Uncrewed Systems Technology 043 l Auve Tech Iseauto taxi l Charging focus l Advanced Navigation Hydrus l UGVs insight l MVVS 116 l Windracers ULTRA l CES 2022 show report l ECUs focus I Distant Imagery

52 “Although hydrodynamics took a back seat to packaging, the outer hull is still designed to be really smooth, to minimise biofouling.” Orr says. “It can be sandblasted with copper particles or anti- fouled in other ways without any issues.” Energy and underwater charging A lithium-ion battery pack is installed at the approximate centre of the UUV, and contains up to 100 Wh. To develop it, Advanced Navigation bought COTS cells and arranged them in an off-the-shelf battery protection system design from STMicroelectronics, before integrating them into a complete module format certified to UN flight safety standards. “That means the Hydrus can be transported in aircraft luggage, which is quite rare among AUVs as far as we’ve seen, so ocean research or protection groups can easily move them between different coastlines,” Orr comments. The BMS is also an STMicroelectronics reference design. Its schematic is robust enough that Advanced Navigation saw little need to deviate from it for its cell monitoring, balancing and charging requirements. And as the Hydrus is fully sealed and omits connectors, charging is performed wirelessly, with two inductive coil systems at the front and two at the rear, which have been designed and installed according to the Qi certification standard. Qi was originally developed as a low- power wireless charging standard for mobile phones, and allows for up to 15 W in most versions of the standard and 30 W in the latest version, which is what the Hydrus supports per coil. “The front and rear protrusions have been designed with docking capabilities in mind,” Orr says. “We demonstrated this in a tank at the Oceanology show, where we showed a Hydrus swimming in and out of its dock. “Its nose or tail will latch onto the dock to charge, without the need for motors for station-keeping. It can emit power too, so accessories can be strapped onto either end; so long as they have an inductive receiver they can be powered on. We’re also developing an accessory payload ‘ring’ that will fit onto the back and be powered wirelessly by the Hydrus this way using a Qi coil.” LEDs are set around the ‘plug’ for the onboard computer vision to use as guidance during docking. Earlier versions used QR codes for optical navigation (similar to the Marin mAUV – see UST 32, June/July 2020), but the risk of QR prints being hidden by algae for example meant this approach was discarded. The 60 W charging rate enables a full charge of the battery within 2 hours. Charging the Hydrus from both ends at 120 W is currently disabled until Advanced Navigation has confirmed the safety from a thermal standpoint of doing so. “The anti-fouling on the hull comes in handy there, because with the underwater docking stations we’ll make available, the UUVs could be sitting still amid algae and seaweed for several hours a day, and we need to minimise the rate of organism build-ups,” Orr notes. Navigation and AI A GNSS receiver and antenna are installed in the back of the UUV for obtaining position fixes during deployment and brief moments of surfacing. It is integrated with a repackaged version of the company’s Subsonus USBLs, which provides real-time positioning updates while the Hydrus is submerged. Both positioning systems feed into the onboard INS, which is a variant of the company’s Spatial products. It has been customised to run at 1 MHz, instead of the usual 30 kHz rate. This is the same frequency as the Subsonus and many other USBLs, and might have caused degraded consistency or integrity in inertial data feeds. “We’re using specially designed MEMS chips in our IMU in order to get that higher frequency,” Orr says. “Then we integrated April/May 2022 | Unmanned Systems Technology The rear of the hull contains a GNSS antenna and receiver for position fixes when surfacing A ring of eight LEDs provides dynamic lighting adjustment to optimise camera visibility