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Lots of horrible shimmey on the Metro in Sydney a while ago, which translated to violent forwards and backwards shaking on the inwards facing pax, the only seats on these Indian imports running on Spanish track in places over the second iteration of a viaduct built by an Italian company (the first collapsed) and controlled by computers overseen by a Chinese company. Labor states build real trains in single deck format, and track is made 100 km south in Port Kembla, the the union hating right wing reactionaries calling themselves Liberals wanted to to destroy as many Aussie jobs as possible, with driverless and guardless imports. Thankfully for heavy rail Labor is back in in NSW,, and will build double deckers here again. Meanwhile despite Victoria building teams they went with Crack And Faulty for light rail, and they formed massive tears in the wheel wells, which were blamed on tight curves, however heavy freight rail was blamed for this. It took a while to transfer T2 / T3 rolling stock over as this is all (segregated) street running with no use of train track, as on L1.
@@JagoHazzardThat's quite a climb in the footage at the end. Was it worth a mention that light rail is inclined to wobble on an incline? Probably not.
The Washington, DC Metro chose less-conical wheel profiles than usual to minimize hunting oscillations, at the cost of more squealing around curves. The adjustment for that with otherwise standard hardware is the reason why its gauge is a bizarre quarter-inch narrower than standard: 4 feet 8 1/4 inches.
The physics of hunting oscillation is quite interesting. And when a train is passing a platform at speed, it really matters that it's taken into account. Not that this will happen on the DLR, which stops at every station.
Main line rolling stock goes to great lengths to suppress hunting, especially on high-speed services. I believe it involves dampers that are a bit like car shock-absorbers and minimising the "unsprung weight", but I'd be interested to learn more from an expert. They probably do things with the permanent way as well.
@@neilturner3658 The most knowledgeable expert is (or was) Dr Alan Wickens. He was employed in the 1960s to investigate the issue. It became the most important & least well known aspect of the APT project.
Very interesting Jago, I always wondered why trains and rolling stock didn't have a form of differential. As in Ackermann's principle of steering. You are my differential to a curve. Thank you.
@@jadeboswell-rz2ly They don't need one, because the taper does it for them. The wheel on the outside of the curve rides up, and because of the taper now has a bigger circumference in contact with the rails than the one on the inside of the curve, which has moved down. That means that the wheel on the outside of the curve travels further for each turn of the wheels, which is exactly what you need to go round a bend
@@norbitonflyer5625 Even more so, if they did have a differential, the self-steering effect wouldn't work! Notably, trains designed for dedicated high-speed lines (think Shinkansen, TGV) have less-tapered wheels to reduce the heroics needed in the suspension. Presumably the Mini-Shinkansen uses a more normal taper to run on the former conventional routes, resulting in a lower maximum speed on the dedicated section of the route.
Hunting Oscillation (or lack thereof) is what causes heavy rail trains to derail at low speeds. The slight taper on the wheels is designed to keep the train stable at high speeds, but at low speeds, especially where there might be “side wear” on the track (that is the inner edge of the head of the rail is no longer vertical and has started to wear off at an angle, most common on points or curves) the wheel taper will begin to climb the rail, and if nothing knocks it back down it will climb over the head of the rail and hey presto, the train is now a bus. That is why when you hear of most derailments, it has been trains in depots or carrying out empty shunting moves at stations. It’s not a happy coincidence that there were no passengers, it’s the slow movement associated with these manoeuvres that contributed with it. Trains travelling at speed (anything over 10mph) don’t derail without outside influence because there’s always enough lateral movement for the Hunting Oscillations to right themselves.
There's a story about oscillation from closer to me, also. The Chicago North Shore & Milwaukee was an electric interurban railway that connected Chicago to Milwaukee, running through the area known as the North Shore (yes, sometimes a railway's name actually indicates where it went). They were known for high-speed service, with expresses covering the 80 miles between Chicago and Milwaukee in 90 minutes. They also operated on the Chicago Elevated structure (organized by that shifty Yerkes fellow) operating above the streets, and so had to negotiate curves as tight as 90-foot radius. After some issues with instability and vibration, they were curious how the wheels were behaving on the track, so they mounted a headlight and a motion-picture camera beneath a car and ran it at high speed. What they saw was extremely frightening, and they worked with a few other railways to develop a new wheel profile that was more stable at high speed. Incidentally, a few of their cars came into the possession of the Illinois Railway Museum when the North Shore shut down in 1963, and I'm going to work as a trainman on some tomorrow.
