Eduardo Steed Espinoza

Second order sliding mode controllers for altitude control of a quadrotor UAS

This article deals with the design and real-time implementation of three second order sliding mode controllers for the altitude tracking of a quadrotor aircraft. A comparative study based on the analysis of the tracking error was performed in order to determine the controller presenting the best performance in a real-time application at outdoors environments. The compared strategies were the Classical First Order Sliding Mode Controller, the Super Twisting Sliding Mode Controller, the Modified Super Twisting Sliding Mode Controller and the Nonsingular Terminal Super Twisting Sliding Mode Controller. The last three controllers are based on the second order sliding mode technique, and they ensure robustness with respect to modeling errors even under external disturbances while reducing the chattering phenomenon in comparison with first order sliding mode controllers. Lyapunov stability theory is used to prove convergence in finite time of the altitude tracking error in the different proposed control laws. In order to demonstrate the effectiveness of the proposed solutions, an extensive set of simulation and real-time experimental results are presented.

Modeling and Sliding Mode Control of a Micro Helicopter-Airplane System

This paper presents the regulation and trajectory tracking for a Micro Coaxial Rocket Helicopter (MCR UAV), as well as the control of a mini aircraft. The former vehicle has the characteristic of performing hover and forward flight while the latter vehicle is considered as an external air transporter for the MCR UAV. For control purposes, the helicopter stabilization is based on sliding mode controllers which avoid the chattering generated during the flight and allow the MCR UAV to perform tracking of smooth trajectories, Furthermore a PD controller stabilizes the aircraft in order to execute semi-autonomous flight. A flight computer for these aerial vehicles consists of a homemade embedded system, low-cost sensors, and signal conditioning circuits, analog filters and actuator. The proposed control algorithms are implemented on the embedded system. Simulation and experimental results show the good performance of the developed system during the flight.

A UAS obstacle avoidance strategy based on spiral trajectory tracking

This article proposes a methodology for enabling Unmanned Aircraft Systems (UASs) to avoid obstacles. The strategy, which makes use of a Robust Exact Differentiation (RED), relies on spiral trajectory tracking maneuvers, and is based on a backstepping controller with disturbance compensation. The RED strategy has been adopted since it enables the exact estimation of disturbances from the first moment, a characteristic that may be useful for real-time UAS operations in environments with obstacles. Our research concentrates in one of the main components of a Sense and Avoid (SSA) system, specifically, conflict resolution, leaving as future work the sensing aspect. To demonstrate the performance of the proposed solution, we present a set of simulation results as well as a real-time experiment where a holonomic UAS makes use of the estimation and control strategy while evolving in an environment with obstacles.

Micro-Helicopter for Long-Distance Missions: Description and Attitude Stabilization

This paper presents the development of a micro coaxial helicopter (MCR UAV) whose main characteristic is that it should be carried by an air shuttle transporter and then released in a desired place far away from the launching site, to develop surveillance missions in hover flight. A real-time embedded system is built in order to validate the proposed aerodynamic prototype, and a classic control law based on a classical backstepping procedure for the dynamic system is implemented to test this vehicle in autonomous flight. Finally, simulation and practical results are presented for hover flight.

Altitude control of an Unmanned Aircraft System using a Super-Twisting controller based on High Order Sliding Mode Observer

In this paper, the altitude tracking problem for an Unmanned Aircraft System (UAS) is considered under the assumption that the altitud velocity is unknown. Since in a practical implementation the employed sensors used to measure the altitude (Barometer and GPS) do not provide the altitude velocity. The proposed strategy was designed by using a Super-Twisting controller based on a High Order Sliding Mode Observer. A comprehensive stability analysis based on the Lyapunov Stability Theory guarantees the convergence of the tracking error in finite time. To demonstrate the performance of the proposed solution, a set of simulation results are presented.

Stability Analysis of a Vision-Based UAV Controller

The stability analysis of a vision-based control strategy for a quad rotorcraft UAV is addressed. In the present application, the imaging sensing system provides the required states for performing autonomous navigation missions, however, it introduces latencies and time-delays from the time of capture to the time when measurements are available. To overcome this issue, a hierarchical controller is designed considering a time-scale separation between fast and slow dynamics. The dynamics of the fast-time system are stabilized using classical proportional derivative controllers. Additionally, delay frequency and time domain techniques are explored to design a controller for the slow-time system. Simulations and experimental results consisting on a vision-based road following task are presented.

Multi-UAV testbed for aerial manipulation applications

This paper addresses the development and implementation of a testbed for objects manipulation by using unmanned aerial vehicles AR.Drone and the VICON Cameras System. Such testbed allows the user to choose among two development environments to perform aerial manipulation establishing a communication with LabVIEW, ROS and the C++ Qt library; thus, the user can employ the development environment more suitable for his application. This testbed allows us to establish communication between a computer and the A.R. Drone (v1 or v2) via a WiFi connection which sends and receives data using the communication protocol UDP and sockets for connection with the vehicle UDP ports. This platform sends control and navigation commands to the UAVs in order to position them in the space with user interaction by means of a graphical user interface. This testbed enables the implementation of more complex applications, such as complex controllers. In addition, to validate the effectiveness of this testbed, experimental results of aerial manipulation between two quadrotors are presented.

Research on Swing up Control Based on Energy for the Pendubot System

In this paper, we present a class of nonlinear control scheme for swinging up and stabilization of an underactuated two-link robot called as Pendubot. The main objective of this paper is to present a switched control that swing up and stabilize for almost all combination of initial states given on the four equilibrium points of the double underactuated pendulum. The proposed methodology is based on two control strategies to swing up and stabilize the Pendubot system. The first one is based on Lagrangian dynamics, energy analysis, and stability theory, while the second one is based on linear quadratic regulator. Moreover, here we present a stability analysis of the switched control algorithm. In order to verify the proposed control strategy, experimental results were performed.

Towards Gun- and Aircraft - launched MAVs: Embedded Flight Control System

The actual paper presents an embedded flight control systems (EFCS) of two micro air vehicles (MAVs) concepts, the gun-launched MAV (GLMAV) and the aircraft-launched MAV (ALMAV), meant to rapidly reach a target zone further away from the launching point. The paper details the embedded architecture used by both vehicles at software and hardware level. The software layer contains the algorithms to process the onboard sensors information as well as to compute the control law. The hardware layer features the bidirectional communication link with the ground workstation and interfaces the control commands with the actuators. The key element of the overall embedded processing architecture is the Gumstix-COM which operates under the Xenomai real-time framework. Concerning the configuration of the airframe, we provide a descriptive study of the transition phase, covering the dynamic model and control scheme. The evaluation of the two concepts implies a comparative, regarding to identify similarities and differences of the configuration, i.e. advantages and drawbacks. Motivating simulations results were obtained in the evaluation of the flight controller within the transition phase. The experimental evaluation of the proposed EFCS during autonomous attitude-stabilized flight has returned promising results.

Semi-global leader-follower consensus for networked unmanned multi-aircraft systems with input saturation

This paper deals with the design of a consensus algorithm for a multi-aircraft (type Quadrotor) leader-follower system. This algorithm uses directed communication topologies, as well as input saturation for the follower agents. The convergence analysis of the proposed strategies is analyzed by using Lyapunov stability theory. Semi-global asymptotic consensus tracking is obtained for the case of leader with input zero, while semi-global practical consensus tracking is achieved for the case of leader with input non-zero. To demonstrate the effectiveness of the proposed solution, a set of simulation results is presented.