Car physics; Pacejka and friction coefficients

Hi there, I'm trying to deal with sliding in my sim at this moment. For skid sounds, it seems looking at slip angles and slip ratios getting large are a nice way to go. For sliding, I'm not too sure. I use Pacejka to get long/lat forces based on slipRatio/Angle/normal force and camber (camber is still 0 at the moment). So I get an Fx (longitudinal) and Fy. For sliding, I should check if the resultant force (Fx+Fy) doesn't exceed the maximum force of the tire. ( |Fx+Fy|<=maxForce ) However, how do I extract a friction coefficient (or similar, the maximum total tire force) for a given situation? Could the Pacejka constants help here? I think so, since the peak of the Fx force for a given set of Pacejka input parameters will be the maximum force that the tire can generate. However, this means I would have to search for the optimal slipRatio (which delivers the highest Fx), which delivers the highest output. Or perhaps, it's just D+Sv, because the formula is like D*sin(...)+Sv (or was it Sh, haven't got the book at hand right now). Second, an effect that I'm still missing is the car switching ends when flooring the throttle from a standstill. Given a large wheel spin velocity, at the rear, the car won't move forward quickly, because of the reduced Fx force. However, since slipAngle is calculated as the ratio of longitudinal and lateral wheel speed (wrt the road), the slipAngle builds up as the car wants to drift left or right, I just get a Pacejka Fy which stabilizes the car in yaw. So, where do I go wrong? It seems that because of the large spinning velocity the lateral friction coefficient becomes almost 0 (like with a motor where you can let the rear wheel drift along the track, keeping the front wheel locked on the tarmac). Thanks for any ideas, Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

Hi Ruud, I do skid sounds by checking for the size of the slip vector (ratio and angle combined), and slightly below the optimal value I turn the volume up to full when past the optimum, and then also change the pitch when the value of the slip vector increases. About Pacejka, I have absolutely no experience with that, but it seems to be you are using the lateral and longitudinal forces separately based on slip angle and ratio. For illustration, as an approximation (which I still use :) ) you can combine them in a slip vector, calculate the force that corespods to the magnitude of this slip vector, and point it in the opposite direction to it. The (complete, if such a thing exists) Pacejka formula should do something similar and enable you to plug in both the ratio and angle values simultaneously and getting both the lateral and longitudinal forces from that. The calculations should not be done independently for both axes. You really don't need to perform any special sliding checks if this is done correctly. This will also take care of the twitching problem, by the way. -Gregor Ruud van Gaal wrote:

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> > Hi there, > > I'm trying to deal with sliding in my sim at this moment. > For skid sounds, it seems looking at slip angles and slip ratios > getting large are a nice way to go. > For sliding, I'm not too sure. I use Pacejka to get long/lat forces > based on slipRatio/Angle/normal force and camber (camber is still 0 at > the moment). > So I get an Fx (longitudinal) and Fy. For sliding, I should check if > the resultant force (Fx+Fy) doesn't exceed the maximum force of the > tire. ( |Fx+Fy|<=maxForce ) > However, how do I extract a friction coefficient (or similar, the > maximum total tire force) for a given situation? Could the Pacejka > constants help here? I think so, since the peak of the Fx force for a > given set of Pacejka input parameters will be the maximum force that > the tire can generate. However, this means I would have to search for > the optimal slipRatio (which delivers the highest Fx), which delivers > the highest output. > Or perhaps, it's just D+Sv, because the formula is like D*sin(...)+Sv > (or was it Sh, haven't got the book at hand right now). > > Second, an effect that I'm still missing is the car switching ends > when flooring the throttle from a standstill. Given a large wheel spin > velocity, at the rear, the car won't move forward quickly, because of > the reduced Fx force. However, since slipAngle is calculated as the > ratio of longitudinal and lateral wheel speed (wrt the road), the > slipAngle builds up as the car wants to drift left or right, I just > get a Pacejka Fy which stabilizes the car in yaw. > So, where do I go wrong? It seems that because of the large spinning > velocity the lateral friction coefficient becomes almost 0 (like with > a motor where you can let the rear wheel drift along the track, > keeping the front wheel locked on the tarmac). > > Thanks for any ideas, > > Ruud van Gaal, GPL Rank +53.25 > Pencil art : http://www.marketgraph.nl/gallery/ > Free car sim : http://www.marketgraph.nl/gallery/racer/

