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Thread: Rod end Bearings

  1. #31
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    Yep, sphericals seem to be almost requisite before the judges will consider your car "upper tier," which I think is a real shame. But it certainly doesn't guarantee a decent design score. One year we did rod ends and caught crap for it at design judging. The next year we spent lots of time making spherical holders that saved weight, etc - and the design judges didn't care one bit. Don't build your car for the design judges - you never know what they'll like or dislike any given year. Using sphericals simply because everyone has been trained for years to say rod ends are evil is not the right answer in my opinion.
    University of Texas 2002 & 2003
    University of Houston 2007

  2. #32
    I think I have to go with Tom on this one. Why would you not do spericals? Too hard to make the suspension adjustable otherwise. I feel, and maybe my feelings matter as much as which pop star is turning to porn star, that using rod ends is a bad idea. you can design your suspension mounts and upright to have just as much adjustability, safety (breakaway), and faster adjustability then a rodend.

    Anyway, If 50% of the time the judges cared, and the other 50% they were neutral and more interested in other things, why would you chance it to make yourself happy. Well, shit, if you don't agree with the judges, that doesn't qualify you for design finals, just an arguement that you can't win. If you are the suspension engineer for your team, you should be shot for be so arrogant about your design that you won't "compromise" it to try to make design finals.

    Anyway, if this is for the weekend autocrosser, how much time are they going to spend adjusting the car for different tracks? Its not like you get a whole lot of adjustment time at the different courses, do you? For those of you that autocross, once you have your car set up, what changes do you make to the car at different courses?

  3. #33
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    A simple difference of opinions I suppose - I would sooner shoot the suspension engineer for compromising a good rod end design just because some judges dislike it. I have a fundamental problem with changing a well developed engineering decision (be it rod ends or anything else) just to suit design judges. It's not being arrogant, it's making a personal choice.
    University of Texas 2002 & 2003
    University of Houston 2007

  4. #34
    Guys, give the design judges some credit for once... Just maybe...maybe it is a bad idea to put rod ends outboard and thats why the prefer it. When you do implement sphericals outboard they don't talk about it much because its so god damn obvious to anyone with half a brain to do it that way. If you plan a head, a outboard spherical joint will be lighter and stiffer. Period. If you want to build a crappy car that can be built very quickly, go a head and put rod ends out there. And then come back complaining when the design judges don't like it.
    ----
    Mike Cook
    It's an engineering competition, not an over-engineering competition!

  5. #35
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    Ha! Strong words there Mike Cook.

    Of course a properly designed spherical is lighter and stiffer. I doubt anyone would argue that point with you. I'm just sick of hearing everyone rag on using rod ends when the only basis for their viewpoint is tired old rhetoric. Sure they might break if you pick the wrong ones. So do plenty of other stupidly undersized components. Sure they could be lighter. But so could almost every frame or upright I've ever seen. My point here is simply that saying it's a "bad idea to put rod ends outboard" isn't a justified engineering decision. And I certainly don't think you can say that a team who decides to run rod ends after careful consideration of the pros and cons has put together a crappy car.
    University of Texas 2002 & 2003
    University of Houston 2007

  6. #36
    This is sort of stupid. Why would you argue to keep something on a vehicle that has to be "oversized" due to a design issue. Putting threads, anywhere on a vehicle, in bending is stupid. The kind of stupid that forgets to pack a parachute when jumping out of a plane.

    If you think that the drive shaft splines need to be larger in diamter than the shaft they drive to avoid stress risers, then you should be against threads in bending. Or better yet, why not make the driveshaft big enough so that it won't break despite its poor design elements?

    Let's try to go through this design arguement:

    Design judge: "why did you use rod ends outboard?"

    Student: "For adjustability"

    DJ: "How have you acounted for the stress risers in the thereads?"

    Student: "I made it bigger!"

    DJ: "Do you think that you could have come up with a better design?"

    Student: "I don't like that rhetoric you are using with me!"


    Yeah, that has design finals, and overall good design, written all over it.

  7. #37
    But let's say the conversation goes like this:

    Student: so we used rod-ends outboard in order to be able to adjust camber easily
    Design judge: What about the stress risers due to threads in bending
    Student: we went with a larger rod-end to account for this, but the difference in weight between the big rod-end and a properly sized spherical is less than the weight we would need to add for adjustable inboard points (i.e. two 1/4" bolts to adjust each of two inboard brackets, plus shims) or outboard points (some shims and two bolts to hold everything together)

    I think if you said this, and came up with the numbers to back it up, you'd leave a positive impression on the judges.

    Matt Gignac
    McGill Racing Team

  8. #38
    I've intentionally stayed out of this again for a couple days, but it's interesting to watch the back and forth. On stupidity, I think people ought to be careful calling things stupid that do work. I find it arrogant to assume that successful companies that build and make money on $40k trackday cars or $650,000 are incompetent or stupid designers (although I don't know if the Koenigsegg is making profit yet, Ariel certainly has). Maybe it could be done better, but I get the sense that people like to insult an idea rather than just leaving it at "I wouldn't do it that way and here I'll show you what I think would be better".

    I do tend to like Matt's student to judge conversation. The prior looked more like someone with a lip trying to start and simultaneously lose an argument.

    This doesn't need to be a competition with contest judges. A good judge may have an opinion, but a good designer will always respect a well-considered design. When I find people who will not listen to or respect any other opinion, these are people that I would rather not work for or with.

    The quotes around "oversized" are a bit over the top. There is a proper size for a ball joint to do the job and a proper size for a spherical to do the job. If one is heavier than the other or takes more time to adjust than the other, so be it. Each has its own merits though or nobody would make rod ends.
    Kevin

  9. #39
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Matt Gignac:
    But let's say the conversation goes like this:

    Student: so we used rod-ends outboard in order to be able to adjust camber easily
    Design judge: What about the stress risers due to threads in bending
    Student: we went with a larger rod-end to account for this, but the difference in weight between the big rod-end and a properly sized spherical is less than the weight we would need to add for adjustable inboard points (i.e. two 1/4" bolts to adjust each of two inboard brackets, plus shims) or outboard points (some shims and two bolts to hold everything together)

    I think if you said this, and came up with the numbers to back it up, you'd leave a positive impression on the judges.

    Matt Gignac
    McGill Racing Team </div></BLOCKQUOTE>

    Or they could mention the fact that out board adjustment is unsprung weight.

    We could keep arguing and arguing. I guess my point is that there are stiffer/better ways to do outboard balljoints, but they may be more expensive or time consuming.
    ----
    Mike Cook
    It's an engineering competition, not an over-engineering competition!

  10. #40
    the name of the game here is to do well at competition, is it not? thats usually what you shoot for in any competition, and in fsae you simply will not perform well in design with rod ends in bending. especially not with the increased calibre of cars and level of competition. the judges need to make sure you have all the basics covered in your design before they can really appreciate the detailed work or unique features of your car. and why would you default yourself out of a potential good result in design? i would normally agree with matt and say if you bring numerical justification for any design decision it should be acceptable, but the judges seem particularily harsh on this subject, so run sphericals and the judges will spend less time telling you not to run rod ends in bending, and more time listening to you talk about the design highlights of your car.
    John Valerio
    Queen's FSAE
    http://engsoc.queensu.ca/formulacar/

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