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How complicated can a tire model become
(143 posts, started )
#1 - Be2K
How complicated can a tire model become
Quote :The snap oversteer is inherent with a steady state tire model. It underestimates grip during dynamic transition in a corner. GPL had it. rF1 had it. iR OTM has it peek through their patch-ups from time to time. Even nKp used to have it. The dynamic tire models tend to not have it, such as LFS, VGP3, and maybe rF2. B

So everybody and their mother using a steady state model has to find ways to patch it up. How I did it with rF1, given that all I had was the parameters they expose in their tbc files, was to exaggerate pneumatic trail....dramatically. Like an order of magnitude dramatically.

I do not recommend we do that, since that has side effects (thick feel and some understeer on turn in) that I do not like. However, it is a clue, since now I have access to the code itself, to a path we might try. That is why I keep coming back to Mz (which for your model is basically directly related to pneumatic trail) as A) first something we need to feed back up into the car physics, which we are currently ignoring except for FFB and B) maybe get clever with Mz to smooth over the grip underestimation on transition.

However, the eventual 'right' answer is to not use a steady state model at all. The model I am working on is fully dynamic, and does not have this inherent underestimation problem. Attached is a quick little example demonstrating why...this is a quick little jolt in alpha.

In the shorter term this indicates that maybe there is a heuristic we can use on the steady state brush to lag and smooth grip buildup and release...which we can use the offline (which is not yet officially plugged into Aries) dynamic model to calibrate some initial parameters for.

This is what actually happen in pCars. But a complete Dev. Team is developing a hole new Tire Model since 2012 and they aren't nearly done with it. I don't understand anything on that but i have a lot of respect for the people which doing this things as a full time job. So since i've access to the pCar Alpha (around early 2012) i read many about the physics development and the progress on every tire model for every Car in pCars its crazy what these Group of Devs are mainly programming.
Anyway what i like to introduce is, that i've compare every new SIM with LFS and what Scawen must do too on his side of learning and try & error coding

If he could handle this then LFS S3 is a blast like a Timewarp for LFS
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Nice post and probably first in a long time where Scawen actually gets some credit..
I didn't think that the LFS tyre model was dynamic (at least, the version currently released to the public). Though I could be mistaken.
#4 - Be2K
Quote from Bob Smith :I didn't think that the LFS tyre model was dynamic (at least, the version currently released to the public). Though I could be mistaken.

Quote :The dynamic tire models tend to not have it, such as LFS...

We dont know it exactly. But maybe LFS tyre mode is dynamic, because u can see the deformation when the car is accelerating
didnt understand half of this but good to know :]
Quote from shimon-ifraimov :didnt understand half of this but good to know :]

Yeah... that....
Any how.... How much harder would it be to model spoked rims? I only ask that because I read somewhere that one of the reasons they quit using spokes in race cars and started using more solid rims was because of the deformity and lack of stability that occurred at high speeds and eventually the spokes coming loose.
Could you imagine how much of a pain it would be to model THAT?
#7 - Be2K
I'd like to hear some thoughts from Scawen and his opinions about the progress he made.

And maybe a simple yes or no if we can hope for something released this year or not.
It's done when it's done.

Like everything else, patience is key, now end the fuzz about this already.
Quote from Dennis93 :It's done when it's done.

Like everything else, patience is key, now end the fuzz about this already.

Wouldn't want to interrupt you Dennis, but what if people just want to talk about tyre models? If they want to talk about it, let them.
#10 - Be2K
Quote from Dennis93 :It's done when it's done.

Like everything else, patience is key, now end the fuzz about this already.

you know.. its their private project and it could be over in no time if thei dont have any motiviation to go on and we're still waiting till 2020 and nothing happen and then he poped in and say "hey i am out long time ago, just let you know".

Sure he intimated he had some demotivation on his project but he will go on.

So to give him some help it could be usefull to talk about some problems he cant get rid of
Quote from Be2K :you know.. its their private project and it could be over in no time if thei dont have any motiviation to go on and we're still waiting till 2020 and nothing happen and then he poped in and say "hey i am out long time ago, just let you know".

Sure he intimated he had some demotivation on his project but he will go on.

So to give him some help it could be usefull to talk about some problems he cant get rid of

It's been explained dozens of times and quite obviously, if it's taken 5 years +, It's not a simple one.
#13 - Be2K
Quote from Dennis93 :It's been explained dozens of times and quite obviously, if it's taken 5 years +, It's not a simple one.

Then what the problems are ??
Quote from Be2K :Then what the problems are ??

It's far more complicated than what they originally thought, and thus it could have bugs I.E a fully inflated tyres increases the grip level by 1003%, instead of a realistic tyre pressure which would have more grip.

I'd rather wait in interest and be amazed of how the tyre works, instead of thinking of what could be wrong, because nothing I would or have said would ever change the final decision is.

The problem could be a good few pages of A4 papers worth, and frankly I don't worry too much about it, I've been in LFS long enough to trust that things get done, the right way, waits can be longer, but the final product is so much greater than expected, always.

Don't get me wrong, I hope the absolute best for LFS, As it's been in my life, half the time of it so I wouldn't like if it disappeared.
Quote from MoMo92i :Enjoy :

That model developed by Michelin looks awesome : http://www.ipg.de/index.php?id=tametire&L=2

But price is also awesome...

