Sub: pilot override in POSHOLD mode results in "bounce back"

[clydemcqueen]

Bug report

Issue details

Pilot override in POSHOLD mode results in a ~1m "bounce back".

I saw this on real hardware (BlueROV2 heavy + DVL) running a DEV build. I moved the ROV away from the dock while in POSHOLD mode, when I let go of the stick the ROV seemed to jump back towards the dock.

I can reproduce this in SITL on master and Sub-4.5. I was not able to reproduce on Sub-4.1.

To reproduce:

• run sim_vehicle.py with -w, etc.
• run QGC w/ joystick
• wait for EKF3 IMU0 is using GPS
• arm, poshold
• use the joystick to move forward aggressively a few meters
• let go of the stick, the sub will move back a meter or so

Version

master, Sub-4.5

Platform [ ] All [ ] AntennaTracker [ ] Copter [ ] Plane [ ] Rover [ x ] Submarine

Airframe type

All

Hardware type

All

Logs

I can provide the BlueROV2 logs, but they are a bit big (replay on, long-ish guided mode test). LMK.

[Williangalvani]

I could replicate this on Sitl, but not on a real vehicle. On SITL the target_position keeps changing when we let go of the sticks:

This doesn't seem to happen on my rov:

[clydemcqueen]

This is from a dive with a BlueROV2 heavy w/ DVL on 2024-sep-11:

I'll try to dig into the code tomorrow.

[clydemcqueen]

Huge thanks to @Williangalvani for tracking this down!

It looks like a few factors contributed:

• Sub poshold mode calls position_control->set_max_speed_accel_xy with WPNAV_SPEED. In our case, we set WPNAV_SPEED very low for running survey transects.
• Sub poshold does not limit the pilot xy speed. In our case, the pilot was easily able to exceed WPNAV_SPEED.
• When the pilot let go of the stick, the PSC velocity controller took over and quickly wound up until acceleration hit the max, and the sub lurched backward.

Proposed fix:

• Add a PILOT_SPEED parameter for xy pilot control, and use it in poshold.

This is important for our use case so we are motivated to fix it. But I suspect that most users have never experienced this, and probably won't.