Caster and the upright

[trave916]

Hi all, I'm currently working on determining caster for our front suspension and I had a few questions.
The first being, how is the amount of caster that we have related to the amount of camber gain that we achieve in cornering? Is it .5 degrees of camber for each degree of caster?

Secondly, when designing the upright, should the caster angle be reflected in a left to right offset of the upper and lower a-arm balljoint locations? ie. should the upper and lower mounting locations be right inline with each other or offset?

Lastly, (and not so much related to caster) how would I go about determining our minimum turning radius? Base it off the skidpad dimensions or a general angle that the front wheels should turn?

Any advice would be greatly appreciated and I hope that I worded this correctly, thanks.

[trave916]

Hi all, I'm currently working on determining caster for our front suspension and I had a few questions.
The first being, how is the amount of caster that we have related to the amount of camber gain that we achieve in cornering? Is it .5 degrees of camber for each degree of caster?

Secondly, when designing the upright, should the caster angle be reflected in a left to right offset of the upper and lower a-arm balljoint locations? ie. should the upper and lower mounting locations be right inline with each other or offset?

Lastly, (and not so much related to caster) how would I go about determining our minimum turning radius? Base it off the skidpad dimensions or a general angle that the front wheels should turn?

Any advice would be greatly appreciated and I hope that I worded this correctly, thanks.

[acedeuce802]

I think you need to do a little more reading and researching.

Determining how much camber is gained isn't as easy as saying x amount of camber per x amount of caster. It's a function of caster, steering wheel angle, KPI, etc... Because, for a given setting of caster, and other geometric values, the camber angle changes as the steering wheel angle is altered.

Looking at the suspension corner from the side (looking at the face of the wheel), the angle of the line drawn through the upper and lower balljoints is the caster angle. If they were in line with each other, the caster would be zero. When the upper ball joint is closer to the rear, it's considered positive caster.

[RobbyObby]

Like Adam mentioned, there are more than a few variables that you need to determine camber gain. There's also camber gain due to roll (or ride), and camber gain due to steering. Most of the situations you encounter involve a combination of the two. Caster angle, static camber angle, King Pin Inclination (KPI) (the lateral offset of the upper and lower ball joints in front view), as well as steering angle and vertical wheel displacement (or roll angle) all come into play. Like I said lots of variables. Designing a suspension that does what you want it to do involves making compromises, and lots and lots of iterations.

As for the minimum turning radius, look at the rules for the minimum autocross hairpin radius and go 25% smaller (to account for anomalies) (watch some on board footage of the 2011 MIS autocross track to get an idea of what I mean). That will give you an angle your wheels need to turn (don't forget though, your tires also need slip angle to generate any cornering force).

[trave916]

Thanks so far guys...we have already done a few iterations of our suspension and I am not totally new to this stuff but there is still a lot I need to learn. I guess i was wondering if there was a kind of "equation" that could help relate the camber gain while turning to caster angle. We have ours set at about 6 degrees right now with a static camber of about 2 degrees, KPI is 6.5 as well.

I will make sure to check out some of those videos as well

[PatClarke]

T916,

Having approximately equal KPI and Caster is going to virtually cancel any camber gain in steer.
There are other things that affect this. Take into account the effect of scrub, trail(s) ackerman etc.
Surely you can model all this stuff in a Suspension kinematic software like Bill Mitchell's or Claude's Optimum K?

So, sorry, there is no simple equivalence like 'X degrees of caster gives Y degrees of camber gain'. FSAE was never easy ;-)

Pat

[Kevin Hayward]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by PatClarke:
T916,

Having approximately equal KPI and Caster is going to virtually cancel any camber gain in steer.
</div></BLOCKQUOTE>

Sorry to correct this but caster has a much larger effect on camber than king pin inclination.

For example running a setup on OptimumK with around 4 deg caster and 6deg kpi, for a turn of 25 deg on the outside wheel there was -1.1deg of camber change, and on the inside wheel with 30deg of turn angle (reasonable ackermann) there was 2.8deg positive change.

Even thought the caster was less than the kpi it was still has the dominant effect on camber. This should make perfect sense when you look at what planes the two angles reference. They are not a one-to-one trade. Caster will provide positve camber on the inside and negative on the outside, KPI will add positve camber to both inside and outside.

You can use some mix of kpi and caster to have your inside wheel approach a more useful camber angle during the turn. While we want negative camber on the outside, we actually want positive camber on the inside. By having some KPI you can run a higher than normal caster without seeing inside edge wear on the outside tyre, and dial in some more positive camber into the inside wheel. You can counteract some of the extra steering effort by introducing some caster offset and reducing mechanical trail. The KPI generally helps with scrub radius.

Kev

[trave916]

Wow so much information to take in. Our team hasn't had access to any such quality softwares like the ones mentioned; but I ded see that OptimumK has a free trial so I'm giong to try that. I still was unsure about the upright though, as to whether the top and lower a-arm connections should be offset (vertically) or do they need to be right above and below each other?

Again, thanks for all the input guys. I should have a handle on this in no time at this rate.

