Call me sceptical, but I suspect if this works very well it will be used in weapons.
Which then leads me to think the whole thing is a smoke screen, not sure why
Tube trains could navigate the Underground using the rules of Quantum Physics
31–40 of 83 posts
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#32Earlier quoted context omitted.
Engaging with the substance of the suggestion ... * What would the Central Limit Theorem give us if a significant number of wheels on loco's and carriages were instrumented and ID logged over the years. * What drift patterns and correction factors can be observed and fine tuned by passing {many} wheel streams through station to station and line end to line end "known distance" corrections. For half a century or so ai…
For half a century or so aircraft height was largely done with air pressure alone. It still is. Flight levels (20000 feet and above in the US) are defined by air pressure without reference to current atmospheric conditions (i.e. the actual altitude of FL200 can vary based on atmospheric conditions). Below 19000 feet, altimeters are calibrated to local conditions which are given to the pilots by air traffic control.
Still used, sure, but not solely ( 'alone' ) - it's augmented by GPS height, feedback from ground radar, onboard radar facing down and forward, etc.
See: https://en.wikipedia.org/wiki/Altimeter that list five types (including trad. air pressure type)
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#33I would have thought a simple device that counts the number of times the wheel has rotated would be vastly simpler and cheaper, and surely accurate to within a few centimeters.
It has to be for research purposes or something. They own the whole system of trains and tunnels, so there’s got to be loads of ways they can easily implement to see if a train passes a particular point.
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#34It's kind of annoying that they don't go into specifics about why this is good. The problem with traditional accelerometers is that the error accumulates, and so even small errors accumulate. The article doesn't really address what makes this different - and in fact I don't think it is different. You're still just measuring acceleration using a sensor and that sensor will have errors that accumulate. So the question…
At every station at least it should be very cheap to install optical markers that could allow for many opportunities for recalibration.
Agreed, but then said optical markers regularly positioned in tunnels and a map of the tube is enough to position yourself already. That's likely how it works right now, and it's fine.
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#35Earlier quoted context omitted.
It wouldn't. Wheels slip in the wet, they develop flat areas with differential friction, minor differences in wheel circumference would soon add up over long distances, and all dimensions change with temperature. But fiberoptic gyro navigation is already a thing, and has been for decades. It's not super cheap, but it's cheap enough for an industrial application like this one. So I'm not sure what problem is being sol…
If it's wet inside a tube tunnel something has usually gone very wrong surely? Also trains have quite a large number of axles, I'm sure you could reduce error by counting all of them.
A number of the tube lines have large sections above ground.
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#36Earlier quoted context omitted.
It wouldn't. Wheels slip in the wet, they develop flat areas with differential friction, minor differences in wheel circumference would soon add up over long distances, and all dimensions change with temperature. But fiberoptic gyro navigation is already a thing, and has been for decades. It's not super cheap, but it's cheap enough for an industrial application like this one. So I'm not sure what problem is being sol…
If it's wet inside a tube tunnel something has usually gone very wrong surely? Also trains have quite a large number of axles, I'm sure you could reduce error by counting all of them.
Trains in tubes have a lot of suction that draws in condensation from outside air.
A curious advantage of instrumenting all axles for wheel turn counting is calibration against actual known distances (end to end, etc) over time reveals slow wheel degradation that can trigger carriage maintainance.
Not all operators do this, it's been done at various times for heavy rail mining operators with loooong trains and heavy daily usage.
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#37Cool technology, but seems a bit of an extreme effort just to check train position. Why can't they just use markers on the tunnel walls (or under the tracks)?
> Naturally, trains already have track-based location systems, but they are usually based on a train being within a “moving block”, so their accuracy is down to metres rather than centimetres. If you want to monitor track conditions, the more accurate the location of the suspected fault, the less time staff spend repairing it. Agree in principle though, is this extreme precision really needed?
> their accuracy is down to metres rather than centimetres. If you want to monitor track conditions, the more accurate the location of the suspected fault, the less time staff spend repairing it.
Considering the tracks are linear, I would estimate the additional time needed to locate a fault within two meters as compared to two centimeters at "negligible".
On the alternative assumption that the faults are too small for humans to detect and we just need to replace the affected track... I would also estimate the additional time needed to replace two meters of track, as compared to two centimeters, at "negligible". It doesn't actually take less time to cut out a specific 1cm strip (containing no visible indications!) from a piece of cloth as to cut out a 1m strip that includes the 1cm strip somewhere.
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#38It's kind of annoying that they don't go into specifics about why this is good. The problem with traditional accelerometers is that the error accumulates, and so even small errors accumulate. The article doesn't really address what makes this different - and in fact I don't think it is different. You're still just measuring acceleration using a sensor and that sensor will have errors that accumulate. So the question…
> I would wager that actually this is probably just a way of funnelling money into research around quantum rather than genuinely trying to solve this specific problem.
You’re absolutely correct, from the government’s perspective the interest in the technology is for high accuracy inertial navigation systems for defence purposes, not for the London Tube. If you look at the other companies involved in this project, there’s a number of defence contractors involved.
This project isn’t really new, and historically the pitch has always been: We want to develop GPS grade navigation that doesn’t depend on satellites, and is smaller and better existing inertial navigation units. Oh look the London Underground is the perfect test bed for our technology!
It’s underground, so no GPS or many external signals. It’s already well mapped so we have something to compare against. Tube trains are loud, hot and vibrant a lot, which makes it a challenging environment for inertial systems. Plus it’s cheap and very easy to roll a box on an existing train, drive a few km under the city, and then compare your results to GPS from when you go underground, to when you surface again.
https://www.theguardian.com/science/article/2024/jun/15/lond...
The idea of using it map the underground I think is a bit of a red herring. Makes a good story, and TfL will probably be grateful for the data. But it’s not the kinda thing anyone thinks is worth developing quantum accelerometers for.
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#39Sounds like a grift with the only redeeming quality of advancing technology perhaps useful elsewhere. There's no way encoders on wheels with resets on stations/junctions is not enough for precise train positioning.
Re: Tube trains could navigate the Underground using the rules of Quantum Physics
#40You might be at Victoria Station, but there's a slim but tangible chance you are in fact in Paddington.
We won't know until someone looks at you. Until then you are on every station possible in the underground sorted of smeared out into a probability wave.