

How do trains stay on track? (2009) [pdf] - scrrr
http://materials.mcmaster.ca/Condensed%20Matter/December2009.pdf

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userbinator
It's similar to the principle that keeps flat belts from slipping off their
pulleys...

[http://woodgears.ca/bandsaw/crowned_pulleys.html](http://woodgears.ca/bandsaw/crowned_pulleys.html)

...even in extreme situations such as this:

[http://en.wikipedia.org/wiki/File:Transmissionsriemen.jpg](http://en.wikipedia.org/wiki/File:Transmissionsriemen.jpg)

~~~
TheLoneWolfling
I wonder at what point you start getting a convex pulley having a (local)
optimum in terms of how likely the belt is to stay on the pulley?

For low speed / low friction between belt and pulley, you'll just pull the
belt off of the pulley if the pulley is convex.

And for high speed / high friction you'll end up with the above effect.

So I wonder: where does it transition?

~~~
jessaustin
If the belt is rubber, the friction is high enough, even when the system is
starting from zero. (Assuming pulleys shaped like the ones linked above, of
course.)

~~~
TheLoneWolfling
Is that the case even for a (mythical and completely useless) frictionless
pulley?

~~~
logfromblammo
Whether a frictionless pulley is useless or not depends largely upon whether
you are using it to change the direction of the line, adding tension to it, or
using it to perform work. Such a pulley is only useless for the latter, such
as a belt turning a drum, but a frictionless block and tackle or tensioning
pulley would be incredibly useful.

~~~
TheLoneWolfling
Good point.

So my question isn't as odd as it might first appear then.

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derrasterpunkt
additionally, here is Richard Feynman explaining it:
[https://www.youtube.com/watch?v=y7h4OtFDnYE&index=7&list=PL0...](https://www.youtube.com/watch?v=y7h4OtFDnYE&index=7&list=PL04B3F5636096478C&spfreload=10)

~~~
cmsmith
A great video, and I noticed the actual linked article here suspiciously
follows the exact same structure and examples that Feynman does in his
explanation. It would have been nice to acknowledge the fact that the author
was probably watching Feynman explain it while writing. But it seems to be a
student fun journal, and has made a few hundred people think, so why get
upset?

~~~
hackuser
Maybe both Feynman and the author copied the explanation from a third source.

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kps
I wondered, how would this work with an axle-less low-floor bogie? The answer
I found here[1] is — it doesn't. “ _… there is only a single series of trams
that have these bogies, later versions returned to the traditional type with
axles. … The wear problem is because those bogies don 't seem to track as
well, they go from left to right in the track_”. The implication is that there
were people designing rail vehicles who didn't know how they stay on the
track.

[1] [http://modeleng.proboards.com/thread/4521/chilled-iron-
tram-...](http://modeleng.proboards.com/thread/4521/chilled-iron-tram-
wheels#ixzz3Y3IbKD3i)

~~~
Animats
There are more trams with axle-less bogies now.[1] The goal is to lower the
floor height, eliminate steps, and improve wheelchair accessibility. It gets
complicated. Some systems use big driven wheels and small trailing wheels.
Some have a geared axle between the wheels. Siemens has a system with motors
on each wheel, with the wheels locked together electronically. AEG tried
something like that, with less success. Speeds of the more elaborate systems
are rather low, below 70km/h (44mph). That appears to be a limit of the axle-
less design.

[1]
[http://onlinepubs.trb.org/onlinepubs/tcrp/tcrp_rpt_02.pdf](http://onlinepubs.trb.org/onlinepubs/tcrp/tcrp_rpt_02.pdf)

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guardiangod
Here's a video demonstration by Richard Hammond of Top Gear.

[https://www.youtube.com/watch?v=OEo-
hQbyy30](https://www.youtube.com/watch?v=OEo-hQbyy30)

~~~
EliRivers
That is really good, and also a massive reminder of how meaningless and
inconsequential my work is, compared to people doing serious electrical and
mechanical engineering like that.

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msravi
Also, a great video explaining the working of a differential:

[https://youtu.be/K4JhruinbWc?t=110](https://youtu.be/K4JhruinbWc?t=110)

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anentropic
anyone know if this was an intentional part of wheel/rail design from the
start... or they originally intended it to work how we naïvely imagine and by
accident it worked this way and was subsequently refined ?

~~~
bontaq
I don't know much about it, but in looking at some of the first locomotives I
saw this:
[https://upload.wikimedia.org/wikipedia/commons/e/e2/Richard_...](https://upload.wikimedia.org/wikipedia/commons/e/e2/Richard_Trevithick_1804_Pen_y_Darren_locomotive_\(6636003439\).jpg)

and this:
[https://en.wikipedia.org/wiki/Richard_Trevithick#/media/File...](https://en.wikipedia.org/wiki/Richard_Trevithick#/media/File:TrevithicksEngine.jpg)

That was probably a terrible screeching thing to witness going around bends,
just being held in line by the inner lip of the rail.

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ChuckMcM
In a similar note I wondered what the patent on the railroad ties on the
Caltrain bed were (#5104039) and found this:
[https://www.google.com/patents/US5104039?dq=5104039&hl=en&sa...](https://www.google.com/patents/US5104039?dq=5104039&hl=en&sa=X&ei=s-Y3VevVL5O4oQSvk4HgAw&ved=0CB0Q6AEwAA)
which has an interesting discussion about how the tracks manage to stay
underneath the trains.

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RockyMcNuts
Does the rail have some flexibility to twist and meet the wheel cone at the
right angle, and/or is it pitched to match the angle of the wheel surface?
When I look at the tracks and this wheel shape, I see the wheel riding on a
corner of the rail, which is obviously not the case.

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anonu
The portion on the structural properties of wood a bit further down the PDF
are just as interesting.

~~~
jessaustin
Yes and I really appreciated the reference to the USFS's _Wood Handbook: Wood
as an Engineering Material_.

Available online:

[http://www.woodweb.com/Resources/wood_eng_handbook/wood_hand...](http://www.woodweb.com/Resources/wood_eng_handbook/wood_handbook_fpl_2010.pdf)

~~~
hackuser
Thanks; I hadn't heard of it. For what it's worth I looked up the source:

[http://www.fpl.fs.fed.us/products/publications/specific_pub....](http://www.fpl.fs.fed.us/products/publications/specific_pub.php?posting_id=18102&header_id=p)

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a-dub
[http://en.wikipedia.org/wiki/Hunting_oscillation](http://en.wikipedia.org/wiki/Hunting_oscillation)

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noir_lord
Edit
[https://cmnewsletter.wordpress.com/](https://cmnewsletter.wordpress.com/)
typical, find the answer just after asking the question below.

This was brilliant but I'm really struggling to find an index page with the
rest of them, I can find some of them via google directly.

Anyone figure it out?

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fishanz
I've been on and around many trains and yet I never quite understood the
concept of the wheel flange and how track junctions worked until very
recently, thanks to a kids show: chuggington.

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exDM69
I would love to try to simulate this with a computer program some day.

I really enjoy playing train simulator games, but as far as I understand, none
of them actually simulate the physics of cone wheels and flanges.