[AxelRipper]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by trave916:
Wow so much information to take in. Our team hasn't had access to any such quality softwares like the ones mentioned; but I ded see that OptimumK has a free trial so I'm giong to try that. I still was unsure about the upright though, as to whether the top and lower a-arm connections should be offset (vertically) or do they need to be right above and below each other?

Again, thanks for all the input guys. I should have a handle on this in no time at this rate. </div></BLOCKQUOTE>

Well thats where you need to make some decisions about what you want your suspension to do, as there is no "right" or "wrong" way to do it, just what you decide works. If you haven't already, grab the Carroll Smith and Milliken books and start reading. Loads of information there.

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by trave916:
I am not totally new to this stuff but...
i was wondering if there was a kind of "equation" that could help relate the camber gain while turning to caster angle. </div></BLOCKQUOTE>
I rest my case. The education system has truly gone to crap!!!

Trave916,

Why don't you work it out for yourself?

It is a very simple problem. The equation is extremely simple (and the KPI version is almost as simple).

Has your school ever taught you anything?

Are you sure you want to be an engineer?

What are you going to do when you get out into the big bad world, and nobody wants to help you???

Z

[trave916]

I believe that what I am trying to do by posting on this forum is figure it out by myself. This site is meant as a reference to others knowledge and guidance.

In regards to my mechanical engineering classes, we don't have any vehicle dynamics specialty courses offered. And yes, my school has taught me well enough to know that there will always be someone willing to help or at least suggest paths to learn things on your own.

[Jay Lawrence]

Z,

You make me wish I was one of those freakish people that knew everything in the world on the day they were born. Unfortunately, like Trave916, I am forced to learn things. Clearly, what is simple to you is not so simple to Trave916. I suspect he has not been taught any vehicle dynamics classes (hence the legitimate 'equation' question) so I don't think this has anything to do with his school.

Edit: looks like you got there just before me...

[Z]

Trave916 & Jay,

This problem has nothing to do with "vehicle dynamics". What next? "I've got to work out how many wheels on the car. I know it's got two at the front and two at the back, but how many in total??? Oh, it's all too hard. I better ask a vehicle dynamicist..."

The problem is a disc shaped object (the wheel) making a small rotation around an inclined axis lying in its plane. You don't even need trigonometry to solve this. (Hint: I don't know why I should bother, but use radians and small angle approximation.)
~o0o~

Trave916 "I believe that what I am trying to do by posting on this forum is figure it out by myself."

So what is the equation?

Z

[kcapitano]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content"> use radians and small angle approximation </div></BLOCKQUOTE>
Did it ever occur to you that some people may not even know what "small angle approximation" is? This sort of thing may seem elementary to you but it really isn't.

I agree that the mathematics involved really aren't that hard, some basic trig (or you're method) and one could figure it out, but the math isn't the hard part. The hard part is figuring out where and how to start. In many cases just drawing the proper FBD is half the battle.

I know it may seem to you like most of the people here are just little kiddies trying to get other people to do their homework for them, but have you been in a first year engineering calculus course recently? At least the people here are trying to expand their knowledge and solve real problems. Believe it or not, there are people out there who are content with just getting an engineering degree while doing as little work as possible.

[Kevin Hayward]

Trave916,

While software like OptimumK is good it is not necessary. You are looking at a relatively straightforward problem of rotation about an axis in three dimensions. Searching for this will give you some complex looking but quite simple rotation matrices. This material is generally well covered in general kinematics classes. I would recommend robotics units if you have them as electives. One example after a quick google search gave this link (amongst many others):

http://inside.mines.edu/~gmurr...bitraryAxisRotation/ (http://inside.mines.edu/%7Egmurray/ArbitraryAxisRotation/)

Any of the suspension mechanisms can be solved with similar geometric means. OptimumK uses a Newton Raphson solvers but as a student I found it easier to implement closed form geometric solutions. They are more accurate and generally easier to implement as one-offs. Double a-arms are just four bar linkages with links that have rotation about arbitrary axes. A rocker arrangement is very similar.

There is no escaping the fact that when you want to understand the kinematics of suspension systems that you need to develop a decent grounding of geometry. Once you understand how linkages move you can get to the more diffcult part of understanding where you want them to move.

I would highly recommend getting a hold of OptimumK or a similar package, but if you want a very simple first go just solve front-on 2D four bar linkages for the wishbone movement, and do separate steering studies using the rotation of a wheel axes around a line defined by upper and lower ball joints. You can use some well documented empirical ideas for toe control in bump. While doing this please understand that the simpler processes will most certainly not lead you to the best solutions.

Kev

[trave916]

Wow thank you very much. I did download the free trial of Optimum K and it is very helpful. I do have fron, side and top views of our setup drawn out but I have never tried applying four-bar concepts to them. I was thinking of drawing the axis of rotation defined by caster, static camber, KPI etc in solidworks just to make it easier to see. Thanks again.

[Tim.Wright]

The funny thing is that there actually is an equation relating steer angle, caster, kpi and camber and it is not trivial. I dont have it on me now but its in the tire suspension and handling book by Dixon. Do a google seach and you might find it in an ebook.

Its a useful equation which I have used a few times on a new suspension design. Each time Ive used it Ive had to look it up because its quite complicated and lifes too short...

Find this equation, put it into excel and you can very quicly trial different caster and kpi values without stuffing about with pickup points in 3d space.

