Suspension and Tiredata is my point of view correct?

[SteveOr]

Hello,

We are planning to buy the Tire Data from TTC. But today I have a few problems of how can they help to make my suspension better in depth.

What I understand at the moment (I read books and talk to other teams) and what I hear from other teams:

The Working order:

I start to compare the tires with an averaged wheel load and differed chamber settings to look what tire has the most transverse force potential at a spec. Chamber.

So I choose my tire perhaps the Hoosier that works perhaps best between x and x, x Deg of Chamber.

Then I calculate my wheel loads in static cornering perhaps Skid pad for each tire.

Then I put the Wheel loads into the Tire data and look at what slip angle the best point for transverse force potential at my Chamber I choose before is.

So I have to develop my Kinematics in that direction that all tyre or rather the higher loaded outside wheels gets in Skid pad the Chamber I chose before for best lateral forces and the slip angle I found, perhaps interaction with the steering geometry.

So that is my point of knowledge at the moment. Is my understanding correct?
What else can give me the Tire data? To get more goal parameters for the kinematics?

Is it possible to work with the tire data without Matlab? And perhaps use MS Excel or National Instruments DIAdem or so?

Thank you

I´m waiting for competent answers

Steve

[exFSAE]

Step 1 - Understand at a high level what you want your vehicle to do in various quasi-steady or dynamic situations.

[rmk36]

Steve,

You can import the tire data into excel and manipulate it how you please.

[Edward M. Kasprzak]

How you use the TTC data depends on what level of understanding you and your team are currently at. In engineering we work from general concepts to specific designs. Don't worry about details until you understand the big picture.

I always encourage new TTC members to start by making a ton of plots. How does one variable vary against another? Over what range? Which effects are independent and which are coupled? Understanding the trends can be more important than dealing with specific values.

[SteveOr]

Thanks for your answers.

@exFSAE what are the Keywords for the 1 Step? Where should i read it?
Generally i want the the car is fast and the driver feels well so that the driver feels the reaction of the car early enough to react in time. ;-)

Any other comments?

Thank you!

[Adambomb]

For keywords, "camber" will return more results than "chamber." Or at least more relevant results.

You may be able to access some of the raw test data without Matlab, but to use the Pacejka model (which you will really want to do), you will have to call a Matlab function to look up the values. And, as Dr. Billy V. Koen points out, "you just can't make it in modern engineering if you can't use Matlab!" You should have little problem picking up on it, at least if you're smarter than Bill O'Reilly:

The importance of Matlab (http://matlabmadness.ytmnd.com/)

[exFSAE]

Originally posted by SteveOr:
@exFSAE what are the Keywords for the 1 Step? Where should i read it?


Keywords: Vehicle dynamics. Furthermore, see below...


Originally posted by Edward M. Kasprzak:
In engineering we work from general concepts to specific designs. Don't worry about details until you understand the big picture.

IMO Edward hits on the most important thing here. Start high level, work down to details. Seems very easy at the FSAE level to fall into the trap of working the opposite way up, being lost in the details quickly. I was just as guilty.

You might start Steve, with the ever-popular Race Car Vehicle Dynamics. Some good high-level fundamentals in there. Start with that and work down, and the specifics about important aspects of tire data should become more obvious.

[ben]

I think Edward and exFSAE are on the money as usual.

We've had a lot of success using the moment method approach (Milliken Moment Method (MMM) - RCVD Chapter 8) the top level design targets you will get from that are:

1. Control moment (Basically front cornering stiffness x front axle to CG distance if you can do a model)
2. Directional stability (restoring moment for a pure sideslip input with zero steering)
3. Limit balance (do the fronts or the rears slide first)

For that (on a simple level) you need Fy vs. Slip angle curves as a function of vertical load. Do that for a simple bicycle model (assume two tyres worth of grip at each end) ignoring load transfer and you'll get surprisingly close.

Ben

[woodsy96]

One of of looking at it from top down a la exFSAE is to compare the effects of camber on driving forces, braking forces and cornering forces. Then, based on your knowledge of FSAE tracks weight the relative importance of each one (maybe with a simple Excel simulation of the track for lap time). Use that to determine your "ideal" vehicle characteristics, i.e. camber compensation in roll , pitching rates etc.

