Suspension Design

Z,

1. "And then there is the whole issue of the "2 x 2-D" version of kinematics that is almost universally taught to FSAE students, even though it is wrong!" That is why we have OptimumKinematics which is real 3 D software contrarily to many others (or none in less than 500 $ (FS version) price range). You can have a trial version whenever you want and your comments will sure be analyzed in great details, I promise you. Email engineering@optimumg.com

2. "And BTW, in Mechanics it is very misleading to say "A force is defined by a application point...", because ANY point along the force's Line-of-Action is as good as any other point..." OK mister purist.

3. ""Kinematics" and "compliance" are two entirely different subjects. (FWIW, Kinematics is a field of Applied Mathematics where the idealized geometric bodies are perfectly rigid, friction-less, mass-less, etc...) By conflating the two subjects you are misleading the students." See above comment + Yeah then what... The term AND in Kinematics AND Compliance does not exclude or necessarily mix one with the other. Also K&C is a term that the automotive engineers commonly uses and I am fine with that. Are you in touch and do you speak a common language with these people on daily basis?

4. "Something is clearly wrong with this system of "education"." Yeah ... Yeah.. Yeah.... And what have YOU done or plan to do to change that? Time to change the song, Z.

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Originally posted by Claude Rouelle:
4. "Something is clearly wrong with this system of "education"." Yeah ... Yeah.. Yeah.... And what have YOU done or plan to do to change that? Time to change the song, Z.

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Claude,

Well, in the last year, in my spare time (ie. unpaid), and just in the field of suspension design, I have;

1. Pointed out that the concept of a "Roll Centre" is very poorly defined in the automotive industry (see 3 below), and is frequently misused and abused.

2. Explained that, contrary to what many design judges preach, "RC migration" is not necessarily a bad thing. In fact, a great many suspensions have RCs that shoot off to infinity with the slightest body roll, yet there are no adverse effects at all! This is something that should be common knowledge, but isn't.

3. Reminded the students of the centuries old and very useful concept of "n-lines". Amongst other things this concept allows much better definitions of RCs to be made. Better than, say, the SAE definition, which describes a "point" but in such a way that only its height can be determined.

4. Explained that the conventional automotive kinematics that is taught in almost all textbooks is, in fact, only a dumbed down 2-D simplification of real world 3-D kinematics.

5. Introduced the students to the centuries old concept of the "motion screw", aka "Instantaneous Screw Axis", or "ISA". And explained that knowing a suspension ISA's position can be used to determine important characteristics "at a glance". (BTW, does your OptimumK software show the position of the suspension's ISA. If not, why not? You were made aware of it over ten years ago...)

6. Introduced the students to the equally old and useful concept of the "force screw", aka "action screw" or "wrench". This fundamental concept is also very useful outside of suspension design, and is also very easy to understand. But for some reason many students, and their teachers, have never heard of it. Why???

7. Briefly touched on the "cylindroid", another old and useful concept for understanding kinematics. Will provide more detailed explanation when time permits.

8. Pointed out some aspects of "Ackermann". In particular (and contrary to your advice Claude), how in FSAE the Ackermann requirements have very little to do with tyre properties, and are mostly determined by geometric factors.

9. Explained "jacking", and that the all too common argument that "the tyre Fy forces must be moved to some special point (IC? RC? FAP?)..." is nonsense.

And some other stuff. But going into double figures would make me look like a real dick... http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~~~~~~~~o0o~~~~~~~~~~

To any Newbie students interested in Suspension Design,

I have written out the above issues because they are either wrongly taught in the standard textbooks, or else never discussed. You should at least be aware of them now. More details are available scattered throughout this forum.