As to what the angles you need, that depends pn your tyres. Dont forget caster and kpi affect your load transfer distribution as well...

Tim

[Claude Rouelle]

A simple 3D Geometry analysis will show you that the camber variation in steering is
= KPI Angle x (1-cos(Steering angle))- Caster angle x Sin (steering angle)

The KPI is related to the COSINE of the steering angle and the Cosine of an angle is the same sign whether the angle is positive or negative
The KPI is related to the SINE of the steering angle and the Sine of an angle is different if the angle is positive or negative

As you can see both the KPI and the Caster angle influence the amount of camber variation in steering but the caster influence not only the amount but also the sign of the camber variation.

Hope this helps.

A bit more comments.... Camber is heave, roll, steering (front) dependent. And compliance! Do not neglect compliance: a usual simple 3 pieces 13" rim has a camber compliance of 1 deg / G of lateral acceleration

I guess your next question will be " OK now what is the ideal camber?" The answer will be the similar to other questions on tire such as.... "What is the ideal tire temperature?" or "What is the ideal tire pressure?" The answer will always be the same: That is the one you got when you were winning race.

A few years ago I gave that answer in an in-house seminar for a Formula One team who did not win the race despite 7 years of trying. They looked at me and one of the engineers said: "So we will never know?...." Oops...

In a simple, short way I would describe an ideal tire exploitation in these words: Try to get the biggest contact patch surface (only problem with that could be bigger rolling resistance) but mainly try to get the most homogeneous load tire distribution inside that contact patch surface. If the load is pretty even the tire temperature measured across its width will probably be pretty even too.

But let me help you with a theoretical answer and practical approach in ideal camber.

Theory first

Before I answer the ideal camber question I should first ask you: what are you looking for? Lateral or longitudinal grip?

If you try to maximize lateral grip (skip pad) look at your TTC data and analyze the graphs of lateral grip Vs slip angle Vs vertical load for different camber and try to see what the ideal camber is. Hint: Look at the ideal tire average temperature as well as inside / center / outside tire temperature. There are things to see there....

If you try to maximize longitudinal grip (driven wheel in acceleration) look also at your TTC data and analyze the graph of longitudinal grip Vs slip ratio Vs vertical load for different camber and try to see what the ideal camber is. Same hint about tire temperature.

If you have looking for the ideal camber for a combination of lateral and longitudinal grip (autocross / endurance) I suggest you look at the shape of your racing circuit G-G diagram and weight the relative importance of pure braking, pure in-line acceleration, left and right lateral acceleration or combination of those.

You could come with different needs of static and dynamic camber (different pick up points) dependent which dynamic event you compete in.

However that is only the theory.

A practical way to find what the ideal camber is, is to use tire temperature measurement from tire temperature probe and / or from Infra-red tire temperature sensor.

The first type of sensor will give you the core compound temperature. Tire manufacturers will tell you that core compound temperature is what matters and they will be right. On a race tire energy resulting from rubber molecule shocks creates hysteresis and temperature and grip (until you go too far) much more than surface adhesion. That is why 2 or 3 mm deep core temperature "speaks" better than surface temperature. The problem is that this measurement will give you the tire temperature at rest! When I was in Indycar we could observe as much as 30 deg C difference on core tire temperature if the pit was at the entrance or the end of the pit lane...

The infra red temperature sensors give you the surface tire temperature, not the core one but it give it too you life!

If I was developing a FS car I would use both.

Today I don't know how I would tune a car without tire temperature sensors. A few years ago a FS team which used IR tire temperature sensors after one day of testing used exactly the same words as the ones I used with a professional team I worked for on 1989 and with which we also used IR temperature sensors for the first time: "It is embarrassing! We do the same progress in 1 day of testing that we did previously in 5 days without these sensors.The difference is that we know WHY we get faster"

I would use both theoretical approach (TTC data exploitation)and the practical one (on track tire temperature measurement). If the TTC data are perfectly accurate (remember the Calspan tire testing belt is not exactly the asphalt of Michigan or Hockenheim) the TTC info will help you to better understand the tire. If not giving you all the answers, it will help you to create the right list of questions. Once you go the race track you will know better the "how", the "why" and the how much" which will allow you to better exploit the tires. When I was in F1 I was told that a race tire is a system of 220.000 degrees of freedom. You can never be spot on; you work in DELTA. Tire models help you to see tendencies and sensitivities.

A bit more info than just the answer about Caster and KPI. When I have the time (or find the time) I love to share a bit of experience and perspectives on that stuff

[Claude Rouelle]

I meant

If the TTC data aren't perfectly accurate (remember the Calspan tire testing belt is not exactly the asphalt of Michigan or Hockenheim) at least the TTC info will help you to better understand the tire.

Sorry

[trave916]

Wow thank you for the input. I would like to hear more about some references you have gained through the years working on F1. Although I am not completely familiar with all the terms you've thrown out there, I am sure I will come across them in my future reading/analyzing of suspension and driving dynamics. I can totally relate to the statement about 220 degrees of freedom, as I have learned that once you think you've found a place to start in creating a suspension, there is something which that part depends on, and so on.

Again thank you for the input and I look forward to becoming more adept at all of this.

