7 ms·

search: >'train-track grinding/profiling'< @DDG : <https://html.duckduckgo.com/html/?q='train-track grinding/profiling' https://html.duckduckgo.com/html/?q='tra

search: >'train-track grinding/profiling'< @DDG : <https://html.duckduckgo.com/html/?q='train-track grinding/profiling' https://html.duckduckgo.com/html/?q='train-track grinding/pr...>

mc32 4y ago
Most rail profiles are like: |\ /| _| |_ _| |_ But BARTD's are more like: _ _ | | | | _| |_ _| |_ Correction: the rails are flat, it's the wheels that are also flat. So pretend the above are the upper half of the wheel profiles. End result is more surface contact = more noise/squealing, also less self-centering of the wheels on the tracks, so the lips also brush against the rails. I think this also exacerbates the washboarding of the rails.
- xnx 4y ago
  Are you sure about that? I thought it was most common to have flat tracks and conical wheels. That's what I see on Google Image Search too.
  - phs2501 4y ago
    BART had regular rail profile and non-tapered wheels, so flange squeal (and wear) was apparently a real issue. I'm not sure why they decided on this, since it runs counter to normal railway practice. This article has a story but I wonder if it wasn't just more NIH. https://sf.streetsblog.org/2018/06/08/bart-makes-headway-against-headache-inducing-howl/ https://sf.streetsblog.org/2018/06/08/bart-makes-headway-aga...
  - mc32 4y ago
    Ah, yes. Correction. BARTD wheels are flat like the tracks, unlike other rail profiles which are tapered on flat. BARTD wheels are flat on flat.
- 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.
  - 4y ago
- dredmorbius 4y ago
  It's rail wheels which are beveled, with the radius decreasing to the outside of the wheel. Your top image has the wheels reversed. There's also a flange which extends below the rail depth on the inner edge of the wheel Should be, showing from the axel to the rail: _ __________________________ _ _ __________________________ _ | | | | | | | | | | | | \ | | / \_| |_/ | | As the car rounds turns, the inner wheel rides down and the outer wheel rides up, increasing the relative rotational radius of the outer wheel. This compensates for the fact that rail wheelsets rotate on a single fixed axis, not independently, and without a differential. For a non-ASCII image see: https://steemitimages.com/DQmUjS7PbhzAYpkTi5A3c2QQQa7jn1c52sfFu9RDK3hnDzX/32r34t5y67543.PNG https://steemitimages.com/DQmUjS7PbhzAYpkTi5A3c2QQQa7jn1c52s... Longer explanation: https://www.popularmechanics.com/science/a25581/science-behind-train-tracks-wheels/ https://www.popularmechanics.com/science/a25581/science-behi... Wikipedia also discusses geometry: https://en.wikipedia.org/wiki/Train_wheel https://en.wikipedia.org/wiki/Train_wheel
  - geokon 4y ago
    is there a reason why they don't have the wheels spin separately? Does it make it more complicated? Or there is a disadvantage?
    - nikanj 4y ago
      It makes it more complicated. The wheels need to be fixed to the axel for breaks to function, so you can’t just stick a bearing in the wheel and call it a day.
      - dredmorbius 4y ago
        This seems unlikely.
      - geokon 4y ago
        I'm imagining two half length axels. I guess this creates some torque but the breaks and bearing would be identical

search: >'train-track grinding/profiling'< @DDG : <https://html.duckduckgo.com/html/?q='train-track grinding/profiling' https://html.duckduckgo.com/html/?q='train-track grinding/pr...>

mc32 4y ago

Most rail profiles are like: |\ /| _| |_ _| |_ But BARTD's are more like: _ _ | | | | _| |_ _| |_ Correction: the rails are flat, it's the wheels that are also flat. So pretend the above are the upper half of the wheel profiles. End result is more surface contact = more noise/squealing, also less self-centering of the wheels on the tracks, so the lips also brush against the rails. I think this also exacerbates the washboarding of the rails.

xnx 4y ago
Are you sure about that? I thought it was most common to have flat tracks and conical wheels. That's what I see on Google Image Search too.
- phs2501 4y ago
  BART had regular rail profile and non-tapered wheels, so flange squeal (and wear) was apparently a real issue. I'm not sure why they decided on this, since it runs counter to normal railway practice. This article has a story but I wonder if it wasn't just more NIH. https://sf.streetsblog.org/2018/06/08/bart-makes-headway-against-headache-inducing-howl/ https://sf.streetsblog.org/2018/06/08/bart-makes-headway-aga...
- mc32 4y ago
  Ah, yes. Correction. BARTD wheels are flat like the tracks, unlike other rail profiles which are tapered on flat. BARTD wheels are flat on flat.
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.
- 4y ago
dredmorbius 4y ago
It's rail wheels which are beveled, with the radius decreasing to the outside of the wheel. Your top image has the wheels reversed. There's also a flange which extends below the rail depth on the inner edge of the wheel Should be, showing from the axel to the rail: _ __________________________ _ _ __________________________ _ | | | | | | | | | | | | \ | | / \_| |_/ | | As the car rounds turns, the inner wheel rides down and the outer wheel rides up, increasing the relative rotational radius of the outer wheel. This compensates for the fact that rail wheelsets rotate on a single fixed axis, not independently, and without a differential. For a non-ASCII image see: https://steemitimages.com/DQmUjS7PbhzAYpkTi5A3c2QQQa7jn1c52sfFu9RDK3hnDzX/32r34t5y67543.PNG https://steemitimages.com/DQmUjS7PbhzAYpkTi5A3c2QQQa7jn1c52s... Longer explanation: https://www.popularmechanics.com/science/a25581/science-behind-train-tracks-wheels/ https://www.popularmechanics.com/science/a25581/science-behi... Wikipedia also discusses geometry: https://en.wikipedia.org/wiki/Train_wheel https://en.wikipedia.org/wiki/Train_wheel
- geokon 4y ago
  is there a reason why they don't have the wheels spin separately? Does it make it more complicated? Or there is a disadvantage?
  - nikanj 4y ago
    It makes it more complicated. The wheels need to be fixed to the axel for breaks to function, so you can’t just stick a bearing in the wheel and call it a day.
    - dredmorbius 4y ago
      This seems unlikely.
    - geokon 4y ago
      I'm imagining two half length axels. I guess this creates some torque but the breaks and bearing would be identical