Hey, that’s really impressive (congrats on the second place), you should’ve posted the video too:
I have so many questions 
It is pretty funny seeing an estop button on an AUV, though I suppose it makes sense when there’s no tether nor wifi once you drop it in. I see you’re using direct RC override in MAVROS for ardusub, did you have any problems getting that to work in terms of the endpoint ID needing to be some specific number? I remember having some issues along those lines at one point since it clashed with qground’s ID and it never quite worked reliably, I had to use velocity control instead which pulled along ardusub’s stabilization and had its own downsides.
Anyhow that is some serious yaw and velocity stability over time, and this is just the imu + bar02 + thruster feedback motion model if I’m reading the code right or are the YOLO landmarks used too? A DVL would definitely double your BoM and wouldn’t work in a pool anyway (far too much multipath) so the visual slam method does sound much more promising. Have you got anything concrete planned for that if you intend to continue the project? Coincidentally I was just looking at OpenVINS since it’m told it’s the thing use on quadrotors for monocular odom atm and it might work underwater as well as long as it’s paired with a downward facing camera.
Would be cool to see if you have any videos on how yolo26n performed in practice, I’ve never thought of that size as very.. uh.. reliable, plus the quantization bit had to make the accuracy even worse? Still, 10Hz on a Pi 4 that’s already under load from BlueOS is really quick.
These ZF-S30s have gotta be the first actual pressure rated underwater servos under $300 I’ve ever seen and they do undercut that by a wide margin, do they perform reliably? If so I have to order a few…