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Post by Deleted on Jun 20, 2012 16:58:11 GMT
On another thread I noticed that a train was described as being at a certain point at "01 23 3/4" which I found quite impressive. Are there (presumably digital) clocks built into train cabs? I can hardly believe drivers are expected to use their own wristwatches (or indeed mobiles )
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mrfs42
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Post by mrfs42 on Jun 20, 2012 17:02:23 GMT
On another thread I noticed that a train was described as being at a certain point at "01 23 3/4" which I found quite impressive. Are there (presumably digital) clocks built into train cabs? I can hardly believe drivers are expected to use their own wristwatches (or indeed mobiles ) Things have got a lot easier of late - in the early days of the Yerkes tubes Motormen were expected to drive to a certain set period in seconds. Inspectors were given stopwatches, they occasionally appear for auction.
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Post by Harsig on Jun 20, 2012 18:09:40 GMT
Generally only lines equipped with ATO are timed to the nearest quarter minute. Conventionally signalled lines are only timed to the nearest half minute.
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mrfs42
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Post by mrfs42 on Jun 20, 2012 18:59:05 GMT
Generally only lines equipped with ATO are timed to the nearest quarter minute. Conventionally signalled lines are only timed to the nearest half minute. ..err.... I *do* have a 1916 C&SLR TTN that's timetabled to the quarter minute.... ;D
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Post by d7666 on Jun 20, 2012 20:38:39 GMT
ATO are timed to the nearest quarter minute. Signals control system control data - the timetable the relevant ATS processors actually run - is timed to the nearest second for any intermediate location from wheel roll at any station to wheel stop at the next station. At the latter station it is then rounded up or down to the nearest quarter minute, the rounding being in the ATS data. -- Nick
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Colin
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Post by Colin on Jun 20, 2012 22:08:54 GMT
I can hardly believe drivers are expected to use their own wristwatches (or indeed mobiles ) We are indeed expected to provide our own time devices, and ensure we're in place to pick trains up on time, though mobile phones in cabs are frowned upon (it suits when there's an emergency ). More & more platforms these days do have some form of clock, whether it be stand alone or built into the 'next train' dot matrix - and most [though not all] terminal platforms have a clock.
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Deleted
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Post by Deleted on Jun 21, 2012 9:58:24 GMT
Many thanks for all those replies - fascinating, especially the historical stuff.
The fact that a train's wheels will always go round exactly the same number of times in travelling from A to B is one of those things that is obvious when you think about it!
There was recently an allegation (not on this Forum) that the DMI "count down" clocks operate on minutes longer than 60 seconds. From what I can make out, this is only so in one case: "1 minute" is indicated from 1:59 minutes away until the train is about to enter the platform - presumably a H&S device to discourage people from moving to its edge until they actually need to. Is this so?
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castlebar
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Post by castlebar on Jun 21, 2012 10:19:38 GMT
innocentabroad says "The fact that a train's wheels will always go round exactly the same number of times in travelling from A to B is one of those things that is obvious when you think about it!", but l'm afraid this is wrong!
On a circular service, the non-motorised wheels on the outer rail will get more revolutions than those on the inner rail. That is also obvious when you think about it!
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Post by bruce on Jun 21, 2012 17:37:27 GMT
Don't forget to take into account wheel diameter due to tyre wear. A worn wheel will turn more revolutions travellling from A to B than a wheel with a new tyre on it.
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Post by Deleted on Jun 21, 2012 20:34:11 GMT
innocentabroad says "The fact that a train's wheels will always go round exactly the same number of times in travelling from A to B is one of those things that is obvious when you think about it!", but l'm afraid this is wrong! On a circular service, the non-motorised wheels on the outer rail will get more revolutions than those on the inner rail. That is also obvious when you think about it! Not to me, alas. How can different sets of wheels move at different speeds?
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rincew1nd
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Post by rincew1nd on Jun 21, 2012 20:46:18 GMT
I remember reading a few years ago that the R&ER were interested to find out how far their carriages travelled in a year. Their Guards noted which locomotives travelled up and down with their trains but not the carriages involved. At the end of the season the Staff eagerly gathered around as the cap was taken off the revolution counter to reveal that, over the year, the carriage had travelled a grand total of: 10 yards. It subsequently transpired that when running in reverse the axle counter fitted proceeded to count down. It is about ten yards from The Ratty carriage shed to their works. I'm told that most domestic water meters are made by the same manufacturer....
