Unit arcs towards surface in forwards and video pixelation

Unit purchased in 2020 not many hours of use since then.
Currently testing in pool, when driving forward at full speed (at all gain levels) the unit immediately starts to arc towards surface, only way it stays level in forwards is at very slow speed, it seems this effect is worst when in depth hold mode but still quickly climbs when in forwards in all flight modes, I have to actively trim down to try to keep level at all but very slowest speeds. Is it possible due to testing in shallower water? Also get pixelation of video feed when tilting camera up/down and occasional stalling of video feed (freezes for a second). All firmware is updated, have done all calibrations and motor auto calibrations as well as have buoyancy set to slightly positive in fresh water.

I am getting an occasional error message, something about IKF?

Would be interested to know if there is a video around showing the typical expected performance of the unit operating in all directions at various speeds/gains to see what is typical performance to base my expectations against? I feel like when I first used unit it ran more level. I know it will tilt a bit when running ahead a higher speeds but I assume it should hold depth?

Hi @Airon,

If your motors are all positioned and rotating as expected, and you’re not setting a pitch target for the vehicle, then my main thought for a cause for unexpected upwards pitching would be if the weight is balanced too far backwards relative to the centre of buoyancy. There’s some more discussion on that here, but you may want to try moving some of your ballast weights further forwards if possible.

ArduSub’s Extended Kalman Filter (EKF) sensor fusion algorithm resets its state if it gets too uncertain, which can happen if the sensors are poorly calibrated or if there’s too much integration drift from a noisy sensor (e.g. that is common when the ROV is sitting still instead of moving, especially if the gyroscope calibration was performed while the vehicle was on a moving platform or boat). If it’s happening frequently during operation then it’s likely worth redoing your sensor calibrations, and making sure not to be too close to large magnets or metallic structures when doing so.

Hmm, I’m not aware of something specifically showing this, but it does seem like it would be useful. I’ll raise it internally as something we should look into providing, but don’t know how long it will take us to do that. Thanks for the suggestion/question :slight_smile:

Depth hold mode operates in the vehicle’s frame of reference (rather than the “world frame”), so I’m aware that if you’ve explicitly set/commanded a non-flat pitch angle and move forwards then the depth target will change to match the current depth when the controls are released. That said, if the pitch is set to flat (which is normally the case) then I believe the depth target should only get changed when a depth increase or decrease is commanded, not from horizontal motion input commands.