Experimental Study of Aerodynamic Disturbance Rejection On Multirotor Unmanned Aerial Vehicles

PID (Proportional-Integral-Derivative) controllers are the most widely used control algorithms in different industrial applications. Multirotor Unmanned Aerial Vehicles (UAVs) are not an exception in this regard. This success is due to the efficiency of this type of algorithms. In fact, they are easy to understand, to tune and to implement. Added to that, PID controllers perform surprisingly well in most operational cases, even when those start to become challenging. But this effectiveness becomes questionable when the conditions are far fro

Robust active disturbance rejection control for systems with internal uncertainties: Multirotor UAV application

Abstract Active Disturbance Rejection Control (ADRC) has recently stood out as a viable alternative to the proportional–integral–derivative controllers. An interesting field of application of this approach is the control of multirotor unmanned aerial vehicles (UAVs) which are inevitably subject to various force and torque disturbances. What makes ADRC attractive is the enhanced trajectory tracking and disturbance rejection capabilities that it allows while requiring minimal knowledge about the system. Although in theory, larg

Linear dynamics of flexible multibody systems : a system-based approach

A new methodology to derive the linear model of flexible multibody system dynamics is presented in this paper. This approach is based on the twoport model of each body allowing the model of the whole system to be built just connecting the inputs/outputs of each body model. Boundary conditions of each body can be taken into account through inversion of some input-output channels of its two-port model. This approach is extended here to treat the case of closed-loop kinematic mechanisms. Lagrange multipliers are commonly used in an augmented differential-algebraic equation to solve loop-closure constraints. Instead, they are considered here as a model output, which is connected to the adjoining body model through a feedback. After a summary of main results in the general case, the case of planar mechanisms with multiple uniform beams is considered and the two-port model of the Euler-Bernouilli beam is derived. The choice of the assumed modes is then discussed regarding the accuracy of the first natural frequencies for various boundary conditions. The overall modeling approach is then applied to the well-known four bar mechanism

Novel Model-Based Control Mixing Strategy for a Coaxial Push-Pull Multirotor

A Coaxial push-pull multirotor is a Vertical Take-Off and Landing (VTOL) Unmanned Aerial Vehicle (UAV) having 2n (n ∈ IN*) rotors arranged in n blocks of two coaxial contrarotating rotors. A model-based control allocation algorithm (mixer) for this architecture is proposed. The novelty of the approach lies in the fact that the coaxial aerodynamic interference occurring between the pairs of superimposed rotors is not neglected but rather nonlinear empiric models of the coaxial aerodynamic thrust and torque are used to build the mixer. Real flight experiments were conducted and the new approach showed promising results

Control of underactuated multirotor UAVs in disturbed aerodynamic conditions : Contribution to the robustification of control laws for an industrial application

Les drones multirotor ont un énorme potentiel d'application dans le milieu industriel. Un exemple pertinent est celui de la société Donecle, la première au monde à développer des drones d'inspection visuelle pour la maintenance aéronautique. Les freins au déploiement à plus grande échelle de ces drones (pour inspecter tout type de structure, et en toute condition) sont d'abord législatifs et ensuite technologiques. En effet, les interactions entre le vent, les hélices et le corps du drone créent des perturbations complexes qui peuvent dégrader la précision du suivi de trajectoire au point de rendre le vol à proximité des avions risqué et donc non certifiable. Cette thèse financée par Donecle vise à augmenter la capacité des contrôleurs de ses drones à résister aux perturbations aérodynamiques.L'approche adoptée pour répondre à ce problème a été motivée par l'objectif pratique de la thèse : fournir des techniques de contrôle qui peuvent être rapidement déployées sur des drones industriels existants sans apporter de modifications matérielles. L'idée fut alors de partir des contrôleurs PID, qui fonctionnent très bien dans la plupart des cas, de comprendre leurs limites en termes de rejet des perturbations et de les surpasser en apportant progressivement de nouvelles briques algorithmiques qui s'adaptent bien au cas d'utilisation de Donecle : un drone en configuration contrarotative coaxiale, des vols à basse vitesse et une carte autopilote à mémoire limitée.Deux contributions principales sont proposées : D'une part, une nouvelle stratégie d'allocation des commandes moteurs (mixage) qui ne néglige pas les interférences entre les hélices coaxiales. D'autre part, la généralisation d'une technique de contrôle robuste au cas d'un contrôleur avec un observateur de perturbations (à savoir le contrôle actif de rejet des perturbations ADRC) pour garantir que les incertitudes sur les paramètres du système (variant dans des plages préétablies) ne causeront pas de dégradation des performances ou ne conduiront pas à l'instabilité. Cette amélioration de l'ADRC permet de rendre le même algorithme, avec le même réglage initial, capable de gérer les changements de configurations et de régimes de vol. Les essais expérimentaux ont accompagné toutes les phases de cette thèse et forment de ce fait une part importante des contributions. Ils ont notamment permis d'orienter notre choix vers certaines techniques de contrôle.Multirotor UAVs have huge potential for industrial applications. A relevant example is Donecle, the first company in the world to develop visual inspection UAVs for aeronautical maintenance. The obstacles to a wider deployment of these UAVs (to inspect any type of structure and in any condition) are firstly legislative and secondly technological. Indeed, the interactions between the wind, the propellers and the UAV body create complex disturbances that can degrade the accuracy of the trajectory tracking to the point of making the flight close to aircraft risky and therefore non-certifiable. This Donecle-funded thesis aims to increase the ability of its UAV controllers to withstand aerodynamic disturbances.The approach adopted to address this problem was motivated by the practical purpose of the thesis: providing control techniques that can be rapidly deployed on existing industrial UAVs without making hardware modifications. The idea was then to start from PID controllers, which work very well in most cases, understand their limitations in terms of disturbance rejection and to outperform them by gradually bringing new algorithmic bricks that fit well to the Donecle use case: a drone with a contra-rotating coaxial configuration, low speed flights and a memory-limited autopilot board.Two main contributions are proposed: On the one hand, a new control allocation strategy (thrust mixing) that does not neglect interference between coaxial propellers. On the other hand, the generalisation of a robust control technique to the case of a controller with a disturbance observer (namely Active Disturbance Rejection Control ADRC) to ensure that uncertainties on the system parameters (varying in pre-established ranges) will not cause performance degradation or lead to instability. This ADRC enhancement allows making the same algorithm with the same initial setting capable of handling changes of drone configurations and flight regimes. Experimental tests have accompanied all phases of this thesis and thus form an important part of the contributions. In particular, they have helped steer our choice towards some control techniques