05292016, 09:46 AM,
(This post was last modified: 05292016, 09:51 AM by NaN.)


NaN
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RE: Tire force combining review
According to literature contact patch pressure distribution is not constant.
The probably most simple approximation is parabolic 3 / 4 (1  x) (1 + x), which results in the following tire friction curve:
Now this is something we can work with.
Playing a bit with the parameters we get this:
The right half of the curve is constant (tire fully sliding) due to the simple constant sliding friction model I am using. Using Stribeck friction function should fix this.
I'd also like to try a few other distributions that should match the real pressure distribution a bit better: a skewed parabolic and a simpler trapezoid function.


06072016, 02:25 PM,
(This post was last modified: 06072016, 02:40 PM by NaN.)


NaN
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RE: Tire force combining review
Things are starting to shape up nicely. Fixed a bug in my force calculation and have been working on tire carcass bending, so that combined forces look as they should.
Still need to go through the math a couple of times, to be sure that I've got it right.
After that will be working on camber and aligning momentum.


06092016, 09:57 AM,
(This post was last modified: 06092016, 10:01 AM by NaN.)


NaN
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RE: Tire force combining review
Have got tire carcass bending working, softer carcass reduces peak and slope of lateral force fy.
stiff vs soft carcass
Now camber is somewhat harder to model. I've been thinking about approximating it, pacejka style, by shifting fy and some carcass bending.
Camber also has an effect on fx, mz though, which can not be approximated by simple shifting.


06112016, 09:00 AM,


NaN
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RE: Tire force combining review
Carcass bending due to camber
8 vs 8 degrees camber:
There are some additional effects that camber is causing. But this looks surprisingly good already, maybe good enough for us.
The graphs show a discontinuity at slip angle close to zero, but that is my fault, will be fixed.


06122016, 04:54 PM,


arturo
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RE: Tire force combining review
(06112016, 09:00 AM)NaN Wrote: 8 vs 8 degrees camber: Something missing here I guess...
By the way, I've noticed some strange ingame tyre behavior that may be relevant to what you are doing.
One place at which it is very obvious is the left turn after the (closed) connections with the GP circuit in Ring2007. If you barely touch the kerb with "racing" tyres, you'll take a big hit, but with "sports" tyres nothing will happen.
I'd say it has to do with the interaction between track features (in this case, the kerb) and tyre features.


06132016, 11:00 AM,
(This post was last modified: 06132016, 11:23 AM by NaN.)


NaN
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RE: Tire force combining review
(06122016, 04:54 PM)arturo Wrote: 8 vs 8 degrees camber: I mean 8 vs +8 degrees here
You can look at the friction curves of the tires with tire.py from here: github.com/logzero/vdrifttools
"Load" data/carparts/tire/racing.tire and "Load Ref" touring.tire as reference to compare with.
Compared to the graphs I've seen in the literature the camber effect of all three (touring, sports and racing) is somewhat exaggerated, way too much vertical shift.
Still, I don't think it is the reason for the behavior you are observing.


06132016, 03:58 PM,
(This post was last modified: 06132016, 04:01 PM by NaN.)


NaN
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RE: Tire force combining review
Initial aligning torque implementation, doesn't include carcass bending yet.
Compared to hankook tire data (light colored curves):
At large slip angles torque drops to zero due to symmetric contact pressure model. Will be interesting to see how/if carcass bending affects this.


