MIT Marine Robotics Team

 

Oil-Sniffing Underwater Glider Projects

Past Work:

The team has successfully built two underwater gliders over the past two years - a small mini glider to gain experience with gliders and a better understanding of their components and one larger glider we have successfully deployed. Both gliders use a piston-based buoyancy engine system and have internal roll and pitch mechanisms. The large glider dove autonomously to 50 ft during a testing trip in Ketchikan, Alaska and was also tested in the Carderock Naval Base in Bethesda, Maryland.

Image of glider taken from a SeaBotix ROV during an autonomous dive in Ketchikan, Alaska.

Current Project

We are currently working on an updated version of the glider to implement improvements on previous glider designs (based on observations from testing), to explore innovative buoyancy engines, and to include provisions for testing sensors.

Main Objectives:

•Design an inexpensive and modular system that is capable of diving to 200m autonomously
•Evaluate the use of a gear pump in a bladder-based buoyancy engine system
•Reduce system leakage by removing the need for a moving seal
•Modular main pressure vessel that to externally attach to different buoyancy engines enclosed by flooded chamber for sensor testing

Bladder-Based Buoyancy Engine

We are working on a buoyancy engine design that explores the use of an inexpensive gear pump as the main system actuator. The gear pump has has a fixed displacement of .128 cubic inches/revolution, and is rated to 3000 psi. The motor is couples to an electric motor with an in-built worm gear.

SolidWorks design for bladder-based buoyancy engine

We have assembled and tested the engine in the laboratory and are now working to complete fabrication of the pressure vessel and finalize the electrical components and motor control in the engine.

Nitinol Buoyancy Engine

We are also working to evaluate the potential of nitinol, a shape memory alloy, for use in a passive thermal buoyancy engine that derives energy from the thermocline of the ocean. Initial work characterizing the material properties of candidate nitinol wires has been done and we are in the progress of conducting further studies. After a full evaluation of nitinol properties, we plan to demonstrate its use in a small buoyancy system in a simulated environment in the laboratory

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CAD model for preliminary nitinol glider design

ROV Chase Vehicle

Past Work

A complete system was designed and fabricated during summer 2013. The system is modular, easy to use and assemble, and can be easily adapted to suit specific purposes. We also did preliminary testing on a system that can be used to track light off the vehicle. A summary of the system is presented below.

Structure:
  • Two pressure vessels mounted on an 80/20 chassis
    • One pressure vessel contains the controls systems (an Arduino Mega, BeagleBone Black, and an XBee Series I) and a camera
    • The controls pressure vessel is housed in a clear acrylic tube and will send the depth, camera angle, vehicle orientation, camera visual, and motor information to the surface via the tether
    • The second pressure vessel includes the motors, 4 ESCs, an Arduino Mega, and an Xbee

Controls:

  • The main controls goal is to autonomously track a light below the surface
  • The system will come with a built-in override for autonomous movement so that the motors and camera angle can be controlled from the surface

Power:

  • The electrical components are powered with 9V batteries
  • The motors are powered with two NiMH 7.2 V Batteries

Propulsion:

  • The ROV utilizes small, brushless motors as brushless motors perform better in salt water


Current Project

•Design and fabricate a tethered vehicle capable of tracking and navigating to 200 m depth
•Provide tracking and retrieval support during future glider deployments
•Provide a carriage for a sensor bay to continue the characterization of sensors in open water
•Explore the use of wireless data transmission between modules onboard a submerged vessel

We are currently experimenting with the use of inductive couplings nad RF to transmit wireless data. We are also designing wireless thruster modules that can be easily added to or removed from the vehicle and are updating the mechanical design of the ROV to include a sensor mounting system.

 

 

Current Work

Our team began to explore wave energy in fall 2013. We have a general interest in wave energy conversion and its applications in providing nominal power to and communicate with underwater vehicles. We are currently in the stage of researching and evaluating current wave energy conversion designs. We are planning on using a modular buoy system to do initial wave energy tests and data collection. We are exploring the potential of the following energy conversion methods: (1) oscillating water column systems, (2) compressed air energy systems, (3) pizeoelectric systems , and (4) thermoelectric systems. A summary of each potential system is presented below.

Oscillating Water Column

•Water level oscillates with waves
•Change in air pressure inside column drives turbine
•Wells turbine spins in the same direction regardless of the direction of air movement

Compressed Air Energy

•Float acts on pump to compress air
•Accumulates pressure to release air at high velocity
•Drives turbine

Pizeoelectric

•Small random movement in the buoy
•Requires inertia component to act on the system
•Utilizes LTC3588 (Low-Loss Full-Bridge Rectifier and Buck Converter) to gather energy
•Operate in erratic motion

Thermoelectric

•Use Dissipated Heat
•Environment as Heat Sink
•Optimal operation in cold environment