ramming the cars involved in accident and stopped on track or lag-related bumps will probably also be treated as big relative speeds. Or else Avoidance Tool woul be very complicated. I think it is the drivers to learn not an automated tool and the judgement is sometimes difficult for human looking at all aspects.

I would say - keep it simple and have PBs and track record as best experience indcators.

Quote from jtw62074 :

Looking forward to seeing your new graphs. I have a question concerning my attachment. The red circles correspond to the highest force possible in pure slip (unless the friction ellipse turns into some kind of off-axis egg shape). It's difficult to tell from the graph, but is any force in the region with the blue circle higher than the red circles? To me it appears to be, but I'm not sure.

I have problems with showing slip angle units because Excel treats them as Series and doesnt want to take the units

The place you showed with blue circle would be for around 6%-8% (I dont have access to this file now hard at work :tilt of Slip Angle. So combined force sums with Fx for 6-8% of SA and Fy for 8-10% SR (where the peak for non-combined Fx is) - as on the lower diagrams. And combined force in fact is higher on the diagram - hence the hump.

Last edited by AndRand, Wed, 7 Apr 2010 10:23.

Quote from jtw62074 :

The pure slip force is the combined force when you're moving directly along one axis with the other axis at 0.

yup, you can see it on the front walls of the diagram.

Quote :

Perhaps you could try doing this with 2 flat curves that do not have any drop off after the peaks and see what the combined slip area looks like. I'm curious if the hump in the middle goes away and the nose-dive at high slip angle and ratio disappear.

You can see on those empirical diagrams that mainly 2 things happen - the curve gest flatter and the available force lowers a bit, but longitudinal stays almost at the steady level for off-grip values.

As far as I experimented with inputs - the more flat characteristics is the more hump gets flattened also. And nose-dive at the edge disappears when the curve doesnt go lower along with increasing the opposite coordinate. I'll post some in the afternoon (GMT+1 ). I also obtained perfect saddle with flat characteristics that lowers along the opposite coordinate.

So far it is all sensible for me - it is perfectly clear why rally drivers on tarmac with very grippy tyres (they have stints around 10 minutes so they dont bother) drift all along at peak values of grip (SA at 3-5deg offset and SR 5-10%).
The more confusing are the characteristics for rain conditions (big threshold and drop off) - combined force shows big valleys of combined drop off and then regain when peak values for one coordinate sums up with off-grip value for another.

Last edited by AndRand, Wed, 7 Apr 2010 09:47.

Quote from bosbrandje :

I'm a hobby programmer; it could be surprisingly simple; cars have a speed vector V , if both vectors are on a collision course which can not be avoided , action can be taken . Of course reality is more complex. The computer can not decide if it is intentional or simply race accident. Therefore one could introduce a crash rating just like safety rating. I have no knowlegde about networking or lag problems so if it's not possible then it's not..
But i don't know if it's needed; I raced demo for a few months and there it was needed but then I upgraded to S2 and the multiclass server I drive is fairly clean. Without much interfere from admins afaik. Because it is in everybody's interest to not cause crashes , and gain points.

you know - BECAUSE it is computer sim I would like it NOT having such Avoidance Tool

Last edited by AndRand, Tue, 6 Apr 2010 21:55.

Quote from jtw62074 :

This is something along the lines of the magnitude of the total force ((Fx * Fx + Fy * Fy)^0.5), right?

If so these are not right:

http://www.lfsforum.net/attach ... d=103471&d=1270423573

If we start at the front corner at 0,0 slip and trace along the left axis, the force rises and somewhat levels off. I assume this is combined force in slip angle, which in this case is simply the lateral force.

Nope... I perceive it is combined force in function of both slip angle and slip ratio.

Quote :

If I'm misunderstanding what was plotted, please explain.

This is http://www.lfsforum.net/attach ... d=103383&d=1270299686 those characteristics (Fy and Fx for slip angle, there is second one for slip ratio) plotted here separatedly and on my diagram combined and plotted on one 3 dimensional plateau. Imagine those diagrams from "Dynamic Tire Friction..." as segment views on that 3d diagrams.

Now I am fiddling this mathematical model and in fact, first I make theoretical changes to see what would be the result and if it is correct with empirical data. I hope you understand that at this stage I dont really care for detailed precisio of the numbers because for me everything is scalable and I am rather experimenting with limits of that Pacejka model.

