The notification came through for this whilst I was wobbling on the DLR, just coming out of bank

You should have titled the video _Good Wheel Hunting_ .

Conical wheel profile → better self-correcting at tight curves But also Conical wheel profile → worse over-correcting on straight runs

0:34 Finally, we’re in the Hazzardous Lair

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.

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 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.

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.

2:59 Well, IKEA does sell light rails. I'll get me coat.

Some trams like the Variobahns in Croyden actually have near cylindrical wheels. They have independent motors on each side, and with the computer they effectively tank steer around the corners. It also means they don't need the axle though the middle so they can be low floor throughout.

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.

Nice to see the model railway having a brief outing.

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.

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.

One of the best experiences of my trip to the UK was sitting "in the captains seat" at the front left of the DLR. Great view!

2:59 I had no idea the DLR's wheels are produced in Sweden.

Thanks, I've never noticed or thought about the wobble when travelling on the DLR and now I'm going to think of nothing else.

Sounds like the "shoogling" of the original Glasgow Subway trains.

Ooh, DLR stuff, excellent.

Hunting oscillation is a great term. Thank you for the explanation.

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.😊

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.

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.

This was wheely good

Last time I went on the DLR it was to a beer festival at the Docklands Arena. I got my bag caught in the bus-like folding doors of the tiny train.

I loved this scientifically wobbly tale from the tu... Oh wait the DLR. Nicely done Jago, keep it up

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!

Riding the DLR brought back memories of travelling on Romanian railways 😭

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 😇 😊!

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 😂

I ask myself this every time I'm on these trains, thank you Jago 🙏

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.

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.

Thank you, Jago, for bringing model trains into the story!

Good Morning Jago. Enjoyed you adding a few shots of your model trains to illustrate the point. You really "went to town" on this one. CHEERS!

Here in Ottawa the line 1 LRT is having lubricators installed because some of the curves are so sharp they probably contributed to wheels falling off.

Sometimes you really do need to re-invent the wheel

0:34 jago has a science corner

Every day is a School day with Jago - I didn't know about this Jago - Thanks for sharing 😊🚂🚂🚂

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.

I have been using the DLR ever since it first opened and for myself the most wobbly section is between Shadwell and Bank.

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.

Jagotastic TALE FROM THE DLR, Sir Jago!! ….and you are the *”Equilibrium to my Wobbly KZfaq”.*

love the wobbly bois. probably my favourite mode of transport in london

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.

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.

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

And this explains the real difference between Light and Heavy rail. Thank you.

I always felt that this channel needed more crockery. Useful explanation. Thanks.

As a West Londoner, the DLR seems to alien to a Hammersmith and City user.

One of the best and clearest explanations of a physical phenomenon I've ever heard - well done !

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.

Amazing, I’m in my late 60s and still learning about the technical aspects of railways. Thanks Mr Wobbly Wheels ! I love the DLR.

"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.

As informative as ever. I always learn something new.

Remind me never to travel on the DLR. I suffer from Vertigo and have balance issues as a result. Buses also cause me much aggravation.

The return of Jago’s Trains! Congrats on the new place with room for the hobby.

It all adds to the Rollercoaster feel

Love it! I have learned something this sunny Saturday afternoon,

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.

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 knew the trains wobbled, but had no idea why. Thanks! 😁

Thanks!

Interesting and comprehensive explanation, Jago... thanks!

One of my favourite videos of yours, Jago

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.

Thankyou, Jago. Appreciate the information.

After a ride on the DLR a trip on the peter pan dragon rollercoaster at Southend is a doddle

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 😎

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.

Good clear explanation. And not longer than it needed to be. Thanks!

Absolutely fascinating.

If I ever got married, "you are the equilibrium to my wobbly wheels" would be in the vows.

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

The LNER made some suburban rolling stock by taking old 4 & 6 wheel coaches and putting them on articulating bogies, three between two.

As always, most informative and entertaining.

Thank you. Well explained and as always in a very entertaining way.

Properly fascinating. Great vid!

Skytrain in Vancouver has this "feature" to it aswell! Especially with the oldest trains, with their old (and pretty busted) suspension. Constructed in the same vain as the DLR, too, using old Interurban alignments

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.

What a _very_ interesting episode. Thank you for this … ‘most informative’ 😊

Very interesting and informative one of your best

I liked the picture of Millwall wall.

I had never heard of "hunting oscillation" before, but it makes sense. I learn something new from every one of your videos.🙂

Thanks for answering.

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.

Great video, I'd often wondered about the wobbliness on that faster section too!

"I've gone all wibbly wobbly!" (Lee Evans)

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

Great as ever 😊 Jago

a wibbly wobbly wonder

Great video jago, very interesting,i now know more about the DLR 👌😀👍

On Metrolink, the issue was also identified as being partly due to the articulation both on the T68 (which were basically trains with skirts) and the newer M5000 fleet too not helping matters. I suspect this also plays a part on the DLR. It also led to some rail damage during the transition between T68 and M5000 with a number of speed retrictions on straight sections of line, particularly on the Altrincham line.

Great explanation, I’ll look out for it next time

Try going around the curve at Hartlepool.

The Manchester Metrolink suffers quite badly with hunting now that the T68 LRVs have been replaced by the M5000s, the T68s were a much more robust vehicle and were around 49 tonnes so had a very smooth ride, the M5000s that replaced them are 10 tonnes lighter and on the former heavy rail sections (like the former Bury Electric line) they are notoriously bad - even after they've reprofiled the track. Also that section of track by Bury South signal box is quite a challenge for drivers, it has a very low speed limit (for obvious reasons) but the weight of the train coming down the "ski-jump" will begin to push quite hard, there is also a slight dip meaning if you are just a bit off touch with the brakes then the whole lot grinds to an embarrassing halt (still it's better than the alternative!).

What a nice short and direct to the point explanation. So refreshing to focus on the technical issues and not immediately move to establishing political blame.

Super interesting! Was also trying to match each DLR shot to where it was as quickly as possible. Think I got em all!

Funny how I find this video a day after riding the DLR and noticing how wobbly it is