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Background

The University of Idaho Center for Intelligent Systems Research (CISR) currently maintains and employs a small fleet of miniature submarines for carrying out ongoing research efforts funded by the Office of Naval Research. Once deployed, a small group of these autonomous underwater vehicles (AUVs) can cooperatively arrange themselves into an ordered group, and carry out tasks such as searching an area for objects of interest or collecting data from attached sensor packages. Measuring less than a meter long and weighing under 20 pounds, the AUVs have proved to be an extremely portable and effective platform for developing multi-vehicle autonomous operation and underwater communication.

Recently, the AUVs pattern-flying behaviors have been earmarked for a new application: measuring variations in the magnetic flux of a ship's hull while underway.  A group of AUVs fitted with data acquisition systems will swim from bow to stern beneath a target vessel, recording variations in the magnetic flux of the ship's hull using a tri-axis magnetometer, and acoustic anomalies using a hydrophone. Effectively performing this task will demand a great deal of accuracy in vehicle navigation algorithms and data collection.

 

Problem Statement

As a part of the magnetic signature research effort, the CISR group has sponsored Team Nessie in a project to update the electrical and mechanical systems of the AUVs.  The goal of this effort is to design a next-generation AUV. The improvements to the vehicle will provide greater depth and range capabilities, and optimized integration of sensor technology. In addition, the AUVs' software must be migrated to utilize MOOS-- a Linux-based software system endorsed by the Office of Naval Research.

In order to effectively address the challenges of developing a next-generation underwater research vessel, Team Nessie has divided the tasks into separate mechanical and electrical/software designs:
 

Electrical and Software Systems

The embedded computing systems that provide navigation and control in the AUVs are based on the Rabbit 3000 series of microcontrollers and a DSP-based data acquisition system.  Though these systems are adequate for the current AUV design, they present some limitations:
  • The Rabbit microcontrollers lack sufficient resources to run a Linux operating system.
  • Rabbit microcontrollers use a proprietary software development system that is not compatible with MOOS.
  • The data acquisition module used to record magnetometer and hydrophone signals is limited to a data rate of 100kb/s. This limits the rate at which data can be sampled to 16.7 kHz.  For effective acoustic measurements, a sample rate of 200 kHz is desired.
  • Magnetic flux measurements collected by the AUV cannot be closely associated with the position and orientation of the vehicle.
  • In order to retrieve data files or change the AUVs' mission configuration, the vehicles must be disassembled by a technician on dry land.

ECE Design Requirements

General Requirement
Specific Requirements
Acceptable Performance
Replace Rabbit 3000 Guidance Module with an Embedded Linux hardware platform
Must provide sufficient computing resources to execute a moderate scale MOOS software suite
CPU speed > 250 Mhz CPU memory ≥128 MegaBytes
E-Linux hardware should not require excessive power
E-Linux module should require no more than 1.5 Watts
Embedded module(s) must fit within the current AUV chassis
Module must have dimensions ≤ (3.2 x 4.2 x 1.0) inches
Embedded module(s) must have Ethernet connectivity
Module must supply at least one 10-baseT Ethernet port
Implement all existing AUV functionality using MOOS software
AUV software must conform to Front Seat/Back Seat software paradigm
Guidance module sends commands that system-specific modules (motor control, sensors, etc.) implement independently
AUV module communication must implement MOOS communication paradigm
No direct module-to-module communication. All communication is passed through MOOS database using character String or double-precision floating-point values
AUV must be able to carry out autonomous waypoint-based mission
AUV will navigate autonomously along a pre-defined set of GPS waypoints.
AUV must be remote-controllable via MaxStream radio modem
AUV will respond to commands sent via MaxStream radio modem from existing dockside control software.
AUV must be remote-controllable via WHOI acoustic modem
AUV will respond to acoustic modem command to abort mission or return to base.
Autonomous operation must include failsafe manual override
Remote commands received via radio or acoustic modem will override or cancel autonomous operation.
Vehicle status information must be available via radio modem
Vehicle status info will be periodically broadcast via radio modem when sub is at surface
AUV must provide flexible scheduling of acoustic modem communications
AUV will implement exisitng WHOI communication timing cycle using reconfigurable timing parameters
AUV must provide LBL communication and positioning
AUV will send and receive LBL ping messages using WHOI modem and use them to provide position calculation
Autonomous operation must include fault detection and handling
AUV will cancel autonomous mode and return to surface on fault condition (water leak, battery voltage, etc.)
AUV will integrate with existing DSP data acquisition module
AUV will implement existing command protocol used to start and stop acquisition/recording of magnetic signature data
AUV embedded hardware will attempt to minimize power consumption
AUV will automatically disable and/or power down WiFi and radio modem transmitters when submerged by > 1 meter
AUV will provide a web interface
AUV will host a web page showing vehicle status and parameter info and/or allowing limited configuration
Add software to provide upload/download of missions, configuration, and acquired data via WiFi connection
Missions should be configurable via WiFi
MOOS configuration files used for missions will be accessible via WiFi as files using FTP protocol
Front seat driver module settings must be configurable via WiFi
Configurations used by front seat driver modules (elevator/rudder trim, calibration constants, etc.) will be accesible via WiFi as files using FTP protocol
Acquired magnetic signature measurement files must be downloadable via WiFi
Acquired data files from DSP data acquisition module will be accessible via WiFi using FTP protocol
Integrate readings from IMU unit into DSP acquired data files
IMU readings must be included in acquired data files such than their timing relationship is preserved
IMU readings will be sent to DSP data acquisition system and interleaved with sample data such that their relative timing can be determined within ±150 milliseconds by their proximity to sample data
Increase data acquisition module data rate
DSP data acquisition module must be capable of acquiring one channel of 16-bit data at 200,000 samples per second
Data acquisition module will support high-speed FLASH media cards capable of disk write bandwidths of > 450,000 Bytes per second.

 

Mechanical Systems

The current AUV layout includes a magnetometer which is belly mounted.
  • The current magnetometer mounting system causes both sluggish sub response to directional changes and a rocking motion when speeding up or slowing down.
  • When placed in the water, the propeller is not completely submerged, making diving difficult.
  • The sub’s operational depth limit is unknown.
  • The current pressure sensor onboard only operates up to 25psi.
  • A Reson TC4032 hydrophone must be added for acoustic signature assessments.
  • The acrylic tube that encases the sub’s electronics is brittle and prone to crack on impact.
  • Only a friction seal is used to secure the nosecone to the sub’s body. This could cause the nosecone to "pop off" when surfacing.
  • Newly purchased Gumstix boards need to be mounted in the AUV.