Slip ratio problem at low speeds.

Hi all!
I've got a problem with implementing a simple car physics to my secret
game It's regarded to calculating the slip ratio at low speeds. I
searched the whole web, but i couldn't find a valid solution. I only
found this article:
http://web.archive.org/web/200503080...s/tutstab.html

It should help me, but there are no important images there (I bet
it's because the article is 7 years old!) :-/
I also know, that something called SAE950311 has a solution to this
problem too. But it's not a free article and I cannot find any summary
of it or something.

Can anybody help me, please?

soku11 wrote:
> Hi all!
> I've got a problem with implementing a simple car physics to my secret
> game It's regarded to calculating the slip ratio at low speeds.
> I also know, that something called SAE950311 has a solution to this
> problem too. But it's not a free article and I cannot find any summary
> of it or something.

SAE950311 integrates small steps and thus make slip ratio a slowly
changing variable, instead of something that you calculate at once.

Check out Erick Lowndes thesis, still online:
http://www.lib.ncsu.edu/etd/public/e...842941/etd.pdf

From page 122 onwards he basically explains the SAE950311 method,
although not in these terms, but the principle is exactly the same.
Notice the Erick gives damping equations, which I think SAE950311 does
not use.
Also, you may want to limit your slipratios/slipangles, if only that you
may use Pacejka tire curves, which mostly suck at high SR/SA/camber/load.

An alternative could be to use a spring tire method, for example. There
you generate Fx/Fy using slip velocities (wheel velocity vs surface
velocity). Near 0, you'd interpolate between the spring method results
and Pacejka (smoothly to avoid sudden jerks).

Still, the SAE950311 makes for a nice added benefit: relaxation lengths
(starting values: 0.9 (meters) for laterial, 0.09 for longitudinal).

I trust this helps,
Ruud