Carrick Detweiler

Experiments with Underwater Robot Localization and Tracking

This paper describes a novel experiment in which two very different methods of underwater robot localization are compared. The first method is based on a geometric approach in which a mobile node moves within a field of static nodes, and all nodes are capable of estimating the range to their neighbours acoustically. The second method uses visual odometry, from stereo cameras, by integrating scaled optical flow. The fundamental algorithmic principles of each localization technique is described. We also present experimental results comparing acoustic localization with GPS for surface operation, and a comparison of acoustic and visual methods for underwater operation.

AquaNodes: an underwater sensor network

This paper describes an underwater sensor network with dual communication and support for sensing and mobility. The nodes in the system are connected acoustically for broadcast communication using an acoustic modem we developed. For higher point to point communication speed the nodes are networked optically using custom built optical modems. We describe the hardware details of the underwater sensor node and the communication and networking protocols. Finally, we present and discuss the results from experiments with this system.

AquaOptical: A lightweight device for high-rate long-range underwater point-to-point communication

This paper describes AquaOptical, an underwater optical communication system. Three optical modems have been developed: a long range system, a short range system, and a hybrid. We describe their hardware and software architectures and highlight trade-offs. We present pool and ocean experiments with each system. In clear water AquaOptical was tested to achieve a data rate of 1.2Mbit/sec at distances up to 30m. The system was not tested beyond 30m. In water with visibility estimated at 3m AquaOptical achieved communication at data rates of 0.6Mbit/sec at distances up to 9m.

Autonomous Aerial Water Sampling

Obtaining spatially separated, high-frequency water samples from rivers and lakes is critical to enhance our understanding and effective management of freshwater resources. In this work, we present an aerial water sampler and assess the system through field experiments. The aerial water sampler has the potential to vastly increase the speed and range at which scientists obtain water samples while reducing cost and effort. The water sampling system includes 1 a mechanism to capture three 20i¾?ml samples per mission, 2 sensors and algorithms for altitude approximation over water, and 3 software components that integrate and analyze sensor data, control the vehicle, drive the sampling mechanism, and manage risk. We validate the system in the lab, characterize key sensors, develop a framework for quantifying risk, and present results of outdoor experiments that characterize the performance of the system under windy conditions. In addition, we compare water samples from local lakes obtained by our system to samples obtained by traditional sampling techniques. We find that even winds of 5.8i¾?m/s have little impact on the water sampling system and that the samples collected are consistent with traditional techniques for most properties. These experiments show that despite the challenges associated with flying precisely over water, it is possible to quickly obtain scientifically useful water samples with an unmanned aerial vehicle.

Resonant wireless power transfer to ground sensors from a UAV

Wireless magnetic resonant power transfer is an emerging technology that has many advantages over other wireless power transfer methods due to its safety, lack of interference, and efficiency at medium ranges. In this paper, we develop a wireless magnetic resonant power transfer system that enables unmanned aerial vehicles (UAVs) to provide power to, and recharge batteries of wireless sensors and other electronics far removed from the electric grid. We address the difficulties of implementing and outfitting this system on a UAV with limited payload capabilities and develop a controller that maximizes the received power as the UAV moves into and out of range. We experimentally demonstrate our prototype wireless power transfer system by using a UAV to transfer nearly 5W of power to a ground sensor.

Autonomous Depth Adjustment for Underwater Sensor Networks: Design and Applications

To fully understand the ocean environment requires sensing the full water column. Utilizing a depth adjustment system on an underwater sensor network provides this while also improving global sensing and communications. This paper presents a depth adjustment system for waters up to 50 m deep that connects to the aquanode sensor network nodes. We performed experiments characterizing and demonstrating the functionality of the depth adjustment system. We discuss the application of this device in improving acoustic communication and also verify the functionality of a decentralized depth adjustment algorithm that optimizes the placement of the nodes for collecting sensing data.

Passive Mobile Robot Localization within a Fixed Beacon Field

This paper describes an intuitive geometric algorithm for the localization of mobile nodes in networks of sensors and robots using range-only or angle-only measurements. The algorithm is a minimalistic approach to localization and tracking when dead reckoning is too inaccurate to be useful. The only knowledge required about the mobile node is its maximum speed. Geometric regions are formed and grown to account for the motion of the mobile node. New measurements introduce new constraints which are propagated back in time to refine previous localization regions. The mobile robots are passive listeners while the sensor nodes actively broadcast making the algorithm scalable to many mobile nodes while maintaining the privacy of individual nodes. We prove that the localization regions found are optimal–that is, they are the smallest regions which must contain the mobile node at that time. We prove that each new measurement requires quadratic time in the number of measurements to update the system, however, we demonstrate experimentally that this can be reduced to constant time.

AMOUR V: A Hovering Energy Efficient Underwater Robot Capable of Dynamic Payloads

In this paper we describe the design and control algorithms of AMOUR, a low-cost autonomous underwater vehicle (AUV) capable of missions of marine survey and monitoring. AMOUR is a highly maneuverable robot capable of hovering and carrying dynamic payloads during a single mission. The robot can carry a variety of payloads. It uses internal buoyancy and balance control mechanisms to achieve power efficient motions regardless of the payload size. AMOUR is designed to operate in synergy with a wireless underwater sensor network (WUSN) of static nodes. The robot’s payload was designed in order to deploy, relocate and recover the static sensor nodes. It communicates with the network acoustically for signaling and localization and optically for data muling. We present control algorithms, navigation algorithms, and experimental data from pool and ocean trials with AMOUR that demonstrate its basic navigation capabilitrials with AMOUR that demonstrate its basic navigation capabilities, power efficiency, and ability to carry dynamic payloads.

Self-assembling mobile linkages

Self-reconfiguring robots are modular robot systems that are physically connected and capable of making different geometric structures. Most current research in this field is focused on homogeneous systems in which all the modules are identical. This article explores the concept of self-assembling robot systems consisting of passive structural modules plus active robotic modules.

Shady: Robust Truss Climbing with Mechanical Compliances

Many large terrestrial structures—towers, bridges, construction scaffolds—are sparse assemblies of rigid bars connected together at structural nodes. This is also true of many in-space structures such as antennae, solar panel supports, and space-station members. A long-term application of truss climbing robots is automated assembly, repair, and inspection of such truss-like structures: one or more climbing robots could grip the bars and locomote about the truss, conveying sensors, tools, or construction materials. The robot could then either carry out the desired task on its own or cooperate with a human [1,7].