On Fri, 06 Apr 2001 14:36:32 +0200, Gregor Veble <[email hidden]> wrote: >I do skid sounds by checking for the size of the slip vector (ratio and >angle combined), and slightly below the optimal value I turn the volume >up to full when past the optimum, and then also change the pitch when >the value of the slip vector increases. I wondered about that, if pitch increases. It seems though you only do it slightly, couldn't hear much variation from a testrun with your SimEngine. I now use the slipvector for lateral skid sounds, and the slip ratio to detected skidding in the long. direction. Somehow I think the two sounds sound different (because of other spring rates long vs lat), but it will do for now. >About Pacejka, I have absolutely no experience with that, but it seems >to be you are using the lateral and longitudinal forces separately based >on slip angle and ratio. For illustration, as an approximation (which I >still use :) ) you can combine them in a slip vector, calculate the >force that corespods to the magnitude of this slip vector, and point it >in the opposite direction to it. I used the slipvector in v0.1 (not to be funny, lol), and it worked great for lowspeed; no low-speed instability whatsoever. Perhaps it's something useful after all when doing lowspeed. :) Got the idea from RARS, which targets more to robot simulation actually. I can't really point it in the opposite direction, because I take the resultant force vector as the sum of the lateral and longitudinal force. I will try capping it (am now only reducing the lateral force if the longitudinal force gets large, so this changes the direction of the force, which doesn't feel right intuitively). Pacejka indeed inputs: SR, SA, camber and Fz. From that you get Fx, and Fy (and Mz) from 3 separate formulae. I don't have the book from Genta here, so I can't check whether the lateral force looks at the slip ratio. In my carsim, it doesn't seem to do so though. I'll check it out when I get home. (first have to get v0.4.1 going tonight)

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>The (complete, if such a thing exists) Pacejka formula should do >something similar and enable you to plug in both the ratio and angle >values simultaneously and getting both the lateral and longitudinal >forces from that. The calculations should not be done independently for >both axes. You really don't need to perform any special sliding checks >if this is done correctly. This will also take care of the twitching >problem, by the way.

You would think so, yes, but it doesn't seem to. Likewise, for wheel locking, I have to interpolate the total force vector to move to -slipVector as the locking becomes greater (SR nearing -1 or worse). The twitching is almost gone by the way, and thanks for your replies! I got it working in the end because of a stupid bug where I used the suspension force on the wheel as a normal force, instead of taking the REAL road force up (which is tireRate*(ySurface-yContactPath) in my sim). Having fixed that, suddenly it all started working, although with a damping coefficient of ~30, really magical values here. ;-) I suspect Pacejka doesn't handle fast-spinning wheels correctly for calculating Fy (lateral force). The tire will go stiff and the lateral spring effect would reduce greatly, if I picture it. Perhaps that should be reflected in the Pacejka constants (where at a certain point you have BCD which is the cornerning stiffness; I use that in the SAE950311 damping method, just like BCD for longitudinal stiffness). I'll go read some more RCVD 'Simultaneous longitudinal and lateral forces' to see what it says. v0.4.1 btw displays lateral and longitudinal forces (and SA/SR for each wheel) so it might be interesting to watch. I'll tweak my force capping algorithm just a little more now. Thanks, Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

Ruud, What you ideally need is the 'combined slip' Pacejka formula. This deals with the interactions between long and lat slip. It is based on the seperate formulae for 'pure' lat and 'pure' long slip, but then applies a new additional calculation to give the 'combined slip' Fx and Fy. This is what I use in my simulation work within my PhD. I have the documentation if you're desperate. Cheers, Neil

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> > >The (complete, if such a thing exists) Pacejka formula should do > >something similar and enable you to plug in both the ratio and angle > >values simultaneously and getting both the lateral and longitudinal > >forces from that. The calculations should not be done independently for > >both axes. You really don't need to perform any special sliding checks > >if this is done correctly. This will also take care of the twitching > >problem, by the way.

