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Thread: Direct Acting Spring Damper

  1. #41
    Ritwikdas18,

    I did mean 'wheel rate' or 'ride rate' when I said it was too stiff. Really I didn't even look at your installed spring, just know that your natural frequency is too high, by ~50% from my experience.

    I can't see your calculation for the damping ratios on mobile.
    If you use the slope of the high speed line to compute them, I think that's not good - Better to use the average damping.

    Anyway, the code you show (4?) is still far too soft damping ratios. Probably because the motion ratio is outside the range these are designed to accommodate.

    Sorry not to explain fully, would rather not have a one sided conversation about this:
    I would suggest damping ratios between 1 and 1.5 low speed, and effective ratio of ~.65 to .85 high speed.

    ~~~

    Don't recall you saying - can you change any suspension geometry? Could you raise the roll centers to stiffen roll?
    That's not as adjustable, but easier to implement sometimes than ARBs.
    Austin G.
    Tech. Director of APEX Pro LLC
    Auburn University FSAE
    War Eagle Motorsports
    Chief Chassis Engineer 2013
    Vehicle Dynamics 2010-2012

  2. #42
    Here are some optimization results to get you thinking.

    'Stability' should be called 'ride' probably.
    'Grip' in this case is almost, but not quite, related to tire deflection.

    Please be careful as they will be different for different sprung/inspiring mass ratios, and for different tires.

    The parameters are however on the right range for a reasonable lightweight FSAE

    These charts Do Not explain low speed damping or asymmetric damping rates rebound/compression.
    Attached Images
    Austin G.
    Tech. Director of APEX Pro LLC
    Auburn University FSAE
    War Eagle Motorsports
    Chief Chassis Engineer 2013
    Vehicle Dynamics 2010-2012

  3. #43
    Quote Originally Posted by Z View Post

    3. The best FS/FSAE driver in the world will not be able to feel any change from your 3% MR change. Especially not when this 3% is over your quoted +/- 4 cm range. As you note, the practical movements during cornering will be more like +/- 1 cm, giving ~0.007 x MR change. And since these changes are likely same F&R, then NO change to "SS-balance".
    Coming from a softly sprung car this year, I'd like to note: Yes, you can tell the difference in single digit motion ratio changes. The difference for us was a linear rate curve vs a single percentage progression. Both drivers who tested the change noted the difference, agreed on it, and preferred the same setting. It's noticeable.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

  4. #44
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    Quote Originally Posted by MCoach View Post
    Coming from a softly sprung car this year, I'd like to note: Yes, you can tell the difference in single digit motion ratio changes. The difference for us was a linear rate curve vs a single percentage progression. Both drivers who tested the change noted the difference, agreed on it, and preferred the same setting. It's noticeable.
    That's interesting, but I'd still be really skeptical about getting a placebo effect. How did you swap out bellcranks without the driver seeing what you did?

  5. #45
    Ritwik,

    You do not know for sure if you car will be "born" with a U/S or O/S characteristic, correct. No simulation, tire model and driver adaptation skills will give you that spot-on combination that early.

    So you need to give your self the opportunity to adjust your balance (or your TLLTD if you want), depending upon your driver comment, tire temperature, analyzed data etc... But you have no ARB? So what will you do? Change the springs probably, front, or rear or both. But then you will destroy your ride frequency target. You will fill a hole by creating another one

    Also you will need to switch to a spring of let's say 125.0 lb/in to a 137.8 lb/in ... that doesn't exist. It will be 125 or 150 lb/in. While with a good front and rear ARB design, you can have a wide range of roll stiffness choice AND TLLTD choice too.

    Up to you but in my opinion front and rear ARBs should have been part of your initial design.

    That being said nothing prevent you to design, install, test and develop them after the video submission deadline.

    Cheers,

    Claude

  6. #46
    Changing you MR 3 % will change you wheel rate to about 6 % which is in the zone that a) will be sensed by any decent driver (including FS / FSAE decent average driver) and b) will change your tire temperature enough that it will affect your car performances one way or the other

  7. #47
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    Goost,

    ... arguing over this is not fruitful...
    Grooaaannn... [Commence Rant ->]

    It is the process of discussing things in a WELL-REASONED way that has, most "fruitfully", given everyone here their oh-so-easy lifestyles (...too easy!). In the hope that just a few of you eventually learn this process, I repeat its bare bones here.