Of course, criticisms, questions, or counter-arguments to the above are welcome. But preferably rational.
~~~o0o~~~

To date I have mostly promoted the beam-axle as being well suited to FSAE. I have done this because, besides having many good characteristics, it is widespread in many racing series so I thought it would be readily accepted by FSAEers. Maybe not? Yet?

Anyway, IMO there is a very close second on that short list of five (in earlier post).

But what is your suggestion for a simple suspension that is "good enough" for FSAE?

Z

Z,

Your contribution to this forum is appreciable. But it could be way more useful. I simply wish you would use a less rude, negative and pessimistic language. I think of my self as a provocative guy but there you add 5 more layers of negativity (if not vulgarity) and use words in this forum which makes no one a winner. You could simply be excluded (again I think) from this forum. What would you gain from that? What would the community gain from that?

I have been teaching dozens of course in universities and over 300 seminars in big corporation and small race teams to close to 10.000 people in 15 years and 34 different countries. I have learned that is indispensable to be spectacular if you want to keep your audience awake and interested. But there are ego levels and aggressive statements lines that you do not want to cross if you want to gain reputation, respect and simply keep your business growing.

But that was not my question. My question is: who are you? You came to my seminar long time ago, you were much quieter than in this post but I still do not know who you are and what you have accomplished. What are your credentials and what success have you achieved in the industrial automotive (which race team or race car or passenger car manufacturer?) world which would support that the ideas you develop in this forum have effectively been tested and applied with success?

One more question: Have you ever have been wrong? Have you ever learned from mistakes? If so why don't you explain how and why and when a bit more often; it will be make us feel that you are more than a knowledgeable but grumpy man, it will make us fell that you are one of us.

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Originally posted by Claude Rouelle:
Z,
. . . .
But that was not my question. My question is: who are you? You came to my seminar long time ago, you were much quieter than in this post but I still do not know who you are and what you have accomplished. What are your credentials and what success have you achieved in the industrial automotive (which race team or race car or passenger car manufacturer?) world which would support that the ideas you develop in this forum have effectively been tested and applied with success?

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You may not have intended it this way Claude, but this line of argument is dubious because it smells like "You don't have success, peer acclaim, lots of experience etc therefore your views carry less weight than mine"

Gruntguru,

I DID intend it that way. But it is not about me. It is about PRACTICALLY demonstrate your point of view. You win race on the track not at the office.

Believe me in 35 years I had more failure than success. But that is how I learnt. I won race and championships but I was also fired twice in my career and I most probably deserved it. My career was a mix of intense satisfactions, lots of frustration, sometimes bitter humiliations but most of it is good memories of hard work, short nights, often decent sense of achievements and amazing spirit of camaraderie (even if in the intensity of the fight and the stress that is not the biggest feeling which emerges) but definitely no regrets.

I am very aware that one (but no all) of the reasons I had (so far) a successful career is that I often worked with the right team , the right team manager, the right mechanics and definitely the right drivers at the right time.

However I always like people who take risks, believe in their elaborated theories, car design and setup choices, who can objectively explain and share the reasons of their choice, have the guts to take risk in order to demonstrate these choices on race tracks. And if their theories do not work I like them even better if they understand and explain why, admit it, maybe suffer the consequences and move on. That is how I work.

You can be the best vehicle dynamicist in the world but if it is only on papers, in front of your computer, alone in an office you do not prove anything. That is why in our consulting business we never stop asking ourselves: does it work? did we prove it? and my approach is sure not different with FSAE students or anybody else.

This is FSAE, this is not a theoretical competition for the Nobel price of physics. Maybe you will find the world cruel but until you theories are validated on the track they won't have the same recognition.

Interestingly (and except some sad, heart breaking reliability issues of most of the time 1 or 2 $ car parts), FSAE / FS teams who can demonstrate solid arguments for their car design choices most of the time do well on the race track. You think there isn't a link?

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Originally posted by Claude Rouelle:
Yep except there is a logical and a chronological order: you cam always decide different springs and ARB and damping later while you test the car while it will be difficult to change the suspension type and majorly change the kinematics as it will influence your car chassis (and other parts) design.

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This is a good point. Though as you're aware there are series in which there is an appreciable room for adjustment in kinematics even if the topology itself (5-link vs double control arm vs trailing arm) is stipulated by rule.

On a somewhat related note to suspension design but purely out of my own curiosity, is this Optimum Dynamics development item on the OptimumG site to be multi-body / kinematic solved... or lumped parameter / lookup table kinematics?

exFSAE,

Thank you for asking. We use OptimumDynamics with pretty good success with our consulting clients in ALMS, WEC, Indycar, Touring car in South America and Australia. We keep improving it and making it bug free (ahaha, well let's say better and better). It is not over complicated and it is very useful to find good setup and setup DOE. We plan to make a first version available to the public sometimes in 2013. Using OptimumKinematics could be but won't necessarily have to be used with it but there will be other features. It is clear that tire models and OptimumLap (which is "only" a mass point simulation) are part of the building puzzle.

Speaking of OptimumLap we have been amazed about the amount of users (close to 1000!). Some critics told us that it was too simple to be true but amazingly these are the same people who make their software so complicated that they have to "fudge" the on track recorded data to prove their usefulness. One of my motto has always been "make it useful before you make it complicated"

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Originally posted by Claude Rouelle:
I have been teaching dozens of course in universities and over 300 seminars in big corporation and small race teams to close to 10.000 people in 15 years and 34 different countries.

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Claude,

You might have done all that teaching, but a lot of what you teach is plain wrong (yes, I was there...). In an earlier post I described the "Three-Step-Dance" that takes us nowhere good. Sadly, it seems that it is people like you (and some of the other judges) who are taking us there.

Step 2. Early in your career you learnt to talk-the-talk of motorsports. "Migrating roll-centres", "force application points", and so on.

Step 3. You then made a career of teaching this talk to many of the "newbies" of the industry.

Step 1. But then ten years ago it was pointed out to you that some of what you were teaching was plain wrong. There was a better, 3-D, explanation for suspension kinematics that you should adopt.

What did you do? Did you try to learn this quite simple, and at one time well known, body of knowledge? No! It seems you ignored that helpful advice. Why? Did you just want to maintain the "status quo" that exists at the centre of the motorsport flock? Was that the easiest option? Is that not laziness?

Anyway, you closed the above loop and kept teaching the same nonsense to another ten years worth of students. And you suggest that is a good thing???
~~~o0o~~~

