Pacejka - combined forces computaion

Hi I implement simulation ( used in game like environment but for other than game experiance purposes - mainly for research studies in perception ( but driving is essential) where I use combined lateral and longitudal forces using approach described at Tyre and Vehicle Dynamics by Hans Pacejka Chapter 4 I have implemented non - related force computations and this worked fine .. but moving one step forward.... I got to the point on page 189 where the formulas for term Eyk reads Eyk=rEy1+rEy2*dfz (4.E64) and for term Exa reads Exa=rEx1+rEx2*dfz (4.E56) but though other coeffs for all formulas used befire are provided as sample data on page 614 in appendix 3 the values for these coeffs rEy1,rEy2,rEx1,rEx2 are not provided :( as seems it is not matter of great importance... but I wonder is it possible to use coeffs pEy1, pEey2 (4.E24) pEx1,pEx2 (4.E14) page187 ( or maybe though the coeffs are somewhat realted they have essentially different in their numerical values?) Maybe there is a place to ask for book errata. as seems these coeffs are ommitied unintentinally? there are other minor issues ( unused expressions etc..) so maybe Prof. Pacejka has a support page where additions to his work could be found? or for ex there are number of works on the net using his previous formulas... are their newer publications whihc migh shed light on these coeffs? it is just really good to try his apporoach for simulationg dynamics.... but this is a sort of - there is almost all to move with it.. except some minor ommitions :) Regards Serge

You might want to try Ruud Van Gaal's computation of Pacejka to see how Racer (www.racer.nl) does it, the source code is freely available there, and it uses Pacejka, I believe he has written a Pacejka class. I'm afraid although I have used G. Genta's book on Motor Vehicle Dynamics which covers some of Pacejka, I am not familiar with Pacejka's books, or the coefficients offhand. "Serge Kourdakov" <[email hidden]> wrote in message news:[email hidden]...

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> Hi > > I implement simulation ( used in game like environment but for other than > game experiance purposes - mainly for research studies in perception ( but > driving is essential) where I use combined lateral and longitudal forces > using approach described at Tyre and Vehicle Dynamics by Hans Pacejka > Chapter 4 > > I have implemented non - related force computations and this worked fine

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> but moving one step forward.... > I got to the point on page 189 > > where the formulas for term Eyk reads > > Eyk=rEy1+rEy2*dfz (4.E64) > > and for term Exa reads > > Exa=rEx1+rEx2*dfz (4.E56) > > but though other coeffs for all formulas used befire are provided as

sample > data on page 614 in appendix 3 the values for these coeffs > rEy1,rEy2,rEx1,rEx2 are not provided :( > > as seems it is not matter of great importance... but > I wonder is it possible to use coeffs pEy1, pEey2 (4.E24) pEx1,pEx2(4.E14)

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> page187 ( or maybe though the coeffs are somewhat realted they have > essentially different in their numerical values?) > > Maybe there is a place to ask for book errata. as seems these coeffs are > ommitied unintentinally? > > there are other minor issues ( unused expressions etc..) so maybe > Prof. Pacejka has a support page where additions to his work could be > found? > > or for ex there are number of works on the net using his previous > formulas... are their newer publications whihc migh shed light on these > coeffs? > > it is just really good to try his apporoach for simulationg dynamics.... > but this is a sort of > - there is almost all to move with it.. except some minor ommitions :) > > Regards > Serge

"Alex Smith"

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>wrote in message news:<bkqfan$ev6$[email hidden]>... > You might want to try Ruud Van Gaal's computation of Pacejka to see how > Racer (www.racer.nl) does it, the source code is freely available there, and > it uses Pacejka, I believe he has written a Pacejka class. I'm afraid > although I have used G. Genta's book on Motor Vehicle Dynamics which covers > some of Pacejka, I am not familiar with Pacejka's books, or the coefficients > offhand.