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Post by norbitonflyer on Jun 21, 2012 21:34:47 GMT
Not to me, alas. How can different sets of wheels move at different speeds? Consider a simple circular track. If the radius of the inner rail is x, its circumference is 2 pi x. But the outer rail's radius is x+g (where g is the gauge), so the circumference is 2 pi (x+g) . Thus the wheels on the outer rail must travel 2 pi g further on each circuit. If the two wheels on an axle are free to turn at different speeds they will therefore turn a different number of times as they negotiated a curve. If they are not (for instance because they are attached to the same traction motor) there will be some dragging or sliding of the wheels as they try to maintain an average rotation rate somewhere between the two free rates. In addition, if wheels are different sizes, the smaller wheel will turn more times to cover the same horizontal distance. This is why freight steam locomotives have smaller driving wheels than express ones - effectively steam locos have only one gear, and for a freight engine low gearing is needed to get the train moving, and for an express higher gearing is used for outright speed, at the exense of lower starting torque.
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Post by Deleted on Jun 21, 2012 23:26:59 GMT
Virtually all rail vehicles (exceptions are things like Talgo and some low floor trams) have rigid wheelsets, of two wheels fixed to an axle, so both wheels do make the same number of revolutions. But the wheel treads have what is essentially a conical profile (AIUI, in times past it was a plain cone, nowadays more subtle profiles are used), so, depending on where the wheels are actually in contact with the rail, the effective diameter of the wheel varies - and this, in conjunction with the rigidity of the wheelset, effectively steers the wheel along the rails - it it is only exceptionally that the flanges get involved in keeping the wheels on the rails, and in that case sliding of the contact points occurs. See e.g. here
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Post by 1018509 on Jun 22, 2012 10:10:13 GMT
I remember, years ago, on Tomorrow's World, I think it was, or that programme with James Burke, they marked the inside of a fixed axle wheelset and filmed the axle going round a tight curve. With the use of a strobe light and the markings on the wheels they actually proved, somehow, that there is a point at which one wheel moves in the opposite direction to the other at a certain radius of curve.
I don't pretend to understand this and sort of half disbelieve it although I saw the programme.
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Post by norbitonflyer on Jun 22, 2012 13:16:54 GMT
With the use of a strobe light and the markings on the wheels they actually proved, somehow, that there is a point at which one wheel moves in the opposite direction to the other at a certain radius of curve. . Whilst it might be possible on a very tight curve, I can't visualise it. What is undoubtedly true is that patr of each wheel is moving backwards - namely that part of the flange that is below the level of the rail surface - since the part in contact with the surface is instantaneously stationary.
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Post by grahamhewett on Jun 22, 2012 15:37:07 GMT
etr220 is correct -it's the conacity (if that's the right word) that steers the wheel. A long time ago - at the time of the APT - BR Research produced a terrifying film of what actually happened to the wheels at high speed. Quite often in the course of trip, the wheels ran on their flanges on one side relying on the depth of the tread and its degree of conacity on the other. More prosaicaally, the engineers demonstrated it to we lay people with a pair of coffee cups (empty).
GH
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Phil
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Post by Phil on Jun 22, 2012 21:52:52 GMT
With the use of a strobe light and the markings on the wheels they actually proved, somehow, that there is a point at which one wheel moves in the opposite direction to the other at a certain radius of curve. The wheel itslef can't be travelling in the opposite direction - obvious!!! (ALthough it CAN be stationary at minute times). What the experiment showed was that the FLANGE of the wheel would under certain conditions be moving opposite to the directi0on of the train.
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Post by Deleted on Jun 23, 2012 17:33:43 GMT
Many thanks for all your thoughts since I was last here. Mind you, I do feel a little like a fox in a henhouse ;D
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Post by tubeprune on Jul 8, 2012 8:58:32 GMT
innocentabroad says "The fact that a train's wheels will always go round exactly the same number of times in travelling from A to B is one of those things that is obvious when you think about it!", but l'm afraid this is wrong! On a circular service, the non-motorised wheels on the outer rail will get more revolutions than those on the inner rail. That is also obvious when you think about it! No! I missed this. The two wheels on a conventional railway axle are fixed. The tyres are coned so that, on a straight track, the contact patch is central but on curves it is on the outside of the inside wheel and on the inside of the outside wheel. It is a natural steering mechanism. See www.railway-technical.com/whlbog.shtml
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