Neil, I'm also interested in the documentation you're talking about. Most of all I'm interested in Pacejka Coefficients for different kind of tires if you have some. I hope you can help me. Best regards, Ernesto Fina Neil Everett wrote:

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> Ruud, > > What you ideally need is the 'combined slip' Pacejka formula. This deals > with the interactions between long and lat slip. It is based on the > seperate formulae for 'pure' lat and 'pure' long slip, but then applies a > new additional calculation to give the 'combined slip' Fx and Fy. This is > what I use in my simulation work within my PhD. I have the documentation if > you're desperate. > > Cheers, > > Neil > > > > > >The (complete, if such a thing exists) Pacejka formula should do > > >something similar and enable you to plug in both the ratio and angle > > >values simultaneously and getting both the lateral and longitudinal > > >forces from that. The calculations should not be done independently for > > >both axes. You really don't need to perform any special sliding checks > > >if this is done correctly. This will also take care of the twitching > > >problem, by the way.

On Sat, 7 Apr 2001 08:17:01 +0100, "Neil Everett" <[email hidden]> wrote:

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>Ruud, > >What you ideally need is the 'combined slip' Pacejka formula. This deals >with the interactions between long and lat slip. It is based on the >seperate formulae for 'pure' lat and 'pure' long slip, but then applies a >new additional calculation to give the 'combined slip' Fx and Fy. This is >what I use in my simulation work within my PhD. I have the documentation if >you're desperate.

Believe it, I'm desperate! :) But really, I've bought an entire book for the Pacejka formula (G. Genta's Modeling and Simulation), and it only contains the separate formulae and an approach to combine them, but I'm having trouble with the lateral force being allowed to keep big when the rears are spinning. Example (going the Genta route): - I calculate Fx and Fy separately - I use the elliptical approach to hold down Fy, this is done by: Fy=Fy0*sqrt(1-(Fx/Fx0)^2) Where: - Fy is the lateral force we want to know - Fy0 is the lateral force as calculated by Pacejka Fy=... - Fx is the calculated long. force (Pacejka separate) - Fx0 is the MAXIMUM long force (calculated from the Pacejka separate formula as D+Sv) - I stamp on the throttle, slipRatio goes up to say 2 or 3 - Fx at the rear becomes 1400, from a maximum (at optimal slip) of 2700 (at say, slipRatio=0.3). - Fy is about 2000 (Pacejka Fy) - Fy is reduced to not exceed a total force length of 2700. As Fx is about half of it's maximum peak, the lateral force is allowed to grow a lot. Here's what I don't believe; when spinning, the method above keeps the friction circle (or ellipse height/width, but let's stick to circles for now) constant (because it takes Fx0 as the maximum force the tire could ever generate). However, I known from doing donuts with GPL for example, that when spinning the wheels, the friction coefficient goes down considerably. So a car with spinning rear wheels and braked fronts can be pushed even by someone and it will start rotating. This is nowhere reflected in the calculations. So the problem then becomes, how to calculate the maximum friction coefficient, based not only on load and a generic track coefficient (1.7 for example), but also on slip ratio? Or heat, although I don't think that heat is the thing here that makes things slippery (at the start). Thanks for the help, Neil, I'd love to take a look at your simulation work, and how you take on combined Pacejka. Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

On Sat, 07 Apr 2001 13:12:05 +0200, ernesto fina <[email hidden]> wrote: >Neil, > >I'm also interested in the documentation you're talking about. Most of >all I'm >interested in Pacejka Coefficients for different kind of tires if you >have some. It seems these coefficients are often copyrighted or something. Not really good for what's called a standard. :) But well, I'm have low-priority plans on a Pacejka editor where you can tweak the constant and see what it does (and hopefully mimic known curves). Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

