Organizational Unit:

Unmanned Aerial Vehicle Research Facility

Permanent Link

https://hdl.handle.net/1853/70748

Parent Organization

Organizational Unit

Daniel Guggenheim School of Aerospace Engineering

ArchiveSpace Name Record

https://finding-aids.library.gatech.edu/agents/corporate_entities/1139

Full item page

Publication Search Results

Now showing 1 - 10 of 11

Design, Development, and Testing of a Low Cost, Fully Autonomous Indoor Unmanned Aerial System

(Georgia Institute of Technology, 2010-08) Chowdhary, Girish ; Sobers, D. Michael Jr. ; Salaün, Erwan ; Ottander, John ; Johnson, Eric N.

This paper is concerned with the design, development, and autonomous flight testing of the GT Lama indoor Unmanned Aerial System (UAS). The GT Lama is a fully autonomous rotorcraft UAS capable of indoor area exploration. It weighs around 1.3 lbs (600 gms), has a width of about 27.6 inches (70 cm), and costs less than USD 900. The GT Lama employs only five off-the-shelf, extremely low-cost range sensors for navigation. The GT Lama does not rely on other expensive and sophisticated sensors, including inertial measurement units, Laser based range scanners, and GPS. The GT Lama achieves this by using simple wall following logic to ensure that maximum perimeter of an indoor environment is explored in a reasonable amount of time. The GT Lama hardware, and the Guidance, Navigation, and Control (GNC) algorithms used are discussed in detail. The details of a MATLAB based method that facilitates rapid in flight validation of GNC algorithms on real flight hardware is also discussed. Results from flight tests as the GT Lama autonomously explores indoor environments are presented.
Minimum-Time Paths for a Light Aircraft in the Presence of Regionally-Varying Strong Winds

(Georgia Institute of Technology, 2010) Bakolas, Efstathios ; Tsiotras, Panagiotis

We consider the minimum-time path-planning problem for a small aircraft flying horizontally in the presence of obstacles and regionally-varying strong winds. The aircraft speed is not necessarily larger than the wind speed, a fact that has major implications in terms of the existence of feasible paths. First, it is possible that there exist configurations in close proximity to an obstacle from which a collision may be inevitable. Second, it is likely that points inside the obstacle-free space may not be connectable by means of an admissible bidirectional path. The assumption of a regionally-varying wind field has also implications on the optimality properties of the minimum-time paths between reachable configurations. In particular, the minimum-time-to-go and minimum-time-to-come between two points are not necessarily equal. To solve this problem, we consider a convex subdivision of the plane into polygonal regions that are either free of obstacles or they are occupied with obstacles, and such that the vehicle motion within each obstacle-free region is governed by a separate set of equations. The equations of motion inside each obstacle-free region are significantly simpler when compared with the original system dynamics. This approximation simplifies both the reachability/accesibility analysis, as well as the characterization of the locally minimum-time paths. Furthermore, it is shown that the minimum-time paths consist of concatenations of locally optimal paths with the concatenations occurring along the common boundary of neighboring regions, similarly to Snell’s law of refraction in optics. Armed with this representation, the problem is subsequently reduced to a directed graph search problem, which can be solved by employing standard algorithms.
An ILS Inspired Approach and Departure System Utilizing Monocular Vision

(Georgia Institute of Technology, 2009-07) Christmann, Hans Claus ; Johnson, Eric N.

This paper introduces a simple system to provide relative position between a base unit and an active unit. The proposed system is directional and allows the active unit to approach or depart from the base unit along a linear path, determined by the orientation of the base unit. The system does not require a data link between the base and the active unit, just a clear line of sight. The proposed system utilizes monocular vision on the active unit and requires the availability of enough computational power to perform simple computer vision algorithms. Part I describes the physical characteristics of the beacon utilized on the base unit, Part II describes the algorithms utilized to compute the relative position of the active unit to the base, utilizing the vision data. Part III presents simulation results. Part IV discusses the results and findings and proposes future work.
Bank-to-Turn Control for a Small UAV using Backstepping and Parameter Adaptation

(Georgia Institute of Technology, 2008-07) Jung, Dongwon ; Tsiotras, Panagiotis

In this research we consider the problem of path following control for a small fixed-wing unmanned aerial vehicle (UAV). Assuming the UAV is equipped with an autopilot for low level control, we adopt a kinematic error model with respect to the moving Serret-Frenet frame attached to a path for tracking controller design. A kinematic path following control law that commands heading rate is presented. Backstepping is applied to derive the roll angle command by taking into account the approximate closed-loop roll dynamics. A parameter adaptation technique is employed to account for the inaccurate time constant of the closed-loop roll dynamics during actual implementation. The path following control algorithm is validated in real-time through a high-fidelity hardware-in-the-loop simulation (HILS) environment showing the applicability of the algorithm on a real system.
Multiresolution Path Planning Via Sector Decompositions Compatible to On-Board Sensor Data

(Georgia Institute of Technology, 2008) Bakolas, Efstathios ; Tsiotras, Panagiotis

