Mathematical Modeling and Experimental Identification of an Unmanned Helicopter Robot with Flybar Dynamics

This paper presents a mathematical model for a model-scale unmanned helicopter robot, with emphasis on the dynamics of the flybar. The interaction between the flybar and the main rotor blade is explained in detail; it is shown how the flapping of the flybar increases the stability of the helicopter robot as well as assists in its actuation. The model helicopter has a fast time-domain response due to its small size, and is inherently unstable. Therefore, most commercially available model helicopters use the flybar to augment stability and make it easier for a pilot to fly. Working from first principles and basic aerodynamics, the equations of motion for full six degree-of-freedom with flybar-degree of freedom are derived. System identification experiments and results are presented to verify the mathematical model structure and to identify model parameters such as inertias and aerodynamic constants. © 2004 Wiley Periodicals, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/34939/1/20002_ftp.pd

Biologically Inspired Vision and Control for an Autonomous Flying Vehicle

This thesis makes a number of new contributions to control and sensing for unmanned vehicles. I begin by developing a non-linear simulation of a small unmanned helicopter and then proceed to develop new algorithms for control and sensing using the simulation. The work is field-tested in successful flight trials of biologically inspired vision and neural network control for an unstable rotorcraft. The techniques are more robust and more easily implemented on a small flying vehicle than previously attempted methods. ¶ ..

A Continuous-Time Nonlinear Observer for Estimating Structure from Motion from Omnidirectional Optic Flow

Various insect species utilize certain types of self-motion to perceive structure in their local environment, a process known as active vision. This dissertation presents the development of a continuous-time formulated observer for estimating structure from motion that emulates the biological phenomenon of active vision. In an attempt to emulate the wide-field of view of compound eyes and neurophysiology of insects, the observer utilizes an omni-directional optic flow field. Exponential stability of the observer is assured provided the persistency of excitation condition is met. Persistency of excitation is assured by altering the direction of motion sufficiently quickly. An equal convergence rate on the entire viewable area can be achieved by executing certain prototypical maneuvers. Practical implementation of the observer is accomplished both in simulation and via an actual flying quadrotor testbed vehicle. Furthermore, this dissertation presents the vehicular implementation of a complimentary navigation methodology known as wide-field integration of the optic flow field. The implementation of the developed insect-inspired navigation methodologies on physical testbed vehicles utilized in this research required the development of many subsystems that comprise a control and navigation suite, including avionics development and state sensing, model development via system identification, feedback controller design, and state estimation strategies. These requisite subsystems and their development are discussed

Model-Based Control Using Model and Mechanization Fusion Techniques for Image-Aided Navigation

Unmanned aerial vehicles are no longer used for just reconnaissance. Current requirements call for smaller autonomous vehicles that replace the human in high-risk activities. Many times these activities are performed in GPS-degraded environments. Without GPS providing today\u27s most accurate navigation solution, autonomous navigation in tight areas is more difficult. Today, image-aided navigation is used and other methods are explored to more accurately navigate in such areas (e.g., indoors). This thesis explores the use of inertial measurements and navigation solution updates using cameras with a model-based Linear Quadratic Gaussian controller. To demonstrate the methods behind this research, the controller will provide inputs to a micro-sized helicopter that allows the vehicle to maintain hover. A new method for obtaining a more accurate navigation solution was devised, originating from the following basic setup. To begin, a nonlinear system model was identified for a micro-sized, commercial, off-the-shelf helicopter. This model was verified, then linearized about the hover condition to construct a Linear Quadratic Regulator (LQR). The state error estimates, provided by an Unscented Kalman Filter using simulated image measurement updates, are used to update the navigation solution provided by inertial measurement sensors using strapdown mechanization equations. The navigation solution is used with a reference signal to determine the position and heading error. This error, along with other states, is fed to the LQR, which controls the helicopter. Research revealed that by combining the navigation solution from the INS mechanization block with a model-based navigation solution, and combining the INS error model and system model during the time propagation in the UKF, the navigation solution error decreases by 20%. The equations used for this modification stem from state and covariance combination methods utilized in the Federated Kalman Filter