[Claude Rouelle]

220000: Two Hundred Twenty THOUSANDS degrees of freedom per tire. No computer cam simulate this real time. And there are FOUR tires. Now take the rest of the car and, worse, the driver mind http://fsae.com/groupee_common/emoticons/icon_smile.gif and you will find many, many more degrees of freedom http://fsae.com/groupee_common/emoticons/icon_smile.gif

[trave916]

Oh right commas and Periods being used for the same thing, haha my bad

[Claude Rouelle]

Here are some pictures of IR tire temperature data extracted from the OptimumG race car engineering seminar.

As you can see tire surface temperature
- change a lot during one outing
- change a lot during one lap
- are quite different from one tire to another
- are quite different at the beginning and at the end of the outing
- are quite different from the temperature you will measure with the core compound usual probe.

http://i.imgur.com/3y7gz.png

http://i.imgur.com/7nOHB.png

http://i.imgur.com/FZn3z.png

Want an additional challenging question? What is give you more grip: one more degree of camber or one more degree of toe. Look at your TTC data!

[trave916]

I would think that 1 more degree of camber would do the trick. And I know this is most likely a bonehead question; but what exactely are these TTC charts that you like so much?

[Claude Rouelle]

Tire Testing Consortium. Just make some search on this forum. As race car performance is mostly coming for the titre ground friction, TTC tire data is indispensable if you want to understand how and why any car (race or passenger car) design starts with tire model.

With the help of Calspan and tire manufacturers Doug Milliken, Bob Woods Edward M. Kasprzak created the TTC. FS / FSAE students have no idea how lucky they are. Depending how extensive you want a tire model to be it could cost anywhere between 15 and 50 K$ (Per tire!; nearly double the cost if you have different front and rear tires!), while several FSAE tire data are accessible for FSAE / FS university for 500$.

[Z]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by kcapitano:
... some people may not even know what "small angle approximation" is? </div></BLOCKQUOTE>
So, given the above confirmation that the education system has gone down the gurgler...

For small angles (&lt; ~10deg);

Sin(Angle) = Tan(Angle) = Angle (in radians),
Cos(Angle) = 1.
~~~o0o~~~

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Claude Rouelle:
A simple 3D Geometry analysis will show you that the camber variation in steering is
= KPI Angle x (1-cos(Steering angle))- Caster angle x Sin (steering angle) </div></BLOCKQUOTE>
So, using above approximation for small angles (all in radians),

Camber-Angle variation = (KPI-Angle x 0) - (Castor-Angle x Steer-Angle), or,

Camber = - Castor x Steer.
********************************

Which is about as simple an equation as you can get. Also confirmation that KPI makes no difference for small steer-angles.
~o0o~

For more accuracy of KPI effect at larger steer-angles use the second term of series expansion of Cosine (the above only uses the first term), giving,

Camber = KPI x Steer x Steer / 2.
****************************************
~~~o0o~~~

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by trave916:
...my school has taught me well enough to know that there will always be someone willing to help... </div></BLOCKQUOTE>
Well, yes, so far...

But by getting the answer spoon fed to you, do you think you have actually LEARNT anything?

Will you be able to solve a similar, or perhaps harder, problem when working in a competitive situation with people that no longer want to help???

Z

[Kevin Hayward]

trave916,

If we look at the equation Claude presented we can see the larger effect of caster.

1-cos(30) = 0.13
sin(30) = 0.5

I would stick with the rotation about a line however as it will help you with the next problem you will have when deciding caster and that is the steering jacking forces. If you rotate the contact point of the tire around the same line you will find how much it will raise or fall relative to the body. If you couple this with your vehicles warp stiffness you can calculate the jacking effect.

All this being said your team should seriously consider getting hold of some kinematics software. The programming team for OptimumK had a reasonable number of ex-FSAE students who made sure the program was just as well suited built for designing suspension as well as analysing existing setups. It is offered at a very good price for universities.

Kev

[Claude Rouelle]

Z

I feel it is important that both content and form of answers to students carry some positive message.

Sometimes giving a part of the answer create more curiosity and interest from the students. And from there often more sophisticated questions and answers.

There was a time I was critical and sarcastic. That was the time my business nearly went down.

I am still very demanding with my employees, my university students and with FSAE / FS participants. I am far from being perfect but still a bit better every year. Mostly I learnt that I have to be less aggressive in written than verbal answers.

Want an opportunistic perspective? The more "the education system goes down the gurgle" the bigger the need for good teachers. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Humbly,

Claude

[Z]

Claude,

I wish I could be more optimistic, but reality keeps getting in the way.

The main reason for my comments re: education is that I am hoping that when the kiddies currently reading this ask in 50 odd years time "What happened???", they might realise that giving every student a "gold star", regardless of effort, was not such a good idea.

Anyway, my second and third favourite books of all time are Chinese, so I'm not too fussed (though I was hoping for a better contest). http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

[Kevin Hayward]

Z,

A gold star is a horrible reward for effort. Rather the reward for effort is excellence. I'm not sure that spirit has been killed by kindergarden teachers.

