After a few issues I now can arm my ROV but when I do so both horz motors start spinning. Slowly at first then quickly into full speed with out any input. What would be causing this?
This is actually completely normally and it’s caused by the control system reacting to the vehicles orientation. For example, the vehicle might be rolled slightly and so the control system tries to correct that by changing the thruster inputs. The integral “I” term of the PID loop builds up very slowly. Since the vehicle doesn’t react to these inputs when it’s not in the water, it keeps building up.
If you want to top that you can change the control system (ATC section) “I” terms to zero.