USE Network launch I UAV Works VALAQ l Cable harnesses l USVs insight l Xponential 2020 update l MARIN AUV l Suter Industries TOA 288 l Vitirover l AI systems l Vtrus ABI

66 gives other advantages too, such as hull rigidity, sufficient strength for installing lifting hooks on the main structure, and good pressure resistance.” The aluminium modules are designed with connection points for O-ring seals, which waterproof the joints between segments to a maximum depth rating of 200 m. Optical-aided navigation To achieve the high degree of control needed for the vertical and transverse thrusters to orient the mAUV as desired, MARIN needed to select inertial sensors capable of outputting position, speed and acceleration measurements to a high degree of accuracy. To achieve this, an iXblue PHINS C3 fibre-optic gyro IMU has been installed to estimate attitude, rotation speed and position. An Xsens MTi-300 attitude and heading reference system is also installed and operates as a secondary source of these data estimates. For further positioning precision, most UUVs will use some form of acoustic aid such as USBL, LBL or DVL systems. However, as the mAUV’s trials are to take place largely in MARIN’s test basins – which have concrete walls and floors – acoustic positioning technologies would be hampered by reverberations. Also, although the UUV can surface frequently thanks to its shallow test operation depths, GNSS cannot be used as an occasional source of position reference updates, as the test basins are indoors. Instead, the team has installed an optical aid system in the test chambers. This is based on stereo vision cameras (installed on a moving rail-based carriage located above the basins) that detect and localise ArUco markers across the mAUV’s body in real time, to measure its position and attitude underwater. In addition to being recorded in the team’s test equipment, this information is also intermittently transmitted to aid the onboard INS. This is achieved using VHF radio antennas (one on the nose and another at the rear, near the main propulsion thrusters) which use the restricted bandwidth in the basins to transmit inertial data estimates as correction aids to prevent INS drift, as well as receiving basic operational commands. Lastly, this measurement data tells the overhead towing system where it needs to pull the camera carriage in order to keep a close eye on the UUV’s whereabouts. Naturally, for tests outside MARIN’s basins, acoustic aid systems such as DVLs and sidescan sonars (and possibly USBL transceivers) will be integrated. De Kruif adds, “In a future research project we will look into the position estimation of an autonomous vehicle – underwater or on the surface – based on information coming from a camera mounted on the vehicle itself. “As well as the question of how to do this in a harsh maritime environment, we’re very interested in how accurate and fast the data and processing would need to be for this kind of system to work. “This is crucial for autonomous vehicles: steering actions are based entirely on this information. If you want to recover your vehicle in a high sea state, your positioning measurements need to be reliable and fast, with robust algorithms to interweave your vision sensors with your control systems.” Power Power to thrusters, sensors and so on is provided by a 24 V lithium-ion battery pack installed between the centre and rear of the vehicle. The pack consists of seven cylindrical NCA (lithium nickel cobalt aluminium oxide) cells. Each cell measures 6 cm across and has a capacity of 45 Ah, or 162 Wh of energy storage. When the cells are connected together, the pack thus stores 1.134 kWh and supplies it at around 25 V to the onboard systems. “The cells are mounted in a circular or annular way, to provide an open space through the middle, through which the aforementioned moving mass can travel to adjust the mAUV’s CoG,” Van Der Schaaf adds. Ypma notes, “Currently, the capacity of the batteries is relatively limited compared with long-endurance UUVs, as the pack is tuned mainly to suit the June/July 2020 | Unmanned Systems Technology Four thrusters provide forward propulsion, which is currently limited to 4.5 kph for the basin experiments