Automatic Landing of a Rotary-Wing UAV in Rough Seas

Rotary-wing unmanned aerial vehicles (RUAVs) have created extensive interest in the past few decades due to their unique manoeuverability and because of their suitability in a variety of flight missions ranging from traffic inspection to surveillance and reconnaissance. The ability of a RUAV to operate from a ship in the presence of adverse winds and deck motion could greatly extend its applications in both military and civilian roles. This requires the design of a flight control system to achieve safe and reliable automatic landings. Although ground-based landings in various scenarios have been investigated and some satisfactory flight test results are obtained, automatic shipboard recovery is still a dangerous and challenging task. Also, the highly coupled and inherently unstable flight dynamics of the helicopter exacerbate the difficulty in designing a flight control system which would enable the RUAV to attenuate the gust effect. This thesis makes both theoretical and technical contributions to the shipboard recovery problem of the RUAV operating in rough seas. The first main contribution involves a novel automatic landing scheme which reduces time, cost and experimental resources in the design and testing of the RUAV/ship landing system. The novelty of the proposed landing system enables the RUAV to track slow-varying mean deck height instead of instantaneous deck motion to reduce vertical oscillations. This is achieved by estimating the mean deck height through extracting dominant modes from the estimated deck displacement using the recursive Prony Analysis procedure. The second main contribution is the design of a flight control system with gust-attenuation and rapid position tracking capabilities. A feedback-feedforward controller has been devised for height stabilization in a windy environment based on the construction of an effective gust estimator. Flight tests have been conducted to verify its performance, and they demonstrate improved gust-attenuation capability in the RUAV. The proposed feedback-feedforward controller can dynamically and synchronously compensate for the gust effect. In addition, a nonlinear H1 controller has been designed for horizontal position tracking which shows rapid position tracking performance and gust-attenuation capability when gusts occur. This thesis also contains a description of technical contributions necessary for a real-time evaluation of the landing system. A high-infedlity simulation framework has been developed with the goal of minimizing the number of iterations required for theoretical analysis, simulation verification and flight validation. The real-time performance of the landing system is assessed in simulations using the C-code, which can be easily transferred to the autopilot for flight tests. All the subsystems are parameterized and can be extended to different RUAV platforms. The integration of helicopter flight dynamics, flapping dynamics, ship motion, gust effect, the flight control system and servo dynamics justifies the reliability of the simulation results. Also, practical constraints are imposed on the simulation to check the robustness of the flight control system. The feasibility of the landing procedure is confimed for the Vario helicopter using real-time ship motion data

Rotorcraft Blade Pitch Control Through Torque Modulation

Micro air vehicle (MAV) technology has broken with simple mimicry of manned aircraft in order to fulfill emerging roles which demand low-cost reliability in the hands of novice users, safe operation in confined spaces, contact and manipulation of the environment, or merging vertical flight and forward flight capabilities. These specialized needs have motivated a surge of new specialized aircraft, but the majority of these design variations remain constrained by the same fundamental technologies underpinning their thrust and control. This dissertation solves the problem of simultaneously governing MAV thrust, roll, and pitch using only a single rotor and single motor. Such an actuator enables new cheap, robust, and light weight aircraft by eliminating the need for the complex ancillary controls of a conventional helicopter swashplate or the distributed propeller array of a quadrotor. An analytic model explains how cyclic blade pitch variations in a special passively articulated rotor may be obtained by modulating the main drive motor torque in phase with the rotor rotation. Experiments with rotors from 10 cm to 100 cm in diameter confirm the predicted blade lag, pitch, and flap motions. We show the operating principle scales similarly as traditional helicopter rotor technologies, but is subject to additional new dynamics and technology considerations. Using this new rotor, experimental aircraft from 29 g to 870 g demonstrate conventional flight capabilities without requiring more than two motors for actuation. In addition, we emulate the unusual capabilities of a fully actuated MAV over six degrees of freedom using only the thrust vectoring qualities of two teetering rotors. Such independent control over forces and moments has been previously obtained by holonomic or omnidirection multirotors with at least six motors, but we now demonstrate similar abilities using only two. Expressive control from a single actuator enables new categories of MAV, illustrated by experiments with a single actuator aircraft with spatial control and a vertical takeoff and landing airplane whose flight authority is derived entirely from two rotors

