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Remotely Operated Vehicle Design and Function


Remotely operated vehicles show us pictures from the bottom of the sea where no diver and few submarines could travel. These science platforms are now finding their place in commercial roles so some general knowledge is helpful. Job seekers and students should understand the parts and basic operation of an ROV just in case an opportunity appears.

Years ago designers tried to place all of the instruments and operating gear in a pressure vessel. A pressure vessel is a watertight and pressure resistant chamber that holds something that should not be immersed like a submarine crew or electronic equipment.

The electronics produced for earlier ROV's were not easily waterproofed and so everything needed to be in a pressure vessel. This makes maneuvering and propulsion difficult since any thru-hull fitting would need to be massively engineered.

Then lower voltage electronics came along with much less need for residual heat removal. Optical sensors dropped dramatically in price while rising in resolution. Now augmented reality is on the horizon for academic and commercial use and it is expected to overcome the two dimensional shortfalls of today's systems.

Modern ROV architecture is much different too. The pressure vessels are small and components like cameras and lights are suspended from a frame which is usually a rectangular box. The cameras and other components are separately waterproof so they don't need to be located together in a dry environment.

This design is versatile but not hydrodynamic. Most ROV's are slow; the 4.5 ton JASON from Woods Hole Oceanographic Institute averages 0.5 knots over ground when examining the seafloor.

The frame, or chassis, is connected to a neutrally buoyant tether that holds data and power transmission cables. This tether can go directly to the ship in shallow environments, Deeper dives or rough waters require a suppressor.

A suppressor can be a simple buoy acting as a shock absorber between the ship and vehicle, or it can be complex with additional power distribution, cameras, and lighting in support of the remote unit.

The Woods Hole team deploys an advanced suppressor called Medea in tandem with the JASON machine.

The suppressor helps support a neutrally buoyant tether that feeds power and data to the subsurface units. The tether must be supple to so it does not pull the ROV off course or make it difficult to maneuver. Deep divers like JASON have fiber optic data lines to prevent data loss over the four mile tether. Remote vehicles working in shore waters of less than 300 feet can still use category 5 data cable like you find in a home or office.

The tether on the JASON/Medea pair is about the size of your garden hose in diameter but it's four miles long and much stronger.

Thrusters must move the vehicle against resistance from currents and the pull of the ship and equipment. Thrusters are now almost always self contained electric motors and pumps which use a jet of water for propulsion and steering. Most open source ROV designs use inexpensive bilge pumps as thrusters which is essentially the same equipment as the professional model.

Ballast systems are also similar and use a liquid ballasting system like a submarine. Larger ballast changes are done manually with weights on the surface. A well designed ROV also has an emergency drop ballast for events like a non-responsive vehicle or severed tether.

Instruments are the whole reason for the platform and each job has it's own needs. Side scan sonar is valuable for science as well as commercial applications. It is one of the well tested and refined instruments with photographic resolution even in low end systems. Sensors can also detect pollution sources and broken pipes below ground using sound or chemically sensitive electronics.

Tools are now found on some commercial units. Percussion hammers and welders are fitted for cleaning and maintenance tasks. Core sampling machines can now test century old pilings for decay without risking a diver in the forest of underwater trees.

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