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Thread: Upright Mass Comparison

  1. #1

    Upright Mass Comparison

    Good afternoon everyone,

    My name is Matt Smith and I am a member of Team SURTES at the University of Surrey. Last year I was a placement student working within the team and this year I am a member of the Suspension sub-team, primarily responsible for the design and manufacture of the uprights.

    In previous years of upright design within our team, the responsible has often fallen upon those who are not exactly keen on partaking in the competition and so their designs have been lackluster which gave me a very poor benchmark to improve upon with regards to stiffness and mass.

    What is the lightest upright your team has ever produced (ignoring those which may have failed or had extreme deflections? I've been trying to find information on this previously but to no avail.

    My uprights this year are ~0.35kg for both the front and rears.

  2. #2
    Senior Member
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    That sounds very light, from memory. Can you post up a picture?
    Jay

    UoW FSAE '07-'09

  3. #3
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    Matt,

    I agree with Jay.

    A reasonably low mass for the whole "corner assembly" (= tyre/wheel/axle/upright/brake/suspension-bits/etc.) is about 15 kg (to nearest 5 kg). Your upright is ~2% of that. So...

    DO NOT MAKE IT ANY LIGHTER!

    You are now near the very end of the "Law of Dimishing Returns" curve. Namely, infinitely more "optimisation" only saves you ~2% of the corner mass. A very poor Return on Investment!

    Better is to focus on making that part stronger and stiffer, at same mass, or find other parts of the car to rework.

    Good idea to post an image of the part. I suspect that in reality, as opposed to CAD, it will be exceedingly weak and floppy...

    Z

  4. #4
    Either your upright is unfinished or you have not specified you mass properties correctly. Under 400g is hardly even a bearing housing.
    UQ Racing

  5. #5
    Just to confirm a few things.

    Firstly, the uprights are already in manufacture for FS:UK and so no further changes can be made.
    Secondly, the mass of these is purely the upright and does not include any bearings, clevises, shims etc.

    The masses are 0.308 kg and 0.387 kg for the front and rear respectively.

    For some reason, my photo uploads keep failing so I have hosted them with Imgur, available in an album here.

  6. #6
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    Whenever people start talking about upright weights there's lots of "That sounds too heavy / that sounds too light, they must not be stiff enough" type handwaving.

    One thing I've never seen is someone put a specific value on how stiff they need to be for camber & toe control, with solid reasoning behind it. Especially toe compliance.

    Isn't that the first logical step if you want to do some "optimisery" on weight? Sounds like a good application of BillCobb's transient sim script. How much toe compliance can you have before the response metrics start to suffer drastically?
    Last edited by JT A.; 04-15-2016 at 12:38 PM.

  7. #7
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    I Toed You so...

    "Toe Compliance" (Aligning Moment Steer and Camber Complaince) is probably the most important to specify and also the most difficult to control. The elements of this nasty compilance factor are the steering I-Shaft (Steering wheel to gear pinion nose if you have an R&P gear), wheel bearing, rack pushaway, and "upright" lateral restraint (rod ends, brackets, frame, steer arm). The reason I call it nasty is because it's nonlinear (soft initially then tightens up) and the tire self aligning moments are nonlinear (stiff initially then zero, then negative in the max tire useage arena. There is also a component of this from lateral force (caster etc.)

    Once a front cornering compliance budget is prescribed based on all the other front and rear cornering compliance elements and a linear range understeer/oversteer value is set, the breakdown of your "toe compliance" must be engineered. A pie type chart can/will guide you. This an engineering management issue, not a science project.

    Under the best of circumstances, as a starter, I'd specifiy 1/6 fraction of the total allowed to the I-shaft, 2/6ths to the wheel bearing, 1/6 to the rack pushaway, and 2/6ths to the "upright" restraints. Lets say a reasonable scalar parameter value for a car is 1.0 deg/100 Nm. Now tell me what you have. I can show you stats from production car enginnering, but these are almost all power assisted steering.

    In power steering applications, the rack power amplifier needs a soft element to resolve the appropriate boost force, but in manual type gears, this is generally not an issue. In all cases, wheel bearings are the surprising marshmallows, newbies doing suspension modeling are perplexed by the lack of correlation to K&C data for steer and camber compliance values, UNTIL they put in a bearing fudge factor to mimic the wheel bearing. Presto-Changeo, the bearing maker comes back wuth "gee, I thought you knew that".

    Note that R&P gear pushaway is supposed to be managed by springs and slipper bearings, but the more you try to reduce it, the more rack friction will bite you back. This is a reason to stay away from low steering ratios (10:1 is stiffer that 3:1) too. Or maybe a reason to stay away from an R&P gear setup if you can't afford a "good" one.

    Meanwhile, a soft underbelly is bad news, too. Suspension designers still use unobtainium metal to represent their attachment points. Oops, bad assumption.

    If your front cornering compliance is TOO low, try to stay away from just dumping in a lot of ride/roll steer (the Porsche solution). Cars don't roll a lot, the soggy roll bars have variability and the roll frequency can collide with yaw velocity and/or sideslip frequency. These two are speed dependent, so things will seem fine until there is a crossover. Then you'll probably blame the tires or the driver (The Paul Walker phenom).

    This is why you MUST have tire data in the slip load and camber ranges you car will work best with. This why you need to run lab and road tests. A simple constant radius test will tell you where you stand or sit. If you have high confidence in your analytics, you can take the difference between measurements and simulation and attribute it to surface and temperature effects. That's the ChassisSim methodology. I have it built into all by simulations since the early '70's. This technique is also good for so called "Round Robin" tire tests. You test tires from the same build batch at several different facilities and figure out what to do with the difference. BTW: The new Camber Ridge test facility will attempt to end all the diffugalty between real pavement and real sandpaper. (BTW: It's not "sandpaper", its "3M-Mite" which is a very highly controlled tire test belt surface skin. Now what you do with it after putting fresh stuff down is another matter. (Hone it, talc it, put a very sticky race tire on it, put a baloney skin on it for a few miles, or just spit on it until you want to get some "tire data").

    Tha-Tha-Tha-That's all, folks!

  8. #8

    Camber Ridge

    Quote Originally Posted by BillCobb View Post

    BTW: The new Camber Ridge test facility will attempt to end all the diffugalty between real pavement and real sandpaper.

    This. I'm very excited to see anything that comes out of Camber Ridge.

    https://www.youtube.com/watch?v=vPmBNaIduJo
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  9. #9
    Front Upright: 690 gm
    Rear Upright 890 gm
    One part / Single Shear.
    They are CNC Manufactured from an Aluminum Billet. we had some materials from last year and a CNC facility so we went in this solution.
    Next year we will try sheet metal uprights (The cheapest and time efficient solution at least for our case).

  10. #10
    2015 Models:
    4130 0.025" fabricated sheet steel

    Front: .590 kg
    Rear: .545 kg

    About .45kg of that was dedicated to the bearing bore itself.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

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