3 ms·

I was under the impression that subs mostly use dead reckoning when submerged.

colechristensen 3y ago
Good inertial navigation units are really good. I had a professor who liked to tell the story of having one on the top floor of the engineering building and if you left it on all day you could watch your altitude go up and down as the building warmed up with the sun and cooled down at night.
- rlpb 3y ago
  I think any unit that couldn't do that would be useless as it wouldn't have the accuracy required - it would drift within a day otherwise. More interesting would be to understand how much its position drifts over a period of days or weeks.
  - nradov 3y ago
    Some level of drift is acceptable depending on the mission. Aircraft and missiles only fly for a few hours at most, and may be able to get a satellite or stellar fix at least intermittently.
willvarfar 3y ago
dead reckoning has to account for currents etc, which is something you could use AI to improve as per the paper. It's actually a _good_ application of AI? Subs use very expensive and very impressive inertial guidance systems, which can go up-to a week without correction. But that doesn't scale down to the modern world of small autonomous systems.
- actionfromafar 3y ago
  The currents would accelerate the dead reckoning unit just like any other force, including from the impellers. Not arguing that small autonomous systems could use something smaller and cheaper.
  - chrisdalke 3y ago
    many INS packages also include a DVL (Doppler velocity log) which measures speed over ground if you’re in range of the bottom.
  - willvarfar 3y ago
    The dead reckoning itself doesn't detect the ocean currents; these are separate estimates that need to be integrated to determine actual position https://en.wikipedia.org/wiki/Submarine_navigation#Deep_water_navigation https://en.wikipedia.org/wiki/Submarine_navigation#Deep_wate...
    - actionfromafar 3y ago
      Huh, I don't understand why. :-D Someone please explain. If I tugged the sub, wouldn't the IMU detect that? Why is a current doing the tugging any different.
      - willvarfar 3y ago
        now I'm guessing, but perhaps it's like if you walk up the aisle of a moving train, how fast are you travelling? And how fast does it feel like you're travelling?
        actionfromafar 3y ago
        Sure, I would get confused by that too, but I thought the point of the IMU is that it has its own frame of reference. Elsewhere in these comments was someone mentioning an IMU which could detect a building growing in size when warmer. The IMU doesn't "know" there's water outside or how the water is moving. It knows how much force it's been pushed around by.
        willvarfar 3y ago
        Aha! IMU <> "dead reckoning"? In the wikipedia article they are listed separately. Dead reckoning is meaning tracking things like the revolutions of a propeller and a compass to compute position, whereas an IMU is three accelerometers, three gyros and three magnetometers? https://en.wikipedia.org/wiki/Inertial_measurement_unit https://en.wikipedia.org/wiki/Inertial_measurement_unit

Good inertial navigation units are really good. I had a professor who liked to tell the story of having one on the top floor of the engineering building and if you left it on all day you could watch your altitude go up and down as the building warmed up with the sun and cooled down at night.

rlpb 3y ago
I think any unit that couldn't do that would be useless as it wouldn't have the accuracy required - it would drift within a day otherwise. More interesting would be to understand how much its position drifts over a period of days or weeks.
- nradov 3y ago
  Some level of drift is acceptable depending on the mission. Aircraft and missiles only fly for a few hours at most, and may be able to get a satellite or stellar fix at least intermittently.

willvarfar 3y ago

dead reckoning has to account for currents etc, which is something you could use AI to improve as per the paper. It's actually a _good_ application of AI? Subs use very expensive and very impressive inertial guidance systems, which can go up-to a week without correction. But that doesn't scale down to the modern world of small autonomous systems.

actionfromafar 3y ago
The currents would accelerate the dead reckoning unit just like any other force, including from the impellers. Not arguing that small autonomous systems could use something smaller and cheaper.
- chrisdalke 3y ago
  many INS packages also include a DVL (Doppler velocity log) which measures speed over ground if you’re in range of the bottom.
- willvarfar 3y ago
  The dead reckoning itself doesn't detect the ocean currents; these are separate estimates that need to be integrated to determine actual position https://en.wikipedia.org/wiki/Submarine_navigation#Deep_water_navigation https://en.wikipedia.org/wiki/Submarine_navigation#Deep_wate...
  - actionfromafar 3y ago
    Huh, I don't understand why. :-D Someone please explain. If I tugged the sub, wouldn't the IMU detect that? Why is a current doing the tugging any different.
    - willvarfar 3y ago
      now I'm guessing, but perhaps it's like if you walk up the aisle of a moving train, how fast are you travelling? And how fast does it feel like you're travelling?
      - actionfromafar 3y ago
        Sure, I would get confused by that too, but I thought the point of the IMU is that it has its own frame of reference. Elsewhere in these comments was someone mentioning an IMU which could detect a building growing in size when warmer. The IMU doesn't "know" there's water outside or how the water is moving. It knows how much force it's been pushed around by.
        willvarfar 3y ago
        Aha! IMU <> "dead reckoning"? In the wikipedia article they are listed separately. Dead reckoning is meaning tracking things like the revolutions of a propeller and a compass to compute position, whereas an IMU is three accelerometers, three gyros and three magnetometers? https://en.wikipedia.org/wiki/Inertial_measurement_unit https://en.wikipedia.org/wiki/Inertial_measurement_unit