Pacejka model in fact has 3 tyre physics coefficients: load, load sensitivity, maximum tyre force it can generate. All of other are purely geometrical. And they are of 2 types: base coefficients for polynomial equations (like A = b1*x^3 + b2*x^2 + b3*x) which are then used in trigonometral equations, like Ax*sin(Bx)*atan(Cx). I just put simple "coefficients" there, like (m*x+1)^n, to obtain something similar to "Dynamic Tire Friction.." results because I don't mind (and probably don't have experience with such models) to implement their model which, they say, is completely correct with empirical data. But my purpose was to imagine how do combined force look like with empirical data deployed.

I am quite happy with this modelling and I attached two more examples. I got this first one with characteristics of slick type tyres. Second one is on the other hand very surprising - I called this type of characterisics as "unforgiving" because of steep and high threshold and significant drop afterwards (rain type conditions?). So here you go with those 2 types and segment views of Fx and Fy characteristics in function of opposite input value (SR, SA).


About "Grip Circle": using these kind of characteristics there is no use for Friction Circle term. Why? Combined force is combined force - if you have both forces measured in function of oppsit value you combine two components to get combined force, right? So there is no such thing as Friction Circle - it is just combining data for given Slip Ratio AND Slip Angle.

Last edited by AndRand, Tue, 6 Apr 2010 21:50.

Quote from TypeRacing :

First picture is ruined by that wierd blur imo, without that this picture would be killer

Now I have a hint: don't use big blur - rather use smaller several times

some time ago...

Quote from JBiturbo :

i just wanted to know how's the progress. Should we expect something soon or will we have to wait another year?

I can advise you one thing: click "Search" on coammand tab of this forum, choose advanced, then Scawen in "Search by user name", type Scawen, click "Show results" as posts and find the last post. Add 30 days and do not expect anything before this date - as I know Scawen doesnt post reports any more frequent

Quote from Anthoop :

LFSEI is not linked to the safety rating system, it is simply an indication of your LFS experience. Your LFSEI will increase everytime you drive or make a pb, or try new track/car etc. It is simply reading your LFSW stats.

So I am all for that I thought it was using just igniting yelllow flag warning. So newbies have to learn at least PRO AI level with lower classes to get faster cars, and experienced users dont have to do it all over again. It is just the next (last) race that counts

You are both discussing NON-COMBINED characteristics (these are the differences between slicks, flatrounds and so on): Fx measured with slip angle equalings 0 and Fy measured with slip ratio equaling 0. I used characteristics EMPIRICALLY measured (Dynamic Tire Friction Models f ... nd Lateral Vehicle Motion) for combined situation (the first diagram). The 2 following diagrams are derived per analogy (flattening and lowering the characteristic) for 2 different types of tires.

And there you have significant drop when adding second component and then because of flattened characteristics rise of combined force.

Last edited by AndRand, Mon, 5 Apr 2010 16:53.

I dont hear calls for objection so I think its roughly right Although the last diagram is derived by analogy to dynamic change of characteristics of the previous 2 type.

If I can do it in 1 day so I think anybody can Or I'll charge you with freelance consultant rate of thousand €€ per hour since 2004 or before Damn, I feel like being robbed

Quote from hansonator69 :

See the problem with LFS is that there isn't any real consequence of crashing out.
People need to compromise so they don't f*cking end up in the barrier at the first corner, or at any other corner for that matter.

Really? I found T1 rampage, especially in higher positions (when start grid based on last race results or laptimes), is not that common. Especially after 3rd restart and kicking deliberate crashers problem doesnt show (servers could have a reminder on T1 - piling up makes brake points closer).

So what I found annoying was deliberate crashing out ppl by blockes knowing nothing will happen - not a kick, not a ban.

Quote from franky500 :

Quote :

Maybe safety rating should be more of a deciding factor in LFSEI rather than what place you achieved in races. It might change the way people want to achieve LFSEI because position wont matter as much as safety. This way someone in fifth place could achieve more points than someone in first who had a poor safety rating for that race

This is kind of what i was getting at. As far as i am aware right now a big part in the LFSEI is where you finish in races.

As far as I know LFSEI safety system doesnt like qualifications or time attempts during races... why - a spin or a slide or any other situation frequent on time attemps is regarded as safety issue.

Therefore when not battling for position I would just cruise to get safety points
Showing the issue 'cos IMO replacement for sincere judgement will always lead to some unexpected(?) results

Quote from majod :

no one who causes these crashes won't read this message

I think 5haz addressed this to admins

I am racing at LFS for a quite time, occasionally now, what I can say I wouldn't agree for any requirements (that's why I didnt race at any of insim ladder systems) apart lap time - this is any problem to go on any empty server and get required laptime if you dont have one (I don't on every combo still :tilt

What I can say when I jump on some servers - if ppl knew that admins check reports for wreckage and they ban wreckers, there would be less of them. (admins always can ban someone they dont like so it shouldnt be a question - you cant really do anything about that - you avoid those :rolleyes.

