Robust post-stall perching with a simple fixed-wing glider using LQR-Trees

Birds routinely execute post-stall maneuvers with a speed and precision far beyond the capabilities of our best aircraft control systems. One remarkable example is a bird exploiting post-stall pressure drag in order to rapidly decelerate to land on a perch. Stall is typically associated with a loss of control authority, and it is tempting to attribute this agility of birds to the intricate morphology of the wings and tail, to their precision sensing apparatus, or their ability to perform thrust vectoring. Here we ask whether an extremely simple fixed-wing glider (no propeller) with only a single actuator in the tail is capable of landing precisely on a perch from a large range of initial conditions. To answer this question, we focus on the design of the flight control system; building upon previous work which used linear feedback control design based on quadratic regulators (LQR), we develop nonlinear feedback control based on nonlinear model-predictive control and 'LQR-Trees'. Through simulation using a flat-plate model of the glider, we find that both nonlinear methods are capable of achieving an accurate bird-like perching maneuver from a large range of initial conditions; the 'LQR-Trees' algorithm is particularly useful due to its low computational burden at runtime and its inherent performance guarantees. With this in mind, we then implement the 'LQR-Trees' algorithm on real hardware and demonstrate a 95 percent perching success rate over 147 flights for a wide range of initial speeds. These results suggest that, at least in the absence of significant disturbances like wind gusts, complex wing morphology and sensing are not strictly required to achieve accurate and robust perching even in the post-stall flow regime.United States. Office of Naval Research. Multidisciplinary University Research Initiative (N00014-10-1-0951)National Science Foundation (U.S.) (Award IIS-0915148

Systems and Methods for Gravity-Independent Gripping and Drilling

Systems and methods for gravity independent gripping and drilling are described. The gripping device can also comprise a drill or sampling devices for drilling and/or sampling in microgravity environments, or on vertical or inverted surfaces in environments where gravity is present. A robotic system can be connected with the gripping and drilling devices via an ankle interface adapted to distribute the forces realized from the robotic system

Nonlinear control of aerial vehicles subjected to aerodynamic forces

International audienceThe paper contributes towards the development of a unified control approach for longitudinal aircraft dynamics. It states conditions that allow to adapt the control strategies developed for orientation-independent external forces to the orientation-dependent case. The control strategy presented here is a step to the automatic monitoring of the flight transitions between hovering and cruising for convertible aerial vehicles

Powerline perching with a fixed-wing UAV

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.Includes bibliographical references (p. 109-112).Small and micro UAVs have enabled a number of new mission capabilities, including navigating in and around buildings and performing perch-and-stare surveillance. However, one of the primary limitations of these small vehicles is endurance, simply because they cannot carry sufficient power for long missions. Recent advances in fixed-wing perching have made it possible to consider a new solution to this problem - landing on a powerline to recharge. Furthermore, because a current carrying conductor generates a magnetic field, a unique opportunity exists to use the powerline not just for recharging, but for localization as well. In this thesis, we seek to develop technologies that will enable a fixed-wing aircraft to land on a powerline using only the powerline's magnetic field and an inertial measurement unit for localization. To achieve this goal, an experimental set-up and preliminary sensing hardware are developed to detect the magnetic field at least 4 meters from the wire. Then, the necessary signal processing and state estimation algorithms are applied to achieve successful localization and overcome problematic field ambiguities. Following this, an onboard sensing system is developed and the high speed tracking of a perching trajectory is demonstrated experimentally. Finally, the position error associated with the aircraft tracking algorithm is analyzed carefully and assessed to be suitable for achieving closed loop perching. The work culminates in a light weight, 30 gram, on-board sensor system with the capability of estimating the position of a perching aircraft in real time at update rates up to 320 Hz, positional accuracies ranging from 2 to 20 centimeters, and delays of about 17 Ms.by Joseph L. Moore.S.M

Design of novel adaptive magnetic adhesion mechanism for climbing robots in ferric structures

The work presented in this thesis proposes a novel adaptive magnetic adhesion mechanism that can be implemented in most locomotion mechanisms employed in climbing robots for ferric structures. This novel mechanism has the capability to switch OFF and ON its magnetic adhesion with minimal power consumption, and remain at either state after the excitation is removed. Furthermore, the proposed adhesion mechanism has the ability to adapt the strength of the adhesive force to a desired magnitude. These capabilities make the proposed adhesion mechanism a potential solution in the field of wall climbing robots. The novel contributions of the proposed mechanism include the switching of the adhesive force, selectivity of the adhesive force magnitude; determination of the parameters that have an impact in the final adhesive force. Finally, a final prototype is constructed with customised components and it is subject to a set of simulations and experiments to validate its performance

Distributed sensing in flexible robotic fins: propulsive force prediction and underwater contact sensing

There is recent biological evidence that the pectoral fins of bluegill sunfish are innervated with nerves that respond to bending, and these fish contact obstacles with their fins. However, it is not known how fin-intrinsic sensing could be used to mediate propulsion and touch in engineered fins. The objective of this thesis is to understand the use of distributed sensing in robotic fins, inspired by bony fish fins, for the prediction of propulsive forces and for the discrimination between fluidic loading and contact loading during underwater touch. The research integrates engineering and biology and builds an understanding of fin-intrinsic sensing through study of swimming fish and robotic models of fish fins and sensors. Multiple studies identify which sensor types, sensor placement locations, and model conditions are best for predicting fin propulsive forces and for predicting the state of contact. Comparisons are made between linear and nonlinear Volterra-series convolution models to represent the mapping from sensory data to forces. Best practices for instrumentation and model selection are extracted for a broad range of swimming conditions on a complex, multi-DOF, flexible fin. This knowledge will guide the development of multi-functional systems to navigate and propel through complex, occluded, underwater environments and for sensing and responding to environmental perturbations and obstacles.Ph.D., Mechanical Engineering and Mechanics -- Drexel University, 201