The lateral capability of the tire is reduced considerably as the tire spins, as is discussed in this thread. One source of a lateral dispersion for some suspensions is asymetry in the rear tire normal forces caused by the driving torque. The engine torque is converted to driving torque (turned 90 degrees) at the wheels, and this torque on the driveshaft is reacted laterally partly in the front and part in the rear suspension. To summarize: One rear tire sees a higher normal force than the other. For a locked differential, with the tires both rotating at the same slip ratio, it's easy to see that the tire with the larger normal force will have a larger forward force and this difference in forward force between the two rear tires creates a yaw torque. Combined with the reduced lateral force capability of the spinning tires (that can make the car unstable), this yaw torque can start the car around. - Matt

Check out Millikin & Millikin's Race Car Vehicle Dynamics, chapter on tire data non-dimensionalization... this lists formulas for combining slip angle, slip ratio, and camber into one unified slip variable, giving you all those "friction circle" behaviors you're wanting... they've also go a number of datasets for various types of tires scattered throughout the book. Make sure you get the load sensitivity curves for your friction and cornering/camber stiffness, otherwise your roll stiffness adjustments won't produce the correct understeer/oversteer effects. (The formulas make "mu" and "C" look like constants, when in fact they're functions of normal force/load--this lead me astray the first time I tried to use them!) If you've got the rotational inertia of the wheels/drivetrain modeled, once you plug these guys in, you'll be able to replicate just about any vehicle behavior you can think of (donuts, brake-lockup understeer, trailing throttle oversteer, etc) Once you get to this point, you can get pretty far in modeling different types of tires just by tweaking the "C" and "mu" curves, without (at first) having to mess with the "magic numbers". "Ruud van Gaal" <[email hidden]> wrote in message news:[email hidden]...

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> On Sat, 07 Apr 2001 13:12:05 +0200, ernesto fina <[email hidden]> > wrote: > > >Neil, > > > >I'm also interested in the documentation you're talking about. Most of > >all I'm > >interested in Pacejka Coefficients for different kind of tires if you > >have some. > > It seems these coefficients are often copyrighted or something. Not > really good for what's called a standard. :) > But well, I'm have low-priority plans on a Pacejka editor where you > can tweak the constant and see what it does (and hopefully mimic known > curves). > > > Ruud van Gaal, GPL Rank +53.25 > Pencil art : http://www.marketgraph.nl/gallery/ > Free car sim : http://www.marketgraph.nl/gallery/racer/

Thanks for the nice comments below. I think that they are all correct, except the spelling of our name<grin> -- see below. I'm very curious -- what program(s) or product(s) have you used the non-dimensionalized tire data in? On Sun, 8 Apr 2001, Dave Pollatsek wrote:

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> Check out Millikin & Millikin's Race Car Vehicle Dynamics, chapter on tire > data non-dimensionalization... this lists formulas for combining slip angle, > slip ratio, and camber into one unified slip variable, giving you all those > "friction circle" behaviors you're wanting... they've also go a number of > datasets for various types of tires scattered throughout the book. Make > sure you get the load sensitivity curves for your friction and > cornering/camber stiffness, otherwise your roll stiffness adjustments won't > produce the correct understeer/oversteer effects. (The formulas make "mu" > and "C" look like constants, when in fact they're functions of normal > force/load--this lead me astray the first time I tried to use them!) > If you've got the rotational inertia of the wheels/drivetrain modeled, once > you plug these guys in, you'll be able to replicate just about any vehicle > behavior you can think of (donuts, brake-lockup understeer, trailing > throttle oversteer, etc) > Once you get to this point, you can get pretty far in modeling different > types of tires just by tweaking the "C" and "mu" curves, without (at first) > having to mess with the "magic numbers". > "Ruud van Gaal" <[email hidden]> wrote in message

