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

54 Digest | Advanced Navigation Hydrus grain sense and control over lighting, which allows us to produce really high-quality imagery that you wouldn’t usually be able to get underwater, not like this,” Orr remarks. For further details on water quality, the aforementioned water sampling suite contains sensors for measuring levels of salinity, dissolved oxygen, CO 2 , temperature, pressure and more (some optional or customisable on request). Computing hardware Despite the many different subsystems to be managed, the Hydrus is able to run on only two computer boards. A motherboard sitting near the front contains most of the processing units, including the single FPGA that forms the core of most of the sensors’ operations, and a main CPU running ROS-2 is the vehicle’s middleware. The second board sits near the back for the acoustic comms modem and USBL transceiver. The FPGA is ideal for running the forward-looking sonar, DVL, optical modem and 4K camera owing to the heavy signal processing loads that would be challenging to accomplish with a normal microcontroller or CPU. While this has been commonplace in UUV engineering for many years, modern advances have been key to allowing multiple subsystems to run simultaneously off a single FPGA unit, with separate systems for clocking to enable synchronisation without interference between subsystems. Also, the FPGA is a particularly large one, to handle the signal processing requirements without driving up the UUV’s total power consumption. “The FPGA also runs the processing for the USBL and acoustic modem,” Orr adds. “There’s a flex ribbon that passes through the middle of the UUV to the circuit board at the back; the board is largely just there for data link management. “By connecting everything this way, with subsystems running within their own clock barriers but connected by sync lines, everything is time-stamped really well. All the geo-referencing and ranging in images, video and point clouds are precisely lined up in the metadata of our recordings.” The main processor is an eight-core system with 32 Gbytes of RAM, running at 1.8 GHz on each core. A 1 Tbyte SSD is also available for data recording, which can be retrieved between missions via an onboard wi-fi access point. ROS-2 was selected for its flexible environment for robotics development and to enable an open platform for end-users to load their own software modules and access the different subsystems, without being able to access Advanced Navigation’s own IP. “ROS-2 is a great layer for that, and customers can test all their code in the simulator and check that it works before trialling it in the sea,” Orr says. “It has also allowed us to integrate our mission- planning system quite seamlessly.” Data is transmitted about the UUV’s subsystems using a high-speed RS-422 network. This relatively simple approach has been found to be suitable for managing two computer boards and an overall low part count. Mission software Advanced Navigation’s mission-planning software is designed to provide a 3D map of the user’s operating environment in a similar interface to Google Earth (and in the GCSs often seen among professional UAVs), allowing largely untrained operators to draw out their waypoints with coordinates and altitudes. “And through the interface you can do mission reviews,” Orr says. “There are integrated walkthrough functionalities for mission recordings, but it also exports recorded data in compatible formats for all the industry-standard survey packages.” In addition to pre- and post-mission analysis, the Hydrus also integrates an e-ink display screen on its tail for operators and divers to view performance and health indicators such as charge status, and the latter can interact with the vehicles through this system. Comms As standard, the acoustic modem at the rear can transmit and receive at up to 10 kbit/s over a range to 1 km. Higher bandwidths are extremely challenging to achieve a 30 kHz frequency, regardless of the encoding scheme. As such, it serves mainly for telemetry monitoring or alert deliveries to the GCS or other Hydruses, rather than delivering live feeds of the huge amount of data a Hydrus will capture during missions, although being able to do so without a tether remains a critical upgrade for most potential users. The optical modem allows for far larger dumps of data – up to 10 Mbit/s within 10 m. While that could be used, say, to deliver data to a laptop on a boat or pier near the UUV’s mission setting, April/May 2022 | Unmanned Systems Technology The rear tail also integrates an acoustic modem for up to 10 kbit/s over a 1 km range, and an e-ink display for operators and divers to check performance indicators