When we move the joystick forward, the ROV moves forward correctly, but at the same time it slowly goes down (loses depth) even without any down command.
This behavior is consistent in both Stabilize and Depth Hold modes.
Yes, I see this issue on 4.5 branch as well, I have tried 4.5.3 tried eariler. I will try to get the logs and share with on latest release 4.5.7 as well.
I am curious whether this is just caused by your vehicle design / mass/buoyancy distribution.
As some examples:
If it’s negatively buoyant, it will sink even while disarmed
If your forward-facing thrusters are above your vehicle’s centre of mass (e.g. from some heavy payload at the bottom of the vehicle), or there is a large drag surface at the bottom of the vehicle then it will pitch its nose down when it moves forwards, in which case moving forwards pushes it downwards a bit as well
Similarly, if the centre of mass is further forward than the centre of buoyancy the vehicle’s resting orientation will have the nose pitched slightly down, and the same effect occurs
Alternatively, if your vehicle is heavy on one side it could be roll stabilising and incidentally causing vertical motion due to thruster asymmetry (which we’re working on compensating for, but haven’t merged or released yet)
That said, none of those explain why depth holding apparently doesn’t work. Does it sink unconstrained, or does it go down slightly and then maintain that depth effectively?
Or are you saying the vertical thrusters are turning on during pure forward commands (e.g. including in manual mode), and actively pushing the vehicle downwards?