....... > > It seems these coefficients are often copyrighted or something. Not > > really good for what's called a standard. :) > > But well, I'm have low-priority plans on a Pacejka editor where you > > can tweak the constant and see what it does (and hopefully mimic known In my experience this is not "copyright", it is "trade secret" material. Laboratory tire tests can cost many thousands (or 10's of thousands) of US dollars, so companies don't normally give it away. Then there is the extra cost of reducing the data to some useful format like Pacejka or our non-dimensional. A Pacejka editor would be a very nice thing - if it was fairly complete, I'd gladly pay a small (shareware) price for a copy. I think that some of his papers list all the formula and give samples of the different shape curves that can be generated. Check at U of Delft (Holland), and also at TNO (Dutch National Labs?) -- there have been many versions of the Magic Formula scheme and many papers over the years. -- Doug Douglas Milliken <[email hidden]> Milliken Research Associates Inc. And the shameless plug... Best place to order our book - good price, cheap shipping for card orders: <http://www.sae.org/servlets/productDetail?PROD_TYP=BOOK&PROD_CD=R-146> There is even a little bit of Pacejka in our book - in the picture on page 423, the hand holding the pencil is Pacejka! He worked at Cornell Aero Lab for some time in the 1960's.

You go away for a few days and miss a whole physics thread on R.A.S. :) Ash

Hi Doug and all Have you seen TyreGene from Yearstretch. http://www.yearstretch.com/yearstretch/Shop/product.asp?intProdID=1 Chris

On Mon, 9 Apr 2001, Chris West wrote: > Hi Doug and all > > Have you seen TyreGene from Yearstretch. > http://www.yearstretch.com/yearstretch/Shop/product.asp?intProdID=1 Chris, Thanks for the link. It is kind of surprising that there is no reference for Pacejka-96 (paper title and publisher). Are there plans to complete the job? To be useful to us, it needs aligning torque, longitudinal force (and Fy-Fx roll-off), overturning moment, etc. -- Doug Douglas Milliken <[email hidden]> Milliken Research Associates Inc.

Hi Doug Iam not envolved with Yearstretch :O) Its something Ive come across in my searches of the internet. I have my own little proggy for my pacejka needs :O) Chris Doug Milliken <[email hidden]> wrote in message news:[email hidden]...

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> > On Mon, 9 Apr 2001, Chris West wrote: > > > Hi Doug and all > > > > Have you seen TyreGene from Yearstretch. > > http://www.yearstretch.com/yearstretch/Shop/product.asp?intProdID=1 > > Chris, > > Thanks for the link. It is kind of surprising that there is no > reference for Pacejka-96 (paper title and publisher). > > Are there plans to complete the job? To be useful to us, it needs

aligning > torque, longitudinal force (and Fy-Fx roll-off), overturning moment, etc. > > -- Doug > Douglas Milliken <[email hidden]> > Milliken Research Associates Inc. >

Doug, ARe you helping Ruud with the Racer Project? Just asking since I know the level of respect your name garners in the circles I run around in and well I am wondering if I need to start downloading the Racer game now. Dave Doug Milliken <[email hidden]> wrote in article <[email hidden]>...

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> > On Mon, 9 Apr 2001, Chris West wrote: > > > Hi Doug and all > > > > Have you seen TyreGene from Yearstretch. > > http://www.yearstretch.com/yearstretch/Shop/product.asp?intProdID=1 > > Chris, > > Thanks for the link. It is kind of surprising that there is no > reference for Pacejka-96 (paper title and publisher). > > Are there plans to complete the job? To be useful to us, it needs

aligning

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> torque, longitudinal force (and Fy-Fx roll-off), overturning moment, etc. > > -- Doug > Douglas Milliken <[email hidden]> > Milliken Research Associates Inc. > >

