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Thread: Best Bell Crank Bearing?

  1. #11
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by D J Yates:
    Do not use needle rollers for this application </div></BLOCKQUOTE>

    99% of professional cars use needle roller bearings.

    That said, I don't think it's necessary for FSAE.
    "Gute Fahrer haben die Fliegenreste auf den Seitenscheiben."
    --Walter Röhrl

  2. #12
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    Just would like to note it all really depends on your rocker arm setup. If your rocker arm and pullrod stay on the same plane throughout its motion then things get real easy in the bearing use department.

  3. #13
    [QUOTE]Originally posted by D J Yates:
    For reasons the following reasons, i'd only ever use a plain bearing:

    - very high (almost static) radial load
    - shock loads
    - probable moment loads
    - never seeing a full rotation
    - no need for low friction rolling resistance
    - contamination and opperating enviroment
    - cost
    - stiffness

    IMO, using a rolling element bearing would be fundamentally wrong for this application. I appreciate that stiction is an issue, but all of the other things that Rob mentioned are design issues for which simple effective solutions can be found. Do not use needle rollers for this application - they hate moment loads; and unless your pushrods and bellcranks are in plane throughout the full suspension travel you will get moment loads.

    QUOTE]

    I'll use the example of a cup rocker arm.
    They like starting and stopping much better (no static friction), how do you define moment loads, nascar cup pushrod loads are 6 times what a formula car weighs and the only thing that will work is a needle bearing. We've tried plain bearings (without success) for the stiffness which is very important for valvetrain but I doubt the extra .001" matters at the tire. They also never see a full rotation. They have higher loading at the lowest rotational speeds. Cost for the bearing in our rockers is like $11. Is that high?

    If it's necessary i don't know, but the upgrade is to needles, not to bushings.

    Contamination is a problem for both, without seals neither will last very long. Motorcycle linkages are sealed.
    'engine and turbo guy'
    Cornell 02-03

  4. #14
    D J, you may very well be correct, I'd like to look into the issue more. Some of the reasons you brought up are addressed by my solution. By using two bearings, you can resist moments. Using a needle bearing should prevent brinelling.

    As flavor pointed out, needle bearings are almost exclusively used in this application which leads me to believe that the friction from a bushing setup is too much compared to a roller bearing. Also, cost is probably not so much of an issue in motorsports.

    I also agree with Rob (imagine that!) on some of the practical issues; I don't think there is necessarily simple effective solutions.



    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by D J Yates:
    For reasons the following reasons, i'd only ever use a plain bearing:

    - very high (almost static) radial load
    - shock loads
    - probable moment loads
    - never seeing a full rotation
    - no need for low friction rolling resistance
    - contamination and opperating enviroment
    - cost
    - stiffness

    IMO, using a rolling element bearing would be fundamentally wrong for this application. I appreciate that stiction is an issue, but all of the other things that Rob mentioned are design issues for which simple effective solutions can be found. Do not use needle rollers for this application - they hate moment loads; and unless your pushrods and bellcranks are in plane throughout the full suspension travel you will get moment loads.

    There are wealth of low friction polymer bearings out there. I expect you'd find something suitable from the iglidur range - i've never used one them, but they look good to me. </div></BLOCKQUOTE>
    ----
    Mike Cook
    It's an engineering competition, not an over-engineering competition!

  5. #15
    <BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Mike Cook:
    leads me to believe that the friction from a bushing setup is too much compared to a roller bearing. </div></BLOCKQUOTE>

    this is what we have found and what the pros already know. Put some friction and inertia in your bellcrank in a 1/4 car model and see what happens.
    "Gute Fahrer haben die Fliegenreste auf den Seitenscheiben."
    --Walter Röhrl

  6. #16
    Roller bearing, without a doubt. You can get relatively small ones for cheap, as VFR points out.

    I'd use medias.ina.de to pick out a bearing, and then order from a manufacturer other than INA/FAG. They are way expensive. You can get stuff that's just as good for this application and service life, for 1/2 to 1/3 the price.

    Bell cranks, anti-roll bars.. definitely rolling element bearings. After having tried bushings in said application, I hate em! Judges really liked the very low mechanical hysteresis in our suspension.

    Only thing I'd use a bushing for MAYBE, would be as a guide to the ends of the steering rack (rack extenders). And that only if your tie rods are pretty dead perpendicular to the centerline of the car.

  7. #17
    The best?

    Nadella

    What is actually needed? Definitely less.

  8. #18
    Needle rollers are typically used in applications where there are high shaft speeds, low-medium radial loads, absolutely no axial or moment loads and where radial space is limited. Which is why you'll find loads of them in transmissions. I can see the attraction of using a needle roller in a bellcrank because packaging is tight, but opperating requirements are just wrong for needle rollers, IMO.

    Those Nadella bearings look very pretty, but $34+, ouch! At all 4 corners that would have used up most of the suspension budget at NRacing! Even using exotic polymers, a plain bearing would cost a (very small) fraction of that. Also, it's worth pointing out that the added design complexity of using a rolling element bearing will push up costs and lead times: tight tolerances, surface finish, shaft heat treatment, design features such as snapring groves and sealing surfaces. It's a very complex solution for a very simple problem. All those steel parts will start feeling heavy after a while.

    Mike, too true, you could use a pair of needle rollers, but that just adds to the cost and complexity. By the same argument, why not use a pair of plain bearings to reduce edge loading, adhesion and therfore stiction?

    Rather than discount plain bearings for reasons of alleged high friction and stiction - i must emphasise 'plain bearing', i'm not talking about some nasty bushings - consider what actually causes friction and stiction and how they can be mitigated through design, material selection and lubrication. Get those three things right and i'm sure you'd find a solution that had acceptable levels of fricion and stiction (it'll never be ideal, but could be acceptable) at reduced cost, weight and assembly complexity and improved reliabilty in comparison to a needle roller.

    Of course, without quantifying either the bearing loads, contact stresses and friction; and the effect of those on suspension performance, this is all just speculation. I am, however, inclined to trust in my own educated opinion and suggest that if you've (no one in particular, just a generalisation) previously failed to get something to work in the past that doesn't mean the technology or principle is fundamentally wrong, you just might not have been doing it right.
    David

    Torotrak (Development) Ltd
    University of Newcastle upon Tyne Graduate
    Newcastle Racing 2003-2006

  9. #19
    Suspension joint friction (whatever the source) is Coulomb friction (proportional to load) and is a nightmare for tuning dampers which are viscous friction devices (or J dampers which are inertial devices).

    Speak to any engineers working with highly loaded racecars and they will emphasise the point about reducing all friction sources.

    Rocker bearings are a key friction source, so don't skimp on the bearings. But, in my experience, rod ends / sphericals contribute substantially also. You need a 'system' approach (as always...).

    Only you can prioritise for your design, but avoiding geomtries that can increase joint friction through out-of-plane forces is the best first step. Then consider rod ends / sphericals, then consider rockers.

    Regards, Ian

  10. #20
    Let me point out that the loads in many anti-roll torsion bar bushings are VERY low. In this case a regular bushing seems to be a no-brainer. I bought the RULONJ bushings off of McMaster. They are AMAZYING... the stiction difference between them and nylon is off the hook. Trying to walk on a sheet of RULONJ would be like trying to walk on ice.

    Also, let me point out that most FSAE teams are using ball joints/rod ends/sphericals for most of the suspension joints. How much different are these than a plain bearing?

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