Or, before that, choose your vehicle goals. A tyre with a very high peak to slip ratio is not going to fulfill an "easy to drive" goal, but may fulfill a "Win skidpad" goal.

Another thing you could do is see what your car will be most sensitive to in doing balance tuning- ARB, camber, toe or tire pressure adjustments (or rim widths or whatever).

What are the tyres combined lateral / longitudinal force curves like? Should we run an open diff/torsen/salisbury/spool etc.

Oh, and don't forget to account for your tyre spring rate when working out your sprung mass natural frequencies http://fsae.com/groupee_common/emoticons/icon_smile.gif

The world of possibilities are endless. As in all things motor racing, You are limited by budget (including time), imagination, knowledge and rules.

[woodsy96]

Or try and determine the transient characteristics of your tyre http://fsae.com/groupee_common/emoticons/icon_smile.gif

[BillCobb]

Here's a simple way to determine the proper transient characteristics of tires. Hey, there's my name. As you can in the transfer functions, this is a complex quantity. The relaxation length notion is not a good model especially for Mz. And, now you can see why shock absorbers / dampers make a big difference in handling / racing as they apply to the important tire responses needed for top performance there.

http://www.patentgenius.com/patent/8006550.html

Now all you need is to know the transient traits of a 'good' tire vs. a 'poor' tire, especially when the steady state response of both are pretty much identical.

[exFSAE]

Or... they can keep it simple and understand what cornering stiffness is first, as it is a more first order driver of transient vehicle response.

Gets back to not getting lost in the details too quickly.

[SteveOr]

Hey thanks for your answers.
It looks like a lot of work and try to understand the basics. I think i have to work with the RCVD Book and did some calculations which i can compare to what ever.

Is there an other good books out there beside RVD and Tune to win?

I think at moment it is very difficult to get any goal parameters. Because i can calculate lots of parameters but i don´t now if the numbers and data are good or bad. So that is a thing i have to work on. Are there basic Data to compare or any other workaround?

At the moment there lot of input for my head ;-) i have to sort it out, make a little brake to get a clear view on that topics i think

Tank you for your help.

[exFSAE]

Are there other sources to learn about vehicle dynamics? Absolutely. Check out the SAE website and its archive of technical papers. Chances are you'll have too MUCH rather than too little to look through.

Are there a lot of parameters you can calculate? Yes. Can you build your car such that they take just about any value? Yes. But don't let that discourage you!!

As far as I'm concerned, setting up a car is like preparing dinner. Asking what the "optimal setup" is might as well be like asking, "What's the optimal meal?" It varies! Varies by person and by occasion. Do you want something sweet, or sour? Spicy, or mild? Hot, or cold? Light, or heavy? They can all be equally good depending on circumstance.

Anyway, let's circle back to vehicle dynamics. What happens when you're overloaded with variables and parameters? Keep it simple. Pick something and just go with it. Doesn't even matter if it's "right" or "wrong" so long as you have a ballpark starting value.

If you look at any vehicle dynamics text, the fundamentals usually start with some flavor of bicycle model... which we could argue means that things like inertial properties, load distribution and BASIC tire properties (e.g. cornering stiffness) are the most important things to start with. So pick some parameters and go! Maybe a roll stiffness gradient, a static weight distribution, and an understeer gradient. You should be able to find very ballpark values as a rough starting point - see if you can make a car that meets those targets.

From an engineering process perspective, it's important to (a) establish your targets, (b) figure out a way to meet those targets, (c) when complete, verify you achieved those targets. Looking back on my own FSAE team... there was no A -> B -> C process. We weren't engineering, we were just throwing some crap together more or less haphazardly guessing what would be good or bad. It was tinkering. Don't fall into that trap.

In any event if (a) is difficult to completely understand - as we've alluded to it will be indeed - just pick something to start with and move onto (b) and (c). The more you work with this stuff and the more experience you gain, the easier (a) will become and the more honed in your end product will be.

My 2 cents.