rec.autos.simulators

by **Ruud van Ga** » Wed, 11 Apr 2001 07:43:07

On Sun, 8 Apr 2001 17:08:16 -0500, "Dave Pollatsek"

>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).

...

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.

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.racesimcentral.net/
Free car sim : http://www.racesimcentral.net/

by **Ruud van Ga** » Wed, 11 Apr 2001 08:07:24

On Mon, 9 Apr 2001 09:38:27 +0100, "Ashley McConnell"

>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/

by **Doug Millike** » Wed, 11 Apr 2001 08:15:42

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

Milliken Research Associates Inc.

> > > 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

> > Milliken Research Associates Inc.

by **Ruud van Ga** » Wed, 11 Apr 2001 21:37:34

On 9 Apr 2001 22:14:10 GMT, "David"

>Doug,

>ARe you helping Ruud with the Racer Project?

Haha, he's only doing that indirectly, Dave.

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/

by **Ruud van Ga** » Wed, 11 Apr 2001 21:42:22

On Mon, 9 Apr 2001 23:15:42 GMT, Doug Milliken

...

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.

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/

by **Doug Millike** » Thu, 12 Apr 2001 12:10:13

> >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>.

by **Ruud van Ga** » Thu, 12 Apr 2001 19:38:34

On Wed, 11 Apr 2001 03:10:13 GMT, Doug Milliken

...

Too bad, we'll just have to wait then. :)
(or do our own derivations)

Sure is. I'm going to do multiple tire models and interpolate I guess.
Even then...

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/

by **Ashley McConnel** » Thu, 12 Apr 2001 19:40:19

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

|
| 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/

by **Ruud van Ga** » Fri, 13 Apr 2001 02:54:56

On Wed, 11 Apr 2001 11:40:19 +0100, "Ashley McConnell"

>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/

by **Doug Millike** » Sun, 15 Apr 2001 03:44:21

> > 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

Milliken Research Associates Inc.

by **Ruud van Ga** » Sun, 15 Apr 2001 06:01:24

On Fri, 13 Apr 2001 18:44:21 GMT, Doug Milliken

>> > 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/

by **Doug Millike** » Sun, 15 Apr 2001 12:40:44

> On Fri, 13 Apr 2001 18:44:21 GMT, Doug Milliken

> >> > 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!

rec.autos.simulators

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients

Car physics; Pacejka and friction coefficients