If there is one great thing to come out of encouragement for young students is that they are less likely to worry about asking questions, unafraid that they may be mocked. Shared knowledge is a much bigger part of the modern learning process than it once was. While previous generations may have tried to find that one definitive text, it is becoming more common to ask questions of peers and educators. Is it better that people ask questions to simple problems or keep silence and make big mistakes? My hope is that by helping point students to further learning that we avoid the next generation from repeating mistakes such as the Holden Camira.

By the way thank you for recommending "Freedom of Machines". It is quite informative, and I wish I had more free time to get through it quicker.

Kev

[Steve Fox]

Interesting thread. But in a way, it is typical of the questions we see, with some really stellar responses! Formula SAE, Formula Student, FSAE.com, and other similar forums are all about sharing ideas, open communication, and most importantly: EDUCATION. As we all know, not everyone on this forum works at the ‘Z’ level. In fact, there are a handful of students from disadvantaged countries or schools who struggle just to get their hands on a lot of the textbooks we take for granted.

Kev, I enjoyed seeing you ‘spank’ the master with a corrected answer! It is not often that you see that happen to Pat. Of course, I read it with the sincere honesty you intended, as I am sure Pat did as well. I have not talked to you in a while, and I miss that. I hope you and the family are well. You have the gift of teaching, and you are not afraid to bring those around you up a level or two, with your clear, simple explanations of a remarkably complex subject. Keep up the good work. I hope that our paths cross sometime soon.

Claude, you are truly a giving human being. You have a passion for what you do, but maybe most importantly, you do not sit atop a pedestal, and look down on those around you. I have seen you on many occasions answer all questions posed to you (no matter how elemental) with the same zest for the subject as if you were discussing theory with Albert Einstein. Goodonya!

Eric Z, where do I begin? How about with the most simple lesson my parents taught me from as far back as I can remember: “If you cannot say anything nice about someone, do not say anything at all.” I do not know you personally, but I know of you, through persons acquainted with you. I have watched your ramblings on this forum for years. Sad, would be my best assessment of your ‘contributions’ to this forum.

Like the seven year locust plague you seem to run in cycles of hateful, disdainful, sarcastic responses aimed at putting down those you take aim at. The way you go about this is hurtful, and negative to the learning process. Perhaps it has been too long since you have truly ‘learned’ what it is like to learn. Calling people on this forum names (kiddies) is unproductive at the least, and provoking (or worse) in other’s eyes. You should be glad you can hide in the anonymity of a forum alias (on another continent!), because if you called me a kiddie to my face, you and I would have a ‘discussion’, and it would NOT be about the weather!

I suggest you take a cold hard look in the mirror and reassess what Eric Z is really all about, and where you want to go from this point, forward. If you want to make meaningful, helpful contributions to this forum (at the educational level of the students asking the questions) then we welcome your input.

I have volunteered my time for well over a decade now to various FSAE/FS competitions. I would like to think that my aggressive pursuit of open, honest Design Judging, as well as a long list of improvements to the way these competitions are run will stand on their own merits. Maybe most importantly, in my mind at least, is the satisfaction in knowing that I have helped (in some small way) to educate a generation of upcoming engineers for the better.

I am very optimistic about the engineering students coming up through ‘the system’ today. To use a saying that I have heard Carroll Smith say quite often: “Coming to the FSAE competition and seeing all the talent reaffirms my faith in our educational system.” The staff at Formula Student Germany also have a saying: Formula Student = ‘For The Students’. Pretty simple…

Trave916, You go man! As you can see, it is not hard to ask for help. It is also not hard to sort the good answers from the Bravo Sierra. If you are at Michigan this year, please look me up. I would like to shake your hand.

Mom, if you see this somehow, I am sorry for breaking the first rule you ever instilled in me…

Sorry to kind of hijack this thread. Claude, Kev, Pat, etc, you all can get on with your lesson plan!

[trave916]

Thank you very much for the post, as I am honored to have someone of your standing have input on this topic. I unfortunately won't be making it to MI this year as I have to report for work with Honda on the 14th, otherwise I would love to meet you. i am glad tgat I finally did decide to post on this forum, as it has given me many leads to start my research.

I again thank everyone for their input and I look forward to next year's competition.

[Z]

Steev Fox,

So many double standards in your above post. Where to begin?
~~~o0o~~~

1. "If you cannot say anything nice about someone, do not say anything at all.”

This followed by three paragraphs of irrational criticism, including a veiled threat of ... just what, Steev?

I like criticism (it is an essential part of education), but I prefer it to be well reasoned.
~~~o0o~~~

2. You describe my "ramblings on this forum" as "Sad, would be my best assessment ...".

In 2005 I pointed out, quite rationally, the nonsense of suggesting that "migrating roll centres" are "a bad thing". Yet in 2009 a Senior Design Judge yet again (!) advises Newbies (http://fsae.com/eve/forums/a/tpc/f/125607348/m/551104293?r=350106293#350106293) that "A mobile roll axis ". This is the same SDJ who gave the wrong advice above, about Castor and KPI effects on Camber. (Really, Pat, you should think these things through before posting, or go back and edit them to acknowledge your errors.)

And then there is the issue of the flawed "flatland" kinematic analyses used throughout the auto industry, and my attempts to point towards the correct 3-D approach (not helped by wasting time here). Interestingly, it is only some of the students (and Kevin) who have shown interest in this. One FSAE official suggested it is irrelevant, and NO officials, Design Judges, etc., have made any educational efforts in this direction.