There's an interesting story there about the ground conical wheel profiles of railway rolling stock. Essentially, no train has any differential gears, as road motor vehicles have, that is due to the the different circumferential lengths of the inner and outer curved rails, and the fact that rolling stock has fixed axle sets - due to points and switches - the inner and outer wheels would have a tendency to rotate at different speeds. The way the early rail engineers overcame this problem was to grind a tapering conical profile into the wheels so that the effective circumference of the outer wheel increases, effecting an apparent decrease in its rate of rotation. The physicist Richard Feynman cited this as one of the hidden triumphs and treasures of engineering.
For those wondering this is actually what keeps a mainline train on the track most of the time. The outer wheel effectively gaining speed through larger contact circumference steers the train into the curve. The flanges are only needed for safety and tighter corners. The screeching noise made by trains crossing between lines for example is the sound of flanges doing their thing
@@oliverbooth2872 Very good explanation, but I thought I'd seen elsewhere that the screeching is not necessarily the flanges even then, but the wheels slipping a bit on the rail to "catch up" their opposite number.
This actually explains why all the light rail trains in Edmonton tend to wobble, and also why the new Valley Line trams seem to be wobblier than the bigger light rail trains on the Capital and Metro lines, since the trams traverse much tighter radius curves.
Partially - the other contributing factor for the Valley Line relative to the others is that it uses low-floor vehicles, which require most of the electrical and HVAC components to be roof-mounted, making them top-heavy. It's the same thing with other low-floor light rail and tram systems to varying degrees.
The flanges are not what keeps the train on the rails, except in extreme conditions. The conical profile means that if on wheel is higher up the rail than the other it will have a larger circumference and travel faster. This will steer the train back to the centre of the track.
Essentially, the hunting oscillation is caused by each bogie travelling in a wavy line on top of the straight track.One way to stop this is to have damping on the rotation of the bogie in relation to the body, wich will discourage this and damp it down to travelling staight.
Way back in the mid 80s I was travelling on a Class 101 DMU east of Hunts Cross, and the hunting was so severe people's shopping bags were getting thrown about like leaves. 101s weren't especially prone to that in my memory, so I can only assume there was a wheel or bogie fault. Crew weren't interested, presumably they were used to it.
2:59 so does everyone have at least one of these bowls? Excellent video, answers the question I ask myself as I spill my coffee between Shadwell and Limehouse.😊
What Jago means is that the cone angle on the DLR wheels is larger than on heavy and fast rail systems. This is related to the curve radius which can be negotiated. (Tight curves require more cone angle)
Well how about that? We were in London last week, we took the DLR for the first time and both of us remarked on how it seemed to excessively rock back and forth. I actually assumed Jago would have a video about it and here it is, just as we made it home. Excellent service I have to say!
I've found many unusual parts of Bank station where I've had to throw up because of the DLRs wobble - and thanks to the lovely staff who knew what was happening and let me into those parts.
Years ago on South West Trains a passenger was concerned about the speed. I explained we could go much faster but it would be too uncomfortable for the passengers.
Fun fact - early motor cars didn't always have dampers, and if they did, they were friction dampers rather than the conventional oil and piston damper we have today. This meant that on the early, rutted roads it was possible for a cars axles to meet their natural frequency of oscillating up and down leading to the bounce getting progressively greater and greater until the car would literally jump in the air and throw itself over the nearest hedge 😂
The normal streetcar radius curve in the US,was/is approximately 50 feet,and that limited the length,and width requirements! One of tightest curves on Chicago's elevateds,is on the LOOP,downtown,whch had a fatal derailment,in the 1970's,and that also happened in Brooklyn, and Manhattan on the old elevateds! That was because of speeding,and overhunting on the trucks[bogies],so there can be consequences to that degree! Thank you,Jago,your technical prowess is showing up,and well presented! Thank you 😇 😊!
@@AtheistOrphana lot of Londoners don't leave their patch. I'm from our if London but visit when I can and suspect I've seen more different parts of London than most Londoners
Excellent video episode, thanks! Well my grandfather used to call that “wobble” the Shim Sham Shimmy. Apparently it’s highly appreciated in Philadelphia subway trains and beautiful women! A thing of beauty & a joy to behold in both cases.
