Whenever i move the throttle stick forward only the vertical motor 5 responds. I’ve tried flashing the latest firmware on to the pixhawk and downloaded the latest build of Q ground control and tried changing the directions for the parameters(Reverse/forward). I also changed both the motor 5 and 6 ESC, and there is no change. Vertical motor 6 only repsonds if i move the left stick up for the Roll.
I actually had this exact same problem myself yesterday while setting up an ROV at Blue Robotics HQ, and went through the same troubleshooting steps. It turns out I had the wrong firmware flashed to the pixhawk- the PX4-bluerov firmware is actually for the original BlueROV, not the BlueROV2. The BlueROV2 uses the PX4-vectored firmware. Can you make sure you have the proper firmware installed?