4 ms·

Are you sure? I was just watching a video that explained the wheel edges are sloped, not the rails, to help fixed axel wheels to around curves. Wish I could f

by DougN7 4y ago

Are you sure? I was just watching a video that explained the wheel edges are sloped, not the rails, to help fixed axel wheels to around curves. Wish I could find it again - quite ingenius!

texaslonghorn5 4y ago
https://youtu.be/WAwDvbIfkos https://youtu.be/WAwDvbIfkos (video of Feynman explaining how trains stay on the track) Is this it? I found it in my YouTube history. Or this one, which superimposes free body diagram (of forces) on the wheels to show how it is self stabilizing? https://youtu.be/XzgryPhtc1Y https://youtu.be/XzgryPhtc1Y
- lazide 4y ago
  That is for normal trains no?
  - texaslonghorn5 4y ago
    Thought they were asking about trains in general. Oops
hadlock 4y ago
Have you ridden BART? Worst acoustical echo chamber I've ever ridden in (twice, once to the fox theater, once home from SFO, never again)
- jrowley 4y ago
  The new trains aren’t as loud due to their conical wheels.
  - hadlock 4y ago
    ....sometimes. You can still hear them from a mile away.
inferiorhuman 4y ago
Yes. The wheels were flat, apparently Bombardier saw room for improvement and suggested a tapered profile that was retrofitted to the older cars. Unfortunately the track pitch (I'm forgetting what the proper term is) is also wrong, the spacing in the curves is too tight. Normally you'd increase the spacing a bit in curves to encourages the wheels to rotate at different speeds instead of destroying the track. Unfortunately even with the new profile BART is still incredibly loud, and it's not helped at all by low speed curves like the Oakland Wye.
- iggldiggl 4y ago
  > the track pitch I think the term you're looking for is track gauge. And as for a need to widen it in curves, the answer is basically it depends. On mainline railways gauge widening in curves basically stems from the days of steam locomotives, which mostly didn't have bogies (at least for the main driving wheels) and comparatively enormous wheelbases. On straight(ish) track, some minor gauge widening as compared to the nominal standard gauge might nowadays also be beneficial, especially on high speed lines. Within the context of streetcars/trams, which often need to negotiate very tight curves on the other hand, current state of the art seems to indicate that a slight gauge tightening might actually be more beneficial in order to avoid too large a skew angle between the bogies and the rails. (Compare http://interfacejournal.com/archives/472 http://interfacejournal.com/archives/472) I'm no wheel/rail-interface guru, so quite what the conclusions from that would be for BART I can't say, either, but just wanted to point out that the topic is somewhat more complex, and nowadays gauge widening in curves might not actually always be the right answer.
  - inferiorhuman 4y ago
    > I think the term you're looking for is track gauge. No. Track gauge is the nominal width, no? I'm talking about how the width changes in the curves. A while back a former BART engineer went on the record claiming the spacing in the curves was contributing to the noise. Top to bottom BART fully embraced NIH. Fifty years ago there was good reason but now the rest of the rail industry has moved on and BART is stuck with a lot of tech and engineering debt. For e.g. BART can't grease or sand their tracks either, and you can feel the older trains slip and slide (and damage the track) as they exit the station. Edit: Here's an interesting piece on noise. Note how nearly every other rail system lubricates the tracks (BART can't) and how no other rail system uses (noisy) solid aluminum wheels. https://www.bart.gov/sites/default/files/docs/noisereport.pdf https://www.bart.gov/sites/default/files/docs/noisereport.pd...
iggldiggl 4y ago
Normally you do both: The running surface of the wheels is sloped, but the rails are also mounted onto the sleepers with a corresponding inclination. (Some grooved rail profiles for streetcars/trams have the inclination built directly into the profile of the railhead, so the rail itself is mounted upright, but you get the same effect at the railhead level.)

by DougN7 4y ago

Are you sure? I was just watching a video that explained the wheel edges are sloped, not the rails, to help fixed axel wheels to around curves. Wish I could find it again - quite ingenius!

texaslonghorn5 4y ago

https://youtu.be/WAwDvbIfkos https://youtu.be/WAwDvbIfkos (video of Feynman explaining how trains stay on the track) Is this it? I found it in my YouTube history. Or this one, which superimposes free body diagram (of forces) on the wheels to show how it is self stabilizing? https://youtu.be/XzgryPhtc1Y https://youtu.be/XzgryPhtc1Y

lazide 4y ago
That is for normal trains no?
- texaslonghorn5 4y ago
  Thought they were asking about trains in general. Oops

hadlock 4y ago

Have you ridden BART? Worst acoustical echo chamber I've ever ridden in (twice, once to the fox theater, once home from SFO, never again)

jrowley 4y ago
The new trains aren’t as loud due to their conical wheels.
- hadlock 4y ago
  ....sometimes. You can still hear them from a mile away.

inferiorhuman 4y ago

Yes. The wheels were flat, apparently Bombardier saw room for improvement and suggested a tapered profile that was retrofitted to the older cars. Unfortunately the track pitch (I'm forgetting what the proper term is) is also wrong, the spacing in the curves is too tight. Normally you'd increase the spacing a bit in curves to encourages the wheels to rotate at different speeds instead of destroying the track. Unfortunately even with the new profile BART is still incredibly loud, and it's not helped at all by low speed curves like the Oakland Wye.

iggldiggl 4y ago
> the track pitch I think the term you're looking for is track gauge. And as for a need to widen it in curves, the answer is basically it depends. On mainline railways gauge widening in curves basically stems from the days of steam locomotives, which mostly didn't have bogies (at least for the main driving wheels) and comparatively enormous wheelbases. On straight(ish) track, some minor gauge widening as compared to the nominal standard gauge might nowadays also be beneficial, especially on high speed lines. Within the context of streetcars/trams, which often need to negotiate very tight curves on the other hand, current state of the art seems to indicate that a slight gauge tightening might actually be more beneficial in order to avoid too large a skew angle between the bogies and the rails. (Compare http://interfacejournal.com/archives/472 http://interfacejournal.com/archives/472) I'm no wheel/rail-interface guru, so quite what the conclusions from that would be for BART I can't say, either, but just wanted to point out that the topic is somewhat more complex, and nowadays gauge widening in curves might not actually always be the right answer.
- inferiorhuman 4y ago
  > I think the term you're looking for is track gauge. No. Track gauge is the nominal width, no? I'm talking about how the width changes in the curves. A while back a former BART engineer went on the record claiming the spacing in the curves was contributing to the noise. Top to bottom BART fully embraced NIH. Fifty years ago there was good reason but now the rest of the rail industry has moved on and BART is stuck with a lot of tech and engineering debt. For e.g. BART can't grease or sand their tracks either, and you can feel the older trains slip and slide (and damage the track) as they exit the station. Edit: Here's an interesting piece on noise. Note how nearly every other rail system lubricates the tracks (BART can't) and how no other rail system uses (noisy) solid aluminum wheels. https://www.bart.gov/sites/default/files/docs/noisereport.pdf https://www.bart.gov/sites/default/files/docs/noisereport.pd...

iggldiggl 4y ago

Normally you do both: The running surface of the wheels is sloped, but the rails are also mounted onto the sleepers with a corresponding inclination. (Some grooved rail profiles for streetcars/trams have the inclination built directly into the profile of the railhead, so the rail itself is mounted upright, but you get the same effect at the railhead level.)