Introduction to the OpenROV IMU/Depth Sensor!


As many of you who follow our Google Hangouts may know, a bunch of us have been working on a way to determine the heading and depth (as well as some other things) of our ROV electronically. We've evaluated all sorts of components on the market and have done quite

This is a companion discussion topic for the original entry at
Note: This article was for the original IMU released in October 2014. As part of re-enabling our blog, this discussion topic has a newer date than the original article.

Battery Tubes for Deep ROVs

That's looking pretty awesome, guys - Nice work.


Sign me up for one of these along with the new 2.5x Cape & maybe a BBB

great work all!!!!!!!!!!


Sign me up.

Awesome work guys.


Shut up and take my money!


Defintely interested! Can't wait to see this in the store.


Fantastic. Definitely interested. How's the HUD coming along? I remember seeing some prototype shots of the interface a few months ago.

I just picked up an UNO for my own CTD work that I hope to have built in the next week. I'll implement this solution as well and start testing. We have a 16ft diameter 4ft deep pool out here in Livermore now for ROV/AUV testing. Exciting times.


Hi guys,

Count me in, I’ll definitely have one!

Best regards,



I am ready for one and available to test.

Let me know next steps.



" for all you safety-minded people- don't worry: the 11 bar pressure test was done with the chamber completely filled!"

Could you explain what the issue is regarding doing the pressure test with a chamber filled partially with water and compressing the water with AIR? I have done this in the past where I had a housing that was going underwater and connections that needed to remain dry, using a clear water filter housing 1/2 filled with water and air pressure from the low pressure hose of a scuba tank feeding a standard hardware store regulator. I haven't pushed the pressure beyond the rating of the filter which is 125 psi but would like to know if this is dangerous and why.
Thanks. Bob


I cant wait!



I also want one. :)


Hey Bob,

I love talking about this sort of stuff, so forgive me for being long winded. Just take whatever paragraph answers your question and feel free to roll your eyes at the rest...

The reason having the chamber filled (even partially) with air is dangerous is that it is then holding a tremendous amount of potential energy because the air is compressible. Water is (for all intents and purposes) not compressible, so it is not able to hold potential energy.

If the chamber were to fail when filled with an incompressible fluid (like water) that was under a lot of pressure, it would instantly equalize after only a small amount of water leaked out. For air, the "outward push" of the expanding gas inside would continue after the walls of the container were already breaking apart, so fragments of the chamber would be able to pick up tremendous momentum (which could be transferred into your skull) , and the shock wave from the expanding air could also be damaging.

I like to think of compressible fluids (like air) as a sort of "three dimensional spring". If you took an imaginary cube of air and pushed it inward in all dimensions (compressed it), it would get smaller, but if you let go of that inward push, it would expand outward again. If you tried to compress water, it would not get smaller.

If you picture air being kind of like a spring because it is compressible and water being kind of like.. I don't know.. a brick, because it is not compressible, you can see how one can hold a lot more energy then the other even though they are initially both undergoing the same amount of force. I'll use the amazing graphic capabilities of MS Paint to demonstrate:

Another good way to visualize the difference is to picture two balloons inflated to equal sizes- one with air, and the other with water. Both balloons have about the same internal pressure. If you were to pop them both, intuitively, you can probably understand that the one filled with air would have a much more energetic failure. That's because all the energy stored in the air (basically by pushing the air molecules closer together) would be released at once.

...and a typical balloon is only about 70mBar (1psi) above atmospheric pressure... when we test to pressures equivalent to 100m depth in seawater, we go up to about 11,000mBar (or 160psi)!

Hope this helps. Be safe out there!



That was a great explanation Eric. I have done a lot of pressure testing in the 8 to 10 bar range using rated vessels in air, albeit ones that were not necessarily designed for that purpose. I never considered how much inherently safer it might be to use a hydraulic system for items that can be completely submerged. Compressed air has always been a convenient source of high pressure, but the faucet or a water pump might work just fine for a lot of applications. Bit more of a mess when I forget the O-ring in the filter housing. Thanks. Bob


Count me in Eric. oROV 471 arrived in the mail today so this is great news!


Very much interested!



hi,I want to know how to synchronize the IMU data with the video of Webcam time synchronization,and download them.


this idea is a eye opener for me
very nice of you guys giving me such a good idea


Hello Eric…

I am looking in the github repo (openrov-software), but can find no Arduino directory. In fact, I can’t seem to find any .ino files for Arduino at all…especially nothing about TestCode32. I can’t really even find anything other than javascript source (.js) files–and don’t think I’ve seen a single C++ source or header file in that repo.

What am I missing here? Is there another repo that I haven’t seen somewhere? Might you be able to provide a link to the Arduino .ino file for the new IMU, as I’d love to take a look at it. I’ve done a fair amount of work with the Arduino, and the vast majority of my programming work in the past 4-5 years has been with C/C++, most of it being embedded. So I would be very interested in perusing the code, especially since I just received my v2.7 kit, and the old IMU.