Evaluation of Pilot and Quadcopter Performance from Open Loop Mission Oriented Flight Testing

Title from PDF of title page viewed January 30, 2019Thesis advisor: Travis FieldsVitaIncludes bibliographical references (pages 69-78)Thesis (M.S.)--School of Computing and Engineering. University of Missouri--Kansas City, 2018Ease of control, portability and efficiency in versatile applications have made Unmanned Aerial Vehicle (UAV) very popular. Considering various usefulness, safe operation of UAV is important and to ensure safe operation, proper synergy between pilot and UAV is mandatory. For this reason, individual evaluation of both pilot and UAV performance is vital so that pilot can accomplish a task with the assigned system without any accident. In this study, a new evaluation technique of pilot and UAV performance is presented based on flight test results of a mission task of following a desired path. Seven pilots are categorized into two groups based on their experience level and a quadcopter is categorized into three groups based on level of autonomy associated with it. Path error is calculated in time domain to distinguish between pilot levels and level of autonomy of UAV. Path error metrics show that novice pilots make more error than experienced pilots and error increases from more autonomous to less autonomous UAV. For frequency do main analysis, transfer function modeling is done including human operator in the open loop so that full scenario of the flight, from pilot to UAV can be analyzed. Frequency domain analysis helps to identify system complexity, stability and fastness based on level of autonomy as well as pilot performance based on experience level. Apart from time and frequency domain analysis, Cooper-Harper rating scale is used by the pilots to rate the UAV based on ease of control. Along with time and frequency domain variables, Cooper-Harper rating is included as predictors in the modeling of evaluation of pilot and quadcopter performance. The parameter estimation of regression model shows the change in model outcome for both pilot and UAV level with the variation of predictor values. In the end, a verification test case is included where an eighth pilot flies the same quadcopter to complete the same task and variables derived from the flight data of this single flight test are placed in the binary logistic regression model equation to predict pilot experience level and multinoial logistic regression model equation to predict UAV autonomy level. The established model can predict pilot experience level and UAV autonomy level correctly that matches with the real case. The evaluation technique developed in this thesis shows a path to evaluate pilot and quadcopter performance individually, that can be used to train pilots to accomplish a specific task with the assigned UAV system.Introduction -- Literature review -- Methodology -- Results and discussions -- Conclusion -- Future wor

Advanced control for miniature helicopters : modelling, design and flight test

Unmanned aerial vehicles (UAV) have been receiving unprecedented development during the past two decades. Among different types of UAVs, unmanned helicopters exhibit promising features gained from vertical-takeoff-and-landing, which make them as a versatile platform for both military and civil applications. The work reported in this thesis aims to apply advanced control techniques, in particular model predictive control (MPC), to an autonomous helicopter in order to enhance its performance and capability. First, a rapid prototyping testbed is developed to enable indoor flight testing for miniature helicopters. This testbed is able to simultaneously observe the flight state, carry out complicated algorithms and realtime control of helicopters all in a Matlab/Simulink environment, which provides a streamline process from algorithm development, simulation to flight tests. Next, the modelling and system identification for small-scale helicopters are studied. A parametric model is developed and the unknown parameters are estimated through the designed identification process. After a mathematical model of the selected helicopter is available, three MPC based control algorithms are developed focusing on different aspects in the operation of autonomous helicopters. The first algorithm is a nonlinear MPC framework. A piecewise constant scheme is used in the MPC formulation to reduce the intensive computation load. A two-level framework is suggested where the nonlinear MPC is combined with a low-level linear controller to allow its application on the systems with fast dynamics. The second algorithm solves the local path planning and the successive tracking control by using nonlinear and linear MPC, respectively. The kinematics and obstacle information are incorporated in the path planning, and the linear dynamics are used to design a flight controller. A guidance compensator dynamically links the path planner and flight controller. The third algorithm focuses on the further reduction of computational load in a MPC scheme and the trajectory tracking control in the presence of uncertainties and disturbances. An explicit nonlinear MPC is developed for helicopters to avoid online optimisation, which is then integrated with a nonlinear disturbance observer to significantly improve its robustness and disturbance attenuation. All these algorithms have been verified by flight tests for autonomous helicopters in the dedicated rapid prototyping testbed developed in this thesis.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Development of Cross Style Quadrotor