Thanks Ruud really made a great work of popularization of Pacejka approach. There are several Pacejka formulas each is an improvement of previous. Ruud uses older approach that described in new book. for my purposes older Pacejka formulas are not sufficient ( or gives some head ache.. while newer approach solves these my probs quite elegantly) so thanks for your hint I would rather think on coeefs ( as they have meaning ( they affect on some properties of friction circle ( as all the story about combined forces))and it is possible to draw friction circles and see how coeffs change the shape of the circle ) so eventually just a bit of my efforts :) Thanks once again Regards Serge

On 24 Sep 2003 01:30:09 -0700, [email hidden] (Serge Kourdakov) wrote:

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>"Alex Smith" >>wrote in message news:<bkqfan$ev6$[email hidden]>... >> You might want to try Ruud Van Gaal's computation of Pacejka to see how >> Racer (www.racer.nl) does it, the source code is freely available there, and >> it uses Pacejka, I believe he has written a Pacejka class. I'm afraid >> although I have used G. Genta's book on Motor Vehicle Dynamics which covers >> some of Pacejka, I am not familiar with Pacejka's books, or the coefficients >> offhand. > >Thanks Ruud really made a great work of popularization of Pacejka >approach.

Hehe, nice to hear, although I don't know if I can be credited for that. :) >There are several Pacejka formulas each is an improvement of previous. >Ruud uses older approach that described in new book. >for my purposes older Pacejka formulas are not sufficient ( or gives >some head ache.. while newer approach solves these my probs quite >elegantly) What problems do the new Pacejka formulae solve? Combined Fx/Fy forces? >so thanks for your hint I would rather think on coeefs ( as they have >meaning ( they affect on some properties of friction circle ( as all >the story about combined forces))and it is possible to draw friction >circles and see how coeffs change the shape of the circle ) so >eventually just a bit of my efforts :) The problem is always the coefficients. I might move to a later MF version (MF=Magic Formula), but only when I know how to translate the older versions into the newer. I have done combined Fx/Fy a la Gregor Veble/Brian Beckman, which is a friction circle approach. There are professional tools to create Pacejka coefficients from experimental data, but then you get very deep in all this stuff (most is proprietary). I'm not so sure I even *want* extra coefficients. ;-) I haven't read the Pacejka book yet, so I don't know any nice example values. Mostly starting out with id values (so that nothing really happens) may be the best way to avoid getting too much into the dark. Ofcourse, then you don't really use the formula to its full potential, but on the other hand, for a convincing MF you don't really need it all. A normalized approach (Ch. 14 in RCVD I think, just dividing Fx, Fy by Fz and using that as a base curve) does nicely as well, and a modification of the forces by rational reasoning works ok quickly. With normalization it is only the general notion of 'less tire pressure gives grip increase/decrease in such a curve' is important. And it gives you something to tweak bit by bit, and improve by itself. I think the MF is actually a bit too complex (the tan etc); a base curve would do, with modifiers that all add up, but in a more direct & independent way. Ruud van Gaal Free car sim: http://www.racer.nl/ Pencil art : http://www.marketgraph.nl/gallery/

(Ruud van Gaal) wrote in message news:<[email hidden]>... > What problems do the new Pacejka formulae solve? Combined Fx/Fy > forces? first for me it is important that now friction coeffs are easier to add ... so they have meaning in the new MF ( not like the older approach some coeffs which are looking- like -friction coeff :) ) also it is possible to try more different properties of tire such as effect of turn slip etc .. also seems that camber is now better suits for real time sims ( as now it is included in form of sin .... though not sure ( as currently I omit camber) but seems there suold be less probs....) >(Ch. 14 in RCVD I think, just dividing Fx, > Fy by Fz and using that as a base curve) does nicely as well, and a > modification of the forces by rational reasoning works ok quickly. maybe the problem was my coding :) ( the way I coded approach ) but I did not like the result.... ( just personal :) ) also see some benefits of using newer MF for me this is more important argument - to have "all in one" rather than have something which is fixed here and there to implement the same..... > The problem is always the coefficients. I might move to a later MF > version (MF=Magic Formula), but only when I know how to translate the > older versions into the newer. I have seen papers on genetical algorithms to find fit curves for data. actually for my eyes not too difficult to implement.... ex http://archimedes.ing.unibs.it/papers/documenti/ISATA-genet-02.pdf it also states the approach is OK for newer MF....( also some hints how to get coeffs from experimental data is included at the end of Pacejka book) some day when I'm OK with free time I will code a genetic algo approach.. but so far I use example data .... currently it is OK for me... and as new Pacejak is scalable ( using scale coeffs) I just do that if I need some different properties of tire.... Regards Serge