I used the DLR on Tuesday evening (May 7th 2024) and I did notice the wobbling it was quite bad from Bank to Canary Wharf; more specifically it was on the section from Shadwell to Limehouse
I think this slightly misses the point of variable circumference. In order for a train to go around a corner, the outer wheel needs to physically go further than the inner wheel. The reason why the wheels are conical is so that when this happens, the outer wheel is pushed onto the fatter end, causing the wheel to effectively become bigger, and the inner wheel becomes smaller. Since they are spinning at the same speed, the bigger wheel will travel further with each revolution so the outer side of the train goes slightly faster than the inner. When the train comes out of the curve, the outer wheel is still bigger than the inner, so it steers the train towards the inner side of the track. This causes the inner wheel to be pushed up, and move further than the outer wheel, so the train is steered back towards the outer side. This is what causes the oscillation, not just gravity.
I remember there was a demonstration of this at the National Railway Museum when I was young. It was clear that gravity was unnecessary to see the effect because it worked just with an axle and wheels light enough to not hurt a child.
That is really spooky, I was just talking to someone about this only yesterday and we were discussing about the issues and wheel profiles of Manchester Metrolink and the huntiing issues. We also discussed how at one time some experiments were done with what was called "Worn Wheel Profile" which was relatively successful until gauge widening on curves became the norm, which rendered it ineffective.
An amusing consequence of their operating environments: Light rail vehicles are often heavier (at least for their size and capacity) than heavy rail vehicles (there's a whole bunch of factors that can cause this to not apply, mind you). This is pretty much entirely down to the specific types of accidents they can get into: light rail needs to be a lot more solid to protect it's passengers if it's going slowly and gets rammed in the side by a semi than heavy rail needs to be when going at high speed and hit in a similar manner, not to mention the light rail is far more likely to encounter such issues due to street running being exceptionally common while heavy rail only does so in exceptional (and usually far more controlled) circumstances. Makes the names seem rather confusing at first glance.
Note the check rail at 1:45. This is another measure to stop the wheels straying too far towards the outside of the bend - the flanges of the wheels on the inside of the bend bear against the check rail.
A complex subject very nicely summed up. Really. I mean that. I've spent ages looking at tram rails on curves trying to figure them out where it looked like the tram must be running on the wheel flanges as the rail head was so low. The tyre profile will effectively alter the gearing on a corner as both wheels will be different diameters on different track radii and I assume will self compensate which is very simple, extremely neat, fascinating and thoroughly confusing, because, to my mind, the angle of the tyre profile doesn't seem much so there's a lot more to it, especially as the rails are canted and would imply a whole host of tyre profile ranges for different track gauges. I've no idea if I'm on the right tracks but it must be something along these lines. It's like going in a sudden leap in logic from a wooden wheel to a spoked and tensioned wheel while evolving wheel dynamics and the spoke formula over a cup of coffee at breakfast. So there's a hell of a lot I just don't get, never quite have, and this video helps without giving me uncomfortable flashbacks to maths III at college.
Vancouver's skytrain uses steerable boogies. Which means the two wheel axles on the boogie can independently turn, allowing tighter turns. This allows the trains to use more conventional wheels which permit higher speed without hunting ossalation becoming a problem. It also avoid the squealing sound that trains get when taking tight turns.
At about 1:45 you said the wheels press against the outer edge of the rail. I'm sure you know the wheel flange corner rides on the inner edge of the rail. A very minor point to another otherwise excellent video.
@@telhudson863 Listen more carefully. He says "It's wheels press against the outer edge of the rail". If anything, they press on the inner edge of the outer rail. To be really pedantic the conical part of the wheel tread invokes the differential effect most railway savvy people understand. The wheels most certainly do not press against the outer edge of the rail.
@@boldford I heard what he actually said but Mr. Hazzard abbreviates his comments and makes them sound good. That is why it is so easy to listen to him. Often he is not technically precise but we understand what is meant.
