Electronics > Projects, Designs, and Technical Stuff
Are accurate clocks really the limiting factor in cheap Inertial Navigation?
IDEngineer:
--- Quote from: coppice on March 25, 2019, 04:10:40 pm ---Most optical gyros don't actually use fibre, because they can achieve greater stability by reflecting light off mirrors. The base plate and mirrors form quite a heavy assembly, to achieve the rigidness needed for accurate navigation.
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There are versions that use a single piece of Pyrex, with the mirrors silvered directly onto polished faces in the proper alignment. Solves quite a few challenges with respect to thermal stability, etc.
However, my earlier comments regarding the sensor still apply. That's where the real challenge lies, in having sufficiently high enough sensor resolution to not lose registration due to very low rotation rates.
Doctorandus_P:
Inertial navigation was accurate enough to hit London from the west coast of the Netherlands in WW2.
The amount of drift you can expect of "modern" sensors is related to price you pay for them.
One way you could copensate for drift in road traffic is to map the accumulated data to the road map, ans assume you can only travel over the roads.
If you accumulate enough left and right turns you could even get the location from that even without prior knoledge about the starting position.
No atomic clocks needed.
jc101:
There is a reason why part of the checklist in aviation is to verify the position of an aircraft before departure, all gates have their specific Lat Long available as cross check. This is to verify the aircraft INS (Internal Navigation System) which does dead reckoning has a known staring point. It will drift during the flight. The INS is one navigation system, and it combined with radio Nav beacons and GPS.
coppice:
Inertial navigation and time consuming journeys don't go together very well. An ICBM can reach its target accurately by inertial navigation. A bomber needs corrections, manually applied, along the way. A cruise missile uses inertial navigation to move between way points, where it uses a ground mapping radar to realign itself against a stored map.
ejeffrey:
--- Quote from: IDEngineer on March 25, 2019, 04:12:34 pm ---Ring gyros are a fun topic. Their challenge is loss of registration due to extremely slow rotation rates... there is always some rate of rotation small enough that the pattern shift is smaller than the resolution of your sensor.
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That isn't quite the problem. The detectors have plenty of resolution to detect a small fraction of a fringe. The problem is that at DC, the two modes (clockwise and anticlockwise) are close enough in frequency to cause injection locking of the laser from scattered light or other means of crosstalk, This leads to zero signal. The usual (partial) solution is to mechanically dither the gyro. This isn't perfect and also introduces a signal you have to filter out.
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