What's causing the wobbles on Calcutta Sidings

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Proto87Stores

What's causing the wobbles on Calcutta Sidings

Postby Proto87Stores » Sun Aug 20, 2017 10:10 pm

I came across a video of Calcutta Sidings recently and was very surprised at the amount of body side wobble shown by trains crossing the section of "humpy" track towards the left end of the layout. See elapsed time 2.24, 3.03, 4.48.

I wonder if the obviously shaky trains have rigid or working suspension. And if the latter, what type. It does rather look as if the amount of wheel movement fully requires the legacy +/- 0.5 mm, that has been lately discounted here as way more than necessary.

Andy

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steamraiser
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Re: What's causing the wobbles on Calcutta Sidings

Postby steamraiser » Mon Aug 21, 2017 9:10 am

In your picture looks like heat has caused expansion and distortion in the tracks.

Gordon A

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grovenor-2685
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Re: What's causing the wobbles on Calcutta Sidings

Postby grovenor-2685 » Mon Aug 21, 2017 12:57 pm

Telephoto shots do exaggerate subsidence, probably inspired by this http://www.norgrove.me.uk/history_files/Sep72/Sep-72.htm
Regards

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jim s-w
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Re: What's causing the wobbles on Calcutta Sidings

Postby jim s-w » Mon Aug 21, 2017 5:21 pm

You are looking at 40ft condensed into one telephoto shot. The HST going right to left (mine) I think still had mjt bogies back then. They were pretty tired out by then though and have been replaced since. The mk2 coaches are the as supplied airfix chassis with a straight wheel swap. I don't think they have any form of 3 point suspension and you are right, they are a tad wobbly, especially at a scale 90mph.

HTH

Jim

David Knight
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Re: What's causing the wobbles on Calcutta Sidings

Postby David Knight » Mon Aug 21, 2017 7:31 pm

All things taken into consideration, especially the telephoto shots, it looks pretty good to me. I was recently on a trip to Ottawa by VIA rail that had it's fair share of bounces and wobbles and that was with full suspension, springing and weight!

Cheers,

David

JFS
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Re: What's causing the wobbles on Calcutta Sidings

Postby JFS » Tue Aug 22, 2017 9:23 am

David Knight wrote:... it looks pretty good to me. ...


Me too! Especially looking at the "going away" shot about 3:35 which is a much more forgiving view and looks pretty steady. If this were in 00 or (even worse) EM, it really would look shocking given the excessive amount of play between the flanges and the gauge faces in such standards - there are a few such videos about on the internet.

Obviously, the track is less than perfect in terms of straightness and "top", but anyone feeling in a mood to criticise it should have a go at laying 40' of dead straight and level track AND at maintaining it like that - straight and level track for high-speed is more harder than complex pointwork at a terminus! What we need is a 4mm scale laser liner and tamper...

I presume that the OP's reference to "legacy 0.5mm" refers to wheel width - which I don't think really is an issue here as all the movement seen is roll and pitch - the yaw is pretty good, implying quite reasonable control of gauge. So I suspect that scale width wheels would give no problems at all.

Interesting thread!

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Re: What's causing the wobbles on Calcutta Sidings

Postby grovenor-2685 » Tue Aug 22, 2017 10:52 am

I presume that the OP's reference to "legacy 0.5mm" refers to wheel width

I took him to be referring to suspension travel.
Regards

Proto87Stores

Re: What's causing the wobbles on Calcutta Sidings

Postby Proto87Stores » Tue Aug 22, 2017 1:39 pm

My concern was whether there was working suspension (or bogie mounting slop) which was "magnifying" the underlying track distortion. E.g. undamped springing causing one or more additional oscillations. And yes I was referring to the wheel movement allowed by the various suspensions.

If the coach suspension was using rigid bogies, the that would explain their movement. I am not familiar with MJT bogies, so don't know if those are also rigid. But the various loco(s) shown do seem (to me) to move sideways more than the following coaches.



In response to the "it looks good", I can only offer a similar, also less than perfect clip of 120 mph running video clip, with the new 4 point suspension bogies, but which also is on deliberately imperfect testing track. In this particular instance, there is no leading/guiding locomotive, so the leading coach is free to wander where its physics lets it. There is slight track dip by the freight cars, which if you look closely, does cause a quick single perturbation. My apologies if this is a repeat clip.

Andy

proto87stores

Re: What's causing the wobbles on Calcutta Sidings

Postby proto87stores » Tue Aug 22, 2017 2:41 pm

Keith,

Many thanks for the "Model Railways" link. I hadn't seen it before.

