Networking Assembly and Tether - LoCO-AUV/loco_config GitHub Wiki

The networking system for LoCO is in two parts: the between-enclosure system, and the shore tether system. The between-enclosure system is always required and connects the Raspberry Pi 4 in the left enclosure to the Jetson TX2 in the right enclosure. The shore tether system is optional and connects the Raspberry Pi (and thus, the Jetson), to a computer somewhere above the water on a boat or on the shore.

Between-Enclosure System

This cable allows for an internet connection between the RPI in the left tube and the Jetson in the right. It is assembled from an inter-tube connection cable (a length of gell-filled Ethernet terminated by two cable penetrators), and two in-tube connectors.

Overall Layout

Cable Between Tube

This inter-enclosure communication cable is use-agnostic. We use 2 of them in the current LoCO setup, one for Ethernet communication, and another for passing the magnetic switch circuit's signal to the other enclosure. You can find a guide to fabricating those cables here.

In-tube Connector (RPI)

The in-tube connector is a length of Ethernet cable, terminated on one end with an Ethernet connector, and on the other with Dupont connectors. As you can see in our pictures, we use female Dupont connectors on the in-tube connector, but you could just as easily use male connectors, you just need to then use female Duponts for the inter-enclosure communication cable.

The process is simple: select an appropriate length of Ethernet cable, then terminate each end with the appropriate connectors. As far as the order in which the wires should be connected on the Ethernet plug, you need to use a crossover cable wiring, as we are connecting two computers directly together.

In-tube Connector (Jetson)

The only real difference between the in-tube connector for the Jetson is the length. You can follow the process from the RPI above, just make sure that the length is sufficient for the Jetson.

Shore Tether System

Alongside the inter-tube network connection, we also have a shore tether system, which allows Ethernet connection between LoCO and a laptop, both for field operations where you want more real-time data on the robot's internals, and for bench operations. This has three parts: a USB network adaptor, an in-tube connector, and the actual tether.

USB Network Adaptor

This USB-Ethernet adaptor is used to connect the Ethernet from the in-tube connector to the Raspberry Pi. It is necessary because the RPI only has one Ethernet port, which is in use for the between-enclosure Jetson connection.

Why Not A Network Switch?

Essentially, at the time of writing, we could not find a sufficiently small, reliable network switch. All switches we considered were either found to be too large or were of questionable quality. We would like to replace the USB adaptor with a network switch at some point in the future.

In-tube Connector

This is the same process as the RPI and TX2 network connectors, just terminate one end to Ethernet, and one to the appropriate Dupont.

Tether Terminating

For the tether, you need to terminate one end directly to Ethernet, and one end you need to pot into a cable penetrator, then terminate the twisted pairs to Dupont connectors. We have used a length of gel-filled Ethernet cable as a temporary tether, but a purpose-built cable such as the Fantom Tether from BlueRobotics works far better.

To terminate the Ethernet end, simply strip back the jacketing, then terminate as you would a normal Ethernet cable (use cross-over wiring).

To terminate the robot end, start by stripping off a portion of the jacket. Either terminate the twisted pairs to Dupont connectors first, or have faith that you'll make no mistakes. Then, pot the cable following this tutorial from BlueRobotics, letting the cable cure for at least 48 hours before submerging. Consider getting a cable spool or face tangles.