Thrusters not working in water



When I do "Pre dive test" all functions are working fine. But when I add the ROV to the water it stops working after 5 sec. There is no water in the batt. tubes or in the main champer with the camera etc.

I hope someone can help pointing me in the rigth direction to find the error.

Kind regards Morten Hellemann


This sounds similar to an issue found with the insulation of the brushless motors (see here for details).


Try the solution outlined here

We had the same brown out issue and the reason it works on land is that there is no resistance on the motors.

Check out our video for a demo of the problem




Try testing the motors for the grounding issue that they mentioned; if you have trust fire batteries, they may be the culprit and I may have a solution below, but if you have the lifepo4 batteries, it is not an issue.

The trust fire batteries have problems with built in circuit protection that failed in one of my batteries. Turning on the ROV would trip whatever tube it was in and I would get no power, and then it turned out to be too much draw to run it off of just one tube.

Check to see if you are getting readings from BT1 and BT2 in the information on the right side of the screen, that means both tubes are working. Also pay attention to what it says as you move the motors in and out of the water, if it goes crazy high it may be causing the system to trip.


Hi Paul.

I have added a video here from my last test:

I'm using the Li-FePO4 batt. sold from the OpenROV page.

I'm very new to this and I'm not sure what to look for in the information to the right of the screen. Maybe you can see something?

Regards Morten


It doesn't appear as if you're having the problem that I was describing. Your whole ROV doesn't crash, just the thrusters stop working correct?

I'd check first the resistances the links above describe it, you basically open up the e-tube and unplug the DB25 connector, then you have to take an multi meter, set it to ohms, put one side on the motor base then try each of the 3 motor wires to see if there's infinite resistance or open loop as Alexander said.


Hi Morten

From the video it looks like you have an IMU on the unit and it looks a lot like the I2C is locking up the Arduino from RFI interference (note the freezing of the runtime clock @ 5:22 on the very bottom RHS of the screen and then eventually a Arduino restart)

Brian A has been looking into this and has a software fix being implemented shortly

If I was you I would cut out (or just desolder pins 14/15/16/17 on the DB25) the IMU till this has been fully implemented or looking at putting RFI suppression in the system