Joe Brooksmith's very impressive 1972 analysis work seems to have predated my similar later thinking by about 45 years! I had also originally considered padding the twin rocking W irons movement with rubber sheet. It also appears to be the source of the +/- 0.5 mm wheel movement range suggestion.

FWIW the 4 point wagon suspension has been briefly assembled statically without wheels, but I've been rather busy finishing up on two other projects, (Scale inset track and remote turnout control) to take photos/video yet. It does have remarkable absolute stability on twisted track. So I am now extremely optimistic about the final outcome.

Andy

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Re: What's causing the wobbles on Calcutta Sidings

Postby Tim Horn » Tue Aug 22, 2017 3:27 pm

Calcutta Sidings TJH01 July 2017 Copyright Tim Horn.jpg
Calcutta Sidings TJH01 July 2017 Copyright Tim Horn.jpg


Calcutta Sidings TJH18 July 2017 Copyright Tim Horn.jpg
Calcutta Sidings TJH18 July 2017 Copyright Tim Horn.jpg


Calcutta Sidings TJH08 July 2017 Copyright Tim Horn.jpg
Calcutta Sidings TJH08 July 2017 Copyright Tim Horn.jpg


I think its safe to say that the telephoto zoom is quite harsh, as Jim points out its over 40ft long, compressed, and the trains are running at full speed on hand cut baseboards and hand built track.

Good fun though :)

Thanks for the link, not seen that video before.

Cheers
Tim

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Re: What's causing the wobbles on Calcutta Sidings

Postby JFS » Wed Aug 23, 2017 8:15 am

Proto87Stores wrote:
In response to the "it looks good", I can only offer a similar, also less than perfect clip of 120 mph running video clip, with the new 4 point suspension bogies,

Andy


Hello Andy and thanks for this. Unfortunately, it is not directly comparable as it is shot with a wide angle rather than telephoto lens, and that could mask an absolute multitude of sins! It would indeed be interesting to see how the suspension actually performs when seen under such horrendous scrutiny!

That said, it is pretty impressive - of course, scale flanges can never work ...... :D

Just for information, the MJT compensation pivots the two sideframes to the bolster - a bit like a diamond frame freight bogie. The axles are not sprung to the sideframes.

Best wishes,

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Re: What's causing the wobbles on Calcutta Sidings

Postby billbedford » Wed Aug 23, 2017 9:47 am

Tim Horn wrote:I think its safe to say that the telephoto zoom is quite harsh, as Jim points out its over 40ft long, compressed, and the trains are running at full speed on hand cut baseboards and hand built track.


And you could add that that Calcutta Sidings is an exhibition layout which is put together in a few hours on a limited number of occasions. Not like a permanent builtin layout where much time can be spent getting the baseboards perfectly flat.

I wonder just how that Amfleet set would perform on a layout like Calcutta Sidings.
Bill Bedford
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Re: What's causing the wobbles on Calcutta Sidings

Postby Alan Turner » Wed Aug 23, 2017 4:45 pm

Has anyone seen the real thing lately?

Regards

Alan

Proto87Stores

Re: What's causing the wobbles on Calcutta Sidings

Postby Proto87Stores » Wed Aug 23, 2017 9:22 pm

JFS wrote:
Proto87Stores wrote:
In response to the "it looks good", I can only offer a similar, also less than perfect clip of 120 mph running video clip, with the new 4 point suspension bogies,

Andy


Hello Andy and thanks for this. Unfortunately, it is not directly comparable as it is shot with a wide angle rather than telephoto lens, and that could mask an absolute multitude of sins! It would indeed be interesting to see how the suspension actually performs when seen under such horrendous scrutiny!

That said, it is pretty impressive - of course, scale flanges can never work ...... :D

Just for information, the MJT compensation pivots the two sideframes to the bolster - a bit like a diamond frame freight bogie. The axles are not sprung to the sideframes.

Best wishes,


My little Aiptek video camera doesn't have a wide angle lens. Just a 5:1 zoom, which was set at about 3:1.

Image

In the the clip you are looking along a set of dis-mountable 4 ft baseboard modules plus one 2ft module, totaling 26 ft long. So the viewpoint and construction is definitely comparable, although not as long as 40 ft. The "sharp" curve at the front is actually 52" radius with a 24" lead-in transition curve.



Here 's a looking down view of the end curve with a slightly more moderate lens setting.