You talk about my "negative and pessimistic language". Yet I am on this forum trying to encourage the students to actually build better cars. Not to keep building the same-old-same-old cars, because that is easier to do (no original thought required), and all the other sheep are doing it. Not to keep believing the same old cottage industry fairytales that are passed off as "racecar suspension theory". But actual PROGRESS!

And yet here you are doing your best to stop that... Why the "negativity"???
~~~o0o~~~

Finally, does it really matter what my "credentials" are? On this thread I have stated the empirical fact that suspensionless go-karts can go around corners fast. Elsewhere I have passed on theoretical knowledge that was discovered centuries ago by much smarter people than you or I.

How does my past work experience (or anybody's, for that matter) make any of that less or more true???

"Past experience", Claude, is something people must promote when they no longer have the "ability".
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Anyway...
Anyone want to have a rational discussion about simple suspensions suitable for FSAE? http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

(PS. Oh, yes... Claude, do you really think "pulling your dick" is so much more offensive than one of your favourite, and oft-repeated phrases, namely "intellectual masturbation"??? http://fsae.com/groupee_common/emoticons/icon_smile.gif)

Eh, I'd be wary to say that 2-d kinematic analysis is "plain wrong." It is one method / model / approach. 3-d kinematics may be more complete, but also perhaps a bit less obvious to draw or wrap your head around. Could just as well make the argument that this approach too is "wrong" and that you should be doing everything as elastokinematics in ADAMS; the addition of compliance rates may have more impact on the final answer than going between a 2-d or 3-d approach.

All models or analyses are "wrong" to some extent. You use the right tool / method for the right job depending on what you're trying to achieve... and in my experience I prefer to use the most simple approximation that sufficiently answers a question presented.

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Originally posted by exFSAE:
I'd be wary to say that 2-d kinematic analysis is "plain wrong."

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exFSAE,

Yes, I guess I should say "plane wrong". http://fsae.com/groupee_common/emoticons/icon_smile.gif

More seriously, the 3-D approach is really no more difficult to understand, or use, once you get your head around it. Overall, I find it easier (more answers from less effort).

But the thing that really irks me is that the whole auto industry (production and racing) has promoted the 2-D theory as being the "absolutely" correct kinematic theory. Additional refinements like compliance, to get closer to "reality", are supposedly just added on top of this "accurate" kinematics.

I'd like to see some "truth in advertising" here. Something like a "this 2-D theory may not work properly in 3-D worlds" type of warning. Of course, this will only happen when the promoters of 2-D kinematics realize that it is wrong, which many of them don't yet know.

It is a bit like a builder laying out a house using "flat-earth theory" (spherical geometry not being needed), while the builder's kndergarten children are taught that the world is a "globe", and "we live here, on the underneath part..." (which the kiddies can sort of understand...).

Oh, and BTW, the errors can be significant, 10++%...

Z