Minh-Duc Hua

A Control Approach for Thrust-Propelled Underactuated Vehicles and its Application to VTOL Drones

A control approach is proposed for a class of underactuated vehicles in order to stabilize reference trajectories either in thrust direction, velocity, or position. The basic modeling assumption is that the vehicle is pro-pulsed via a thrust force along a single body-fixed direction and that it has full torque actuation for attitude control (i.e., a typical actuation structure for aircrafts, vertical take-off and landing (VTOL) vehicles, submarines, etc.). Additional assumptions on the external forces applied to the vehicle are also introduced for the sake of control design and stability analyses. They are best satisfied for vehicles which are subjected to an external force field (e.g., gravity) and whose shape induces lift forces with limited amplitude, unlike airplanes but as in the case of many VTOL drones. The interactions of the vehicle with the surrounding fluid are often difficult to model precisely whereas they may significantly influence and perturb its motion. By using a standard Lyapunov-based approach, novel nonlinear feedback control laws are proposed to compensate for modeling errors and perform robustly against such perturbations. Simulation results illustrating these properties on a realistic model of a VTOL drone subjected to wind gusts are reported.

Introduction to feedback control of underactuated VTOLvehicles: A review of basic control design ideas and principles

This article is an introduction to feedback control design for a family of robotic aerial vehicles with vertical take-off and landing (VTOL) capabilities such as quadrotors, ducted-fan tail-sitters, and helicopters. Potential applications for such devices, like surveillance, monitoring, or mapping, are varied and numerous. For these applications to emerge, motion control algorithms that guarantee a good amount of robustness against state measurement/ estimation errors and unmodeled dynamics like, for example, aerodynamic perturbations, are needed. The feedback control methods considered here range from basic linear control schemes to more elaborate nonlinear control solutions. The modeling of the dynamics of these systems is first recalled and discussed. Then several control algorithms are presented and commented upon in relation to implementation issues and various operating modes encountered in practice, from teleoperated to fully autonomous flight. Particular attention is paid to the incorporation of integral-like control actions, often overlooked in nonlinear control studies despite their practical importance to render the control performance more robust with respect to unmodeled or poorly estimated additive perturbations.

Implementation of a Nonlinear Attitude Estimator for Aerial Robotic Vehicles

Attitude estimation is a key component of the avionics suite of any aerial robotic vehicle. This paper details theoretical and practical solutions in order to obtain a robust nonlinear attitude estimator for flying vehicles equipped with low-cost sensors. The attitude estimator is based on a nonlinear explicit complementary filter that has been significantly enhanced with an effective gyro-bias compensation via the design of an anti-windup nonlinear integrator. A measurement decoupling strategy is proposed in order to make roll and pitch estimation robust to magnetic disturbances that are known to cause errors in yaw estimation. In addition, this paper discusses the fixed-point numerical implementation of the algorithm. Finally, simulation and experimental results confirm the performance of the proposed method.

Observer design on the Special Euclidean group SE(3)

This paper proposes a nonlinear pose observer designed directly on the Lie group structure of the Special Euclidean group SE(3). We use a gradient-based observer design approach and ensure that the derived observer innovation can be implemented from position measurements. We prove local exponential stability of the error and instability of the non-zero critical points. Simulations indicate that the observer is indeed almost globally stable as would be expected.

Hardware and Software Architecture for Nonlinear Control of Multirotor Helicopters

This paper presents the design and implementation of a nonlinear control scheme for multirotor helicopters that takes first-order drag effects into account explicitly. A dynamic model including the blade flapping and induced drag forces is provided and a hierarchical nonlinear controller is presented. This controller is designed for both high-precision flights as well as robustness against model uncertainties and external disturbances. This is achieved by using saturated integrators with fast desaturation properties. The implementation of the controller on the flybox hexacopter platform is described. The hardware and software architecture of this UAV is discussed, and useful hints and insights gained during its design process are presented. Finally, experimental results and videos are reported to demonstrate the successful implementation and the performance of the overall system.

Nonlinear control of VTOL UAVs incorporating flapping dynamics

This paper presents the design and evaluation of a nonlinear control scheme for multirotor helicopters that takes first-order drag effects into account explicitly. A dynamic model including the blade flapping and induced drag forces is presented. Based on this model, a hierarchical nonlinear controller is designed to actively compensates for the nonlinear effects these drag forces. Reported simulation and experimental results indicate the significant performance improvement of the proposed drag-augmented control scheme with respect to a conventional nonlinear controller. For completeness, an offline procedure allowing for efficiently identifying the drag parameters is proposed.

A Robust Attitude Controller and its Application to Quadrotor Helicopters

Abstract In this paper, a novel nonlinear hierarchical controller for attitude control is proposed. This controller is obtained using Lyapunov methodology. Model uncertainties in the system are estimated on-line based on a time-delay control approach. The robustness of the flight controller is enhanced using an anti-windup integrator technique and semi-global asymptotical stability is proven. The control law obtained is simple enough for an implementation on a small microcontroller. Simulation results for a model of a quadrotor helicopter illustrate the performance of the proposed control algorithm.

Bilateral haptic teleoperation of VTOL UAVs

This paper presents an intuitive teleoperation scheme to safely operate a wide range of VTOL UAVs by an untrained user in a cluttered environment. This scheme includes a novel force-feedback algorithm that enables the user to feel the texture of the environment. In addition, a novel mapping function is introduced to teleoperate the UAV in an unlimited workspace in position control mode with a joystick which has a limited workspace. An obstacle avoidance strategy is designed to autonomously modify the position set point of the UAV independently of the pilots commands. The stability analysis of the whole teleoperation loop is provided. Experiments demonstrate the successful teleoperation of a UAV using an haptic joystick and a hexacopter UAV equipped with a 2D laser-range scanner.

Haptic-based bilateral teleoperation of underactuated Unmanned Aerial Vehicles

Abstract The bilateral teleoperation of underactuated aerial vehicles is addressed. A force feedback joystick is used to remotely pilot the aircraft and reflect an image of the environment to the operator. This feedback is a virtual force, function of the distance to an obstacle or the rate of approaching it. It can be computed using the measurements of on-board sensors ( i.e. telemetric or optic flow). Input to State Stability of the teleoperation loop with respect to bounded or dissipative virtual environment forces is established based on Lyapunov analysis.

Control of VTOL vehicles with thrust-tilting augmentation

An approach to the control of a VTOL vehicle equipped with complementary thrust-tilting capabilities that nominally yield full actuation of the vehicles position and attitude is developed. The particularity and difficulty of the control problem are epitomized by the existence of a maximum tilting angle which forbids complete and decoupled control of the vehicles position and attitude in all situations. This problem is here addressed via the formalism of primary and secondary objectives and by extending a solution previously derived in the fixed thrust-direction case. The proposed control design is also illustrated by simulation results involving a quadrotor UAV with all propeller axes pointing in the same monitored tilted direction.