Curve Radius Question

Inkaneer Oct 17, 2019

  1. acptulsa

    acptulsa TrainBoard Member

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    It hides some no matter which way you orient your Dick Tracy Two-Way Wrist TV. Put your finger on this word a second or three, and see what it might offer to do for you.
     
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  2. C&O_MountainMan

    C&O_MountainMan TrainBoard Member

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    Not sure what word you're talking about. But, be that as it may, I'm at my home PC, and have the full functionality now.
     
  3. C&O_MountainMan

    C&O_MountainMan TrainBoard Member

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    I thought some of you might be intrigued or entertained by some curvature calculations that makes circular curve layout look fairly simple; here is a link determining coordinates of spiral curves:

    https://www.academia.edu/9377925/DE...OR_SPIRAL-CURVE-SPIRAL_ASSEMBLY?auto=download

    A spiral is a curve whose curvature (reciprocal of the radius) varies linearly with respect to distance along the curve. Used for highway construction, some railroads some racetracks.

    I think model railroad curves would look a lot better if layout builders used spirals for curve entries and exits. You still have the problem with minimum radius being undersized, but judicious use of spirals can make the curve start and curve end not appear so abrupt. That is one of my layout pet peeves, not merely the minimum radius, but as you watch the line of cars roll into or out of the curve, they just snap straightaway from going strait to min radius and vise versa.

    The drawbacks are, when making a 90° turn you have to begin the spiral curve sooner/end it later than a pure circle, or accept a smaller min radius. On a 180° turn, you're limited by space/table width, and you have to accept both earlier curve start/later end AND smaller minimum radius.

    I had to deal with spiral math in my early days as an engineer in automobile racing, before really precise GPS and laser scanning was readily available. Some tracks furnished me drawings providing tangent, curve, and spiral lengths and degrees of curvature, but not detailed top-down track geometry, so I found info like this for the spirals, and was able to derive the math for circles and straights, and built a "modular" spreadsheet in Excel for putting the sections of each type together, matching the angles at the end of each section, and plotting top-down track maps, which aides in verifying the driving line constructed from accelerometers and wheelspeed.

    When I got back from a long hiatus from railroad modeling last month, I sat down, and rebuilt that sheet from memory, (having to scour the internet, though, for the spiral math, that was beyond memory) for use as a homebrew track layout tool.

    Some of you guys in this discussion might find it interesting or even useful.
     
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  4. Shortround

    Shortround TrainBoard Member

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    I do understand what your referring to and probably used it as the driver in racing. But not the calculations. Yes it also looks a lot better in our hobby but it's not always usable with fixed track. We would have to use flexible.
    Thanks for the link.

    Richard
     
  5. C&O_MountainMan

    C&O_MountainMan TrainBoard Member

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    Yeah, making spirals is a flextrack thing, although you can approximate them by using a succession of decreasing radii pieces at the transitions.
     
  6. Inkaneer

    Inkaneer TrainBoard Member

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    Sounds like an easement to me. So, what is the difference???
     
  7. C&O_MountainMan

    C&O_MountainMan TrainBoard Member

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    An “easement” is a non-specific term, and there are different means of creating them.

    A “spiral” in highway and railroad design is one specific means if creating an easement, with, a specific mathematical formulation that has specific design goals behind it.

    It also was the specific mathematics I needed to become familiar with, to perform specific work in the past, so it’s handiest for me.
     
  8. Shortround

    Shortround TrainBoard Member

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    I wasn't referring to spirals (elevate to next level). But yes adding curves of larger radius before and after a curve does make them more gentle. So does slowly increasing the draft angle and then decreasing it. If you look at race tracks that's were the tire tracks are and on a motorcycle leaning into the curve varies going in and out of the curve as well. With the most lean in the middle. Or when you louse it.
    The same can be said about our toy trains.

    Richard
     
  9. BigJake

    BigJake TrainBoard Member

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    Even when an easement/spiral requires a smaller minimum radius, the smaller radius occurs in a shorter section of the curve, making it easier to obscure the view there with scenery, structures, etc.

    As long as the train will successfully negotiate the curve...

    Unless the scene is that of a train wreck!
     
  10. Inkaneer

    Inkaneer TrainBoard Member

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    OH, so an easement and a spiral are the same with maybe the only difference being that an 'easement' is railroad jargon while spiral is more genetic engineering terminology. But I have never heard the term 'spiral' being used in describing track curvature either in the horizontal or vertical plane. I have heard it used in describing a helix and it is in that context that the word is used in railroading as in the "Spiral Tunnels" on the Canadian Pacific.

    Spiral Tunnels - Kicking Horse Pass National Historic Site (pc.gc.ca)

    Model railroading is like a cat. There are many ways to skin it. You just pick the one that suits you best and as always, Model RR Rule No. 1 applies.
     
  11. acptulsa

    acptulsa TrainBoard Member

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    Not exactly. An easement is a steak; a spiral easement is a t-bone steak.

    A spiral is a spiral, but a spiral easement never maintains the same curvature throughout the way a spiral helix may. Or maybe I'm ignorant about helices.
     
  12. Doug Gosha

    Doug Gosha TrainBoard Member

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    How about spiral pasta?

    :D

    Doug
     
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  13. BigJake

    BigJake TrainBoard Member

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    Perfect, smothered in butter & cheese, right beside my medium rare ribeye steak!

    ...which I devour while watching my trains run on the layout. (I had to relate it back to model railroading!)
     
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  14. C&O_MountainMan

    C&O_MountainMan TrainBoard Member

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    No, an easement is the catch-all term for any change to road geometry that eases the transition at curve entry ir curve exit. It might be as simple as paving/laying a portion with a larger fixed radius than the middle section of a curve.
     
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  15. Inkaneer

    Inkaneer TrainBoard Member

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    Ron White was correct!
     

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