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SWheel - Rail Interface (Back to Back)

RogerB

2440 posts


Community Moderator

Thanks Caiptean, I've always understood that B2B can be a problem but your clearly written explanation has helped me to understand the mechanics of derailment a lot better. R-

OO Gauge : RM Pro : Elite (v1.42) : Dell Laptop W10 : 9 Locomotives

LC&DR

8960 posts

 Wise words indeed.

 

A useful tool is a Vernier gauge, you can get one with digital read-out fairly cheaply so you don't have to squint at little etched lines any more. This will enable you to measure the back to back very easily and you will undoubtedly find other uses for them.

Green trains are best!

LC&DR

8960 posts

 The wheel rail interface was always a troublesome issue for the railway industry, and one that has occupied many learned minds over the years. Derby Research was set up very much as a means of getting to understand it and in the 1960s there was a great deal of experimentation to improve this aspect of comfort and safety.  The French and Japanese were also highly active in wheel/rail interface research.  The APT depended in getting this exactly right and the Shinkansen and TGV likewise.

 

I attended a number of accident investigations, and was fascinated to hear the Derby Scientists explaining how the interface was so important. One element which fortunately doesn't affect model railways all that much, was 'Cyclic Top'. This was a wave form that jointed track adopted which had peaks and troughs over a 60 foot rail, caused as the wheels hammered the joints into the formation underneath.  1960s period tank wagons were falling off plain line track fairly frequently and it was learned tgat at certain speeds the 15 foot wheelbase passing over these waves set up a periodic osscilation which eventually caused instability and the wagon 'bouncing' off the rails. Simply relaying the track even with continuously welded rail was not sufficient to remove the underlying problem, and  a short term measure was to impose a speed limit that avoided the harmonics, and long term to dig out the formation and blanket it with new material before relaying.

 

All this goes on 'behind the scenes' but is what made working for the railway such an interesting experience.

Green trains are best!

RAF96

10149 posts


Community Moderator

Caiptean

This heterodyning where one frequency beats against another frequency to produce coinciding intermediate frequencies resulting from the sum or difference of these beating frequencies occurs in many situations, including radio waves where it was 'invented' (remember superheterodyne tranny radios).

 

Roads made from cast concrete blocks of the same size will cause lorries to tramp over the joints which can turn to bounce same as your wagons, ships will rise and plunge cyclicly according to their length and wave swell pitch. Even clouds do it whereby a band of one cloud type will roil in position whilst other clouds skim past.

 

A sideways version of this is if you try to tow many trailers such as baggage trolleys, etc as the speed increases a snake occurs which gets worse until the whiplash upturns the whole train.

 

Back on topic...

Model rail wheel form is defined in RP25 and NMRA has good coverage of rail form also. They also cover Hi-rail for use with large flange wheels.

Halton Brat - Running Win 10, 64-bit - RM (Pro-Pack) with Elite as Controller-A, Select as Walkabout and E-Link as Controller-B - Locos are mostly TTS. http://www.halton96th.org.uk/page21.html

Ericm0hff

6056 posts

Just a side-comment - without harmonics, your radio wouldn't work!

'Beating' one frequency against another is how the radio waves are converted to sound waves (putting it VERY crudely!)

if it works first time, you did something wrong!

Hi there,

 

as I understand things and confirmed by my son( a motor vehicle technician) suspension is on vehicles to keep the wheels on the road, and the spring rate and damping tuned for passenger comfort.  I don't think that at the speed that our models ron it will be inportant, but is it , has anyboby done any experiments with suspension on model railway rolling stock?

 

John 

RAF96

10149 posts


Community Moderator

You can scale most things but not time and this is why scale water does not flow properly (think 1/76 waves) and models do not move realistically in scale - e.g. coaches wobbling side to side and up and down appear to doing it too fast.

 

Making suspension work in our scale to represent realistic vehicle movement is not possible, but to help spring the wheels for better road holding is possible and can be beneficial if you get the spring rates right.

Rob

Halton Brat - Running Win 10, 64-bit - RM (Pro-Pack) with Elite as Controller-A, Select as Walkabout and E-Link as Controller-B - Locos are mostly TTS. http://www.halton96th.org.uk/page21.html

RAF96

10149 posts


Community Moderator

Should have added you can't get 1/76 scale Gravity either.

Normal G acting on scale mass versus real time = wrong visual effect.

Rob

Halton Brat - Running Win 10, 64-bit - RM (Pro-Pack) with Elite as Controller-A, Select as Walkabout and E-Link as Controller-B - Locos are mostly TTS. http://www.halton96th.org.uk/page21.html

Fireman_Ian

221 posts

It is discussions such as this that make this forum worth following. Thanks guys for a facinating and interesting discussion.

My way of keeping wagon wheels on the track is adding more weight, sometimes as much as doubling the original weight.

Ian.

Torrevieja, Spain, Railmaster Pro, Dell PC with Windows 10 64bit, Elite with 2 Select walkabouts, HO Santa Fe freight railroad.

RAF96

10149 posts


Community Moderator

Ian

NMRA even has a recommended practice for wagon weight...

Rob

Halton Brat - Running Win 10, 64-bit - RM (Pro-Pack) with Elite as Controller-A, Select as Walkabout and E-Link as Controller-B - Locos are mostly TTS. http://www.halton96th.org.uk/page21.html

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