Networking Assembly & Tether

/images/docs2_html_edc21b4683393c6e.png The communication architecture layout provides an insight of how the sensor suite (i.e., Cerulean Omniscan 450 Side Scan Sonar, Water Linked Underwater GPS, Doppler Velocity Log, Low-Light HD USB Camera) interfaces with the computers for data processing. The Ethernet Switches allow the Raspberry Pi 4 (RPi 4) and the Jetson Orin NX to perform inter-enclosure sensor data communication and control commands execution, depending on their processing power capacities.

The GPS, DVL and the USB Camera are connected to the RPi 4 via the Ethernet Switch #1 and the Side Scan Sonars are connected to the Orin NX via the Ethernet Switch #2. The Orin NX, with its higher processing power, is used for data processing from various sensors such as the DVL for localization and the depth camera for vision-based algorithms. The RPi 4, coupled with its inbuilt BlueOS from Blue Robotics, oversees the thruster control and the FPV video feed via the USB camera through the QGroundControl application.

In the future, the usage of GPS and the Side Scan Sonars could be further explored and developed within our system.

Overall Layout

/images/docs2_html_f1d31b4270983ef3.png The layout shows how the vision/AI module and the control module interact with each other via the inter-enclosure communication cable within the ROV.

In tethered mode, the topside computer communicates with the ROV through the RPi 4 via the FXTI and Fathom Tether Spool connection. The maximum length of the tether is 300m, which is the physical limit of communication between the topside and the ROV in open water. Through the QGroundControl application, the user will be able to control the ROV with a remote joystick controller and observe the live video feed of the underwater scenes.

In tetherless mode, by breaking the connection of the removable fathom tether, the topside computer communicates with the ROV through the Jetson Orin NX instead via SSH communication using Wi-Fi to initiate the program. This is only possible on the water surface where wireless communication is possible. The program then establishes a MAVLink communication to the RPi 4, in which the velocity commands will be sent to the thrusters through the onboard Navigator module via the RPi 4. Once underwater, the ROV will run in complete autonomy without communication with the topside computer.

Inter-Enclosure System (BlueROV2)

Cable between Enclosures

/images/docs2_html_863356b0a0f89318.png There are 2 Fathom ROV Tether (yellow cable): the cable that connects the control module and the vision/AI module transmits data bidirectionally between the modules; the other cable relays the communication between the topside computer and the ROV.

In-tube Connector (RPi 4)

/images/docs2_html_5ab04f139f53735c.png Figure A shows the connection point where the Fathom ROV Tether cable used for inter-enclosure data communication between the RPi 4 at the control module found at the BlueROV2 Heavy layer and the Orin NX at the vision/AI module found at the payload skid layer.

Figure B shows the connection point where the JST connector is connected to the Ethernet Switch. This is where data is transmitted bidirectionally between the RPi 4 and the Orin NX via the Fathom ROV Tether-JST cable.

In-tube Connector (Jetson Orin NX)

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Figure A shows the crossover cable wiring between the Ethernet and JST connection. The Ethernet connector (RJ45) has 8 different wires with different pinout connections. Using an RJ45 to JST GH Adaptor to connect both the JST connector and the Ethernet connector, we can determine which color wire is electrically connected to which color wire of the JST connector. Through the connectivity test, the TX and RX wires of the Ethernet connector can be determined and be soldered accordingly to the JST connector’s TX and RX wires.

Figure B showcases the connection between the Ethernet Switch and the Jetson Orin NX. The JST connector is connected to the Ethernet Switch and the Ethernet connector is connected to the Orin NX. This would facilitate the inter-enclosure data communication between the Orin NX and RPi 4 via the Ethernet Switch.

Shore Tether System (Fathom Tether Spool)

Fathom-X Tether interface (FXTI)

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The original FXTI is a simple and expandable topside enclosure to interface with the BlueROV2. However, there were limitations in establishing speedy data communication between the topside computer and the FXTI via the USB connection as the FXTI utilizes an ethernet to USB converter to communicate with the topside computer. Hence, the modifications made to the original FXTI were to remove the USB converter and replace it with only ethernet cable connection to the topside computer to improve communication speed and stability.

/images/docs2_html_d5f015921ce6eaaf.png Figure A & B shows the components used in the modifications of the FXTI. The voltage regulator regulates the output voltage supplied by the LiPo battery to power the 2 Fathom-X Tether Board and the Ethernet Hub. With a stable power supply supplied by the LiPo battery instead of the USB cable, it would ensure a stable connection without irregular power issues. The Fathom-X Interface Boards are connected separately to the Water Linked Underwater GPS and the Fathom ROV Tether, streaming the data to the topside in independent Ethernet connection. The Ethernet Hub providing multiple ethernet ports enables ethernet connections to multiple topside computers for debugging.

/images/docs2_html_b56488d1110e21af.png /images/docs2_html_a487f79c7ec78234.png The green pair wires from the Fathom ROV Tether are connected to the tether input terminal of the Fathom-X Tether Interface Board, where the control commands from the topside computer is sent to the ROV and sensory data from the ROV sent back to the topside computer. The interface board is designed to provide a high-speed, long-distance Ethernet connection to an ROV, which ensures seamless communication with minimal delays.

Removable Tether Configurations

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Transitioning towards tetherless controls, the fathom tether is spliced to make it removable for both autonomous and tethered control applications. The fathom tether cable consists of 4 pairs of wires, with the green pair connected to the Fathom-X Tether Interface Board onboard the ROV for controls and blue-brown pair connected to the GPS. By using the screw terminal blocks, it ensures a strong electrical connection between the loose wires to minimize the loss of communication. The WetLink Cable Splice Kit from Blue Robotics, which is used to house the electrical connection, minimizes the water from entering the housing due to high pressure underwater.