Image

I'm sorry, as I know this is a repeat picture, but it fits the context here. For reference my track is rough all the way along rather than just having that single bad patch on Calcutta Sidings. Note tre cars on the adjacent track are the same length as the Amfleets for comparison with the video telephoto settings and distorted appearance..

I could certainly send over a guest loaner set off Amfleets for testing on Calcutta Sidings later this year or next. The trucks are inside framed, so wider gauging would be no problem. But they would likely have P:87 wheels re-set to 18.83 gauge and P4 BB. Providing loco as well, would be a little more work.

I already put up a video of a single car running over a roughly 1/16" bump at speed with no apparent body movement. I can re-post that here if anyone is that interested

I'm not sure f an exchange in the opposite direction would be as easy.

Cheers

Andy

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Re: What's causing the wobbles on Calcutta Sidings

Postby jim s-w » Thu Aug 24, 2017 1:09 pm

Proto87Stores wrote:There is slight track dip by the freight cars, which if you look closely, does cause a quick single perturbation. My apologies if this is a repeat clip.

Andy


I honestly think you are seeing what you want to see here Andy. If you look at the coach coming down the straight bit it seems to wander just as much as the stock on Phil's layout.

Proto87Stores

Re: What's causing the wobbles on Calcutta Sidings

Postby Proto87Stores » Thu Aug 24, 2017 5:51 pm

jim s-w wrote:
Proto87Stores wrote:There is slight track dip by the freight cars, which if you look closely, does cause a quick single perturbation. My apologies if this is a repeat clip.

Andy


I honestly think you are seeing what you want to see here Andy. If you look at the coach coming down the straight bit it seems to wander just as much as the stock on Phil's layout.


I'm actually very glad that people are looking at running video(s) critically. It's one of the very few easy and economic ways of assessing the effectiveness of the dynamic performance of the various common suspension systems. But what I don't think I'm seeing on the Amfleets is any "overshooting" and subsequent extra wobbles, when they react to my track sideways deviations.

My original curiosity was satisfied when you told me the coaches had rigid bogies and that the loco had MJT equalized bogies. I wouldn't expect any track smoothing in those circumstances. the track holding without suspension is also obviously quite adequate.

Clearly, it's nearly impossible to eliminate yaw, caused by sideways movement of the rails, whether intended (curves) or not . All I wish is to see is that any of the track problems don't visibly create or extend body oscillations, other than the hopefully smooth movement of following the intended track curvatures.

Andy

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Re: What's causing the wobbles on Calcutta Sidings

Postby jim s-w » Fri Aug 25, 2017 7:05 am

Look again at when the coach hits the curve. There's definitely extra wobbles there.

I think you might have misunderstood. The MJT bogies mentioned are on the coaches of one of the HSTs. The power cars are bachmann powered and thus rigid.

Is it impossible to eliminate sideways movement? Some use side control on steam loco bogies, why not try the same on coaches?

HTH

Jim

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Re: What's causing the wobbles on Calcutta Sidings

Postby grovenor-2685 » Fri Aug 25, 2017 9:27 am

Some use side control on steam loco bogies, why not try the same on coaches?

Model coach bogies rarely have any side movement that could be controlled. The sway allowed by sprung bogies is a different issue. IIRC Exactoscale did once produce coach bogies with swing links or similar in the suspension to allow controlled lateral movement however I have never seen any mention of their use.
Regards

Proto87Stores

Re: What's causing the wobbles on Calcutta Sidings

Postby Proto87Stores » Fri Aug 25, 2017 3:10 pm

jim s-w wrote:Look again at when the coach hits the curve. There's definitely extra wobbles there.

I think you might have misunderstood. The MJT bogies mentioned are on the coaches of one of the HSTs. The power cars are bachmann powered and thus rigid.

Is it impossible to eliminate sideways movement? Some use side control on steam loco bogies, why not try the same on coaches?

HTH

Jim


The concerns I had are wobble on the straight section of Calcutta Sidings. I'm not suggesting anyone compare the two videos where one train is on the straight (Calcutta) and one train (Amtrak) is hitting a ridiculously sharp (by scale) end curve at maximum speed. An identical type of a real Amtrak train rolled off the track at a relatively much greater radius and slower speed on May 12, 2015. And it was being pulled, not pushed. That's why so many realistic model layouts hide their realistically impossible direction changing curves behind scenic blocks such as bridges and tunnels.

