I have a pixhawk and a Raspberry Pi 3 b+; how do I install Companion software on the Pi so that I can control my ROV? I think I can figure out how to flash the pixhawk with Ardupilot/sub, but I can’t find any documentation on flashing a Pi with proper software.
Hi @clqsical, welcome to the forum 
Our retired Companion software was only designed for the Raspberry Pi 3B, and is no longer being developed or supported, so is not recommended for installation onto new systems. From a bit of searching around it may be possible to install on a RPi3B+, but we can’t guarantee it will work.
We would instead recommend installing BlueOS, which is actively supported and developed, and has been marketed as supporting the RPi3B+ since version 1.0 released in 2022. To do so you can just flash on the ARMv7 image, via the standard installation instructions