    The essence of this process was chiselled above the doorway to Plato's Academy, namely "Let no one ignorant of geometry enter here!" This approach to thinking about a subject, any subject, was later epitomised in Euclid's Elements, which became the only textbook that all schoolchildren HAD to have for the next two thousand years. Sadly, the Elements were dropped from the curriculum about a hundred years ago... And now we have the nonsense that fills these pages.

    Very briefly, this "geometric" way of thinking consists of a 3-step process.
    1. Start with clear DEFINITIONS of all important terms (these should be at the very beginning of any discussion, but are almost nonexistent these days).
    2. Make very clear statements of what is ASSUMED to be true (again, rarely seen nowadays).
    3. Use a rigorous process of DEDUCTION to find consequences that stem ONLY from the Defined and Assumed "truths", with no drawing of wild and unjustified conclusions (as is so common nowadays).

    It is an easy process!!!

    [Build Up Rant Volume...]

    But the above approach has been too successful. Nobody has to get anything right these days, yet everyone can eat their fill, and more! So the school-kiddies are nowadays taught such codswallop as, "There are NO wrong answers. Everyone's opinion is equally valid. Ah..., yes little darlings, you are all winners. A gold-star for everyone!".

    And when these kiddies grow up and go to University, they learn how to make their magic-boxes draw colourful little pictures. And they believe that all their pictures must be good, and true, and worthy of yet another gold-star. And their ideas must never be subject to any sort of criticism, for "... there are NO wrong answers..."!!!

    Worst of all is that said attitude has now spread throughout the whole education industry.

    So "teachers" can now peddle pure poppycock, with NO clear Definition of terms, and NO clear statements of Assumptions, and NO rigorous Deduction of consequences. And when said "teachers" draw wild conclusions, such as "Pitch and Roll inertias must be calculated using the Parallel Axis Theorem...", they expect the students to swallow this nonsense WITHOUT ANY RATIONAL EXPLANATION, at all.

    So now we have an Education system that is founded on nothing more than "Appeal to Authority" (ie. "I am the Teacher, therefore I am right!). This is regardless of how nonsensical are the teachings. And this is no different to any primitive, superstitious, faith-based belief-system, such as voodoo, black-magic, or [insert the stupidest religion/ideology you can think of here].

    [End Rant] ...for now. Or until Claude attempts to rationally explain his teachings (eg. "Parallel Axis Theorem" above).
    ~o0o~

    ... unfortunately, thanks to these [static-deflection] calculations Ritwikdas18 has springs ... that are about twice as stiff as a 'good soft' FSAE car.
    Oops.
    As Ritwik noted, he is NOT following the flock and fitting ARBs, so his 4 x wheel-springs take all the cornering loads. And as I noted, it is a historical fact that cars have won FSAE with NO suspension movement at all.

    But, for all you students who are firm believers in voodoo, black-magic, etc., ... you had best do what you are told and fit those ARBs...
    ~o0o~

    Many other poorly reasoned arguments, but moving on...

    How can you [Z] say something like ["Ritwik should buy 3 x sets of damper-shims for his rebuildable, but non-adjustable dampers"] after discussing for weeks about how to properly pick springs??
    The Kaz site has Ritwik's chosen non-adjustable QM dampers at $279 each, the "top-of-line" 7800-Double-Adjustables at $750, and 4-way-adjustable Ohlins at $650.

    Why does Kaz sell the adjustable models at such (exorbitantly!) high prices? Presumably, because a great many Teams buy them!

    To spell this out, obviously a great many Teams think they might need to adjust their dampers AFTER they finish designing/building the car. A reasonable idea IMO, given the large number of unknowns involved. (Egs. Just how heavy will the car be? How bumpy, and grippy, will the track be? ...).
    ~o0o~

    I would suggest damping ratios between 1 and 1.5 low speed, and effective ratio of ~.65 to .85 high speed.
    Why? And, very importantly, what does your suggested "damping ratio" apply to (ie. sprung-mass-heave, -pitch, or -roll, or single-wheel oscillations)?

    IMO, in FS conditions, only one of those oscillations needs to be heavily damped (ie. at DR = ~1).

    But suggesting a DR for an unspecified oscillation, ... is meaningless.

    Z
    Last edited by Z; 06-12-2015 at 08:52 PM. Reason: Polishing rant... :)

  8. #48
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    MCoach, Claude,

    To repeat, Ritwik's quoted 3% MR change was over his total suspension movement of ~8 cm!

