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Introduction

The new IMU has been designed to mitigate some of the issues associated with the previous IMU. The features of this unit include: >200m depth sensor capability, reliable compass heading and smaller printed circuit board.

  1. First set up wires accordingly to the IMU, refer to image 1. Red/gray to 3.3v, black/gray to GND, green/gray to SCL, and white/gray to SDA Have the wires go through the top of the board and solder on the bottom side. Clip the excess wires.
    • First set up wires accordingly to the IMU, refer to image 1. Red/gray to 3.3v, black/gray to GND, green/gray to SCL, and white/gray to SDA

    • Have the wires go through the top of the board and solder on the bottom side.

    • Clip the excess wires.

    • Wear safety glasses.

    If i built a new rov, is it possible to measure precisely the length and then directly solder the cables from the db 25 connector, which i have not cut yet?

    Fe3C - Reply

    In case people have the same question in the future see the forum post where this was talked about (https://forum.openrov.com/t/imu-sensor-o...).

    OpenROV (Sofar) -

    May I ask why the "white/gray to SDA" wire come along with the IMU has more strands (thicker) than other wires? It makes the white/gray wire hard to be inserted through the soldering hole. does this white/gray wire carry more current?

    If not, could I replace it with normal 20 awg wire?

    Jianxiao - Reply

  2. Peel off the backing on the two acrylic pieces.
    • Peel off the backing on the two acrylic pieces.

    • With gloves, acrylic cement the thicker piece on top of the thinner piece.

    Is there a must to use acrylic cement ? Would not epoxy glue be sufficent ?

    DiveExplorer - Reply

  3. Start the epoxy process by applying some to the bottom surface. This will ensure there is no air trapped under the electronics board. Insert the IMU board into the epoxy. Insert the IMU board into the epoxy.
    • Start the epoxy process by applying some to the bottom surface. This will ensure there is no air trapped under the electronics board.

    • Insert the IMU board into the epoxy.

  4. With a piece of tape, tape down the wires to the acrylic piece as show in image 2. Keep wires coming out of the board.
    • With a piece of tape, tape down the wires to the acrylic piece as show in image 2.

    • Keep wires coming out of the board.

    • Make sure the entire board is flush to the acrylic.

  5. Epoxy the board onto the acrylic. Cover the board but DO NOT cover the white sensor. Refer to image 2.
    • Epoxy the board onto the acrylic.

    • Cover the board but DO NOT cover the white sensor. Refer to image 2.

    • Let the epoxy cure for 4-6 hours.

    I used a third hand to fix the IMU at the wires into position. So no tape is covering the sensor and it's much easier to apply the epoxy without covering the depth sensor …

    Andreas Franz - Reply

    Great tip, Andreas! Thanks!

    Chris Mentrek -

    Works great, thanks.

    DiveExplorer - Reply

  6. On your ROV, remove the polypro fin. On your ROV, remove the polypro fin.
    • On your ROV, remove the polypro fin.

  7. Pull out the IMU wires from your ROV. Should be tucked on the starboard side of your wire bundle Cut off the heat shrink, and strip the wires. Cut off the heat shrink, and strip the wires.
    • Pull out the IMU wires from your ROV. Should be tucked on the starboard side of your wire bundle

    • Cut off the heat shrink, and strip the wires.

  8. Measure out the IMU wires to the stripped wires on the ROV from the starboard side of the acrylic structure. Refer to image 1. Make sure that the wires will not get in the way of the spinning propeller.
    • Measure out the IMU wires to the stripped wires on the ROV from the starboard side of the acrylic structure. Refer to image 1.

    • Make sure that the wires will not get in the way of the spinning propeller.

    • Clip the wires at that estimated length.

  9. Clip 4 pieces of heat shrink and place on the IMU wires. Clip 4 pieces of heat shrink and place on the IMU wires.
    • Clip 4 pieces of heat shrink and place on the IMU wires.

  10. Solder on the IMU wires to the ROV wires. Make sure the wires you are soldering together match in color. Use a heat gun to shrink the heatshrink around the soldered area of the wires.
    • Solder on the IMU wires to the ROV wires. Make sure the wires you are soldering together match in color.

    • Use a heat gun to shrink the heatshrink around the soldered area of the wires.

    All of the wires coming out of my rov from the db25 are a flat grey. I don't want to continue with my build until I figure this out help please? Open ROV 2.7 kit.

    Aaron - Reply

    Please feel free to reach out to our support team (https://openrov.zendesk.com/hc/en-us/req...). The easiest way is to use a multimeter to test the resistance in order to determine the wire layout. Here is the DB-25 diagram (https://drive.google.com/file/d/0B3CACRX...).

    OpenROV (Sofar) -

  11. Apply hot glue to the bottom of the IMU and place on the starboard side of the acrylic structure handle. Make sure that the pressure sensor is facing down and the IMU is oriented towards the front of the ROV.
    • Apply hot glue to the bottom of the IMU and place on the starboard side of the acrylic structure handle.

    • Make sure that the pressure sensor is facing down and the IMU is oriented towards the front of the ROV.

    why hot melt?

    wouldn't acrylic cement or super glue work?

