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Hard braking at high speed (>250km/h) makes the car slide
07-20-2012, 11:40 PM
Post: #1
Hard braking at high speed (>250km/h) makes the car slide
Hello,
if you try to hard brake at high speed (>250km/h), front wheels start sliding laterally due to a strong lateral forces. Tested with 360, G4 and CO.
Changing the tires doesn't fix this.
The only thing that alleviates this issue is a rear wing with high downforce.
In fact the F1-02, which has a very high downforce rear wing, doesnt suffer this issue.
Disabling Beckman combining algorithm seems to alleviate this problem, too.
My own vehicle simulation package (which uses Beckman combining algorithm) has this problem, too, and if I disable Beckman combining algorithm the issue almost disappear.

What do you think?
Michele
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07-21-2012, 03:51 AM
Post: #2
 
You are testing with ABS disabled, zero camber and toe?

Have you tried to compare the values? Maybe a small app where you feed a set of slip, slide values maybe with fixed/zero camber, fixed load and output the forces with different combing approaches.

From what I remember VDrift has additionally the problem that the velocity at contact is calculated in wheel space and not in contact space. As soon as you correct it the handling deteriorates. You'll get the car drifting to a certain side(right?). But that was more a camber, toe in issue I think.

TBH I'd love to replace the Beckman stuff or even the Pacjeka(won't be possible I guess) with something more simple/predictable as long as one gets somewhat plausible handling.

If you find out more regarding your issue, please share. Smile
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07-21-2012, 07:44 AM
Post: #3
 
NaN Wrote:You are testing with ABS disabled, zero camber and toe?

in Vdrift, ABS, camber and toe doenst affect this problem. In my application, without abs, if brake have enough force to lock the wheels, the problem (of course) is not present.

NaN Wrote:Have you tried to compare the values? Maybe a small app where you feed a set of slip, slide values maybe with fixed/zero camber, fixed load and output the forces with different combing approaches.
you have to take into consideration brakes too.

NaN Wrote:From what I remember VDrift has additionally the problem that the velocity at contact is calculated in wheel space and not in contact space. As soon as you correct it the handling deteriorates. You'll get the car drifting to a certain side(right?). But that was more a camber, toe in issue I think.

I remeber i had this problem at (very) high speed. It was due to slipangle numerical error, fixed with increasing (with speed) lateral relaxation.

NaN Wrote:TBH I'd love to replace the Beckman stuff or even the Pacjeka(won't be possible I guess) with something more simple/predictable as long as one gets somewhat plausible handling.

If you find out more regarding your issue, please share. Smile

well you can take into consideration to use a more recent versionof Pacejka model (5.1 for example). You can find the an implementation in racer web site (In order to view links, you must have to reply to this thread.
The latest pacejka version seems to be 6.1, which even simulates tire pressure (anyway tire pressure can be simulated with pacejka 96 too).
The problem with more recent version of pacejka is that is very difficult to find tire values. So for now im going to use pacejka 96.
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