Master'sMASTER OF ENGINEERIN

Robust and Adaptive Control Methods for Small Aerial Vehicles

Recent advances in sensor and microcomputer technology and in control and aeroydynamics theories has made small unmanned aerial vehicles a reality. The small size, low cost and manoueverbility of these systems has positioned them to be potential solutions in a large class of applications. However, the small size of these vehicles pose significant challenges. The small sensors used on these systems are much noisier than their larger counterparts.The compact structure of these vehicles also makes them more vulnerable to environmental effects. This work develops several different control strategies for two sUAV platforms and provides the rationale for judging each of the controllers based on a derivation of the dynamics, simulation studies and experimental results where possible. First, the coaxial helicopter platform is considered. This sUAV’s dual rotor system (along with its stabilizer bar technology) provides the ideal platform for safe, stable flight in a compact form factor. However, the inherent stability of the vehicle is achieved at the cost of weaker control authority and therefore an inability to achieve aggressive trajectories especially when faced with heavy wind disturbances. Three different linear control strategies are derived for this platform. PID, LQR and H∞ methods are tested in simulation studies. While the PID method is simple and intuitive, the LQR method is better at handling the decoupling required in the system. However the frequency domain design of the H∞ control method is better at suppressing disturbances and tracking more aggressive trajectories. The dynamics of the quadrotor are much faster than those of the coaxial helicopter. In the quadrotor, four independent fixed pitch rotors provide the required thrust. Differences between each of the rotors creates moments in the roll, pitch and yaw directions. This system greatly simplifies the mechanical complexity of the UAV, making quadrotors cheaper to maintain and more accessible. The quadrotor dynamics are derived in this work. Due to the lack of any mechanical stabilization system, these quadrotor dynamics are not inherently damped around hover. As such, the focus of the controller development is on using nonlinear techniques. Linear quadratic regulation methods are derived and shown to be inadequate when used in zones moderately outside hover. Within nonlinear methods, feedback linearization techniques are developed for the quadrotor using an inner/outer loop decoupling structure that avoids more complex variants of the feedback linearization methodology. Most nonlinear control methods (including feedback linearization) assume perfect knowledge of vehicle parameters. In this regard, simulation studies show that when this assumption is violated the results of the flight significantly deteriorate for quadrotors flying using the feedback linearization method. With this in mind, an adaptation law is devised around the nonlinear control method that actively modifies the plant parameters in an effort to drive tracking errors to zero. In simple cases with sufficiently rich trajectory requirements the parameters are able to adapt to the correct values (as verified by simulation studies). It can also adapt to changing parameters in flight to ensure that vehicle stability and controller performance is not compromised. However, the direct adaptive control method devised in this work has the added benefit of being able to modify plant parameters to suppress the effects of external disturbances as well. This is clearly shown when wind disturbances are applied to the quadrotor simulations. Finally, the nonlinear quadrotor controllers devised above are tested on a custom built quadrotor and autopilot platform. While the custom quadrotor is able to fly using the standard control methods, the specific controllers devised here are tested on a test bench that constrains the movement of the vehicle. The results of the tests show that the controller is able to sufficiently change the necessary parameter to ensure effective tracking in the presence of unmodelled disturbances and measurement error