Sergio Esteban

Three-Time Scale Singular Perturbation Control for a Radio-Control Helicopter on a Platform

Control of rotatory wing aircrafts represents a very challenging task due to the nonlinearities and inherent instabilities present in such systems. The versatility of rotorcrafts allows them to perform almost any task that no conventional aircraft can do, but this ability is ultimately associated to the stability and control characteristics obtained via automatic control design. These stability and control characteristics come at the price of complex control designs in order to deal with these highly nonlinear aerospace systems. Historically, classical linear control techniques such design via root locus, frequency response techniques, state space techniques, PID controllers, or gain scheduling to name few, have been sufficient to obtain reasonable control responses of aerospace systems. The evolution of the aerospace industry, and the consequent improvement of technologies, have increased the performance requirements of all systems in general, which has called for better control designs that can deal with more complex systems, making linear control techniques insufficient to cope with the industry demands. Specifically, in the area of aerospace systems, a wide range of different nonlinear control techniques have been studied to deal with the nonlinear dynamics of such systems. From singular perturbation, feedback linearization, dynamic inversion, 10 sliding mode control, or backstepping control methods, to name few. Neural Networks (NN) are also included within the realm of nonlinear control techniques, and seem to provide improved robustness properties under system uncertainties. Some of works include Adaptive Critic Neural Network (ACNN) based

STATIC AND DYNAMIC ANALYSIS OF AN UNCONVENTIONAL PLANE: FLYING WING

The need to investigate the static and dynamic stability for unconventional planes requires development of a code that automates the analysis for the airplanes stability performance. Flying wings are unconventional and challenging to analyze because they lack a tail to control the plane in the longitudinal and the lateral directions. With this motivation, an automated code was designed that was able to accurately predict the stability performance of flying wings. In general most of the stability derivatives that govern the dynamic behavior of an airplane are simplified so they would only include the terms that represent the greatest contribution to its final value. When the greatest contribution to any of the derivatives comes from the tail, and the airplane being analyzed lacks a tail, this represents a problem. This study tries to solve this problem by focusing on decoupling the longitudinal and lateral stability derivatives into its wing and vertical fin contributions.

Singular perturbation control of the longitudinal flight dynamics of an UAV

This paper presents a singular perturbation control strategy for regulating the longitudinal flight dynamics of an Unmanned Air Vehicle (UAV). The proposed control strategy is based on a four-time-scale (4TS) decomposition that includes the altitude, velocity, pitch, and flight path angle dynamics, with the control signals being the elevator deflection and the throttle position. The nonlinear control strategy drives the system to follow references in the aerodynamic velocity and the flight path angle. In addition, the control strategy permits to select the desired dynamics for all the singularly perturbed subsystems. Numerical results are included for a realistic nonlinear UAV model, including saturation of the control signals.

Retrospective cost adaptive spacecraft attitude control using control moment gyros

We present a numerical investigation of the performance of retrospective cost adaptive control (RCAC) for spacecraft attitude control using control-moment-gyroscopes (CMG). The setup consists of three orthogonally mounted CMGs that are velocity commanded without the use of a steering law. RCAC is applied in a decentralized architecture; each CMG is commanded by an independent RCAC control laws. This architecture simplifies the required modeling information and treats the axis-coupling effects as unmodeled disturbances. A rotation-matrix parameterization of attitude is used to implement a dynamic compensator with state feedback. The adaptive controller is able to complete various slew and spin maneuvers using limited information about the mass-distribution of the spacecraft.

LYAPUNOV BASED STABILITY ANALYSIS OF A THREE-TIME SCALE MODEL FOR A HELICOPTER ON A PLATFORM1

Abstract An asymptotical stability analysis is conducted using Lyapunov stability methods to construct a composite Lyapunov function candidate in a step-by-step way extending the procedures defined in [Kokotovic et al., 1986] for the two-time-scale singular perturbation problems, to the three-time-scale singular perturbation problem of a Radio/Control helicopter on a platform.

A Numerical Comparison of Inertia-Free Attitude Control Laws for a Spacecraft with a Discrete Flexible Mode

Structural flexibility in spacecraft can degrade the accuracy of the attitude control system. With this motivation in mind, we compare the performance of inertia-free attitude control laws for a spacecraft with an undamped discrete flexible mode and demonstrate robustness with respect to unmodeled spacecraft dynamics and actuator saturation. First the equations of motion are derived using Lagrangian dynamics. Next we present the inertia-free control laws considered in the study. Next, we establish a baseline model for subsequent comparisons. Finally, we demonstrate robustness of the control laws to actuator saturation and plant uncertainty through variations in the inertia matrix as well as the parameters of the discrete flexible mode.

Use of calculus of variations to determine the shape of hovering rotors of minimum power and its application to micro air vehicles

In this paper, calculus of variations and combined blade element and momentum theory (BEMT) are used to demonstrate that, in hover, when neither root nor tip losses are considered; the rotor, which minimizes the total power (MPR), generates an induced velocity that varies linearly along the blade span. The angle of attack of every blade element is constant and equal to its optimum value. The traditional ideal twist (ITR) and optimum (OR) rotors are revisited in the context of this variational framework. Two more optimum rotors are obtained considering root and tip losses, the ORL, and the MPRL. A comparison between these five rotors is presented and discussed. The MPR and MPRL present a remarkable saving of power for low values of both thrust coefficient and maximum aerodynamic efficiency. The result obtained can be exploited to improve the aerodynamic behaviour of rotary wing micro air vehicles (MAV). A comparison with experimental results obtained from the literature is presented.

Nonlinear Control Techniques for Regulating the Altitude of a Radio/Control Helicopter

This article approaches the problem of obtaining adequate nonlinear control laws to regulate the vertical position of a Radio/Control helicopter on a platform. Two different approaches are considered: the first uses singular perturbation formulation for the three-time scale helicopter model, while the second approach solves the problem using a

Development of an Emergency Radio Beacon for Small Unmanned Aerial Vehicles

Emergency locator transmitters (ELTs) used to locate manned aircrafts are not well suited to find and recover small crashed unmanned aerial vehicles (UAVs). ELTs utilize an international satellite system for search and rescue (Cospas-Sarsat System), which should leverage its expensive resources to save lives as a priority. Besides, ELTs are too big and heavy to be used within small UAVs. Some of the existing solutions for this problem are based on receivers that detect signal strength, which may be a long and tedious process not suitable for user needs. Others do not have enough range or require radio license and expensive amateur radio receivers. This paper presents an emergency radio beacon specifically designed to locate small UAVs. It is triggered automatically in the event of a crash and allows finding and recovering a crashed UAV in a fast and simple way. It meets not only the required specifications of user-friendliness, size and weight of this kind of application, but also it is a high precision and low cost device. Besides, it has enough range and endurance. The experiments carried out show the operation of the proposed system.

A robust adaptive mixing control for improved forward flight of a tilt-rotor UAV

This work presents the modeling and control of a tilt-rotor UAV, with tail controlled surfaces, for path tracking with improved forward flight. The dynamic model is obtained using the Euler-Lagrange formulation considering the aerodynamic forces and torques exerted on the horizontal and vertical stabilizers, and fuselage. For control design purposes, the equations of motion are linearized around different operation points to cover a large range of forward velocity. Based on these linearized dynamic models, a mixed H2/H∞ robust controller is designed for each operation point. Therefore, an adaptive mixing scheme is used to perform an on-line smooth gain-scheduling between them. Simulation results show the control strategy efficiency when the UAV is designated to have a forward acceleration and perform a circular trajectory subject to a wind disturbance.