4 ms·

> Inertial navigation systems in aircraft (which use very stabilised platforms with a lot of math involved) worked before GPS was available. Inertial measureme

> Inertial navigation systems in aircraft (which use very stabilised platforms with a lot of math involved) worked before GPS was available. Inertial measurement units for aircrafts and submarines cost as much as a house in California. Good luck putting those in a phone.

ben_w 2y ago
The IMUs that existed on aircraft before the invention of GPS have been superseded by the ones which actually are in your phone, in much the same way and for much the same reason that a $20 Casio F-91w keeps better time than a fancy Rolex that costs more than a house in California: electronics are cheaper and better than mechanical systems. We have, naturally, also made better IMUs for places where it matters, ones which won't fit in your phone. The question is therefore not suited to "aircraft grade, yes or no?", it's "how expensive is the cheapest IMU that's good enough for the specific need?" which in this case itself depends on how many stops is desired.
- wkat4242 2y ago
  Actually that F91W does not keep very good time. There pretty excellent if you keep them on a shelf bit if you run around outside in the hot and cold (you know, like people use a watch) they'll deviate quickly. Because they don't have a temperature controlled (or even compensated) oscillator. A real TXCO (basically putting the crystal inside a temp calibrated oven) is not feasible on a watch battery but compensation sure would be.
  - ben_w 2y ago
    I picked it not because it's good, but to illustrate the cheapest digital is still better than any analog mechanism that money can buy.
    - wkat4242 2y ago
      Ah ok,I didn't realize analog watches were that bad.
  - minetest2048 2y ago
    > A real TXCO (basically putting the crystal inside a temp calibrated oven) is not feasible on a watch battery but compensation sure would be. Nitpick: You're thinking about OCXO for crystals inside an oven, TCXOs are temperature compensated crystal oscillators
labcomputer 2y ago
Well, that, and there's no such thing as a "solid state laser gyro". I believe the GP is confusing MEMS solid-state gyros and laser-ring gyros (which can use a solid state laser, but AFAIK aren't ever called "solid state laser gyro"). MEMS gyros have too much bias drift (both on a unit basis due to fab processes and on a temperature basis) to be practically useful here. You can measure the earth's rotation with a MEMS gyro, but you're really at the limit.
- jjk166 2y ago
  Laser ring gyros are referred to as solid state laser gyros.
- tonyarkles 2y ago
  Heh, while I get what you're saying... despite being somewhat pedantic... there are in fact MEMS FOGs now too :). https://www.anellophotonics.com/technology https://www.anellophotonics.com/technology

ben_w 2y ago

The IMUs that existed on aircraft before the invention of GPS have been superseded by the ones which actually are in your phone, in much the same way and for much the same reason that a $20 Casio F-91w keeps better time than a fancy Rolex that costs more than a house in California: electronics are cheaper and better than mechanical systems. We have, naturally, also made better IMUs for places where it matters, ones which won't fit in your phone. The question is therefore not suited to "aircraft grade, yes or no?", it's "how expensive is the cheapest IMU that's good enough for the specific need?" which in this case itself depends on how many stops is desired.

wkat4242 2y ago
Actually that F91W does not keep very good time. There pretty excellent if you keep them on a shelf bit if you run around outside in the hot and cold (you know, like people use a watch) they'll deviate quickly. Because they don't have a temperature controlled (or even compensated) oscillator. A real TXCO (basically putting the crystal inside a temp calibrated oven) is not feasible on a watch battery but compensation sure would be.
- ben_w 2y ago
  I picked it not because it's good, but to illustrate the cheapest digital is still better than any analog mechanism that money can buy.
  - wkat4242 2y ago
    Ah ok,I didn't realize analog watches were that bad.
- minetest2048 2y ago
  > A real TXCO (basically putting the crystal inside a temp calibrated oven) is not feasible on a watch battery but compensation sure would be. Nitpick: You're thinking about OCXO for crystals inside an oven, TCXOs are temperature compensated crystal oscillators

labcomputer 2y ago

Well, that, and there's no such thing as a "solid state laser gyro". I believe the GP is confusing MEMS solid-state gyros and laser-ring gyros (which can use a solid state laser, but AFAIK aren't ever called "solid state laser gyro"). MEMS gyros have too much bias drift (both on a unit basis due to fab processes and on a temperature basis) to be practically useful here. You can measure the earth's rotation with a MEMS gyro, but you're really at the limit.

jjk166 2y ago
Laser ring gyros are referred to as solid state laser gyros.
tonyarkles 2y ago
Heh, while I get what you're saying... despite being somewhat pedantic... there are in fact MEMS FOGs now too :). https://www.anellophotonics.com/technology https://www.anellophotonics.com/technology