30 Orin Nano is used for the execution of the machine learning and vision algorithms, for which access to an embedded GPU is required. “The decision to use commercial computers such as the RPI4 or NVIDIA Jetson platforms originates from the idea of keeping things simple and focusing on the most critical aspects related to autonomous underwater navigation, as well as leveraging our internal knowledge of optimised software development for embedded platforms,” says Arteaga. “Moreover, while using RPI computers was not considered a professional approach a couple of years ago, this is not the case anymore. Nowadays, those platforms offer the ideal trade-off between computing capabilities and power consumption for all mobile robotics projects.” The main control board features a plethora of input buses to take data from the onboard camera systems, pressure barometer, DVL and IMU. Although an input port for a ranging sonar is also present, the stereo vision camera has effectively replaced sonar in uWare’s obstacle-avoidance approach. The IMU is mounted on a separate board, along with a 5 V power-distribution module and an I2C switchboard. I2C and UART are the main communications interfaces used between the main computing unit board and the rest of the subsystems. While the Jetson Orin and RPI4 are connected via ethernet, some sensors and actuators – such as the barometer, DVL, IMU, thruster-control system and cameras – are connected using either I2C, UART, MIPI CSI-2 or USB. “If the Jetson Orin should stop functioning mid-mission, the RPI4 can still continue. For instance, if the AUV has a preprogrammed survey path, it can still autonomously follow that using, for instance, the bottom camera or any external payloads for viewing and recording pipelines or other infrastructure below. But it will try to send the operator an alert via the acoustic modem that says it no longer has its machine vision and asks if they want it to continue the mission or return to the point of deployment,” says Arteaga. An additional board mounts the company’s proprietary acoustic modem electronics, as well as a 12 V powerdistribution board. The last board is responsible for motor control, mounting eight electronic speed controllers (ESCs) – one per thruster – and a power input from the battery, as well as data input from the BMS. Unique touches Although uWare has sought commercial off-the-shelf (COTS) components to avoid reinventing the wheel where possible, a few components have been made in-house ad-hoc to fit the uOne’s evolving needs. For example, its own voltage regulators were developed after going from four to eight thrusters to increase current throughput by 5x without incurring the expense of a market-ready component capable of doing that. A similar approach has been followed for the creation of a proprietary acoustic modem. “Currently, the most affordable acoustic modems cost a couple of thousand dollars and their specifications are not aligned with our requirements,” Arteaga explains. “They’re built to send tiny packets of data over multiple kilometres, sometimes up to 10 km, and we don’t need that kind of transmission distance in a short-range AUV. We therefore built one that costs just a couple of hundred euros, with a maximum range of just 2 km and increased data rate.” Additionally, uWare plans to “replace” the cables running between the boards with a single, unified, printed circuit board (PCB), which embeds all the components of the four boards mentioned, improving the overall speed and reliability of all the data interconnections, and hence functions, while optimising the space available in the watertight enclosure. Track and sense The uOne’s IMU is a COTS component from Bosch, which integrates an accelerometer with a Zero-G Offset of -150 to +150 mg and a noise-density output of 150-190 μg/√Hz, as well as a gyroscope with a Zero Rate Offset of -3 to 3°/s and 0.1 to 0.3°/s noise output, along with a magnetometer with a Zero-B Offset of 40 μT. Its DVL, supplied by Water Linked, integrates a four-beam convex Janus array transducer with a frequency of 1 MHz and a 22.5° beam angle, as well as a ping rate of 4-15 Hz. It operates within altitudes of 0.05-50 m from the seabed at a maximum velocity of 3.75 m/s. While the uOne’s guidance and motion tracking comes from the standard combination of an IMU and DVL, for localisation, uWare has forgone beaconbased systems such as ultra-short baseline (USBL) and long baseline February/March 2024 | Uncrewed Systems Technology The uOne’s main computer is a Raspberry Pi 4, as an ideal trade-off between computing capacity and power consumption, while an NVIDIA Jetson Orin is used for AI algorithms
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