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Thread: Hubs with built-in tripod joint

  1. #31
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    MCoach,

    In short, your advice to Josh (and other newbies) is,

    * DO only what the majority are doing.
    * DO NOT attempt any engineering analysis that estimates the relative merits of different designs.
    * ABSOLUTELY DO NOT try to build a car that is faster than those currently running around.


    Because that would make the work of other FSAE Teams look really stupid, eh?

    Z

  2. #32


    My $0.02, it's a first-year team with their first-ever car, let them walk before sprinting.

    Josh, if you're still checking this thread, hope you got something out of it.

  3. #33
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    Tromoly,

    In ten years time Boston could be a tenth-year-Team that has still not finished a single Enduro. It is quite common...

    (Although, as noted earlier, I think Josh has a better chance than many of being successful, because at least he is asking questions.)
    ~~~o0o~~~

    Further to the subject of "Subjective Opinions vs Objective Facts".
    ================================================
    The appropriate saying here is that "opinions" are like "@r$#oles", in that everyone has one.

    Each person has their own unique opinion on any issue, and these opinions are generally as fickle and variable as the wind coming from said source.

    But objective facts are CONSTANTS. They stay fixed, regardless of anyone's opinion.

    For example, put one hundred people in a room, ask them to measure the "mass" of a single given upright, and the result should be one hundred equal numbers, within some tolerance range. If students are doing the measuring, then there might be some "outliers" because some students have not yet learned how to use the weighing-machine properly. If FSAEers are in the room, then, and based on much of this thread so far, there will likely be some useless non-numerical results, such as "it's waaay too heavy!". But such erroneous and non-objective results can simply be ignored.

    The key point is that good progress happens when objective thinking is used. The alternative is religion and ideology, and any "progress" there is generally downhill, fast.
    ~o0o~

    So, anyone care to share their objectively measured numbers for their uprights (mass, stiffness, ultimate-strength, MTBF, etc.)?

    Z
    Last edited by Z; 11-03-2015 at 08:05 PM.

  4. #34
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  5. #35
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    Last edited by theTTshark; 11-03-2015 at 09:19 PM.
    Trent Strunk
    University of Kansas
    Jayhawk Motorsports
    2010-2014

    Now in NASCAR land. Boogity.
    Opinions Are My Own

  6. #36
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    Not even the hard deck can save you from Maverick!
    https://www.youtube.com/watch?v=z_BEJmY911s


    Josh,

    Just to further derail this thread.
    My two cents is to not lose sight of the project management aspect.
    If your design meets your basic requirements* then move on.
    You could try to optimize it but how does that affect your overall timeline?
    If it delays you a week to save a few kg on a component will that significantly affect your tuning and testing time?

    How are you currently managing the project timeline?
    It looks like you're past the design phase and into the build phase for this year.
    For you next car you might want to do something like use a gantt chart to pick a design freeze date.
    Start by getting a design for each critical system / component.
    Then work on improving the designs until you hit the freeze date.

    There are already several good threads on project management.
    http://www.fsae.com/forums/showthrea...ect-Management

    Just food for thought.

    -William

    *safely holds the wheel on

  7. #37
    An interesting item to do here is to make a toleranced drawing of a fold-and-weld upright.

    If you have a location tolerance on the flat pattern of +/- 3 mm on any bend, go find how much extra material beyond the ends of the hub bearing bores has to be left to be able to actually mill them once the welding is done. Now add a bend angle tolerance of +/- 1 degree and determine how far off the two faces will be from each other (this is a good time to decide how to get those two faces parallel). Next, estimate how far the main section and backer will distort when heated to 1500 deg C, fused together, then allowed to cool to room temperature. Finally, calculate how much the position of the UCA and LCA bolts affect camber or KPI (+/- 0.060" on an 8" distance between UBJ and LBJ gives what camber angle tolerance?) and how much clearance you need between the edge of the upright and the wheel.

    Texas A&M had billet front and welded-from-sheet (aluminum) rear uprights in 2012. The front uprights came out of the mill, were deburred, had bearings pressed in and spherical spacers made up, and worked as designed as long as the car was used. The rear uprights took days of tack-and-tack-and-tack-and-tack welding to reduce distortion, and took what whiltebeitel would describe as "special toolroom methods" to get the holes in the right places with enough metal around them to hold the load.

    Lifespan is determined by stress level and number of cycles; even aluminum parts with no endurance limit can outlast the car.
    Charles Kaneb
    Magna International
    FSAE Lincoln Design Judge - Frame/Body/Link judging area. Not a professional vehicle dynamicist.

  8. #38
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    Come on Erik - your 2 most common recommendations of increasing bearing spacing and increasing the toe base are as subjective as anyone else's.

    At what point did you ever define what is adequate in terms of camber and toe stiffness for these vehicles?

  9. #39
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    Still no useful numbers [insert sound of tumbleweeds blowing through the desert].....
    ~o0o~

    But interesting is that rather than well-reasoned arguments supported by objective numbers ... instead we have so many links to the Grand-Wizard of the Scientology cult*!!!
    (* Or replace "cult" with - religion, ideology, superstition, witchcraft, black-magic, voodoo, or Optimum-G (<- this last one based on another thread now running ).)

    Ahh..., surely a sign/omen/portent of things to come...
    ~o0o~

    Charles,

    As any trade-school student could tell you, the final dimensional tolerances of folded-sheet-steel uprights can be exactly the same as that of billet-machined-aluminium uprights. Or better.

    University engineering students will likely learn more useful things if they spend less time lounging around their ivory-towers dreaming up excuses for why "it cannot work", and more time out in the real-world finding out what ACTUALLY DOES WORK. Study the "prior art".
    ~o0o~

    Tim,

    ... your 2 most common recommendations of increasing bearing spacing and increasing the toe base are as subjective as anyone else's.

    At what point did you ever define what is adequate in terms of camber and toe stiffness for these vehicles?
    I gave those numbers very clearly on this Forum at least as far back as 2005, and many times since then. You should pay attention.

    Which reminds me, I am still waiting for a rational explanation from you supporting your claim that high-R% cars have too slow LART to win a race. Are you still working on that?

    Z
    Last edited by Z; 11-04-2015 at 08:11 PM.

  10. #40
    Back from exams...

    Here is an updated version of my upright. Main changes include an uneven spacing from bearing center to LCA and UCA connection points, thickening of bearing walls and walls that lead to the LBJ clevis surface. This allows for a wider toe-base (105 mm center-to-center). The local area around the UBJ clevis surface has also been strengthened by adding material. The two weight reduction holes in the top half of the part save 99 grams. Maximum stress during FEA shows 145 MPa concentrated at the inner, lower clevis surface, specifically on the radius, seen below. The next lowest concentrations are 80 MPa seen in other locations of the upright.

    The forces used for this simulation were: 8000 N into the lower clevis surface, 5000 N away from the upper clevis surface, 3000 N at each caliper tab. The upright was fixed at the bearing surfaces.

    As for the hubs:

    I am thinking the best course of action is to tap three holes in the face of the hubs. When a small (M4-5) screw is fastened into these holes, the cap will prevent the zinc sleeves from 1 - rotating, and 2 - removing themselves axially. Other suggestions are welcome, but I think this is a viable option which solves this issue.

    Josh

    Screen Shot 2015-11-04 at 8.21.20 PM.jpg
    Joshua Byington

    Boston University Racing

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