rec.autos.simulators

by **Ruud van Ga** » Sat, 11 Aug 2001 23:48:23

On Fri, 10 Aug 2001 10:05:57 +0200, Gregor Veble

>The roll centre description is a linear approximation to a full
>suspension system. If you build the latter properly, the roll centers
>etc. come automatically correct out of it.

Yes well, they're static here. :)
I was wondering, as a general rule, the front RC is lower than the
rear (in racing), right? But is the rear RC generally lower or higher
than the CG?
Or are there indications of how much a RC generally is below the CG at
the front or rear? This one is still an unknown one for me (as a lot
of other parameters ;-)), and it seems like I could abuse the RC's
height as a sort of anti-rollbar.

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** » Sat, 11 Aug 2001 23:53:42

On Fri, 10 Aug 2001 10:04:33 +0200, Gregor Veble

>Hi Colin!

>> It is interesting that you are only running at 100hz, I have my
>> simulator cranked up to 240hz at the moment, I have the quaternions
>> for each of the bodies double buffered which I then interpolate for
>> the current frame, (makes for some really pretty replays :-))

>I'm running at whatever is stable :). Seriously, I can run at 200Hz
>easily,

Geez, the F1 cars and Kart cars people are making for Racer seem to
need at least 1000Hz. I should really do something about that and have
multiplying factors (or RK4 or midpoint things, see gdmag, april '99)
in to get separate frequencies. Probably even dynamic ones depending
on the spring constants (or when touching bumper stops).

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

by **Gregor Vebl** » Sun, 12 Aug 2001 00:34:00

Hi Ruud,

that's because I don't take into account the mass of the wheels in
suspension movement, that's all. Very stiff suspensions/tyres will move
the wheel hopping mode to high frequencies, and if you want that in
you'll need to run at approximately that frequency to keep it stable. No
such problem when you neglect the mass and with it (only) this high
frequency hopping mode. If you keep the wheels rigidly attached to the
suspension (as in a Kart), the required frequency will be much less, as
that eliminates the wheel hopping as well.

-Gregor

> Geez, the F1 cars and Kart cars people are making for Racer seem to
> need at least 1000Hz. I should really do something about that and have
> multiplying factors (or RK4 or midpoint things, see gdmag, april '99)
> in to get separate frequencies. Probably even dynamic ones depending
> on the spring constants (or when touching bumper stops).

> Ruud van Gaal, GPL Rank +53.25
> Pencil art : http://www.marketgraph.nl/gallery/
> Free car sim : http://www.marketgraph.nl/gallery/racer/

by **Jonny Hodgso** » Sun, 12 Aug 2001 05:50:42

> On Fri, 10 Aug 2001 10:05:57 +0200, Gregor Veble

> >The roll centre description is a linear approximation to a full
> >suspension system. If you build the latter properly, the roll
centers
> >etc. come automatically correct out of it.

Yup, I know this; I was wondering how much processing power you were
throwing at doing this as opposed to hard-coding a suitable
approximation ;-)

Lower, I'm pretty sure. IIRC a modern slick-and-wings car tends to
run front RC at ground level, rear maybe 50mm up; my 1/10th scale
off-road buggy runs (very approximately) 3mm front, 7mm rear (this is
a carpet setup; off-road uses a slightly higher rear I /think/).

Yes you can, but this has at least two downsides. One, it can
eliminate body roll in transients to the point where the driver has
too little feedback; and two (which is more serious) it introduces
large jacking effects. I suspect that the camber curves would also
end up being far from optimal.

HTH,
Jonny

by **Ruud van Ga** » Tue, 14 Aug 2001 20:57:24

On Fri, 10 Aug 2001 21:50:42 +0100, "Jonny Hodgson"

>> I was wondering, as a general rule, the front RC is lower than the
>> rear (in racing), right? But is the rear RC generally lower or
>higher
>> than the CG?

>Lower, I'm pretty sure. IIRC a modern slick-and-wings car tends to
>run front RC at ground level, rear maybe 50mm up; my 1/10th scale
>off-road buggy runs (very approximately) 3mm front, 7mm rear (this is
>a carpet setup; off-road uses a slightly higher rear I /think/).

Thanks, I'll try that in some F1 car I have here.

Not that in simming this is too much of an issue. :)

That may be more severe, although jacking effects are still a bit
implicit in my sim.

Thanks for the info,

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

by **J. Todd Wass** » Wed, 15 Aug 2001 07:18:56

Here's a little RC info for F-1 cars:

"This information was provided by M. Mazumdar from the USA.