    Patrick Tessier - Reply

    The reason hot glue was selected was so that the IMU can be removed later. Acrylic cement and super glue will both work but makes removing the IMU very difficult, should you need to take it off.

    OpenROV (Sofar) -

    The second photo is not correct now, the wires should be facing forward (for IMU2 in any case). The current code is written for wires forward orientation. I would change the instructions and the photo, but I'm new here.

    Tim Stentz - Reply

    The 30.0.3 version of the software should be written for the wires in the orientation in the picture. Can you clarify what part of the code you are looking at where you believe this direction is wrong. It very well may be and we would like to get to this bottom of this ASAP.

    OpenROV (Sofar) -

    Any update on this comment? I'm about to complete this installation and if something needs changing now would be the time to do it. Thanks, Paul

    Paul Arena -

    For anyone else like me who didn't get the IMU board perfectly flush and level inside the housing, you can avoid having to into the code and offset the angles by installing the IMU on the frame with the ROV running. Just make sure the ROV itself is level (I learned from my UAV building to use a disk type spirit level like they use for leveling RV's) and then make sure your horizon lines up in the cockpit view while installing. With the hot glue you've got a second or two to adjust it before it sets, which is helpful...and if you don't get it right on the first try you can easily pull it off before the glue completely cools and try again.

    Geoff Ash - Reply

    Oritation

    “Make sure that the pressure sensor is facing down and the IMU is oriented towards the front of the ROV. “

    I don’t quiet understand this note. In the picture the sensor is facing up.

    What is meat with the IMU is oriented towards the front of the ROV. I use the unit on a own buid ROV - how to orient the board?

    Rudi - Reply

  12. Updating the software will be required on most ROVs to get the IMU to work, even if you have the previous version of the IMU.
    • Updating the software will be required on most ROVs to get the IMU to work, even if you have the previous version of the IMU.

    • You need to be running software version 30.0.2 or later for it to function correctly. We recommend running the latest version.

    • Please follow the guide here.

    • Please read about the procedure to calibrate the IMU.

Finish Line

15 other people completed this guide.

OpenROV (Sofar)

Member since: 09/28/2013

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15 Comments

That´s a very fine piece of technology. I would like to have a set. How can I get it.

Looking forward your comments.

Many thanks.

Oscar

Oscar Guzman - Reply

Thanks! You can order it from our store

http://store.openrov.com/products/openro...

-Brian G.

OpenROV (Sofar) -

Where do you get the acrylic housings from? I'm looking into building modules for temperature and light measurements and would like to have something similar to mount the sensors.

Thanks!

Dan L - Reply

We make those in house on a laser cutter. If you want to talk about these please send me an email through our support channel addressed to me (Brian G.) https://openrov.zendesk.com/hc/en-us/req...

OpenROV (Sofar) -

How long after adding this to he ROV should I wait to take it into water?

Ethan Lane - Reply

If you are using our recommended epoxy it has a full cure time of 16 hours. You should wait at least this long before exposing it to water. -Brian G.

OpenROV (Sofar) -

I screwed up and didn't get the IMU flush with the acrylic box.

Now the artifical horizon is off about 10 degree.

Is there a way to compensate for this assembly error?

Patrick Tessier - Reply

We have a software plugin to allow you to zero the references for the IMU. See the end of this forum post for the files and install instructions. https://forum.openrov.com/t/imu-calibrat... -Brian G.

OpenROV (Sofar) -

Given that the IMU is positioned just behind the starboard prop does this have any impact on the reported pressure when the prop is turning? Surely the wash would increase the pressure, or at least cause some significant instability.

I realise that the IMU is above the prop but not by that much.

Surely a better location would be on the underside of the top plate forward of the bulkhead. chop from the vertical thruster should be minimal as the sensor would be practically level with the prop.

Obviously there may still be some chop from the thrusters but possibly less than the rear mounted position.

It would also be closer to the centre of the ROV and could be mounted right on the centre line resulting in a slightly more accurate attitude report from the IMU.

Mark Dunsford - Reply

We have done a little bit of testing of the exact issue you brought up. We have not seen any issue with the placement, or variation in the depth readings. Feel free to experiment with the location and if you find something different we would love to hear about it on the forum (https://forum.openrov.com/). -Brian G.

OpenROV (Sofar) -

Hi. I am about to build my v2.8 from the kit and just saw this add-on that I really would like. Should I wait and get this module before I do the build of the ROV? How long would it take to get this add-on? Are there different assembly instructions for a pre-built ROV? Thanks, Paul

Paul Arena - Reply

You can add on the IMU/Depth module at any time. The shipping time depends on where you live but 1-2 weeks of transit time would be a safe estimate. The instructions are the same.

OpenROV (Sofar) -

Hello I purchased the IMU. I am in the middle of the build out phase of the ROV 2.8 still. I am starting Guide 3 today. Can you suggest which Guide # and which Step # I should add the IMU to the ROV using the instructional guide for the IMU provided online?

Paul Arena - Reply

We have found that installing it after the build is complete is easiest in order to make sure the wire lengths are correct and do not interfere with the motors.

OpenROV (Sofar) -

Step 11 Just to clear up confusion, would it be clearer if it was stated to "place the IMU with the sensor facing down and forward of the wires." (is that correct as I am not sure from the directions?)

Jim Scholz - Reply

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