Motion Control Tagged withMaxonROVSEAMOR Marine
Nanaimo-based SEAMOR Marine's ROVs take underwater exploration to uncharted depths. 0 October 19, 2016
Lindsay Luminoso Built by the Japanese navy in 1944, the Sen Toku I-400 series submarine, at 120 meters long, was the most massive of its day and one of the most militarily advanced. Designed to strike major U.S. targets like New York, each of the three behemoths built sported four 2,250 hp engines, enough fuel the circle the globe and three attack aircraft that could launch from a hanger on its top deck. Ultimately, the I-400 never saw service before the Allied Forces won the war. In the aftermath, the U.S. Navy scuttled many captured ships, including the last Sen Toku submarine, the I-402, off the Goto Islands.
Fast forward nearly 70 years to August 2015, when a team of researchers discovered the World War II submarine 190 meters below the surface of the East China Sea, with the help of a remotely operated underwater vehicle (ROV) built by Canada's SEAMOR Marine. For more than 25 years, the company has been designing and fabricating tethered robotic craft tasked with exploring deep-sea environments deemed too dangerous for human divers. Originally developed by Nanaimo robotic company Inuktun Services Ltd., the SEAMOR ROV became a stand-alone company in 2010.
Since then, the Nanaimo, B.C.-based firm's equipment has helped discover a Soviet-era bomber lost in 1941, explore three historic shipwrecks off the coast of Sicily and stem a potential oil spill when two tug boats collided in the Strait of Georgia near Nanaimo. Of course, not all applications of SEAMOR's ROVs are as adventurous. Most grow out of oil and gas and mineral exploration, but the company says the uses of its diminutive deep-sea divers are ever expanding.
"I think that there has been a lot of work done on ROVs from a single discipline perspective, be it mechanical or electrical or software," says Chris Parker, lead engineer for SEAMOR Marine. "What we really excel at is that we take a multi-disciplinary approach. We have assembled a really great team of designers and engineers. If you are going to push robotics into the harshest environments on the planet, you really need to take into account all of the different variables."
One of those variables is application adaptability, Parker says. Although there are many different sizes and classes of vehicles within the ROV market, SEAMOR has found their sweet spot with their Steelhead and Chinook line. Both are designed for underwater exploration, search and recovery and marine inspection, but the Steelhead ROV is rated for 300m depths while the Chinook ROV is rated for 600m depths.
Under the hood, however, the ROVs' core electronics and sub-components are identical to allow for accessories to be added to the vehicle. This modular design not only ensures that spare parts are always available, but also allows SEAMOR to make their ROVs fit customer needs without expensive modifications.
The ROVs were designed to be the eyes of the operator underwater.
"We developed this all-purpose workhorse vehicle in what we would call the inspection class," Parker explains. "We are in the class size where, at most, you need two people to operate the ROV - one to deploy the tether and the other to operate the controls," says Parker. "It's as easy as placing the vehicle in the water and away it goes."
"This makes sense on the engineering and business side of things," adds Elaine Ho-Parker, marketing consultant for SEAMOR Marine. "It also makes things easier for the customer as they can always upgrade an existing vehicle."
For example, the customer can begin with a basic twisted pair tether configuration where power and signals are carried over traditional copper wires. Parker explains that the vehicle doesn't know what type of tether it is using because the ROVs incorporate a universal tether interface that is included in the two models. Because of this, for more enhanced capabilities, the system can be moved to a fiber optic tether, with the options of a longer of tether length, Ethernet, or HD video, without having to change the vehicle. The SEAMOR ROV allows the user to observe the environment through a camera system as well as physically interacting with the environment through a number of accessories.
The vehicle was designed to be the eyes of the operator underwater allowing them to investigate and interact with the environment. When developing the vehicle, the team had to keep in mind that diving down to depths of 300-600m meant the vehicle would be subjected to extreme water pressure. The Chinook model is upgradable to a 600m capable version, with stronger glass windows to withstand the greater pressures encountered at such depths.
