Unmanned Systems Technology 028 | ecoSUB Robotics AUVs I ECUs focus I Space vehicles insight I AMZ Driverless gotthard I InterDrone 2019 report I ATI WAM 167-BB I Video systems focus I Aerdron HL4 Herculift

26 Dossier | ecoSUB Robotics AUVs BP said that a very small autonomous submarine was exactly what it needed to help it make a 50% saving on its operational maintenance budget by 2025. However, it wanted a vehicle that could go deeper and carry more sensors, and offered some development money to come up with a larger version. Sloane already had plans for a bigger ecoSUB, so the company accelerated its development, adding more people to the team. The result was the ecoSUBm25, with a 2500 m depth capability and measuring 1000 mm in length and 146 mm in diameter, with 18-30 hours of endurance depending on the battery type. Without the sonobuoy tube constraint, it can carry its antenna upright, enabling the vehicle to cruise at the surface to maintain connectivity. The m5 is a version of this vehicle, with a lighter pressure case that enables it to operate down to 500 m. In May 2016, BP set Planet Ocean a target to build a working vehicle in seven months, which it achieved, putting a demonstrator in the water at Christmas of that year. This turned out to be the first stage in an approval process that included participation in an oil spill response exercise in the Solent, off the south coast of England, followed by a deployment at the Magnus pipeline off the Shetland Islands in the North Sea to search for leaks using hydrocarbon sensors. With the successful completion of this work, BP indicated that the ecoSUB vehicles were well-suited to its future offshore maintenance plans. In parallel, Planet Ocean continued to work with the NOC and ASV on the launch and recovery system, successfully demonstrating it at the end of the project. The company then had two vehicles at around Technology Readiness Level 7, Sloane notes, and began a year-long productionising effort. Navigational challenge At around that time came a new Innovate UK call for a cooperative project, Robotics and AI in Extreme and Challenging Environments, which sought to develop AI that would enable very small AUVs to navigate accurately in harsh environments. This is a challenge for small, low-cost underwater vehicles – the μ5 is priced at about £10,000 and the m5 at about twice that – that tend to use inexpensive sensors to keep the price down and don’t have the volume, power or weight budget to carry a Doppler Velocity Log. “We have a $100 IMU in there, which gives us an error of 10% of the distance travelled, so in 100 m you could be 10 m out,” Sloane says. This IMU-based dead reckoning navigation is adequate for a lot of missions, he says, when supplemented by frequent GPS fixes. If for example a mission requires the vehicle to travel 5 km, it is programmed to pop up for a fix several times en route. For longer missions though, and for sidescan sonar and camera work in particular, it is vital to know the precise location of everything the sensors are looking at, so something better was needed. Fortunately, that arrived in the form of tiny, high-performance, low-cost acoustic modems that enable Long Base Line (LBL) positioning when used in conjunction with beacons in known positions. Planet Ocean and the NOC brought the modems’ developers at Newcastle University into their team, and their winning bid in February 2018 marked the start of the IUK 2 project, which ended this July. The NOC developed the acoustic network protocols and navigation algorithms, using an Enhanced Kalman Filter (EKF) that takes multiple inputs from which it derives a solution that is better than the sum of its parts. The EKF takes inertial data from the IMU, and the acoustic range and bearing data from the LBL system, and outputs more accurate positions. “We did a lot of testing throughout the project, and we now get better than 5 m regardless of how far we’ve gone or how long we’ve been submerged,” he says. Three members of an ecoSUB shoal can be designated as surface nodes in an LBL network, broadcasting their GNSS position and other information from their acoustic modems. To ensure they remain in the right place to serve in this role, they enact a specially developed ‘stay-in-circle’ behaviour. As Sloane explains, “If they drift more than 100 m from where they are supposed to be, they will power back October/November 2019 | Unmanned Systems Technology The m5’s ability to cruise on the surface allows it to act as a surface node in LBL or USBL positioning systems for cooperative shoals of ecoSUBs (Courtesy of ecoSUB Robotics)