Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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Item Applied Aerial Autonomy for Reliable Indoor Flight and 3D Mapping(2024) Shastry, Animesh Kumar; Paley, Derek; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Uncrewed Aerial Systems (UAS) are essential for safely exploring indoor environments damaged by shelling, fire, floods, and structural collapse. These systems can gather critical visual and locational data, aiding in hazard assessment and rescue planning without risking human lives. Reliable UAS deployments requires advanced sensors and robust algorithms for real-time data processing and safe navigation, even in GPS-denied and windy conditions. This dissertation details three research projects to improve UAS performance: (1) in-flight calibration to improve estimation and control, (2) system identification for wind rejection, and (3) indoor aerial 3D mapping. The dissertation begins with introducing a comprehensive nonlinear filtering framework for UAV parameter estimation, which considers factors such as external wind, drag coefficients, IMU bias, and center of pressure. Additionally, it establishes optimized flight trajectories for parameter estimation through empirical observability. Moreover, an estimation and control framework is implemented, utilizing the mean of state and parameter estimates to generate suitable control inputs for vehicle actuators. By employing a square-root unscented Kalman filter (sq-UKF), this framework can derive a 23-dimensional state vector from 9-dimensional sensor data and 4-dimensional control inputs. Numerical results demonstrate enhanced tracking performance through the integration of the estimation framework with a conventional model-based controller. The estimation of unsteady winds results in improved gust rejection capabilities of the onboard controller as well. Closely related to parameter estimation is system identification. Combining with the previous work a comprehensive system identification framework with both linear offline and nonlinear online methods is introduced. Inertial parameters are estimated using frequency-domain linear system identification, incorporating control data from motor-speed sensing and state estimates from automated frequency sweep maneuvers. Additionally, drag-force coefficients and external wind are recursively estimated during flight using a sq-UKF. A custom flight controller is developed to manage the computational demands of online estimation and control. Flight experiments demonstrate the tracking performance of the nonlinear controller and its improved capability in rejecting gust disturbances. Aside from wind rejection, aerial indoor 3D mapping is also required for indoor navigation, and therefore, the dissertation introduces a comprehensive pipeline for real-time mapping and target detection in indoor environments with limited network access. Seeking a best-in-class UAS design, it provides detailed analysis and evaluation of both hardware and software components. Experimental testing across various indoor settings demonstrates the system's efficacy in producing high-quality maps and detecting targets.Item SYSTEM IDENTIFICATION OF A MULTI-ROTOR VEHICLE WITH ACTIVE FEEDBACK CONTROL(2020) Cunningham, Michael A; Hubbard Jr., James E; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)As multi-rotor vehicles become integrated into the national airspace for applications such as package delivery and videography, it is important that the inner-loop control system be robust and able to meet ever-demanding performance constraints. To achieve high bandwidth control designs, it is necessary to have accurate and high bandwidth open-loop models. The material covered in this dissertation was aimed towards the flight-based identification and comprehensive understanding of the open-loop dynamics and aerodynamics of a multi-rotor vehicle despite the active feedback control system. The analytical first principles modeling and the discussion of system identification techniques informed the process for identifying the unstable multi-rotor dynamics. The inherently unstable nature of the vehicle, combined with the available measurements, necessitated a methodical approach towards identification from flight experiments. The non-negligible issue of unstable system identification was addressed by both the experiment design and the applied estimation technique. An individual propulsion system was tested on a hover stand to understand both the static and dynamic behavior of the combined propeller, motor, and electronic speed controller system. The results of the ground experiments influenced the design of the flight experiments, the postulation of the models, and the understanding of the estimated model parameters. The methodology for flight-based multi-rotor system identification involved the combined application of manual pilot inputs and automated multi-sine inputs added to the output of the controller. A series of five main flight tests were conducted for the identification of a high bandwidth open-loop linear rigid body model and two aerodynamic models of a multi-rotor vehicle. The comparison of the linear rigid body model with the two aerodynamics models emphasized the clear and substantial importance of the nonlinear rigid body coupling terms even in operations near hover. The relative improvement from the linear model to the application of the aerodynamics models to the nonlinear rigid body dynamics