Regarding your discussion of roll centers and how much movement is permissible,
I can tell you that current F-1 ,Indy and IRL cars tend to limit the movement
of RC in the lateral & vert. directions to about 10 thousandths of an inch or
less. Of course, the roll center moves vertically with the chassis. For one F-1
car from last year, the front RC was 6mm BELOW ground level and the rear about
an inch ABOVE with a pitch sensitivity of 1:2 front to rear. Typical damper
movements are 7mm or less for a F-1 car. Generally speaking, in F-1 front susp.
rising rate is NOT used. Motion ratios tend to be 1 or greater. I can't recall
exactly what the wheelrates are as of now but I will find out but they are
pretty high. Indy cars tend to have different RC configurations as they run on
4 different courses. They generally run much stiffer at the front than at the
rear. Wheelrates vary widely according to the type of course being run."

Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com

by **Ruud van Ga** » Wed, 15 Aug 2001 18:41:23

Thanks for the info! :)
Seems dynamic rollcenters don't do too much here.

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

by **Gregor Vebl** » Wed, 15 Aug 2001 18:57:29

Hi Todd,

wow, good info, thanks for sharing it!

It appears that the reports of understeer of modern F1 cars from certain
F1 drivers are indeed true, considering how the roll centers need to pe
positioned to cure that.

Also, could you please explain the following statement, as I don't think
I get it:

"Generally speaking, in F-1 front susp. rising rate is NOT used."

Does that mean that dampers are extremely soft on bump?

-Gregor

> Here's a little RC info for F-1 cars:

> "This information was provided by M. Mazumdar from the USA.

> Regarding your discussion of roll centers and how much movement is permissible,
> I can tell you that current F-1 ,Indy and IRL cars tend to limit the movement
> of RC in the lateral & vert. directions to about 10 thousandths of an inch or
> less. Of course, the roll center moves vertically with the chassis. For one F-1
> car from last year, the front RC was 6mm BELOW ground level and the rear about
> an inch ABOVE with a pitch sensitivity of 1:2 front to rear. Typical damper
> movements are 7mm or less for a F-1 car. Generally speaking, in F-1 front susp.
> rising rate is NOT used. Motion ratios tend to be 1 or greater. I can't recall
> exactly what the wheelrates are as of now but I will find out but they are
> pretty high. Indy cars tend to have different RC configurations as they run on
> 4 different courses. They generally run much stiffer at the front than at the
> rear. Wheelrates vary widely according to the type of course being run."

> Todd Wasson
> ---
> Performance Simulations
> Drag Racing and Top Speed Prediction
> Software
> http://PerformanceSimulations.Com

by **Ruud van Ga** » Wed, 15 Aug 2001 20:20:25

>>Regarding your discussion of roll centers and how much movement is permissible,
>>I can tell you that current F-1 ,Indy and IRL cars tend to limit the movement
>>of RC in the lateral & vert. directions to about 10 thousandths of an inch or
>>less. Of course, the roll center moves vertically with the chassis. For one F-1
>>car from last year, the front RC was 6mm BELOW ground level and the rear about
>>an inch ABOVE with a pitch sensitivity of 1:2 front to rear.

>Thanks for the info! :)
>Seems dynamic rollcenters don't do too much here.

BTW More info on this at:

http://www.presspley.com/racecarresearc/roll.htm

Quite a coincidence, I just had some talks with Mark, who runs the
site, if I estimate correctly.

Ruud van Gaal, GPL Rank +53.25
Pencil art : http://www.marketgraph.nl/gallery/
Free car sim : http://www.marketgraph.nl/gallery/racer/

by **Jonny Hodgso** » Thu, 16 Aug 2001 02:02:23

Rising rate: motion ratio (between wheel movement and shock movement)
varies with suspension travel, such that the effective spring rate at
the wheel increases as the suspension moves into bump.

Is that what you were unclear on?

HTH,
Jonny

by **Gregor Vebl** » Thu, 16 Aug 2001 03:17:24

Oh yes. :) Thanks!

-Gregor

> Rising rate: motion ratio (between wheel movement and shock movement)
> varies with suspension travel, such that the effective spring rate at
> the wheel increases as the suspension moves into bump.

> Is that what you were unclear on?

> HTH,
> Jonny

by **J. Todd Wass** » Thu, 16 Aug 2001 06:55:01

Yes, someone from there contacted me yesterday, that's where I got the info.

Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com

rec.autos.simulators

Car Physics: Suspension geometry

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