Sensor Assembly

In-Use Sensors

Blue Robotics Low-Light USB Camera

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The camera provides high quality monocular vision that is excellent in low- light conditions underwater. It also has an onboard H.264 compression chip so that all the video compression is done onboard and does not place much computational load on the main computer. Coupled with the camera tilt system, the camera can tilt vertically to obtain a wider vision.

Bar30 High-Resolution 300m Depth/Pressure Sensor

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This pressure sensor can measure up to 30 Bar (300m water depth) with a depth resolution of 2mm. It includes a temperature sensor accurate to +/- 4 degree celsius, with data accessible through I2C. The Bar30 sensor is placed on the end cap and then connected to the Navigator Flight Controller via the I2C port.

In-Use Sensors (Additional)

/images/docs2_html_74626aed7f764f49.png Comparison between CAD Model and Physical Prototype

Doppler Velocity Logger (DVL)

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Blue Robotics has an installation guide on how to mount the DVL onto the payload skid in the following link: https://bluerobotics.com/learn/dvl-a50-integration/

However, due to the different sized cylinders (3-inch and 4-inch) used with reference to the CAD model design, custom mounting holes must be made on the payload skid bottom panel. As the location of the DVL is off-center of the bottom panel of the ROV, this offset must also be accounted for in the localization aspect of the navigation algorithm.

A DVL measures speed relative to the seafloor by using the doppler effect. It has 4 acoustic transducers tilted at 15 degrees angles that send and receive pulses to the seafloor. Precise velocity measurement relative to the seafloor could be obtained, which enables accurate underwater positioning and measurement of small changes in position. Do note that the DVL only provides relative position but to have an accurate global position, a positioning system like a GPS (Global Positioning System) or USBL (Ultra-Short Baseline) is still required, in addition to the DVL.

Water Linked Underwater GPS

/images/docs2_html_4a016295f1549e66.png The Water Linked positioning uses a method called Short Baseline (SBL) acoustic positioning. The ROV has a locator beacon (i.e., Locator A1) that sends out an acoustic pulse. Near the surface, there are 4 receiver hydrophones lowered into the water, which listen for the pulse from the locator beacon and use difference in the time-of-arrival to each receiver to triangulate the ROV’s position. Once the position is known relative to the receivers, the global position can be found by adding that to the position obtained by a GPS receiver.

Ping360 Scanning Imaging Sonar

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Installation guide for the roof rack and the possible mounting spots of the Ping360 Scanning Imaging Sonar on the roof rack can be found in the following links: https://bluerobotics.com/learn/installing-the-bluerov2-roof-rack/ <https://bluerobotics.com/learn/ping360-installation-guide-for-the- bluerov2/>

The Ping360 Scanning Imaging Sonar is a mechanical scanning imaging sonar that could be used for navigation in low-visibility water conditions primarily, and suitable for other applications such as inspection, obstacle avoidance, target location and tracking, autonomous systems development, etc. The acoustic transducer is mounted to a motor that rotates it in one degree increments, while sending a narrow beam of acoustic energy into the water and then listening back for echoes. In doing so, it generates a circular image of the sonar’s surroundings with a maximum range of 50 meters.

Cerulean Omniscan 450 Side Scan Sonar

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The side scan sonar allows the users to quickly collect imagery of the seafloor to map large areas. The side scan transducers have a narrow, tall beam shape so that when they are mounted to the either side of the boat, they have a full 180 degree view under the ROV.

The side scan sonar uses 450 kHz transducers, which provide a 150 meter range with detailed resolution. When scanning, the transducers emit an acoustic pulse and then record the response as echoes return from the seafloor. This creates a slice of an image and as the ROV moves forward, the image is filled in.

Some common applications could be hunting for shipwrecks, marine archeology, ecosystem mapping, and search and recovery.

As the side scan sonar was developed for the BlueBoat, the penetrator must be replaced with the correct one before it can be used in conjunction with the Blue Robotics tubes. You will need a WetLink M10 4.5 HC Penetrator to replace the BlueBoat penetrator.

Intel RealSense Depth Camera D435i

/images/docs2_html_39dba127c9446ead.png /images/docs2_html_17f411c8c3ca6e26.png Given the limitation of the Blue Robotics Low-Light USB Camera onboard the ROV, which is monocular in nature, there is a need to source a depth camera which could provide a depth estimate of detected objects of interest.

The Intel RealSense Depth Camera D435i fits the 4-inch enclosure in diameter and with the brass standoffs to secure the camera to the electronics tray, it minimizes the gap between the clear acrylic flat end cap and the camera by flushing it as close as possible to the end cap. This also reduces the distortion of the image captured by the depth camera underwater as light would have to pass through a liquid medium underwater, the solid medium of the acrylic end cap, and then air medium that exists in the minimal gap between the camera and the end cap.