...continuing

If anybody interested I created some diagrams for different characteristics and they look quite interesting. First, I show you how do characteristics look separately - with lines on them you can see section views for both forces. Next are three tyre characteristics with longitudinal constant and lateral changing:

• first for very forgiving tyre (Fy is almost flat when off the limit) - separate forces diagram is from this one,
  
• second is for less forgiving tyre - see how the hill of combined force rises
  
• third is for very unforgiving tyre
  

Last edited by AndRand, Sun, 4 Apr 2010 23:27.

Quote from TuomasH :

Thanks!
-

I think you are eagerly waiting for Revolution Pack

Great pic, I wonder how did you make this motion blur? Do you have such feature with different angles?

ok, so I messed around a bit with Pacejka model to see where to insert some simple proportional/exponential formulas, made two separate diagrams for Fx and Fy and combined them (I wasn't sure though, because the diagrams from "Dynamic Tire Friction..." have one axis titled as vector Fx*Fy but they are plotted separate :shrug.

And there is one thing I wouldn't expect - when you are on peak force non-combined (especially with Fx) and add slip angle the combined force diminish... but there is strange hill like island and even very rough steeps of both Fy and Fx have not much impact on it

Last edited by AndRand, Sun, 4 Apr 2010 15:05.

Quote from jtw62074 :

Adding to what Shotglass said about resultant force: AndRand, perhaps you are referring to the magnitude of the force not changing? This is true enough given the context of the discussion, but I think where there might be some confusion between you and Shotglass is that I think he's referring to how Fx and Fy change as a result of trimming to the circle. When tire modelling the magnitude of the force is important of course, but the direction of that force is even more important. I think that's what Shotglass is probably getting at.

Yup, when trimming the circle, or ellipse, combined force is constant. But, when combined force exceeds the ellipse, it is not "trimmed" on the level of non-combined force. It is trimmed on new characteristics.

btw. about availability of sets of data - the paper I found is a scientific paper. It means it is open for verification, so when someone is interested authors are obliged to share with raw data.

Quote from Shotglass :

are you sure you understand the term combined force correctly? of course you will generate a lateral force but the combined force ie the (vectorial) sum of both wont add up beyond the friction ellipse (or whatever probably not quite so idealised shape it actually is)

Are you sure you understand the components in tyre characteristics? Both Fx and Fy that are used here were measured with other component equal to zero. You try to derive a combined force using non-combined characteristic.

Quote :

the point is what you expect to see when you plot the (absolute) combined force under combined slip conditions is a zero at the origin then some kind of rise up to a more or less circular peak and a more or less flat plateau at around peak height anwhere beyond that
you certainly dont expect to see any zeros in there anywhere else but at the origin

Yes, I agree it isnt simple diminishing one force by another. Thing is more complex, but first I tried to figure out what is wrong with elliptic approach. Yes, the plateu flattens. But it is certainly not happening at the level of Fx max as it is with elliptical approach. I just found that paper on Dynamic Response yesterday and I am to figure out an equation for Pacejka model that will generate Fx in function of Slip Angle according to those diagrams attached (and Fy with slip ratio correspondingly).
Hysteresis on dynamic changes is, I fear, beyond my capabilities

Last edited by AndRand, Sat, 3 Apr 2010 13:06.

Quote from Shotglass :

of course it doesnt change the combined force becasue thats the whole idea of the friction circle
the tyre has some of maximum force generation capability and if youd try to exceed the physics work out in a way that limits the combined force to that maximum of what the tyre can generate

Do you mean that longitudinal force is somewhat "chosen" and it consummes all the friction and when you turn wheel nothing happens - no lateral force is generated because it was taken by the longitudinal (component of, in fact, one force applied to the contact patch)?

Quote from jtw62074 :

Have you heard of "friction circle theory?" If not, try searching for it.

yup, I zeroed values outside ellipse as "unknown"

Quote :

All sorts of approaches have been tried successfully to do this and it's an area of constant research. Even artificial neural networks have been done for this. Can you imagine that? Artificial intelligence tire models? (Granted, for that to work, you need seriously large and complete tire data sets that you won't ever find).