In this paper we present a hybrid local-global path planning scheme for the problem of operating a moving agent inside an unknown environment in a collision-free manner. The path planning algorithm is based on information gathered on-line by the available on-board sensor devices. The solution minimizes the total length of the path with respect to a metric that includes actual path length along with a risk-induced metric. We use a multi-resolution cell decomposition of the environment in order to solve the path-planning problem using the wavelet transform in conjunction with a conformal mapping to polar coordinates. By performing the cell decomposition in polar coordinates we can naturally incorporate sector-like cells that are adapted to the data representation collected by the on-board sensor devices. Simulations are presented to test the efficiency of the algorithm using a non trivial scenario.
On-line Path Generation for Small Unmanned Aerial Vehicles using B-Spline Path Templates

(Georgia Institute of Technology, 2008) Jung, Dongwon ; Tsiotras, Panagiotis

In this study we investigate the problem of generating a smooth, planar reference path, given a family of discrete optimal paths. In conjunction with a path representation by a finite sequence of square cells, the generated path is supposed to stay inside a feasible channel, while minimizing certain performance criteria. Constrained optimization problems are formulated subject to geometric (linear) constraints, as well as boundary conditions in order to generate a library of B-spline path templates. As an application to the vehicle motion planning, the path templates are incorporated to represent local segments of the entire path as geometrically smooth curves, which are then joined with one another to generate a reference path to be followed by a closed-loop tracking controller. The on-line path generation algorithm incorporates the path templates such that continuity and smoothness are preserved when switching from one template to another along the path. Combined with the D∗-lite path planning algorithm, the proposed algorithm provides a complete solution to the obstacle-free path generation problem in a computationally efficient manner, suitable for real-time implementation.
Beyond Quadtrees: Cell Decomposition for Path Planning using the Wavelet Transform

(Georgia Institute of Technology, 2007-12) Cowlagi, Raghvendra V. ; Tsiotras, Panagiotis

Path planning techniques based on hierarchical multiresolution cell decompositions are suitable for online implementation due to their simplicity and speed of implementation. We present an efficient multiresolution cell decomposition scheme based on the Haar wavelet transform. The decomposition approximates the environment using high resolution close to the agent and coarse resolution elsewhere. We demonstrate an algorithm to extract the adjacency and transition cost relations of the cells directly from the wavelet transform coefficients.
A Hierarchical On-Line Path-Planning Scheme Using Wavelets

(Georgia Institute of Technology, 2007-07) Tsiotras, Panagiotis ; Bakolas, Efstathios

We present an algorithm for solving the shortest (collision-free) path planning problem for an agent (e.g., wheeled vehicle, UAV) operating in a partially known environment. The agent has detailed knowledge of the environment and the obstacles only in the vicinity of its current position. Far away obstacles or the final destination are only partially known and may even change dynamically at each instant of time. We obtain an approximation of the environment at different levels of fidelity using a wavelet approximation scheme. This allows the construction of a directed weighted graph of the obstacle-free space in a computationally efficient manner. In addition, the dimension of the graph can be adapted to the on-board computational resources. By searching this graph we find the desired shortest path to the final destination using Dijkstra's algorithm, provided that such a path exists. Simulations are presented to test the efficiency of the algorithm using non trivial scenarios.
Modelling and Hardware-in-the-Loop Simulation for a Small Unmanned Aerial Vehicle

(Georgia Institute of Technology, 2007-05) Jung, Dongwon ; Tsiotras, Panagiotis

Modeling and experimental identification results for a small unmanned aerial vehicle (UAV) are presented. The numerical values of the aerodynamic derivatives are computed via the Digital DATCOM software using the geometric parameters of the airplane. Flight test data are utilized to identify the stability and control derivatives of the UAV. The aerodynamic angles are estimated and used in conjunction with inertial measurements in a batch parameter identification algorithm. A hardware-in-the-loop (HIL) simulation environment is developed to support and validate the UAV autopilot hardware and software development. The HIL simulation incorporates a high-fidelity dynamic model that includes the sensor and actuator models, from the identified parameters from experiments. A user-friendly graphical interface that incorporates external stick commands and 3-D visualization of the vehicle’s motion completes the simulation environment. The hardware-in-the-loop setup is an indispensable tool for rapid certification of both the avionics hardware and the control software, while performing simulated flight tests with minimal cost and effort.
Inertial Attitude and Position Reference System Development for a Small UAV

(Georgia Institute of Technology, 2007-05) Jung, Dongwon ; Tsiotras, Panagiotis

This article presents an inexpensive inertial attitude and position reference system for a small unmanned aerial vehicle (UAV) that utilizes low cost inertial sensors in conjunction with a global positioning system (GPS) sensor. The attitude estimates are obtained from a complementary filter and a Kalman filter by combining the measurements from the inertial sensors with the supplementary attitude information from GPS. A method is proposed to deal with the GPS data latency and momentary outages. The inertial position is estimated from a separate Kalman filter that is cascaded after the attitude filters in order to reduce the computational overhead. Numerical simulation results and hardware validation show that this is a simple, yet effective method for attitude and position estimation, suitable for real-time implementation on a small UAV.