Subsea ROV has 6 degrees of Freedom + Autopilot

This is what happens when you give Norwegian engineering students half a year to develop an ROV for their class.

The team utilized 3D printing to design and print their own thruster propellers and ducts for the ROV. It’s powered by HobbyKing motors with VESC speed controllers. This allows them to get from 0.6 to 30N of thrust from each propeller at 12V. Because of this accuracy they’re able to use a PID system to do automatic pitch, roll and depth control!

The electronics are housed in a 200mm acrylic tube (15mm wall thickness) with aluminum end caps and o-rings — an exact pressure rating is not given, but the team could flood the chamber with non-conductive oil to increase that even more — they just don’t need to for tests in a swimming pool. The undersea wire connectors they use (Subconn) are rated for 700 and 600 bar!

To our untrained ROV eye, it looks like one solid little vehicle — in fact its already qualified for MATE’s competition at NASA in June!

For more information about underwater ROV’s check out Hacklet #98 dedicated to just that!

[via r/Engineering]

16 thoughts on “Subsea ROV has 6 degrees of Freedom + Autopilot

      1. You may be able to find a balance of mineral oil and air that gives neutral buoyancy in water. That would probably offer a huge improvement in battery life, assuming the “sloshing around” of mineral oil in the compartment doesnt make the autopilot work harder to stabilize it.

        1. Buoyancy needs to be stable at all times and even a small bubble the size of a coin will cause tons of issues with everything from control to sensors. Your buoyancy elements should never be inside your pressure vessel. It’s a waste of valuable space and you need access to these elements constantly unless you have one standard operating configuration and your product is mature. Too much fussing has led me to only use solid external ballast or air-water ballast tanks depending on depth of the mission. The ROV itself can be made neutrally buoyant very easily; the umbilical is always the thing that causes problems. Free swimming would be great but wireless communication underwater is very difficult to make work consistently and I don’t know if any free swimming ROV could be certified for mission-critical work.

    1. Every time the oil filled technique is mentioned on HAD somebody posts this product. It is ill suited for use in a natural environment because of possible toxicity during a rupture. Even if 3M says it’s non-toxic the governing body in your operational area has the final say if your equipment goes into the water. Mineral oil is well known, a food supplement in some products, and is globally acceptable for pressure enhancement on unmanned craft. Silicone oils are another possibility but some regulators will see it as a spill risk because of the lack of clean-up protocol in their training.

  1. Nice idea but its been done before. I used to pilot industrial ROVs which are designed to be as stable as possible. It seems like a cool idea to be able to pitch and roll into any attitude but the reality of operating in total darkness where visibility might be limited to only a few metres means that navigating in tight spaces around millions of quids worth of assets can be quite a challenge. Having a good degree of certainty as to which way is up has been proved critical, it is just simly beyond most pilot’s cognitive ability to cope with yet another (2) degrees of freedom.

    As a matter of fact the first ROV I ever operated was and old piece of crap that was extremely unstable. It was just as happy upside down as it was the right way up with no attitude indicators or attitude control. Mid water without visual queues the only way to figure out your attitude was to run the thrusters and see which way you moved; vertical command up and I’m moving north with constant depth and the gyro shows my nose is pointing west OK I must be rolled onto my Stbd side!

    1. In the video there’s a section where a student spins and flips the ROV which then rights itself. It looks like it can be “locked” into a given orientation if desired.

  2. Before you get too excited about flooding the canisters with oil, remember that all of the contents of a pressure compensated housing need to be rated for the operational pressure. That means that your PCBs, electrical components, etc. all need to be dimensionally stable at the pressure outside of the canister, as this will be distributed to everything inside the canister.

    1. That’s a good point that deserves more discussion.

      The interaction of oil on plastic parts of components is the bigger problem since they soften and cause plastic confetti that can clog a circulation pump, and it just looks bad when the client sees your “snow globe” design aesthetics. In my shop all plastic jackets are removed from caps, etc. and values marked on the bare case.

      A couple points might make you rethink your component pressure concerns. The actual pressure inside the chamber is atmospheric for depth and salinity minus the deflection of the chamber walls. It’s not the same as chamber pressure in resource extraction where pressure is measured directly, and of course you wouldn’t use the materials in this build for a deep diving ROV. The presence of the oil is structural and only acts as a support to keep the chamber from deflecting.

      The pressure exerted on components inside the chamber is an even squeeze and the only parts that caused me difficulty were SS relays and that meant either drilling or removing the case entirely.The only part that caused a redesign were a couple of big film caps used to buffer servos and motors from noise. They would get crushed in the center so they were glued into a a piece of aluminum tubing; those monsters have now been replaced with a cap array.

      Also, small ROV’s are better suited to this technique because wall thickness can easily be increased on larger machines. An industrial machine that does ground contact tasks is usually built with heavy mild steel or high Mg aluminum alloy that is 15 to 20mm in thickness so the oil filled technique is really for smaller scale ROV’s.

  3. I can see that brushless motors are safe to use in this application, as long as the connections between the motor windings and the external wires are sealed. But what about the bearings?

      1. Bears don’t seem to have a problem with saltwater. Haha.
        .
        I agree; they will have to be replaced. Ceramic bearings or nickel coatings or ‘type 316 stainless steel’ ones can be used. Don’t expose those land motors to the briny deep blue.

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