The research on autonomous miniature flying robots has intensified considerably thanks to the recent growth of civil and military interest in unmanned aerial vehicles (UAV). This paper summarizes the final results of the modeling and control parts of OS4 project, which focused on design and control of a quadrotor. It introduces a simulation model which takes into account the variation of the aerodynamical coefficients due to vehicle motion. The control parameters found with this model are successfully used on the helicopter without re-tuning. The last part of this paper describes the control approach (integral backstepping) and the scheme we propose for full control of quadrotors (attitude, altitude and position). Finally, the results of autonomous take-off, hover, landing and collision avoidance are presented.

Full control of a quadrotor

http://www.esi2.us.es/~rubio/AUT_10_HIQR.pdf

An integral predictive/nonlinear H∞ control structure for a quadrotor helicopter

For a quadrotor, one can identify the two well-known inherent rotorcraft characteristics: underactuation and strong coupling in pitch-yaw-roll. To confront these problems and design a station-keeping and tracking controller, dynamic inversion is used. Typical applications of dynamic inversion require the selection of the output control variables to render the internal dynamics stable. This means that in many cases, perfect tracking cannot be guaranteed for the actual desired outputs. Instead, the internal dynamics of the feedback linearised system is stabilised using a robust control term. Unlike standard dynamic inversion, the linear controller gains are chosen uniquely to satisfy the tracking performance. Stability and tracking performance are guaranteed using a Lyapunov-type proof. Simulation with a typical nonlinear quadrotor dynamic model is performed to show the effectiveness of the designed control law in the presence of input disturbances.

https://www.uta.edu/utari/acs/ee5322/lectures/Dynamic%20Inversion%20IET%20CTA%20published%20version.pdf

Dynamic inversion with zero-dynamics stabilisation for quadrotor control

The dynamics of a quadrotor are a simplified form of helicopter dynamics that exhibit the same basic problems of underactuation, strong coupling, multi-input/multi-output design, and unknown nonlinearities. Control design for the quadrotor is more tractable yet reveals corresponding approaches for helicopter and UAV control design. In this paper, a backstepping approach is used for quadrotor controller design. In contrast to most other approaches, we apply backstepping on the Lagrangian form of the dynamics, not the state space form. This is complicated by the fact that the Lagrangian form for the position dynamics is bilinear in the controls. We confront this problem by using an inverse kinematics solution akin to that used in robotics. In addition, two neural nets are introduced to estimate the aerodynamic components, one for aerodynamic forces and one for aerodynamic moments. The result is a controller of intuitively appealing structure having an outer kinematics loop for position control and an inner dynamics loop for attitude control. The control approach described in this paper is robust since it explicitly deals with unmodeled state-dependent disturbances and forces without needing any prior knowledge of the same. A simulation study validates the results obtained in the paper.

Backstepping Approach for Controlling a Quadrotor Using Lagrange Form Dynamics

This thesis is about modelling, design and control of Miniature Flying Robots (MFR) with a focus on Vertical Take-Off and Landing (VTOL) systems and specifically, micro quadrotors. It introduces a mathematical model for simulation and control of such systems. It then describes a design methodology for a miniature rotorcraft. The methodology is subsequently applied to design an autonomous quadrotor named OS4. Based on the mathematical model, linear and nonlinear control techniques are used to design and simulate various controllers along this work. The dynamic model and the simulator evolved from a simple set of equations, valid only for hovering, to a complex mathematical model with more realistic aerodynamic coefficients and sensor and actuator models. Two platforms were developed during this thesis. The first one is a quadrotorlike test-bench with off-board data processing and power supply. It was used to safely and easily test control strategies. The second one, OS4, is a highly integrated quadrotor with on-board data processing and power supply. It has all the necessary sensors for autonomous operation. Five different controllers were developed. The first one, based on Lyapunov theory, was applied for attitude control. The second and the third controllers are based on PID and LQ techniques. These were compared for attitude control. The fourth and the fifth approaches use backstepping and sliding-mode concepts. They are applied to control attitude. Finally, backstepping is augmented with integral action and proposed as a single tool to design attitude, altitude and position controllers. This approach is validated through various flight experiments conducted on the OS4.

design and control of quadrotors with application to autonomous flying

Modelling and Control of Mini-Flying Machinesis an exposition of models developed to assist in the motion control of various types of mini-aircraft: Planar Vertical Take-off and Landing aircraft; helicopters; quadrotor mini-rotorcraft; other fixed-wing aircraft; blimps. For each of these it propounds: detailed models derived from Euler-Lagrange methods; appropriate nonlinear control strategies and convergence properties; real-time experimental comparisons of the performance of control algorithms; review of the principal sensors, on-board electronics, real-time architecture and communications systems for mini-flying machine control, including discussion of their performance; detailed explanation of the use of the Kalman filter to flying machine localization. To researchers and students in nonlinear control and its applications Modelling and Control of Mini-Flying Machines provides valuable insights to the application of real-time nonlinear techniques in an always challenging area.

https://www.springer.com/productFlyer_978-1-85233-957-9.pdf?SGWID=0-0-1297-39145381-0

Modelling and Control of Mini-Flying Machines

This paper focusses on the attitude stabilization of a mini tail-sitter aircraft, considering aerodynamic effects. The main characteristic of this vehicle is that it operates in either the hover mode for launch and recovery, or the horizontal mode during cruise. The dynamic model is obtained using the Euler–Lagrange formulation, and aerodynamic effects are obtained by studying the propeller effects. A nonlinear saturated Proportional-Integral-Derivative (SPID) control with compensation of aerodynamic moments is proposed in order to achieve the asymptotic stabilization of the vehicle in horizontal mode. In addition, a homemade inertial measurement unit (HIMU) is built for operating the complete operational range of the vehicle (including vertical and horizontal modes). Finally, simulation results are presented for validating the control law, and practical results are obtained in real-time during the flight.

Attitude Stabilization with Real-time Experiments of a Tail-sitter Aircraft in Horizontal Flight

The trajectory tracking problem of autonomous lighter than air vehicles in the presence of wind gusts is studied in this paper. The airship is represented as one point which is its center of volume, and only the kinematic equations are considered for the path tracking design. The control algorithm uses the Lyapunov theory and the Sontag's universal stabilizing feedback. The proposed control laws are robust, by construction, with respect to uncertainties in the model and unknown external parameters. Numerical simulations are carried out to illustrate the performance of the proposed control strategy.

Autonomous Path Tracking of a Kinematic Airship in Presence of Unknown Gust

In this paper, the impact of the medium access protocols on the average consensus problem over wireless networks for a group of quadrotors is established. The stabilization of each helicopter is guaranteed using a simple and bounded nonlinear control strategy. We study the case of a group of quadrotors communicating over a wireless network considering both directed and undirected graphs of information flow. It turns out that the media access control (MAC) protocols have a direct impact in both convergence time and average consensus solution, i.e., the solution of the average consensus is no longer the average of the initial conditions. It will be shown that the solution for the average consensus problem over a wireless network depends directly on the MAC algorithm. Simulations are provided to demonstrate the theoretical results. In addition, to validate the control strategy some experimental tests have been carried out to control the yaw angle of two quadrotors.

/pdf/quadrotors-formation-control-3gudm6asv8.pdf

Pedro Castillo Garcia

Papers

Modelling and Control of Mini-Flying Machines

Attitude Stabilization with Real-time Experiments of a Tail-sitter Aircraft in Horizontal Flight

Autonomous Path Tracking of a Kinematic Airship in Presence of Unknown Gust

Quadrotors Formation Control

Robust prediction-based control for unstable delay systems : Application to the yaw control of a mini helicopter