drone in the formation must reach a given point of interest, while the followers must move accordingly, avoiding interference with the obstacles. The challenges are the uncertainty in the environment, with obstacles of unknown shape and position, the use of LiDAR (Light Detection And Ranging) sensors, providing only partial information of the surroundings of each drone, and the presence of the tethers, which must not impact with the obstacles and pose additional constraints to how the drones can move. To cope with these problems, a novel real-time planning algorithm based on numerical optimization is proposed: the reference position of each drone is chosen in a centralized way via a convex program, where the LiDAR scans are used to approximate the free space and the drones are moved towards suitably defined intermediate goals in order to eventually reach the point of interest. The approach is successfully tested in numerical simulations with a realistic model of the system

Evolutionary space platform concept study. Volume 2, part A: SASP special emphasis trade studies

Efforts are in progress to define an approach to provide a simple and cost effective solution to the problem of long duration space flight. This approach involves a Space Platform in low Earth orbit, which can be tended by the Space Shuttle and which will provide, for extended periods of time, stability, utilities and access for a variety of replaceable payloads. The feasibility of an evolutionary space system which would cost effectively support unmanned payloads in groups, using a Space Platform which provides centralized basic subsystems is addressed