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Thread: Sway bar attachment methods

  1. #1

    Sway bar attachment methods

    Hello, I'm Tarik from Princeton's Formula Hybrid team. I was wondering what are most teams' methods of attaching the sway bar to the lever? Welding seems like an obvious choice, but since our design calls for the bearing housings to be on the inside of the levers, it would prevent it from being disassembled.

  2. #2
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    Your bearing housings could split apart at the centerline, so you unbolt them and the sway bar just drops out with the bearings and half of the housing. Do you think a split journal bearing would work for your application? Or you could have the ends of the sway bar machined with a male hex shape and the "levers" machined with a female hex shape so it just slides over the end of the sway bar, with a screw/cap thing on the end of the bar to hold it on. That's all the thinking I'm going to do for you.
    Last edited by JT A.; 08-18-2015 at 03:52 PM.

  3. #3
    Quote Originally Posted by JT A. View Post
    Your bearing housings could split apart at the centerline, so you unbolt them and the sway bar just drops out with the bearings and half of the housing. Do you think a split journal bearing would work for your application? Or you could have the ends of the sway bar machined with a male hex shape and the "levers" machined with a female hex shape so it just slides over the end of the sway bar, with a screw/cap thing on the end of the bar to hold it on. That's all the thinking I'm going to do for you.
    I was thinking about doing a spline type connection, but more so with just a keyway than a hex spline. Interesting that you mentioned the split journal bearings, I didn't think of that. That's probably the method I'll go with. Thank you!

  4. #4
    Just a perspective; on the many many FSAE / FS cars I have observed in more than 15 years: I would say that 80 % of ARBs are not working; too much play, too much compliance, major design errors (such as droop link not in the plane of the rocker - that is you use inboard suspension, single shear rod end attachment, huge distance between the ARB arm and the ARB housing etc...) The installation stiffness (I should say smoothness) is such that the real TLTDD (or as I call it "magic umber" of front/total weight transfer distribution) must be far, far away from the calculated Excel spreadsheet.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

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    Very true, Claude. We had a front ARB on a fairly recent car that didn't engage until the car was at about 2/3 of its total roll travel. I wanted to just take it off the car, but "Noooo, we have to have our fancy titanium blade electronically adjustable ARB so we look smart in design". But they wouldn't let me hang some titanium blade wind chimes off the roll bar either, leaving me thoroughly confused about my team's decision making criteria.

  6. #6
    JT A,

    Good for you and your team I did not judge your car.

    There is a simple test a judge or any student can do. Grab the car by the roll hoop and push or pull sideways to simulate some lateral force and roll moment. Or ask somebody else to do it and carefully watch the ARB movement. Sometimes the play is very, very visible.

    Want an illustration? On an Indy car on oval the ARB motion ratio is slightly different on the left and right; you can see it when you look at the LF and RF rockers; the ARB droop link attachment point is slightly different. The goal? Even if the suspension movement is the same on the LF and RF (let's say same LF and RF spring and same LF and FR aero downforce - remember in Indianapolis the straight line is flat, no banking) then the front ARB will still be slightly pre-loaded before the driver enter in the corner. If this preload wasn't there it will take about 30 meters (30 meters at 370 km/'h is a short time....but a short time without any ARB weight transfer control) for the ARB movement to "beat" the play.
    Driver subjective feedback, pushrod strain gauge data as well and steering aggle, steering torque, gyro and slip angle, lateral acceleration sensors will show you the difference.

    Of course that does work on a oval because you only turn left but this story, I hope, tells you the importance of decreasing the play ...and by the way the other way around: the compliance

    Cheers

    Claude

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    Claude,

    Admittedly I don't follow and have no interest in oval racing, but I'm confused about why you would need an ARB? I wouldn't have thought there'd be much pitch/heave/single wheel bump/rebound going on at these tracks, so what's the contribution of the ARB that can't be provided by corner springs alone? Is it just that you can quickly access higher resolution adjustments (compared to changing/modifying springs)?

    edit: silly me... I'm guessing the (obvious) answer is load sensitivity
    Last edited by Jay Lawrence; 08-30-2015 at 11:16 PM.
    Jay

    UoW FSAE '07-'09

  8. #8
    Jay,

    That topic has been covered many times in this forum but here we go again.

    The ARBs are there for 2 reasons
    1. Control the roll
    2. Adjust the anti roll stiffness distribution therefore the front and rear weight transfer or if you want the dynamic cross-weight and therefore (and because, as you said, of the tire load sensitivity) therefore the understeer/ oversteer characteristic of the car

    Yes you can control the roll with springs but then a) to get the anti-roll stiffness distribution you want you will need such small spring stiffness increments that does not exist. b) you will change the ride frequency and the attitude of the car and that will be an issue even more if your car is aerodynamically ride height sensitive.

    Good driver can feel a difference of 0.05 % of anti-roll stiffness distribution. Try to do that with springs or bump rubber only. There is a reason why such small adjustments are possible (with adjustable inboard ARB) on professional race cars and there is no reason that wouldn't work on a Formula Student car. hat is of course if there isn't too much play and/or compliance , which was my initial comment.

    Claude

  9. #9
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    Quote Originally Posted by Claude Rouelle View Post
    ... Yes you can control the roll with springs but then a) to get the anti-roll stiffness distribution you want you will need such small spring stiffness increments that does not exist. b) you will change the ride frequency and the attitude of the car and that will be an issue even more if your car is aerodynamically ride height sensitive. ...
    Claude, why do you limit your thinking to coil springs? Torsion bar primary ride springs have been used on many cars. By changing the active length, the spring rate can be adjusted in very fine increments.

    See for example, Bill Milliken's "Equations of Motion" page 498. Dad's MX-1 "Camber Car" has square torsion bar springs with a clamping mechanism (on the chassis end) that slides along the length of the spring for rate adjustment. The clamp also incorporates an angular adjustment for ride height.

    Many other configurations are possible.

  10. #10
    Hello Doug (we miss you as a judge at FSAE events!) ,

    Good thought. I do like Torsion Bars too; possibility of different Motion Ratio than dampers (compared to the coil over), they work both ways (clockwise and anticlockwise) while i never saw a suspension spring working in tension, often better for packaging (at least on race car, often in the center of the rocker. A bit of challenges for some teams when it is about manufacturing splines.

    All that is in page 567 of our 2015 fall seminar
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

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