Samir Bouabdallah

Full control of a quadrotor

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.

From the Test Benches to the First Prototype of the muFly Micro Helicopter

The goal of the European project muFly is to build a fully autonomous micro helicopter, which is comparable to a small bird in size and mass. The rigorous size and mass constraints infer various problems related to energy efficiency, flight stability and overall system design. In this research, aerodynamics and flight dynamics are investigated experimentally to gather information for the design of the helicopter’s propulsion group and steering system. Several test benches are designed and built for these investigations. A coaxial rotor test bench is used to measure the thrust and drag torque of different rotor blade designs. The effects of cyclic pitching of the swash plate and the passive stabilizer bar are studied on a test bench measuring rotor forces and moments with a 6–axis force sensor. The gathered knowledge is used to design a first prototype of the muFly helicopter. The prototype is described in terms of rotor configuration, structure, actuator and sensor selection according to the project demands, and a first version of the helicopter is shown. As a safety measure for the flight tests and to analyze the helicopter dynamics, a 6DoF vehicle test bench for tethered helicopter flight is used.

Modeling and System Identification of the muFly Micro Helicopter

An accurate mathematical model is indispensable for simulation and control of a micro helicopter. The nonlinear model in this work is based on the rigid body motion where all external forces and moments as well as the dynamics of the different hardware elements are discussed and derived in detail. The important model parameters are estimated, measured or identified in an identification process. While most parameters are identified from test bench measurements, the remaining ones are identified on subsystems using the linear prediction error method on real flight data. The good results allow to use the systems for the attitude and altitude controller design.

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.

New design of the steering mechanism for a mini coaxial helicopter

Whenever the realization of a swash plate mechanism is not feasible (e.g. due to miniaturization limitations), center of gravity steering is an interesting alternative to swash plate steering. We present an approach to describe the dynamic behavior of a coaxial micro helicopter steered by a center of gravity shifting mechanism. The mechanical design of an existing system is improved to increase mechanical robustness and steering quality. In parallel, a simulation model is developed and implemented. It is used to estimate the system response to steering inputs, and to compare center of gravity to swash plate steering. Experimental flight results show an improvement of the helicopter performance due to the mechanical redesign.

Modeling and decoupling control of the coax micro helicopter

The dynamics of micro coaxial helicopters are coupled, especially in the presence of a stabilizer bar and in dynamic maneuvers. This paper presents a model-based approach for active decoupling of the dynamics of a micro coaxial helicopter. This allows for easier and more accurate operation of the system. The nonlinear model covers all degrees of freedom for attitude and altitude. It accounts for hover and cruise flight situations and explicitly captures the off-axis dynamics and the dynamics of the stabilizer bar. A six-axis force/torque sensor and an RPM measurement system are used in a custom built test bench. It is applied for analysis of the forces and torques generated by the rotors in combination with the dynamics of the drive train and the swashplate. The parameter identification and the model validation is obtained with flight data recorded with a vision-based motion tracking system. The decoupling controller is implemented on the commercial robotic helicopter CoaX and its performance is shown via a motion experiment.

Micro Helicopter Steering: Review and Design for the muFly Project

The steering system on a micro helicopter is the key element for control and navigation. For a sufficient control authority the steering has to be fast, precise, reliable and lightweight. While on full scale helicopters the choice of the steering mechanism is limited, there exist many possibilities to steer a helicopter in small scale. In this paper a survey on different concepts is given followed by a realization on the coaxial micro helicopter muFly. The mechanism uses piezoelectric actuation and a simplified swash plate to apply cyclic pitch and thus maneuver the Micro Air Vehicle.

The CoaX Micro-helicopter: A Flying Platform for Education and Research

CoaX is a micro-helicopter designed for the research and education markets by Skybotix AG in Switzerland. It is a unique robotic coaxial helicopter equipped with state of the art sensors and processors: an integrated Inertial Measurement Unit (IMU), a pressure sensor, a down-looking sonar, three side looking range sensors and a color camera. To communicate with a ground station, the robot has a Bluetooth (or XBee) module and an optional WiFi module. Additionally, the CoaX supports the Overo series of tiny computers from Gumstix and is ready to fly out of the box with a set of attitude and altitude control functions. One can also control the system through an open-source API to give high-level commands for taking-off, landing or any other type of motion. In addition to presenting the CoaX, this paper reports on three experiments conducted to demonstrate the system’s motto: “simple to fly, simple to program, simple to extend”.