was considerable for the translational dynamics, yet the linear model was similarly applicable to the rotational dynamics in aggressive flight near hover.Item Modeling, Estimation, and Control of Actuator Dynamics for Remotely Operated Underwater Vehicles(2019) Boehm, Jordan; Paley, Derek A; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Modeling and control of remotely operated underwater vehicles is a challenging problem that depends greatly on how the dynamics of their thrusters are compensated. In this thesis a novel method for characterizing thruster dynamics using a six-axis load cell is presented. Multiple dynamic models are characterized with this test setup. Model-based control design strategies are used to compensate for nonlinearities in the dynamics, which include input dead zones and coupling with fluid dynamics. Multiple estimation methods are presented to construct an estimate of fluid velocity which is handled as an unmeasured state. The different models, controllers, and estimators are comparatively evaluated in closed-loop experiments using the six-axis load cell to measure thrust tracking performance. Full vehicle simulations using the experimentally characterized models provide additional opportunities for comparison of control and estimation strategies. The potential tracking control benefits from the variety of presented thruster dynamics compensation strategies are evaluated for a remotely operated underwater vehicle with multiple thrusters.Item A Comparative Framework for Maneuverability and Gust Tolerance of Aerial Microsystems(2012) Campbell, Renee; Humbert, James S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Aerial microsystems have the potential of navigating low-altitude, cluttered environments such as urban corridors and building interiors. Reliable systems require both agility and tolerance to gusts. While many platform designs are under development, no framework currently exists to quantitatively assess these inherent bare airframe characteristics which are independent of closed loop controllers. This research develops a method to quantify the maneuverability and gust tolerance of vehicles using reachability and disturbance sensitivity sets. The method is applied to a stable flybar helicopter and an unstable flybarless helicopter, whose state space models were formed through system identification. Model-based static H-infinity controllers were also implemented on the vehicles and tested in the lab using fan-generated gusts. It is shown that the flybar restricts the bare airframe's ability to maneuver in translational velocity directions. As such, the flybarless helicopter proved more maneuverable and gust tolerant than the flybar helicopter. This approach was specifically applied here to compare stable and unstable helicopter platforms; however, the framework may be used to assess a broad range of aerial microsystems.Item Open Loop System Identificaiton of a Micro Quadrotor Helicopter from Closed Loop Data(2011) Miller, Derek; Humbert, James S; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Quadrotors are a favorite platform amongst academic researchers. Yet there is limited work present on the identification of Linear Time Invariant (LTI) state space models for quadrotors. This thesis focuses on the development of a 70 gram quadrotor with a maximum dimension of less than 6 inches. An MAV this small is extremely agile and in this case, dynamically unstable. Therefore it requires an active control scheme to stabilize the vehicle's attitude. To develop an effective controller using the vast array of available linear control tools, model knowledge is required. The scope of this thesis is to identify an LTI state space model of the 70 gram quadrotor mentioned about hover. Because the quadrotor is unstable, it cannot be flown without some form of feedback control present. To determine the bare airframe dynamics of a closed loop system, the feedback gains must be turned down as low as possible so as to not distort the natural response. Then the bare airframe dynamics can be calculated from the identified closed loop dynamics if the feedback gains and control law are known. Using the derived open loop system this thesis presents options for controller development for both a stabilizing inner loop, and a station keeping outer loop controller.Item Development of a Forced Oscillation Test Technique for Determination of MAV Stability Characteristics(2005-12-08) Everson, Daniel Peter; Pines, Darryll; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This thesis presents the development and validation of a forced oscillation test technique for the determination of Micro Air Vehicle (MAV) stability characteristics. The test setup utilizes a scotch yoke mechanism to oscillate a MAV along a single axis at a fixed amplitude and frequency. The aerodynamic reaction forces to this sinusoidal perturbation are measured and converted into meaningful stability parameters. The purpose of this research is to demonstrate that forced oscillation testing is an effective means of measuring the stability parameters of a MAV. Initial tests show that the forced oscillation test process is returning results which match the expected trends. Comparison of the results to an analytical model of blade flapping shows that the experimental results are of the proper magnitude. It can be concluded from this research that forced oscillation testing is a feasible method for determining the stability parameters of MAVs.