Hugo Romero

Real-Time Stabilization of an Eight-Rotor UAV Using Optical Flow

An original configuration of a small aerial vehicle having eight rotors is presented. Four rotors are devoted to the stabilization of the orientation of the helicopter, and the other four are used to drive the lateral displacements. A precompensation on the roll and pitch angles has been introduced so that the attitude dynamics is practically independent of the translational dynamics. This compensation is directly related to the velocity of the lateral motors. The dynamical model is obtained using the Euler-Lagrange approach. The proposed configuration is particularly useful for image processing since the the camera orientation is held constant. The eight-rotor rotorcraft is simpler to pilot than other rotorcrafts. A control strategy is proposed that uses the optical flow measurements to achieve a hover flight that is robust with respect to perturbations like wind. The new aerial configuration and control strategy have been tested in real-time experiments.

Trajectory Control of a Quadrotor Subject to 2D Wind Disturbances

The paper addresses the flight control of a quad-rotor subject to two dimensional unknown static/varying wind disturbances. A model separation is proposed to simplify the control of the six-degrees-of-freedom (6DOF) nonlinear dynamics of the flying robot. Such approach allows to deal with quad-rotor’s 3D-motion via two subsystems: dynamic (altitude and MAV-relative forward velocity) and kinematic (nonholonomic-like navigation) subsystems. In terms of control, a hierarchical control is used as the overall control structure to stabilize the kinematic underactuaded subsystem. A control strategy based on sliding-mode and adaptive control techniques is proposed to deal with slow and fast time-varying wind conditions, respectively. This choice not only provides well tracking control but also improves the estimation of unknown disturbance. The backstepping technique is used to stabilize the inner-loop heading dynamics, such recursive design takes into account a constrained heading rate. Promising simulations results show the validity of the proposed control strategy while tracking a time-parameterized straight-line and sinusoidal trajectory.

Stabilization and location of a four rotor helicopter applying vision

In this paper, we deal with the problem of local positioning and orientation of a rotorcraft in indoor flight using a simple vision system. We apply two different approaches to obtain a navigation system for the flying machine. The first approach is based on the perspective of n-points and the second one follows the plane-based pose technique. Our aim is to obtain a good estimate of variables that are difficult to measure using conventional GPS and inertial sensor in urban environment or indoor. We propose a method to measure translational speed as well as position and orientation in a local frame

Modeling and Real-Time Stabilization of an Aircraft Having Eight Rotors

We introduce an original configuration of a multi rotor helicopter composed of eight rotors. Four rotors, also called main rotors, are used to stabilize the attitude of the helicopter, while the four extra rotors (lateral rotors) are used to perform the lateral movements of the unmanned aerial vehicle (UAV). The main characteristic of this configuration is that the attitude and translation dynamics are decoupled. The dynamic model is obtained using the well known Euler–Lagrange approach. To validate the model, we performed real-time experiments using a simple nonlinear control law using optical flow and image processing.

Real-Time Attitude Stabilization of a Mini-UAV Quad-rotor Using Motor Speed Feedback

A real-time attitude stabilization control scheme is proposed for the efficient performance of a mini-UAV Quad-Rotor. Brushless DC (BLDC) motor speed sensing is performed by reflective sensors in order to obtain a robust stabilization of the vehicle in hovering mode both indoor and outdoor. The speed measurement has the advantage of introducing this state information directly in the closed loop control which should be very useful for achieving robust stabilization of the mini-UAV. Furthermore a stabilizing control strategy based on Control Lyapunov Function (CLF) is proposed. The control scheme contains two control loops. The inner loop is devoted to control the motors speed while the outer loop is devoted to control the attitude stabilization of a mini-UAV. Assuming that the motors can be considered as a disturbance of the system, then by the standard singular perturbation theory, we may conclude that the system is asymptotically stable. Finally, to verify the satisfactory performance of proposed embedded controller, simulations and experimental results of speed sensing feedback in BLDC motors of the Quad-rotor aircraft in the presence of disturbances are presented.

Predictor-based Position Control of a Quad-rotor with Delays in GPS and Vision Measurements

This paper presents a predictor-based method for the control of quad-rotor with delayed measurements obtained from a GPS or vision system. A predictor design based in Taylor series with integral remainder is presented. The closed-loop scheme is validated by simulations and by real-time experiments on a quad-rotor platform.

A new UAV configuration having eight rotors: Dynamical model and real-time control

In this paper we present an original configuration of a small aerial vehicle having eight rotors, four of them are devoted to stabilize the helicopter and the rest are used to drive the lateral displacements. The dynamical model is obtained using Euler-Lagrange approach, the attitude dynamics (roll, pitch and yaw) are practically independent of the translational dynamics corresponding to the lateral displacements (x and y), except for a small compensation on the angles roll and pitch. This compensation is directly related to the velocity of corresponding lateral motors of each axis. With this particular configuration many task could be simplified, reducing the complexity to develop an autonomous flight. Moreover, we are able to apply an easier control strategy for the flying machine.

Nonlinear and optimal real-time control of a rotary-wing UAV

In this contribution nonlinear stabilizing and optimal nonlinear control strategies for a quadrotor mini helicopter are addressed. These control strategies are an alternative for the control of flying machines not much explored yet. Simulation and real-time experiences are presented in this contribution. Nonlinear stabilizing control algorithm has been successfully implemented on an autonomous aerial vehicle and demonstrates an acceptable performance.

Attitude control of a quad-rotor using speed sensing in brushless DC motors

Recently, the research in the area of autonomous miniature flying robots is growing thanks to the development of new configurations and prototypes of Unmanned Aerial Vehicles (UAV). In this paper, we introduce the problem of attitude and altitude control of a mini-quadrotor UAV in hovering-mode to indoor and outdoor applications. Therefore, we have implemented a control strategy based on speed sensing in each brushless motors. As result, the miniature aerial vehicle has a good and robust stabilization on the horizontal plane. This paper also describes a control strategy to stabilize the quad-rotor using a control algorithm based on PD controller as well as the speed sensing scheme. Finally, the experimental results of speed sensing control for stabilizing the quad-rotor at hover are presented.

Real-time Stabilization of a Quadrotor UAV: Nonlinear Optimal and Suboptimal Control

In this paper a nonlinear suboptimal stabilizing control strategy based on Control Lyapunov Functions (CLF) is synthesized and applied to a quadrotor helicopter. Sufficient conditions are obtained for this control law to ensure the asymptotic stability of the closed loop system. Furthermore, a particular methodology to find a CLF candidate for nonlinear affine system is also presented, which is highly relevant because the dynamical model representing the VTOL aerial vehicles have this affine structure. Using this CLF candidate, we are able to synthesize a nonlinear stabilizing optimal control law which allows energy saving. Numerical simulations were developed for both control strategies and real time experiments have been performed using the nonlinear stabilizing control algorithm. The numerical simulations have shown a successful performance of the autonomous aerial vehicle.