And also the many other myths and falsehoods that pervade this industry, that I have tried to discuss from a rational, mechanical, perspective (and yes, occasionally with some colourful language...). I note that your posts, Steev, have remarkably little to say on any of these technical matters.
~~~o0o~~~

3. [I]"Calling people on this forum names (kiddies)...
If you read my post you will see that I was referring to people still living in "50 years" time. I won't be there. Nor will most of the older readers. That only leaves the "kiddies".

BTW, in these parts old men call each other "boys". If you find that offensive, then stay at home. Just don't expect the rest of the world to adopt your biases.
~~~o0o~~~

4. " Formula SAE ... and other similar forums are all about ... EDUCATION."

The key issue in this thread is that the OP asks for a handout of a very simple equation relating two angles in 3-D (a secondary school problem, at most). If the OP was from a poor country, and had poor English, then his request would be dismissed with a reference to the Find button. But after the OP makes no attempt to solve the problem for himself, you tell him "I would like to shake your hand."!

Where is the "education" in that?

And how can you say "I am very optimistic about the engineering students coming up through ‘the system’ today."??

And when will you, Steev, start contributing detailed "educational" posts on this forum, perhaps covering migrating RCs, or flatland kinematics???
~~~o0o~~~

5. "... my aggressive pursuit of open, honest Design Judging ..."

I have noticing that the general hostility shown by the officials towards my posts (including one outraged response to a compliment I had given!) has "aggressively" shot up since I suggested that more open, honest Design Judging would happen if the students were allowed to "judge the judges".

It is surely a double standard that the Design Judges think that they are above criticism, even though there are clearly many DJs whose knowledge of vehicle dynamics and the like, is definitely sub-standard!

So, Steev, perhaps it is you who should "take a cold hard look in the mirror" and reassess how optimistic you are about the system, and start thinking about ways to improve it.
~~~o0o~~~

To finish with a topical analogy, all this hostility towards my comments on the education system (ie. shooting the messenger) is a bit like the Captain of the Titanic saying,

"Do NOT be alarmed, ladies and gentlemen.
Do NOT listen to that crazy doomsayer!
It is only a little iceberg, and it's just a scratch, so please carry on with your activities as usual.
After all, you are on the UNSINKABLE Titanic!"

Ah, there is no better recipe for disaster than arrogance + stupidity. http://fsae.com/groupee_common/emoticons/icon_smile.gif

Z

PS. Jay, I most certainly was NOT born knowing any of this stuff. I takes mostly a lot of repetitive, boring exercises (still ongoing), and a few good teachers (now, sadly, long gone).

PPS. Kevin, yes "FiM" is long and wordy, but also very thorough, with pretty much every worthwhile reference in it. In your spare time (!!!), and if you haven't already, you might try the "Elements" (even just this Wikipedia page (http://en.wikipedia.org/wiki/Euclid%27s_Elements#Influence) on it), and then "Principia" (same structure as the Elements) ...

[Jay Lawrence]

Z,

You will notice in Pat's advice on general design parameters that he does not say "mobile roll centres are bad" but that people should be aware of the phenomenon and how it might affect their drivers.

I was, of course, being sarcastic when I said you must have been born with all the knowledge. My point was exactly that it takes "a lot of repetitive, boring exercises and a few good teachers." People come here for those few good teachers. Trave916 came here with a question that has a direct answer. It was provided to him by one of those good teachers, whilst you berated him and his education.

[Z]

Jay,

Pat's quote more fully is "A mobile roll axis will send confusing feedback to the driver making accurate control difficult." (my emphasis).

That sounds like "a bad thing" to me. But more importantly, I challenge anyone to give a rational explanation of how this "confusing feedback" and loss of "accurate control" works, or even provide objective evidence (ie. data logging) of it occuring, even when the RCs shoot off past Pluto.

