ArduSub Research & Development: DVL

Blue Robotics Software ArduSub
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Originally published at: ArduSub Research & Development: DVL - Blue Robotics

As you browse through our community forums, you may come across the term “DVL”. What is this piece of equipment and why is it useful?

What is a DVL?

A Doppler Velocity Log (DVL) is an underwater navigation instrument that gets an acoustic “lock” on the bottom like a single-beam echosounder. However, in addition to measuring the distance to the bottom like an echosounder, a DVL also measures the velocity relative to the bottom. This relative velocity measurement can then be used for holding a stable position, obtaining a speed reading or navigating without the need for an acoustic positioning system. The DVL also enables the vehicle to navigate autonomously and facilitates the pilot’s control of the vehicle, similar to the vision sensors in an aerial drone like the DJI Mavic.

Here are some additional references which go into more detail:

Experimental Testing

With these interests in mind, Nortek graciously lent Blue Robotics a DVL1000 for testing purposes. The DVL1000 is an ideal piece of equipment due to its high accuracy and thorough integration documentation.

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Hardware Installation

Mounting the DVL1000 to a BlueROV2 involved drilling appropriately spaced holes on the bottom frame panel and securing the DVL in place. A modified Payload Skid was installed to act as a protective cage.

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A special cable was built using a Seacon MCIL8 in-line wet-mateable connector and a penetrator on the other end. The cable was terminated with an RJ45 connector and spades installed on the appropriate wires to configure for Ethernet communications.

A 3-port Ethernet switch was installed inside the BlueROV2 on top of the Fathom-X and had the following connections:

  • Fathom-X
  • Raspberry Pi 3B
  • Nortek DVL1000

3-Port-Ethernet-Switch-resized

ArduSub Integration

ArduPilot has a series of libraries available for non-GPS navigation. The two libraries that were most applicable for integrating a DVL are Optical Flow and Visual Odometry. The Visual Odometry Library was chosen to try first.

The Blue Robotics software team wrote a driver to convert the position sentences from the DVL into the VISION_POSITION_DELTA messages that could be interpreted by the ArduSub firmware.

Physical Testing

After the driver was tested by using a SITL Simulator (Software in the Loop), physical testing was conducted in the Blue Robotics pool.

Position hold and non-GPS navigation were successfully demonstrated with the results shown in the video below:

Future ArduSub Support

Support for DVLs is not implemented in the current version of ArduSub, but is something the ArduSub developers are currently working on. There is no planned timeline for implementation, as the feature will need to be thoroughly tested with accessible hardware.

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Rusty and Team,

I am looking forward to have this DVL implemented.

regards

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Hi; we have several BR2s here in Western Australia and will shortly have access to a Nortek 1000 for integration into a prototype larger vehicle that we’ve built.

At this stage we’re looking purely to create stationkeep so that when the operator stops flying, the vehicle doesn’t wander off. Hardware and electrically, integration’s no issue, but it would be good to understand the software integration you’ve tried.

Are you able to share the details of how to use the Visual Odometry Library, and would you be willing to share the driver you created ?

I think stationkeep is one of the most important advances for small ROVs, and having seen the Nortek in action on Fusion ROVs, it’s fantastic.

cheers
Rich

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We just launched our new DVL which is designed specifically to fit ROVs like the BlueROV2. Take a look here, we’re sure you’ll like it: Water Linked launches: DVL A50 Doppler Velocity Log

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Yup, saw that - I’m very keen to see the results of the integration :blush:

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If we go ahead and order one, are you able to assist us with the BlueROV integration ? Initially we’re looking for stationkeep, but keen to see what else can be developed on the back of it.

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We are working together with BlueRobotics on an official integration. The beta software supports station-keep like you see in our videos on YouTube, so it sounds like it fits your requirement nicely. Will assist you in get that up and running if you decide to order a DVL now. Please contact our support and we’ll communicate directly there.

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Perfect ! We’ll have an order through in the next few days.

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I see you did your verification testing in your pool. Did you have the compass enabled? If so, do you have issues with rebar in your pool interfering with the compass?

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6 posts were merged into an existing topic: Water Linked DVL A50 Support

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Hi @williangalvani,

here in the Reality and Robotics Lab at Dartmouth College, we have been testing the Nortek DVL1000 with the BlueROV; do you have a branch for the code used for the parsing of the raw data and the integration with the ArduPilot? Following the integration guide, it looks that the response output is slightly different, at least over serial.

Thanks a lot!

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Hi @quattrinili ,

This code hasn’t been touched in a long time (ardupilot’s interfaces could have changed as well), but the script I used back in the day can be found here.

For a slightly more plug-and-play experience, I would recommend Water Linked’s A50 DVL.

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Hello bluerobotics team,

I am working at TU Delft as a PhD candidate and we are planning on buying a blueROV + accessories to apply our research. For one of the research topics we plan on applying we need to have a good localization (I know this is kind of vague), I was wondering if you would be able to tell me what was the accuracy of the VISION_POSITION_DELTA you achieved using DVL1000.

Also, I see that this post is already 1 and a half year old, are there any new developments in this subject? Other alternatives for improving odometry/localization you may know and suggest to me?

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Hi @rezenders, welcome to the forum :slight_smile:

This thread is a good starting point for understanding the various available techniques for underwater positioning. The rough relative costs in the main post haven’t been updated as new devices have come to market.

In terms of actual devices, WaterLinked’s Underwater GPS and DVL pages provide some useful information about the technologies, and the DVL page includes a comparison with some other DVLs and GPS units. Beyond those mentioned there I’m also aware of Cerulean’s ROVL mkII and their DVL.

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