On Sun, 8 Apr 2001 17:08:16 -0500, "Dave Pollatsek" <[email hidden]> wrote: >Check out Millikin & Millikin's Race Car Vehicle Dynamics, chapter on tire >data non-dimensionalization... this lists formulas for combining slip angle, >slip ratio, and camber into one unified slip variable, giving you all those >"friction circle" behaviors you're wanting... Thanks. This book gets more meaning as I understand more of it on the way. :) It seems though, after reading it yesterdaynight, the M&M brothers have a combined (nondimensionalized) slipAngle+camber, and a slipRatio+slipAngle method, but a fully combined slipAngle+camber+slipRatio is missing. Or is this just slipRatio+slipAngle, where you insert the combined slipAngle+camber nondimensionalized slip as slipAngle in the former slip variable (from the combined slipRatio+slipAngle)? I've seen the car spin out with a different algorithm (from Gregor Veble), which is ok, but I use SAE paper 950311 to do lateral/long. force buildup (delay of slipAngle and slipRatio), and its damping is causing me problems. The moment I play around with the forces, the damping goes wrong and I end up with a car sliding from left to right at about 0.5Hz (if not slower). I'll probably try a 3-dimension spring model, since the damping from SAE950311 only works when I set the coefficients at ~30, instead of the 0.7 (of critical damping) that is required according to that paper. I may be doing something wrong but haven't figured it out yet, and I know better how to damp springs, so a 3D spring model would probably be better nevertheless (and hook back to the SAE950311 model of delay slipRatio and tanSlipAngle once the car starts moving at non-lowspeed). ... >If you've got the rotational inertia of the wheels/drivetrain modeled, once >you plug these guys in, you'll be able to replicate just about any vehicle >behavior you can think of (donuts, brake-lockup understeer, trailing >throttle oversteer, etc) Sounds good. I have to get rid of the damping algorithm that doesn't behave right (and that I don't understand completely, there's a lot of forces with the body that's doing gyroscopic effects etc) and get a model that works better, and then tweak the friction coefficients based on nondimensionalize combined slip perhaps. >Once you get to this point, you can get pretty far in modeling different >types of tires just by tweaking the "C" and "mu" curves, without (at first) >having to mess with the "magic numbers". Good to hear; those magic numbers are a bit predictable to what they do, but certainly not how to modify them with load! Thanks, Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

On Mon, 9 Apr 2001 09:38:27 +0100, "Ashley McConnell" <[email hidden]> wrote: >You go away for a few days and miss a whole physics thread on R.A.S. :) Thankfully you have deja.com! And I keep these threads in my archives, intending to put summary version up on the Racer site. Some of them are already up there. Just so many things to do, and so little time... Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

On 9 Apr 2001, David wrote: > Doug, > ARe you helping Ruud with the Racer Project? Just asking since I know the > level of respect your name garners in the circles I run around in and well > I am wondering if I need to start downloading the Racer game now. > Dave No. I just lurk here and cause trouble<vbg>. Go and find an old Atari Hard Drivin' or Race Drivin' (arcade games) or go to Silicon Motor Speedway - I've been involved in those. Separate note to Ruud: At the time that Chapter 14 on non-dimensional tire data was written, it was a reasonable introduction to the concept. It's not the final word - a lot has happened in the last ~7 years (book was finished in mid-1994), and we have not published the new stuff. Btw, Bill (co-author) is my father. Funny that someone called us brothers...a good friend (engineer in Detroit) also calls us the Milliken brothers! -- Doug Douglas Milliken <[email hidden]> Milliken Research Associates Inc.

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> Doug Milliken <[email hidden]> wrote in article > <[email hidden]>... > > > > On Mon, 9 Apr 2001, Chris West wrote: > > > > > Hi Doug and all > > > > > > Have you seen TyreGene from Yearstretch. > > > http://www.yearstretch.com/yearstretch/Shop/product.asp?intProdID=1 > > > > Chris, > > > > Thanks for the link. It is kind of surprising that there is no > > reference for Pacejka-96 (paper title and publisher). > > > > Are there plans to complete the job? To be useful to us, it needs aligning > > torque, longitudinal force (and Fy-Fx roll-off), overturning moment, etc. > > > > > -- Doug > > Douglas Milliken <[email hidden]> > > Milliken Research Associates Inc. > > > > > >