There were many other elements to consider when sending the vehicle down to certain depths, too. One of the biggest design challenges for SEAMOR was in the sealing.
"You have to keep the dry parts dry and the wet parts wet," Parker says. "Things like shaft seals on the thrusters, keeping water out of the motors, were extremely important. Going to higher strength materials...is important as well as ensuring that the tolerances are up to spec particularly on the thruster propeller shafts so they will seal properly with the mechanical seals."
However, it was extremely important for the vehicle to be as lightweight as possible to maximize speed and allow the ROV to operate in high water currents. In keeping with this, the team designed the mechanical aspects of the vehicle to save weight wherever they could.
"To the casual observer, the float actually feels like it shouldn't float at all because it's very heavy," says Parker. "If you use just regular foam, it will compact down to a fraction of its size [under pressure]. The floats are made from syntactic foam, which is composed of glass microspheres in epoxy. It is very expensive, probably the single most expensive part of the vehicle. By making the frame and panels lighter, we are able to decrease the size of the float."
Brushed vs Brushless
The ROVs are equipped with two horizontal thrusters pointing out the back of the vehicle and two vertical/lateral thrusters. The Chinook model can be upgraded to include up to four horizontal thrusters. The rear thrusters give the forward-backward motion as well as pivoting the ROV. The vertical thrusters provide up-down motion and, because they are angled out, they also provide lateral control.
For the drive system, SEAMOR used Maxon brushed DC motors running through mechanical shaft seals to the propellers and Kort nozzles - tubular tapered nozzles around the propellers designed to make the propellers as efficient as possible.
The SEAMOR Steelhead model can reach depths of up to 300m.
"There is contention in the ROV field whether it is better to use brushed or brushless motors," explains Parker. "A lot of people think you should use brushless motors because it is the new technology. But in a field situation, I can test if a brushed motor is still working with a simple battery. A brushless motor needs to have power to drive the motor, power to drive its control electronics, and on top of that it has to have a control signal to tell the control electronics which way to make the thruster go and how fast."
So if there is a problem with the vehicle, there is no way to tell if it is a problem with the thruster or the electronics. For Parker, this made using brushed motors a simple decision and provides the flexibility for customers.
Parker notes though, it is important that the motors run smoothly. When you are sealing at those depths, it is not just how good the seal is, but you also need to make sure that you are not having any unnecessary vibrations, which can cause the seals to misalign. He also points out that in underwater applications, the thrusters don't need to spin as fast as in an aerial application, so many of the advantages of brushless motors don't materialize.
Inside of the vehicle, Parker says it's the onboard diagnostics that really make this system stand out. It was important for the team to develop a system that was robust and resilient to failure due to the harshness of the sub-sea environment. Ensuring that failures are easily identifiable was a significant design feature.
In the case of a failure, all the operator has to do is take off the cover, and the electronic system has indicator lights to show how the functionalities are operating in real time. This allows the user to diagnose problems on-site and plan accordingly.
"We have triple redundancy designed everything," Parker adds. "The power electronics that control the thrusters, if there are any faults, they automatically shut down. There is no risk of short circuits or damage of the vehicle."
Next-Gen ROVs
As for future vehicles, SEAMOR is still in the design phase and is exploring the idea of full autonomy. Dealing with highly sophisticated underwater infrastructure, a fully autonomous vehicle is not always the best solution.
However, having a semi-autonomous ROV with a human operator in the loop or standing by in one area the company is exploring. Parker notes that they are looking at "sliding autonomy" - the idea of human-robot collaboration, where a human operator can take control of an autonomous vehicle whenever necessary.
"There is a really big opportunity for ROVs to move into this field and this is something we are really exploring as we've redesigned our operator interface," he says. "We are trying to build not just a vehicle that meets all of those needs but the accessories, support and documentation as well as aftermarket support to service the market as best we can."
"Whatever we do with our next-generation product, it will be done with the same design philosophy," he adds. "It's really just about looking at where the industry is going, what are the demands we can anticipate so that we can design a vehicle that is top of the line today and we've left all of the doors open to add all the features we see coming down the road."

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