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Thread: Steel Frame Design

  1. #1
    TechTiger with Stanford FSAE. We're starting that new team you're hearing all about: thanks for the great input we've been getting.

    Looking into frame design, nice and simple. Thinking all-steel ladder frame, with X braces, not too many frame members and simple welds. Any pointers?

    Also, we're considering rectangular tubing for the main chassis rails to provide most of the chassis bending stiffness.


    TechTiger
    Stanford FSAE

  2. #2
    TechTiger with Stanford FSAE. We're starting that new team you're hearing all about: thanks for the great input we've been getting.

    Looking into frame design, nice and simple. Thinking all-steel ladder frame, with X braces, not too many frame members and simple welds. Any pointers?

    Also, we're considering rectangular tubing for the main chassis rails to provide most of the chassis bending stiffness.


    TechTiger
    Stanford FSAE

  3. #3
    Hi TechTiger,

    It's pretty difficult to give advice when it comes to chassis design because there are so many effective ways of doing it. Going for a steel spaceframe is a very sensible start though.

    From my limited experience with spaceframes, I would say that connecting the nodes with tubing of whatever type is the easy bit, relatively speaking. The hard part is deciding where the nodes are in the first place, e.g. for suspension pickups, engine mtgs etc, and how to mount these assemblies effectively. Strength and stiffness of mounting brackets is very important - it's amazing how much abuse they get during assembly let alone from the dynamic loads on track! There's no point in having a stiff chassis if the brackets are weak.

    It's a good idea speaking to the person who will be welding the structure - they will tell you what they can and can't do. It's worth noting that if a weld is easy to do, it will probably be of a higher quality than one where the welder has to dislocate their shoulder to get at it!

    It's also important to consider the jig and how it will affect things. Plan the whole manufacturing process carefully – it will save you time in the long run I guarantee it! The jig itself doesn't have to be anything special but should be accurate, especially for the suspension pickups, and fairly substantial to ensure it doesn't move.

    Finally, bear in mind that the chassis will distort during welding – there's nothing you can do to stop it, but a good welder will minimise it by avoiding too much heat build up in one place. To this end, you can help by ensuring a good fit between welded joints – the bigger the gap, the more heat required to weld it and thus more distortion potential. Hand shaping tubes with a hacksaw and file is normal and if done well, perfectly acceptable. However, there are other options, such as laser cutting which can vastly reduce the timescale and stress levels (of the team that is)...

    Overall just remember that CAD and reality are never quite the same

    That's my 2pence worth – hope it helps...
    Cheers,

  4. #4
    am i correct in thinking "ladder frame" meaning the kind of thing you find under a street rod?

    if so, its gonna be tough to meet the side impact, roll hoop, and new front bulkhead bracing requirements.

    a true steel spaceframe is a much better idea, and is easy enough to design, analyze, and fabricate.
    Mike Miles
    Carnegie Mellon SAE/Carnegie Mellon Racing -- Formula SAE 2003, 2004, 2005, 2006

  5. #5
    deano kind of said this, but I'll say it explicitly: make sure all of the loads (bell cranks, a-arms, etc.) go into nodes. You don't want any bending forces in the middle of a tube. Also, look at the load paths. You don't want the loads to be going all over the place.

    I would agree with Mike and make it a steel tube space frame.

  6. #6
    Ladder frames are sweet:
    Alumni, University of Washington
    Structural / Mechanical Engineer, Blue Origin

  7. #7
    Baiting the WWU crew isn't very nice...or challenging...all in all not very sporting of you



    Is that kind of what you mean by ladder frame? It's definitely simple...just make sure you can get it stiff enough.
    UW FSAE 05-06
    WWU FSAE 02-04

  8. #8
    Thanks for the advice and pointers

    I thought that, in a space frame, most (if not all) frame members should experience only compressive or tensile forces. Many of the FSAE frames I've seen, however, have tubes that are experiencing torsional forces as well. It seems that a well built space frame + FSAE minimum tubing specs yields little weight advantage + increased complexity.

    Moving to a simply ladder frame (i.e. supported on two main chassis rails) and using rectangular chassis rails means one might be able to put bending forces in the middle of those tubes, without much of a weight penalty or sacrificing torsional rigidity. Anybody know if this has been tried and the success rate?

    TechTiger
    Stanford FSAE

  9. #9
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Denny Trimble:
    Ladder frames are sweet:
    </div></BLOCKQUOTE>

    ladder frame? what are you talking about? that is a conventional tube frame!
    jack
    College dropout extraordinaire
    (formerly WWU Rev-Hone Racing)

  10. #10

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