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Foale Frame designs

This is a discussion on Foale Frame designs within the Technical forums, part of the Caferacer.net Forums category; Originally Posted by Teazer .095" is pretty thick for a large diameter tube. Do the analysis with thinner gauge and see how much it changes ...

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  1. #11
    Member jordan's Avatar
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    Quote Originally Posted by Teazer View Post
    .095" is pretty thick for a large diameter tube. Do the analysis with thinner gauge and see how much it changes the results.

    Can you rotate the T500 motor slightly forwards (nose down a little) to get a straighter run in the top tube?
    I’m worried about the tubes buckling if i go too thin, plus the total weight of the frame and sub frame should be between 15-18lbs

    I can get the tube a lot closer after a second check. It will raise the neck a little, but the forks have some spare length and if i set the rake angle a little steeper (2-3 degrees) it should be okay.

  2. #12
    Junior Member themotoworks's Avatar
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    the tube frame idea is surprisingly good, moreso than you'd think. the thing that makes them really sweet is the ability to flex along the whole tube if built right, a lot of the challenges of designing frames is making them flexible enough not to overstress certain points, the more energy you can get the whole frame to deal with, the better, and with the big tube frame, you can also very easily "tune" the amount of flex. I played with tube frames in solidworks, as well as a walt siegl frame I own, I have ridden the siegl frame on the track and loved the handling, I could make the tube frame act the same without as much stress in "hotspots" as walt's frame had.
    Geeto67 likes this.

  3. #13
    jcw
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    Quote Originally Posted by jordan View Post
    I’m worried about the tubes buckling if i go too thin, plus the total weight of the frame and sub frame should be between 15-18lbs

    I can get the tube a lot closer after a second check. It will raise the neck a little, but the forks have some spare length and if i set the rake angle a little steeper (2-3 degrees) it should be okay.
    For thin walled tubing, you get way more strength increasing the diameter of the tube rather than the wall thickness.

    Area moment of inertia (the resistance to bending of a hollow tube) is approximately pi x R^3 x T. R is OD and T is thickness. So stiffness is porportional to T, but porportional to the cube of radius.

    Torsional resistance or polar moment of inertia is similar Name:  DC-11V5.png
Views: 95
Size:  2.1 KB

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  5. #14
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    Foale Frame designs

    Quote Originally Posted by jcw View Post
    For thin walled tubing, you get way more strength increasing the diameter of the tube rather than the wall thickness.

    Area moment of inertia (the resistance to bending of a hollow tube) is approximately pi x R^3 x T. R is OD and T is thickness. So stiffness is porportional to T, but porportional to the cube of radius.

    Torsional resistance or polar moment of inertia is similar Name:  DC-11V5.png
Views: 95
Size:  2.1 KB
    that's true
    but i'm not talking about the frame strength/stiffness here, i'm talking about the tube resisting kinking. The larger the diameter for a given thickness, the more liable it is to kink. As the diameter increases, the curvature decreases, so you get less support from the arc and it behaves more and more like a flat piece. This is only for localized stress though.

    so i redid the sketch of the frame to include a beam for the forks and a few for the swingarm so that i could place the appropriate loads and constraints
    3 tests on the frame with no engine support.

    enough force on the lateral test to bottom out the planned spring rate.
    and substantially more on the other 2
    1400 ftlbs of torque twisting the neck with the SA pivot pinned
    and 900lbf pushing the neck across with the pivot pinned.
    if the frame ever sees these magnitudes, the frame holding is the least of my worries.
    i am content with the results

    Edit: the images do not show the actual displacement of the tubes, they are adjusted to for easier viewing.
    Attached Images Attached Images    
    Last edited by jordan; 03-13-2018 at 07:51 PM.

  6. #15
    Senior Member TrialsRider's Avatar
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    Flexi frames you like that do you. I never really enjoyed that wallowing through the corners, wiggling on hitting bumps and vague handling, rubber hinge in the middle of the bike feeling myself, I buy bikes with the stiffest frames possible.

  7. #16
    Member jordan's Avatar
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    Nope, not a fan of flexi frames.
    Luckily this version was lighter than expected so there is wiggle room to add additional stiffening.

  8. #17
    jcw
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    OK, so what are your results?

    Tubes have to bend before kinking. The area moment of inertia tests that very property. A beam's ability to resist deflection for a given cross sectional area.

    Quote Originally Posted by jordan View Post
    that's true
    but i'm not talking about the frame strength/stiffness here, i'm talking about the tube resisting kinking. The larger the diameter for a given thickness, the more liable it is to kink. As the diameter increases, the curvature decreases, so you get less support from the arc and it behaves more and more like a flat piece. This is only for localized stress though.

    so i redid the sketch of the frame to include a beam for the forks and a few for the swingarm so that i could place the appropriate loads and constraints
    3 tests on the frame with no engine support.

    enough force on the lateral test to bottom out the planned spring rate.
    and substantially more on the other 2
    1400 ftlbs of torque twisting the neck with the SA pivot pinned
    and 900lbf pushing the neck across with the pivot pinned.
    if the frame ever sees these magnitudes, the frame holding is the least of my worries.
    i am content with the results

    Edit: the images do not show the actual displacement of the tubes, they are adjusted to for easier viewing.

  9. #18
    Member jordan's Avatar
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    Quote Originally Posted by jcw View Post
    OK, so what are your results?

    Tubes have to bend before kinking. The area moment of inertia tests that very property. A beam's ability to resist deflection for a given cross sectional area.

  10. #19
    Member jordan's Avatar
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    The results indicated that the forces that would cause significant distortion of the frame would more likely result in a crash long before that point of distortion is reached.

  11. #20
    jcw
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    Quote Originally Posted by jordan View Post
    ......ok

    Don't go under...
    50mm=1.96"
    1.2mm=0.047"

    May not need to go over
    75mm=2.95"
    2.0mm=0.078"

    The thicknesses sound about right... I almost always use 16g tubing which is 065. occasionaly 18g tubing for subframes or bracing which is 049.

    084 is 14g, 095 is 13g. Like Teazer said those typically are not in the realm of sport chassis building.


    Harley's maybe...

    but whatever, nobody comes here to listen anyway...

    Quote Originally Posted by jordan View Post
    The results indicated that the forces that would cause significant distortion of the frame would more likely result in a crash long before that point of distortion is reached.
    I meant comparing a thinner walled tubing at one larger size diameter.
    Last edited by jcw; 03-13-2018 at 09:24 PM.

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