Nice read!
However it does not seem to be able to do real time calculations, from my browsing.
That is if I remember correctly where Scawen got stuck: he was first to create a mathematical "testing bench", that could not work real time due to the complexity of the simulation.
From there he would simplify the system to allow real-time calculation, while keeping it close to his "bench" results.
No idea where he is at the moment, but his last post on this topic did show meshes and tire flex from his "bench":

https://www.lfsforum.net/showt ... php?p=1667805#post1667805
hum some beta tester spotted here.
#17 - Be2K
Quote from Mille Sabords :.
From there he would simplify the system to allow real-time calculation, while keeping it close to his "bench" results.
No idea where he is at the moment, but his last post on this topic did show meshes and tire flex from his "bench":

ah okay. Didnt know that. Its so dificult because the real-time calculation need much more calculations in place than the old one ?
Quote from Mille Sabords :Nice read!
However it does not seem to be able to do real time calculations, from my browsing.
That is if I remember correctly where Scawen got stuck: he was first to create a mathematical "testing bench", that could not work real time due to the complexity of the simulation.
From there he would simplify the system to allow real-time calculation, while keeping it close to his "bench" results.
No idea where he is at the moment, but his last post on this topic did show meshes and tire flex from his "bench":

https://www.lfsforum.net/showt ... php?p=1667805#post1667805

I was thinking, would it be possible to make those original complicated calculations calculated by GPU.
This way it should be way faster than processor.
That video game is making the pacejka model working in real time without any problem into several professional driver in the loop simulator. Those simulator aren't using awesome computer btw. Anyway pacejka magic formula are right only for a defined temperature/pressure which is an important limitation.
Quote from MoMo92i :Anyway pacejka magic formula are right only for a defined temperature/pressure which is an important limitation.

Not only this, but for a defined range of loads and camber angles as well. Either clamps or changes to the curves are needed to handle extremes in both directions.

It's not difficult to extend the Pacejka model to consider pressure and temperature. I modify stiffness with pressure, and friction with both pressure and temperature. Of course there is no exact data to do this, but you can invent data that, for a given formulae, gives sensible results. This is usually enough accuracy for a racing sim.
Quote from Bob Smith :...snip...This is usually enough accuracy for a racing sim.

But apparently not for Scawen
Quote from Be2K :ah okay. Didnt know that. Its so dificult because the real-time calculation need much more calculations in place than the old one ?

the problem is to generate a good enough approximation to the "bench" result in real-time.

the "bench" can take as long as necessary to tell you the grip given many parameters, load, temperature, wear, surface, etc. what Scawen is trying to do is generate a real-time approximation using all those same parameters.

the reason all this takes so long is called non-linear dynamics. human math so far (yes as compared to say donkey math.. which iRacing must be using? ) has historically focused on linearisation. mathematicians and scientists are always trying to limit the number of variables in their formulae so they can linearise the result, that is to create a linear function.

linear functions are great because your computer can give you the answer instantly for a given parameter.

non-linear dynamics, informally "chaos", is a branch of math that hasn't got much attention because -- get this -- it's too hard. want to calculate the rate of flow of water in a pipe? no problem, here is a linear (or close) function for that. take a derivative or two and away you go. want to calculate the rate of flow of water in a river as the bank goes from muddy to sandy and the size of rocks on the river bottom changes, also as the temperature of the water changes? no serious function for this exists because the problem is non-linear. there are too many variables for mathematicians to come up with a "useful" formula.

Scawen has decided to add input parameters to his tyre model. he wants to please us and since we don't like the massive gaping flaws in the LFS model (hihihi) he wants the next one to instantly give you about the same answer as his new bench.

the problem is when you switch from say 2 input parameters to 3, the problem is not 1.5 times harder to calculate. to give you an idea, there is NO function to describe the eventual position of as few as 3 celestial bodies interacting in space, even given full initial conditions. we are able to make good functions to tell you their new position after x time, but only for a small x.

so Scawen is trying to come up with a solution to a problem with basically no supporting research being published in the entire math community. no one wants to touch non-linear dynamics because it is too much to wrap your head around. no company wants to invest because they have no guarantee their math worker will come up with anything. Scawen has decided to brave the risk of coming up with nothing and launched on this journey for the holy grail: a real-time (read approaching linear) function for a non-linear problem.

in 100 or 1000 years this should be no problem. Einstein was right, there is a fundamental relation between all forces and as a corollary there is an elegant way to describe the result of SOME aspects of non-linear systems under SOME conditions, enough for an application like the next LFS tyre model to succeed. it's the equivalent of plotting the eventual path of the eye of a hurricane given all the surrounding wind speeds, air temperatures, **relative humidities of the air masses, very important**, ground effects on nearby air temperatures, position of the sun as time goes on, etc. the trick is in reducing these incalculable bodies to points with minimal additional descriptive parameters, and making these bodies appear and disappear over time as their influence becomes more and less important to the result, IN THE CONTEXT of the result you are after.

he could be working on this for the rest of his life if he choses, because even the next LFS tyre model could be improved

anyway, i'm glad he decided to start on this quest and i'll be thrilled to try any result he comes up with, given the quality of what has been accomplished so far.

accomplished. just wanted to repeat that word since some ingrates seem to always forget that.


edit: humidities of the air masses should never have slipped my mind when making that list!!!
Quote from CarlLefrancois :the problem is to generate a good enough approximation to the "bench" result in real-time.

the "bench" can take as long as necessary to tell you the grip given many parameters, load, temperature, wear, surface, etc. what Scawen is trying to do is generate a real-time approximation using all those same parameters.....

CarlLefrancois, my respect for describing so clearly human race limitations. Also, scaling using more human resources is not linear. Communication is a bottleneck. May be the solution is the forecasts of Ray Kurzweil like The Law of Accelerating Returns etc. Or artificial intellicgence.

Any way, just congratulations...
Nicely put, Carl.
#25 - Be2K
nice explanation ! and could be there any possible help for him ? Or is he all up on his own?

How complicated can a tire model become
(143 posts, started )
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