The "myth of migrating RCs" is an old-wives tale. There is no "reason" in it.
~~~o0o~~~

I berated Trave916 (very gently) because he was too lazy to do the "repetitive, boring exercises".
(Edit: More importantly, his school should have insisted on the exercises.)

Z

[Kevin Hayward]

I will try to steer clear of the negativity. It is always a shame that discussions between passionate people often focus on the differences on view point.

Steve,

Thanks for the kind words. You are spot on about Claude. He is very generous with his time and discussions about fundamental vehicle behaviour. My time at OptimumG was a great learning experience. I try to borrow very heavily from Claude's style of teaching when I lecture.

Z,

By Principia I assume you are talking about Newton's work rather than Whitehead and Russell's. I have had a little look into both when studying the history of mathematics. I know it is not geometry but I found the Principia philosophiae by Descartes a little more interesting. I am more familiar with Elements, but it has been a long time since I went through it. These texts, amongst others, form the fundamental structure behind a lot of the techniques we take for granted.

It is amazing how old the fundamentals of engineering and mathematics are. I hope that when all the hustle of career and young families has passed my eyesight is good enough to be able to give full attention to some of the historical texts of our field.

Kev

[Menisk]

Z, all they're saying is that you need to learn some tact. Knowing how to diplomatically deal with people will get you a very long way in this world.

[trave916]

As I see the color red after being called "too lazy" I find solice in knowing that Z has nothing better to do than degrade those trying to learn from and teach in the system that gave him his "great intellect". As for everyone else, I would again like to thank you for the references, etc so that I may learn it ON MY OWN. I am also sad to say that after this experience, I am most likely done posting in this forum as I now know that it os apparently not right to do so since it is the "lazy" way of gaining knowledge.

[Z]

Kevin,

Yes, I meant Newton's Principia (lots of books written about "principles" back then).

I am an admirer of Descartes, but have not yet read first hand versions of his works (like you I guess, not enough time!). Interestingly, Newton was deeply impressed by Descartes in his early years, but later turned more to Euclid, hence the structure of N's P. There is a story that the very studious Newton was only seen to laugh loudly once in public. That was when he was asked something like "What is the use of Euclid?"

W&R's Principia is, IMO, an example of the decline in educational standards. Written about a century ago (ie. modern) they spend 80 odd pages of the introduction considering the "Epimenides" and related logically contradictory, self-referential statements, only to come to an unnecessarily restrictive conclusion. I note that logic is a "trivial" subject, and not suitable for the foundation of mathematics. But now well off-topic...
~~~o0o~~~

Menisk,

IMO it is not about diplomacy. Rather, it is about a fear of change.

