3 ms·

Also, I believe most airliners have 2 or 3 INS systems, so it would be easy to see (or detect) if one of them has failed. It seems unlikely that all the gyros

Also, I believe most airliners have 2 or 3 INS systems, so it would be easy to see (or detect) if one of them has failed. It seems unlikely that all the gyros would silently fail...that would only happen if the gyros tumbled, or power failure to the gyros, but there would presumably be an error indication in either of those situations. (Also, these days they use ring laser gyros, which don't tumble or stop spinning).

jjoonathan 9y ago
Speaking of which, are RLGs actually difficult to manufacture or is the military intentionally stopping them from getting into civilian hands? Even the best cell phone sensor fusion seems to result in an obnoxiously shitty map experience.
- jhayward 9y ago
  The power requirements for even the most miniature RLGs is still pretty large relative to cell phone peripherals, and they are still physically pretty large. DARPA has had focus efforts in the MEMs arena for more than a decade now, including atomic clocks and optical systems but its not stuff you can put in a square mm of silicon and feed with a couple of microamps.
  - jjoonathan 9y ago
    Huh, I'd have guessed the opposite: that a laser, optics, and a piezo vibrator would be easy to integrate, while a MEMS gyroscope would be much harder. I ask anyone who gives the slightest hint of familiarity with the field because I suspect that my surface-level understanding is just missing the juicy photonics challenge that's roadblocking integration. The alternative hypothesis of military heel-dragging (similar to the case of bolometers) is much less exciting, but verifying it would at least allow me to stop poking around :)
- cpncrunch 9y ago
  Phones use MEMS sensors, which are much cheaper than laser gyros. I'm not sure if google maps uses the accelerometer, or just the GPS and compass. In my experience, phone maps work well if the device has a good GPS signal. It's just the compass that gives a shitty experience. I wish google would ignore the compass and just use GPS direction when you're moving. They used to do this, but now they seem to rely in the inherently crappy compass for direction.
  - jjoonathan 9y ago
    > Phones use MEMS sensors, which are much cheaper than laser gyros Yes, but why? To my surface-level understanding, RLGs sound like they would be easier to integrate. > It's just the compass that gives a shitty experience. Yep, that's my experience too, and that's why I'd be ecstatic to hear that the compass was being replaced by a RLG (which could be re-locked to true North every time GPS got a decent movement vector). Then again, I half suspect that something is FUBAR'din the current compass stack. I have one of those fluxgate-magnetometer current probes at work and can report that everywhere I've used it I have seen magnetic field vary as a high-SNR continuous function of direction, yet my phone's maps app has a ton of lag, hysteresis, and jankiness when rotating in the same damn field. Maybe we just need to wait for the cheap compasses to get better.

jjoonathan 9y ago

Speaking of which, are RLGs actually difficult to manufacture or is the military intentionally stopping them from getting into civilian hands? Even the best cell phone sensor fusion seems to result in an obnoxiously shitty map experience.

jhayward 9y ago
The power requirements for even the most miniature RLGs is still pretty large relative to cell phone peripherals, and they are still physically pretty large. DARPA has had focus efforts in the MEMs arena for more than a decade now, including atomic clocks and optical systems but its not stuff you can put in a square mm of silicon and feed with a couple of microamps.
- jjoonathan 9y ago
  Huh, I'd have guessed the opposite: that a laser, optics, and a piezo vibrator would be easy to integrate, while a MEMS gyroscope would be much harder. I ask anyone who gives the slightest hint of familiarity with the field because I suspect that my surface-level understanding is just missing the juicy photonics challenge that's roadblocking integration. The alternative hypothesis of military heel-dragging (similar to the case of bolometers) is much less exciting, but verifying it would at least allow me to stop poking around :)
cpncrunch 9y ago
Phones use MEMS sensors, which are much cheaper than laser gyros. I'm not sure if google maps uses the accelerometer, or just the GPS and compass. In my experience, phone maps work well if the device has a good GPS signal. It's just the compass that gives a shitty experience. I wish google would ignore the compass and just use GPS direction when you're moving. They used to do this, but now they seem to rely in the inherently crappy compass for direction.
- jjoonathan 9y ago
  > Phones use MEMS sensors, which are much cheaper than laser gyros Yes, but why? To my surface-level understanding, RLGs sound like they would be easier to integrate. > It's just the compass that gives a shitty experience. Yep, that's my experience too, and that's why I'd be ecstatic to hear that the compass was being replaced by a RLG (which could be re-locked to true North every time GPS got a decent movement vector). Then again, I half suspect that something is FUBAR'din the current compass stack. I have one of those fluxgate-magnetometer current probes at work and can report that everywhere I've used it I have seen magnetic field vary as a high-SNR continuous function of direction, yet my phone's maps app has a ton of lag, hysteresis, and jankiness when rotating in the same damn field. Maybe we just need to wait for the cheap compasses to get better.