    The MR change is obviously much smaller over the much smaller suspension movement the car experiences in cornering. And if the MR changes are similar F&R, then even less change to "balance". And if the car is set-up to "work well" with whatever MRs it happens to have in the corner, then it is pointless quibbling about any trivially small changes away from the "central" MR.

    The FS/FSAE Rules are such that these cars have the potential to be MUCH, MUCH FASTER than they are now.

    It is beyond me why so many people here are trying so hard to maintain the status quo with their pursuit of over-complicated, slow, and boring "Mini-F1" cars.
    ~~~o0o~~~

    Ritwik,

    Having only now checked the prices for high-speed (= "blow-off") shim-kits on the Kaz site, I agree that they are ridicuously expensive.

    The main damper-rate you might have to adjust is the low-speed bump and rebound. It appears (?) that both of these are controlled by the same slots on the "Bleed Discs", visible half-way down the "Shock Parts & Tools" page. At $85 these may be a more reasonable option for you to buy. Personally, I would be quite happy to modify these Bleed Discs by blocking or enlarging their slots, to custom-adjust the rates.

    Perhaps Kevin, or ECU team-members, can comment on ease of adjustment of these Quater-Midget dampers?

    Z

  9. #49
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    Quote Originally Posted by Z View Post
    As Ritwik noted, he is NOT following the flock and fitting ARBs, so his 4 x wheel-springs take all the cornering loads. As I noted, it is a historical fact that cars have won FSAE with NO suspension movement at all.

    But, for all you students who are firm believers in voodoo, black-magic, etc., ... you had best do what you are told and fit those ARBs...
    Welcome to magically fairy voodoo land! Where being different is better! ALL THE TIME! Different different different! If you're not doing something different you're an idiot! Rah rah rah, hey hey hey!

    Oh right! I forgot, everybody in the vehicle dynamics world are idiots except for you! Shoot, I probably forgot that because I'm an idiot. Or wait, are we just idiots in the threads where you know you can just keep derailing the conversation by being a prick all the time? Because I have yet to see your response to me in the moment diagram with weight transfer thread where you were saying we were idiots for using MMM diagrams and how there was no way any of us stupid peasant vehicle dynamicists could be using it for anything useful. You are simply here to try and make people believe you're the one true savior of VD because for the last 3 or so years I have yet to see evidence that you are here to have conversations and potentially change your opinion based on other people's experiences. I learned a lot from your posts where you aren't trying to constantly compare your e-dick to everyone else who disagrees.

    Moving on. You can get away with running no ARBs some of the time, you can't get away with running only springs all of the time. I would say that a lot of top series in fact run no rear anti-roll bar, but at most places have to accept the front arb as a necessary evil. Why? Because we have constantly changing balance due to conditions, drivers, tires..etc, some tracks are incredibly bumpy and some smooth and everywhere inbetween and they all require different compromises, and time constraints that don't allow spring changes every time you need to make A LLTD change. I don't have to rescale and reset ride height when I make a bar change (assuming we're road course racing). Yes, racecars do exist in the real world and not just as hypothetical objects on a forum.

    Quote Originally Posted by Z View Post
    The FS/FSAE Rules are such that these cars have the potential to be MUCH, MUCH FASTER than they are now.

    It is beyond me why so many people here are trying so hard to maintain the status quo with their pursuit of over-complicated, slow, and boring "Mini-F1" cars.
    And your brown go-kart is the answer right?...All hail the VD messiah! For you are the only engineer ever to think they found the answer to make a racecar faster! We will build all racecars in your image!

    You're the fifth person this month I've heard that thinks they have the answer. If only racing was that easy.
    Trent Strunk
    University of Kansas
    Jayhawk Motorsports
    2010-2014

    Now in NASCAR land. Boogity.
    Opinions Are My Own

  10. #50
    Quote Originally Posted by JT A. View Post
    That's interesting, but I'd still be really skeptical about getting a placebo effect. How did you swap out bellcranks without the driver seeing what you did?
    The bellcranks are already designed with the mounting holes in them, so we only had to take the down time of moving one bolt on each side of the car. I was one of the drivers, so placebo effect may be in effect, but consistently higher lap times don't lie.
    Kettering University Vehicle Dynamics
    Formula SAE 2010 - 2015
    Clean Snowmobile Powertrain 2012 - 2015

    Boogityland 2015 - Present

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