"Why don't they just" suggestion: Wider wheels. In the middle of the wheels and further to the outside the profile is gently conical like on a regular train, so it can go straight properly. On the inside towards the flange it gradually gets steeper all the way to tram steepness, so it can go around curves. Maybe that is already what they have and it doesn't work as well as I imagine? Or maybe wider wheels cause more problems? They would be heavier and slower to accelerate at least.
They would also mess up regular switches (that would be an expensive fix). And you would probably not be able to run in a street, but I don't think the DLR does. And level crossings would probably be bad for the road vehicles, but those are probably rare for an automated system like this. MAYBE on a separate system like I imagine the DLR to be, something like this could work?
Hunting Oscilation you say. What happens if you catch one of these Oscilations? How big are thery? Do you have to release it back into the wild? Can they be kept as pets? Are they suitable to feed a hard up family?
They aren't particularly aggressive in the wild, but they're very quick so you have to be careful. They range in size from that of a small cat to that of a baby elephant. They must be released back into the wild as they're essential for the ecosystem. You can't keep them as a pet since they quickly become aggressive if kept in captivity, and they aren't edible so you can't eat them.
@@wta1518 Finally, I have found an Oscilation expert. I have so many questions. What is their favourite food? Do they live in groups or are they solitary? The former Docklands of London seems to be their preferred habitat. Where else can they be found? Is there more than one species? Like Indian/African elephants or Grey/Red squirrels What is the collective noun for a group of Oscilations? A Shake, Quiver, Frequency, Reverberation, Wave or Vibration? Are they an endangered species? Is an Oscilation's home called a Jago? Or was I being wound up
@@mikehiggins4079 They generally eat iron and alloys containing iron such as steel. They typically live in groups of at least 10. They can be found in most cities in the world, due to the abundance of iron in those areas. They're the only species. The collective noun is wibble-wobble. They aren't endangered, but they could be if we continue hunting them. Yes, they're home is indeed called a Jago.
@@wta1518 Thank you for sharing your abundance of knowledge on the subject. One last question. The same source that told me an Oscilation lives in a Jago also said a male Oscilation is called a Yerkes. Is he correct, and what is a female called? Maybe we have found a worthy topic for a Jago Hazzard video. Unseen Life of the DLR & Underground!
I imagine the distance from the front of the train to the bogie pivot point also has something to do witht he sway. The further from the front of the train the greater the left-right sway of the front seats. Tight curves also give "Flange sqeal" as at St Pancras Thamesling, despite flange greasing equipment.
I remember my first time on the DLR as a kid, I thought the train was going to derail coming out of Tower Gateway. Went on it a few times recently and have come to the conclusion that its just the way it is. This video just the explanation I need. Jago up to the minute aa always 😎
It's good to see your model railway again! You should come to the Model Railway Club near King's Cross on a Thursday one day and make a video about that.
IIRC the Heathrow Express Class 332s had to be periodically rotated (the whole unit, rather than the wheelsets) due to one-sided wear from going to and fro in an arc
Excellent! Were you an engineer? One curve solution you missed was the oiled pad. Shipley Station had them. They were a felt pad and a container with oil, that oiled the inside of the wheel flanges. They worked, but somebody had to refill the container; nobody does that now. Bradford-Keighley trains at Shipley now go very slowly, and still screech like a 200 ton train hard rubbing up a rail, with no oil on its flange.
This was a good video and explanation but it'd have been nice to see a diagram or image comparing the wheel profile on light rail vs heavy rail wheels. If I remember correctly, some of the sheffield supertram tram-trains (class 399) have wheels profiled for one or the other which determines whether they're allowed to operate on some of the shared network rail tracks?
You get this "going faster than ideal" type hunting on the T&W Metro, too, where the green line joins the National Rail network on the way to Sunderland. It always seemed odd to me that when it moved onto a section which had smoother curves then it should hunt more, but I'd not thought about the speed.
Hello Jago, that was a wheelie good explanation of why wobbly wailway trains wobble on the DLR wailway tracks. That’s all folks. I’ll close the door on the way out.
A good explanation of it. Practical Engineering did a whole video on this. I'd say the hunting is most visible when in the tunnels under the Thames, particularly Woolwich Arsenal. And if you're at the front or rear of the train, where the hunting isn't dampened by the next vehicle along.
Every time the train wobbling between Custom House and Prince Regent give me a vibe that a footbridge between West end of PR and East end of CH favourable