On 9 Apr 2001 22:14:10 GMT, "David" <[email hidden]> wrote: >Doug, > > >ARe you helping Ruud with the Racer Project? Haha, he's only doing that indirectly, Dave. > Just asking since I know the >level of respect your name garners in the circles I run around in and well >I am wondering if I need to start downloading the Racer game now. Well, people like Doug have been helping here more than once, and I've gotten help from Chris West (from WSC, probably the most anticipated sim yet) too, if that helps you to convince a download, lol. Not that it all matters really, ofcourse, I'm doing the code by myself. It's just ideas about simulations can grow to heights when people work together with experiences and ideas. There are things to gain for everyone by working together. Well, that's the philosophy behind Racer in any case, and in a large part behind WSC too. Look at Quake and its addons, it's a good way to improve the lifespan of a product (and the quality as well!). Racer is only a 3Mb download, so not too much if you want to check it out sometime. It still has a big problem with lateral friction (power oversteer), but that's being worked (mostly read) on. Differentials are on its way (on paper) and that will result in a physics model that already creeps up on some, if not a lot, of the commercial games. Oh, how arrogant of me! ;-) But really, it's slowly beginning to feel ok, and the formula's used are definitely not trivial anymore like in the beginning. Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

On Mon, 9 Apr 2001 23:15:42 GMT, Doug Milliken <[email hidden]> wrote: ... >Separate note to Ruud: At the time that Chapter 14 on non-dimensional tire >data was written, it was a reasonable introduction to the concept. It's >not the final word - a lot has happened in the last ~7 years (book was >finished in mid-1994), and we have not published the new stuff. Are you working on publishing it then? Sounds interesting, one-curve-fits-all is a nice one. Even though I'm picking up the idea to have several tiremodels included, and use a model where appropriate (which does seem to go and work best). Low-speed is a pain. >Btw, Bill (co-author) is my father. Funny that someone called us >brothers...a good friend (engineer in Detroit) also calls us the >Milliken brothers! Ah yes! Forgot about that. Now I will have to remember the spelling of your name AND the family tree as well. ;-) Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

On Tue, 10 Apr 2001, Ruud van Gaal wrote:

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> On Mon, 9 Apr 2001 23:15:42 GMT, Doug Milliken <[email hidden]> wrote: > >Separate note to Ruud: At the time that Chapter 14 on non-dimensional tire > >data was written, it was a reasonable introduction to the concept. It's > Are you working on publishing it then? Sounds interesting, > one-curve-fits-all is a nice one. Even though I'm picking up the idea > to have several tiremodels included, and use a model where appropriate > (which does seem to go and work best). Low-speed is a pain.

No current plans to publish. We use a more complete version in some of our analysis software, and we aren't ready to give away all of our hard won techniques, at least not just yet. Low speed and stopping/reversing _is_ a pain. I've not heard of many "clean" solutions for this problem, it's always "messy" in some fashion. How come tires are so smart? They know how to work smoothly at low speed, and have been doing it for years, even before computers existed<grin>.

On Wed, 11 Apr 2001 03:10:13 GMT, Doug Milliken <[email hidden]> wrote: ... >No current plans to publish. We use a more complete version in some of our >analysis software, and we aren't ready to give away all of our hard won >techniques, at least not just yet. Too bad, we'll just have to wait then. :) (or do our own derivations) >Low speed and stopping/reversing _is_ a pain. I've not heard of many >"clean" solutions for this problem, it's always "messy" in some fashion. Sure is. I'm going to do multiple tire models and interpolate I guess. Even then... > How come tires are so smart? They know how to work smoothly at low speed, >and have been doing it for years, even before computers existed<grin>. Perhaps we could use a TireStick, where a small tire is run next to your computer, and forces are measured and passed back to the computer, where the sim reads it in. The 'perfect' tire model. Hehe. With addon packs with tiny versions of different tires. You could perhaps even plug in your favorite Mattell car! ;-) Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

I think I am going to have to produce something similar for me to understand 3d space, perhaps some kind of cage that fits over my head ;) Ash