One major point that unexpectedly may have emerged here is that any perceived body roll on the Amfleet models' suspension design can be adjusted by modifying the springing and damping rates between the body and the bogie mountings. The track holding of the wheels on the bogies is separately determined and optimized by their unsprung equalization. If the roll isn't as good as it could be, then I can still work on improving it, using video, (and all these helpful independent Scalefour Forum comments :thumb ) as a test of the effectiveness of each modification.

If you follow the alternative model concept of springing the wheels, then you can't fully isolate or separately adjust the body roll, if you stick with the best combination of wheel springing for track holding. Even added separate secondary springing is still sitting on whatever roll may be fundamentally caused by the best primary wheel springing settings.

Andy

Andy

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Re: What's causing the wobbles on Calcutta Sidings

Postby jim s-w » Fri Aug 25, 2017 4:37 pm

I'm thinking that the springing of the wheels is somewhat irrelevant. We need to be thinking about the interaction between the bogie and the body if you want a visible difference.

You did earlier say the two videos were comparable Andy so you can expect comparisons to be made really.

The important thing here is in both videos once a rock is introduced (however that occurs) to the body both behave the same.

Cheers

Jim

Proto87Stores

Re: What's causing the wobbles on Calcutta Sidings

Postby Proto87Stores » Sat Aug 26, 2017 5:35 pm

jim s-w wrote:I'm thinking that the springing of the wheels is somewhat irrelevant. We need to be thinking about the interaction between the bogie and the body if you want a visible difference.

You did earlier say the two videos were comparable Andy so you can expect comparisons to be made really.

The important thing here is in both videos once a rock is introduced (however that occurs) to the body both behave the same.

Cheers

Jim


Wheel springing fundamentally affects the bogie height and bolster pitch and roll. Body springing resting on top of a wheel sprung bolster in a dynamic case would be akin to putting on lipstick while standing on a trampoline on a windy day. The wheel springing base holding up the body springing isn't stable or predictable.

I think your observational interpretation of the videos, and anyone else's, is as valid as mine. The more people who assess them, the better. AFAIK, there is not yet any sort of Wallace and Gromit "Wobble-o-Matic" we can take accurate, measurements with, so we just have to compare video frames and scale and make our own judgements and compare them with the group's. But I would tend to compare straight with straight, and curve with curve, personally.

All the various vehicles travelling over that distorted Calcutta Track area show various quite noticeable body movements. I wasn't picking on any one particular model. That just happened to be the one with the clearest end on views.

Bill is right. We should try and create situations where we can directly compare like with like. It's just that in my case there is roughly an 8000 mile gap to overcome. :(

Andy

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Re: What's causing the wobbles on Calcutta Sidings

Postby Terry Bendall » Sun Aug 27, 2017 8:09 am

Proto87Stores wrote:We should try and create situations where we can directly compare like with like


That seems a very difficult if not impossible task. It would need all the stock to be tested on the same piece of track at least and probably vehicles built by the same person who will apply the same standards of construction to all the stock involved.

Terry Bendall

Proto87Stores

Re: What's causing the wobbles on Calcutta Sidings

Postby Proto87Stores » Mon Aug 28, 2017 2:30 pm

Terry Bendall wrote:
Proto87Stores wrote:We should try and create situations where we can directly compare like with like


That seems a very difficult if not impossible task. It would need all the stock to be tested on the same piece of track at least and probably vehicles built by the same person who will apply the same standards of construction to all the stock involved.

Terry Bendall


The key issue that raises before you even get to testing is that there is not a single standard of "construction" for maintaining P4 trackholding for designs/implementations to be tested against.

That's what I'm trying to fix for P:87. I'm already preparing a new standard for free wheel movement and standard for track flatness. It now seems that Joe Brooksmith was aware of that omission in setting his own idea of the +/- 0.5 mm wheel movement allowance. Note, the otherwise mostly effective NMRA coarse standards don't include those either. But then coarse standard deep flanges do act somewhat as a substitute for both limits in that case.

Andy

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Re: What's causing the wobbles on Calcutta Sidings

Postby Terry Bendall » Wed Aug 30, 2017 7:46 am

Proto87Stores wrote:I'm already preparing a new standard for free wheel movement and standard for track flatness.


Preparing such standards is all very well but will they be achievable? What do we mean by flatness of track - across the track or along its length or both and over what distance? What will the tolerances be and can they be achieved and maintained? Can they be achieved on layouts that are taken to exhibitions? Even if this can be done will they eliminate the wobble that started this thread?

Terry Bendall

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Re: What's causing the wobbles on Calcutta Sidings

Postby Noel » Wed Aug 30, 2017 10:41 am

... and superelevation on curves?
Noel


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