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DVL-75
DVL-75
  • DVL-75
  • Overview
    • General Specifications
    • General Use Cases
    • The Basic System
    • System Components
    • Comparison of Tracker 650 and DVL-75
  • Usage Considerations and Scenarios
    • General Usage
    • Scenario: GPS Emulation
    • Scenario: Holding Position
    • Scenario: Autonomous Waypoint Navigation
    • Scenario: Returning to a Series of Known Positions
    • Scenario: Returning to Home
    • Scenario: Using GPS Assist
    • Scenario: Doing Your Own Dead Reckoning
    • Additional Connection Possibilities
    • General Hints and Tips
    • Operation in a Pool
  • Using MAVLink and BlueOS for Position Hold on a BlueROV2
    • ArduPilot Parameters
    • DVL Setup for MAVlink Support
  • Using Other Than the Bottom for the DVL (Side-Tracking Capability)
    • Side-Tracking Capability Design Use-Cases
    • Side-Tracking Capability Considerations
  • Mounting the DVL Components
    • Sensor Head Typical Mounting
    • Sensor Head Side-Tracking Mounting Alignment
    • All-in-One and Most-in-One Mounting Considerations
    • Mounting the Electronics Stack
    • Mounting an Auxiliary GPS
  • Assembling the Electronics Stack
    • Cerulean 300m Electronics Enclosure Assembly
  • Inertial Measurement Unit (IMU)
    • Baseline IMU Calibrations
    • Baseline IMU Background
    • Baseline IMU Blind Initial Calibration Procedure
    • Baseline IMU Status-Assisted Initial Calibration Procedure
    • Baseline IMU Calibration for Each Mission or Each Time Power is Applied
    • Upgraded IMU Calibration for Each Mission or Each Time Power is Applied
  • Communicating with the DVL
    • Factory Defaults and Default Messages
    • The Ethernet Interface
    • Tips on How to Find the IP Address Assigned to Your Ethernet Adapter
    • The Serial Interface
    • Resetting the Communications Parameters to Factory Default
    • What Do the LEDs Mean?
    • Outgoing Message Formats, DVL to Host
      • $GPRMC: NMEA standard Recommended Minimum GPS/Transit Data
      • $DVEXT: DVL Extended Data
      • $DVPDL: DVL Position and Angle Deltas Message
      • Freeform Error and Informational messages ($DVTXT)
      • Re-Tweeted GPS Messages
      • Re-Tweeted IMU Messages (IMU Raw Data)
      • $DVKFA, $DVKFB Kalman Filter Support Messages
        • Driving your own Kalman Filter
    • Commands Accepted by the DVL
      • $GPRMC
      • SET-POSITION
      • CONFIGURATION
      • SUPPRESS-GPS
      • DECLINATION
      • SET-SPEED-OF-SOUND
      • SET-VELOCITY-ADJUSTMENT
      • SEND-GPRMC
      • SEND-DVEXT
      • SEND-DVKFA
      • SEND-DVKFB
      • SEND-FREEFORM
      • SEND-DVPDL
      • RETWEET-GPS
      • RETWEET-IMU
      • SET-SENSOR-ORIENTATION
      • GRAB-IMU-CAL
      • VOID-IMU-CAL
      • BAUD-RATE
      • IP-ADDRESS
      • HOST-ADDRESS
      • MAVLINK-ADDRESS
      • FALLBACK-ADDRESS
      • UNICAST-TO-ME
      • PAUSE
      • RESUME
      • REBOOT
    • Blue Robotics Ping360 Discovery Protocol (Ethernet Only)
    • ARP (Address Resolution Protocol)
    • DHCP (Dynamic Host Configuration Protocol)
    • Ping (Internet Control Message Protocol Ping)
    • Mechanical Drawings
      • Mounting Dimensions, Sensor Head
      • Mounting Dimensions, Electronics Stack
      • RAM Mount Adapter Plate
      • Electronics Stack Assembly Drawing
      • Mounting Bracket for 300m Electronics Enclosure
      • Mounting Bracket for Sensor Head or Electronics Enclosure, fits BlueROV2 Heavy Thruster Guard
      • Mounting Bracket for All-in-One Enclosure, fits BlueROV2 Heavy Thruster Guard
      • Mounting Dimensions, Cerulean 300m Enclosure
      • Mounting Dimensions for the Cerulean All-in-One Enclosure
      • Mounting Dimensions, Cerulean GPS
  • Electrical Drawings
    • Serial Cable Supplied with Baseline Electronics Stack
    • DVL Serial Connection Example
    • Power over Ethernet (POE) Cabling
    • Standard Ethernet Pinouts
    • Optional GPS Wiring
    • Sensor Head Wiring
    • Using External Power with Serial Cable
    • Serial to USB Interface Using Blue Robotics BLUART Board
  • CAD Models
  • Appendix – Coordinate Systems
  • Copyright
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  1. Usage Considerations and Scenarios

General Usage

PreviousUsage Considerations and ScenariosNextScenario: GPS Emulation

Last updated 3 years ago

The DVL operates by bouncing four narrow sonar beams off the bottom of the body of water. The DVL measures the frequency of each return beam.

If any of the four transmit/receiver elements are moving with respect to the bottom, that return beam frequency is shifted due to the Doppler effect. By measuring the frequency shift, we can calculate the relative velocity between each transmit/receive element and the bottom. Depending on how the sensor head is angled with respect to the bottom, and the direction of motion, each beam may sense a different velocity. We also measure the orientation of the sensor head with respect to local level and to magnetic north. All this information is run through an Extended Kalman Filter (EKF), which outputs sensor head velocity in all three axes oriented to magnetic north (we do also apply magnetic deviation, if input by the user, to shift magnetic north toward true north). If the sensor head is fixed reasonably rigidly to your ROV, the velocities then also apply to the ROV.

Since the sensor beams are angled, the bottom does not provide as good a return as you might get from sounding sonars that are pointed straight down. Best overall performance comes when the DVL sensor head is operated in a level position. As the head is tilted more and more off vertical, one or more of the returns become weaker and weaker. While the DVL can operate temporarily with as few as two beams locked on the bottom, performance is degraded. Take-away: keep it as level as you can while operating.

The primary product of the DVL process is velocity in three axes. We also dead reckon by mathematically integrating velocity over time, which results in a new position as a delta from wherever the integration starts. The DVL wakes up at position (0,0) (we ignore the vertical axis since that is more accurately determined by other means). If we then reset the current position to a new value, subsequent delta positions are relative to the given new position.

Because we are mathematically integrating, even the tiniest errors will accumulate into an ever-growing position error. By periodically resetting the current position to a known good position, we can discard accumulated errors.

The following are a few scenarios to illustrate how you can use the DVL. The scenarios are not exhaustive, nor are they necessarily mutually exclusive.

The sensor beams are angled from vertical