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| | Perhaps we could use a TireStick, where a small tire is run next to | your computer, and forces are measured and passed back to the | computer, where the sim reads it in. The 'perfect' tire model. Hehe. | With addon packs with tiny versions of different tires. You could | perhaps even plug in your favorite Mattell car! ;-) | | | Ruud van Gaal, GPL Rank +53.25 | Pencil art : http://www.marketgraph.nl/gallery/ | Free car sim : http://www.marketgraph.nl/gallery/racer/

On Wed, 11 Apr 2001 11:40:19 +0100, "Ashley McConnell" <[email hidden]> wrote: >I think I am going to have to produce something similar for me to understand >3d space, perhaps some kind of cage that fits over my head ;) Keeping a 3D axis system built from pencils perhaps helps. :) With a tiny car where you stick out the Y, oh sorry, Z in SAE terms through the roof. Or copy and print out a big version of the SAE vehicle axis system. I often use my right hand and see if I can go from X to Y when my thumb is pointing in Z, to determine righthandedness. If we all looked like ET we couldn't do these things, you know, with only 2 fingers. (oh my, he probably has 25 or something as it will turn out) Makes it hard to believe he travelled through space. Ah, no more beer for me! Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

On Wed, 11 Apr 2001, Ruud van Gaal wrote:

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> > How come tires are so smart? They know how to work smoothly at low speed, > >and have been doing it for years, even before computers existed<grin>. > > Perhaps we could use a TireStick, where a small tire is run next to > your computer, and forces are measured and passed back to the > computer, where the sim reads it in. The 'perfect' tire model. Hehe. > With addon packs with tiny versions of different tires. You could > perhaps even plug in your favorite Mattell car! ;-)

Or, in real life, just buy one of these Flat-Trac Roadway Simulators, cheap at ~$10M! <http://www.mts.com/menusystem.asp?DataSource=0&NodeID=1141> Use the real physics with any car to drive your graphics display. -- Doug Douglas Milliken <[email hidden]> Milliken Research Associates Inc.

On Fri, 13 Apr 2001 18:44:21 GMT, Doug Milliken <[email hidden]> wrote:

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> >On Wed, 11 Apr 2001, Ruud van Gaal wrote: >> > How come tires are so smart? They know how to work smoothly at low speed, >> >and have been doing it for years, even before computers existed<grin>. >> >> Perhaps we could use a TireStick, where a small tire is run next to >> your computer, and forces are measured and passed back to the >> computer, where the sim reads it in. The 'perfect' tire model. Hehe. >> With addon packs with tiny versions of different tires. You could >> perhaps even plug in your favorite Mattell car! ;-) > >Or, in real life, just buy one of these Flat-Trac Roadway Simulators, >cheap at ~$10M! > <http://www.mts.com/menusystem.asp?DataSource=0&NodeID=1141> >Use the real physics with any car to drive your graphics display.

Cool! I'll order two just in case one breaks up during debugging. ;-) Ruud van Gaal, GPL Rank +53.25 Pencil art : http://www.marketgraph.nl/gallery/ Free car sim : http://www.marketgraph.nl/gallery/racer/

On Fri, 13 Apr 2001, Ruud van Gaal wrote:

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> On Fri, 13 Apr 2001 18:44:21 GMT, Doug Milliken > <[email hidden]> wrote: > > > > >On Wed, 11 Apr 2001, Ruud van Gaal wrote: > >> > How come tires are so smart? They know how to work smoothly at low speed, > >> >and have been doing it for years, even before computers existed<grin>. > >> > >> Perhaps we could use a TireStick, where a small tire is run next to > >> your computer, and forces are measured and passed back to the > >> computer, where the sim reads it in. The 'perfect' tire model. Hehe. > >> With addon packs with tiny versions of different tires. You could > >> perhaps even plug in your favorite Mattell car! ;-) > > > >Or, in real life, just buy one of these Flat-Trac Roadway Simulators, > >cheap at ~$10M! > > <http://www.mts.com/menusystem.asp?DataSource=0&NodeID=1141> > >Use the real physics with any car to drive your graphics display. > > Cool! I'll order two just in case one breaks up during debugging. ;-)

Don't forget to stock up on different kinds of cars too!