Re: Patch for wheel spin velocity traction

Hi,

I found the shocking truth that I independently derived
a formula for tire friction. The formula is:

sx = (vt - wrl) / (MAX(fabs(vt) , fabs(wrl)) )

Please read page 2 of this authoritive paper:
http://bsesrv214.bse.vt.edu/Hop/Papers/Tire-Road%20Friction%20Coefficient.pdf

TORCS and Speed Dreams need fixin'

Sincerely,
David Savinkoff


----- David Savinkoff wrote:
> ----- Bernhard Wymann wrote:
> > Hi David
> > 
> > It makes in my opinion no sense in respect to the tire model, the slip 
> > definition looks consistent as is for me
> 
> I cannot make an argument here because I am not absolutely certain how
> the tire model interacts with 'sx = (vt - wrl) / fabs(vt)'
> 
> >
> > (in your analysis there is a little glitch, vt is not the car velocity,
> > it is the wheel specific velocity, all wheels have usually at least
> > slightly different velocities).
> >
> 
> I may have not have expressed myself properly when I said 'car velocity'
> I envisioned a single wheel in contact with the road where 'vt' is the
> velocity in the direction the wheel is pointed... and where 'wrl' is the
> wheel spin velocity (can only be in the direction the wheel is pointed).
> 
> >
> > The proposed change would cause a discontinuity which would usually 
> > lower the grip.
> >
> 
> 'sx = (vt - wrl) / ( 0.000001f + MAX(fabs(vt) , fabs(wrl)) )' has an
> inflection point where the wheel is actuated to slip by
> deceleration, or slip by acceleration.
> The discontinuity is caused by the 'act' of braking or accelerating.
> 
> I believe 'sx' may need three different functions to include:
> 1) braking
> 2) accelerating
> 3) wheels rotating backwards to the direction of travel.
> The formula for 'sx' is my best so far, and it seems to work ok.
> 
> I visualize vt and wrl as two parallel lines showing their respective
> lengths. Where vt - wrl is the length part that differs. eg.
> _________________________
> _____________________________________
> 
> The formula for 'sx' suggests that one wants to determine a 'normalized'
> slip value given vt, wrl, and vt-wrl. Note that the slip happens in
> several different situations.
> 
> > I think a better solution for drifting is to adjust the parameters of 
> > the tire model
> 
> I just tried different tire pressures (other than the default 40 psi).
> I will comment on this list when I come across interesting things.
> 
> ***
> Please actually try my latest patch traction2.diff on different cars
> and tracks. Drive aggressively (off-track also) or ride with Olethros 6.
> ***
> 
> > , differential and suspension. If you don't mind to edit 
> > the XML you can adjust as well the engine braking coefficient (instead 
> > of adapting your accelerator control in your mind;-) ).
> > 
> > Other opinions?
> >
> 
> Others on the list... Your opinions please.
> 
> Sincerely,
> David Savinkoff
> 
> 
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