The high priests want everyone to keep believing that the Earth is flat, and no amount of diplomacy will change that. Ask anyone who has tried, assuming they are not already burnt at the stake! http://fsae.com/groupee_common/emoticons/icon_smile.gif
~~~o0o~~~

Trave916,

Note my editted post. Also, definitely no "great intellect", just a lot of long hours spent mostly in libraries reading old books (not in the education "system").

Z

[Tim.Wright]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:
IMO it is not about diplomacy. Rather, it is about a fear of change. </div></BLOCKQUOTE>

It not a fear of change. Theres a balance that has to be kept between changing/improving and actually getting sh*t done.

Its a typical attitude of a graduate, or intellect to want to keep changing the design or completely re writing standard methodology in the pursuit engineering perfection, and the end result is that nothing gets done.

In the real world, you seldom have this time luxury. You need to go with experience (be it yours or someone elses) and existing methods.

Like I said before. Im an engineer, I could derive this formula if I had nothing better to do. But I dont, lifes too short. When I need that equation, I pick up my book and copy it from there. Job done

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:

Note my editted [sic] post. Also, definitely no "great intellect", just a lot of long hours spent mostly in libraries reading old books (not in the education "system").

Z </div></BLOCKQUOTE>

Exactly: Reading, and not building cars. That's Timo's point.

It called Formula SAE, not Formula Abstruse Suspension Theories with Limited Real World Application. These students need to build cars.

The real world doesn't work if everyone is an intellectual superstar and thinks the boring, hackneyed stuff is beneath them. The simple truth is that most engineers are not capable of deriving the equations they use every day, and the uglier truth is that they don't need to and probably shouldn't, because it's a waste of time and money.

There are many more things to learn in FSAE than how to derive equations. Given the limited time that students have, some may choose to learn other things, while others may have to learn other things out of necessity. We can't all sit in ivory towers, even if we prefer to!

-Ryan

[Z]

Ryan,

"Exactly: Reading, and not building cars. ..."

Tsk, tsk... Such an unjustified assumption.

But it is quite common. Last time I berated the poster for being too lazy to do his homework. This time, in the interests of diplomacy http://fsae.com/groupee_common/emoticons/icon_smile.gif, here is some help: Find [Z Africa] (it's not the only car, just the first "grown-up" one).
~o0o~

"The real world doesn't work if everyone ... thinks the boring, hackneyed stuff is beneath them...
We can't all sit in ivory towers..."

Hmmm...? So a simple, to the point of being crude, "brown go-kart", with a single-speed single-cylinder drivetrain, and beam-axles each end ..... is an impractical, exotic creation, dreamed up in an ivory tower??? http://fsae.com/groupee_common/emoticons/icon_confused.gif

On the other hand, a car with unnecessarily complicated double-wishbones-with-push/pullrods-and-rockers-everywhere IS, in fact, necessary, because, err..., the "boring, hackneyed stuff is beneath"..., err..., umm...

Nope. Sorry. I just don't get it??? http://fsae.com/groupee_common/emoticons/icon_confused.gif
~o0o~

"The simple truth is that most engineers are not capable of deriving the equations they use every day,
and the uglier truth is that they don't need to and probably shouldn't, because it's a waste of time and money."

My experience of "the truth" is seeing far too many, often quite senior, engineers pulling equations out of the back of books and using them where they are simply NOT valid. (Saved, of course, by SF~10+)

All these equations are derived on the basis of a lot of simplifying assumptions, usually set out on page 1 of the particular chapter, and which few working engineers bother to read. The point of getting students to derive the equations, at least once in their working lives, is to expose the students to these assumptions. Any use of the equation outside of its valid assumption range can waste a lot more than just "time and money".

Too many examples to cover here ... but an amusing one was the "rising star" structural engineer at a civil engineering company I briefly worked for. He produced reams of calculations for the roof of a chalet in the Oz Snowy Mountains, but unfortunately mis-used one of the equations. The first time it snowed the roof caved in! http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif (Fortunately, it caved in slowly with the rising snow, so no injuries.)

Z

PS. "editted [sic]" And there are a lot more! My excuse is bad eyes, and, err..., I'm too lazy to figure out how to turn on (?install?) the spell checker. Or to go back and correct them. http://fsae.com/groupee_common/emoticons/icon_smile.gif

[trave916]

In the interest of finally just ending this discussion , which I have become increasingly annoyed by, I will leave you, Z, with the final comment (as I am sure that a person such as yourself will not be able to resist posting after this. In ordr to actually be the last post). I came on here for advice from others (which I recieved) ; but was also belittled by someone not worth my time. So thank you all for this experience, as I am finished with our suspension and ready for MI. So go ahead Z, have your say.

[Kevin Hayward]

The design process is merely a framework around reasoned decision making. One of the most important aspects of effective complicated design is knowing which decisions are important and which aren't. The best path towards developing this skill is to have a strong foundation in the fundamentals of mathematics and science.

While I would not recommend Euclid and Newton as the first books to read regarding suspension systems, they wouldn't be far down my list. We are talking about the foundation of geometry and motion. These are definitely not abstract texts with no relevance. You would be surprised, especially with Euclid just how applicable it is.

It is misleading to newcomers to say build don't read. There are suspension designers in FSAE that find the time to design, manufacture, test, and read (a lot). In order to understand vehicle dynamics and suspension design you will need to have your head in a heck of a lot of books.

FSAE is incredibly competitive. Learn or Lose.

...

To ground this back to the original post. Lets look at the example of adjustability. We have a certain amount of test time for each car. It is incredibly limited even for the very well organised teams. That means there will only be a certain small amount of car setups that you will be able to try. What do we make adjustable?

If we know the importance of different parameters from a fundamental understanding of the motion and forces (including tyre modelling) we can have a pretty good idea. Caster is likely more important to adjust than KPI. Camber more important than kinematic roll centre. Do we want caster to adjust independently of caster offset? Camber independent of KPI?

A little bit of reading and ivory tower design can save a lot of track testing and mistakes.

...

Z is argumentative and can be incredibly negative in his posts, which does not help his cause. I have had more than one online fight with when he was first posting. But please do not disregard some of what he is saying just because you are unlikely to enjoy his company.

Kev

[The Stigg]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">My experience of "the truth" is seeing far too many, often quite senior, engineers pulling equations out of the back of books and using them where they are simply NOT valid. </div></BLOCKQUOTE>
This is by far the best sentence in the whole Topic

It's quite easy to build correct mathematical models - but it's incredibly hard to formulate valid ones for a given problem.
There is a reason for the fact that about 80% of all fundamental mathematical and physical models are build upon empirical research.

BTW. We tried to test the whole "roll-centre migration" shizzle. to be honest at the end we were not able to measure a significant difference in lap time performance. But in this context we learned a lot about how the kinematic layout affected the stiffness of the overall system. That gave us the possibility to increase the stiffness to weight ratio and significantly increase lap time performance.
In vehicle dynamics "~everthing" is interdependent - and this is a chance. Even if you concentrate on a single parameter you are able to learn a lot about the other ones - and if you are lucky enough you pick one of them that significantly improves the performance.

Andy

[flavorPacket]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Z:

Tsk, tsk... Such an unjustified assumption.

But it is quite common. Last time I berated the poster for being too lazy to do his homework. This time, in the interests of diplomacy http://fsae.com/groupee_common/emoticons/icon_smile.gif, here is some help: Find [Z Africa] (it's not the only car, just the first "grown-up" one).
~o0o~

</div></BLOCKQUOTE>

Erik, please don't misunderstand my point. I have a great respect for theory and its proponents, such as yourself. I hope that you already know this from previous discussion.

The scope of my response is far more limited than you inferred. I was not saying that you haven't built cars, but rather that your concept of a 'proper education' is comprised of much more than a capability to derive equations. While this is an important skill, it is not the only one needed to be an excellent engineer. In this thread, you lament that engineers can't start from first principles, which, I agree, is a serious issue. What I find more serious in everyday life, however, is how many engineers can't get a damn thing done on time and on budget (can you tell I'm in management now?).

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Hmmm...? So a simple, to the point of being crude, "brown go-kart", with a single-speed single-cylinder drivetrain, and beam-axles each end ..... is an impractical, exotic creation, dreamed up in an ivory tower??? http://fsae.com/groupee_common/emoticons/icon_confused.gif

On the other hand, a car with unnecessarily complicated double-wishbones-with-push/pullrods-and-rockers-everywhere IS, in fact, necessary, because, err..., the "boring, hackneyed stuff is beneath"..., err..., umm...
</div></BLOCKQUOTE>

I never said that your vehicle concept was 'ivory tower'-type stuff. If I built another formula car, it would have 2 beam axles and 2 dampers, and that's it!

When I get the chance to mentor my old team, I tell them to throw out their photos of F1 cars and go look at a 2CV and a Merc A/B class rear end...we're not so different, really, I just need to make a profit!

Ryan