I guess this is evolutionary approach for solving equations - in theory simple: you get a set (resource) of basic equations with parameters and with evolutionary method leave those giving closest result and by couple of generations get better and better approximation

Quote :

So you have a class of tire models like Pacejka's (pronounced "Puh ZHay Ka" by engineers in case anyone's curious)

I am from eastern Europe - although Pacejka is Dutch the name sounds like Czech

Quote :

If you are a chassis engineer at Ford or something and have tire data where they measured all these combined slip maps and so on, you can tune Pacejka's MM and other empirical models to work just fine and dandy because you've got the real test data to look at.

This is one reason why I abandoned empirical approaches and came up with something physically based. It's not that Pacejka's MM is "bad" at all. It's just that as a sim developer, I don't have a single complete set of data like this for any single tire. Can you imagine poor Scawen trying to tune by complete guesswork something like this for multitudes of different tires all tuned to the bazillions of cars available in LFS? Yikes....

Does it require tons of sets data or just examples on several types? Because many surveys on many types of tyres are made as university science - therefore they are open and available.

And here very interesting paper on Dynamic Tire Friction Models f ... nd Lateral Vehicle Motion - with results from empirical surveys on hysteresis when changing both angle slip and ratio and with differences on steady and dynamic changes.
Of course I read only Conclusions (and chapter DYNAMIC RESPONSE OF THE MODEL )

Last edited by AndRand, Fri, 2 Apr 2010 22:20.

Quote from Shotglass :

the crude and not quite correct (but it should give you reasonably correct tyre behaviour) method would be to take the direction you get from Fy and Fx2 as the direction of the combined force vector but reduce the length of it so it ends up on the ellipse
so the resulting force would be the red vector

But when you add slip you go over the top so the tire characteristics is completely different - it is not symmetrical.

And notice that when you are on longitunal peak you can add as much slip angle as you want - it doesnt change you F combined at all anywhere. This is a better case - as with max lateral force you can obtain overall bigger vector if longitidunal peak is much bigger. Although it is just the same contact patch.

For now I found summary of the empirical survey: http://www.iabg.de/presse/aktu ... _parametrisation_iabg.pdf
Plus one one rain conditions http://www.me.berkeley.edu/~ho ... s_Tire_friction_ACC01.pdf

Last edited by AndRand, Fri, 2 Apr 2010 20:52.

Quote from Shotglass :

no you wont
you might lose some amount of lateral force to longitudinal force but the overall combined force will if anything increase and most certainly it wont drop to 0

Yup, I agree - the idea that one force is diminished by the other is wrong. Although for now I do not have a slightest idea for that situation:

Imagine you have constant slip ratio giving you Fy force lateral, your slip ratio gives Fx1 longitunal, when combined - on the limit (the box shows maximum forces and ellipse as combined). What happens when you add slip ratio so your vector goes out of ellipse?

BTW: I have to excuse Mr. Pacejka I only used his tyre model not "magic formula". The example is with elliptic approach - as soon as I get "magic formula" don't worry, I'll post it

Quote from jtw62074 :

You ought to be thinking more along the lines of Pythagoras, probably. I'm curious how and why you came up with that formula though.

I assumed that the first is diminished by the second (maximum force available for one component)
sqrt((Fx-Fy)^2+(Fy-Fx)^2)...

Quote :

If Fx and Fy are equal to or multiples of each other, then F=0. There isn't going to be a non-zero combination of slip angle and slip ratio that results in 0 force of course. See the valleys in the graphs that are at 0 force? That's probably why.

And it makes sense (maybe with some scaling not to go beneath any force available at that moment) - if you have slip angle getting the highest force and you add longitunal slip you will loose grip very quickly. And with "magic formula" when you are on lateral peak force adding slip ratio to peak longitunal will result with bigger force overall

edit: I suspect there is something very subtle going on and it doesn look like "magic formula". For now I got the ellipse and zeroed everything around it (attachment)

Todd, correct if I am wrong - I was curious about these Pacejkas formulas, that's why I posted them and it looked to me that they are strictly geometrical just to fit the empirical data. Therefore coefficients are also strictly geometrical, not derived from friction theory and that's why friction-related coefficients are like: D+Sv (maximum force).
So when they dont fit the data, some "magic" is needed More complex equation to fit the data... so the thing is: to fit diagram to empirical data, right? So the empirical data for both slip ratio and slip angle changing are crucial...

Last edited by AndRand, Fri, 2 Apr 2010 12:17.

I just wanted to see what this "magic formula" by Pacejka is all about.

So I incorporated Pacejkas tyre characteristics and combined F vector once with this formula, second time with reduction of vector equation I used: modulo(Fx-Fy)*sqrt(2)

I must say... quite different