Re: Patch for wheel spin velocity traction

----- Bernhard Wymann wrote:
> Hi David
> 
> Thank you, I will have a look into this for a later version (1.4.0), I 
> plan as well to study the acual SAE papers and fetching a recent edition 
> of Pacejka's book.
> 
> Kind regards
> 
> Bernhard
>

Thank you very much. I am excited about the potential that
TORCS has. If you, or anyone, has patches or observations
related to TORCS physics... I'll certainly be listening.

>
> On 06/16/2015 01:16 AM, David Savinkoff wrote:
> > Hi,
> >
> > This patch is the same as the previous, and has further fixes.
> > Apply this patch to clean sources (not with my previous patches).
> > This patch is an injection of natural physics, and an improvement.
> >
> > ***
> > In hunk 1:
> >
> > stmp is removed because this line of code in hunk 3
> > is not needed anymore:
> >   stmp = MIN(s, 1.5f);
> >
> > ***
> > In hunk 2:
> >
> > wrl calculation is corrected. wrl is the speed of the
> > spinning wheel (in the direction the wheel is pointed).
> > However, the wheel is sliding sideways due to the
> > slip angle. Thus, the 'vector component' of wrl must
> > derived from the slip angle.
> >
> > else if () code is factored out.
> >
> > Correct percent slip calculation for ALL conditions:
> >   sx = (vt - wrl) / (0.000001f + MAX(fabs(vt) , fabs(wrl)) );
> >   if (fabs(sx) > 1.0) sx /= fabs(sx);
> >
> > The reason for this correction is because it is not
> > physically possible to have more than 100 percent slip
> > (The old code is correct 'only' under braking conditions).
> >
> > ***
> > In hunk 3:
> >
> > if ((v < 2.0f) || (zforce == 0.0f))
> > replaces
> > if (v < 2.0f)
> > because skid marks are otherwise present in the air with this patch.
> >
> >
> > car->carElt->_skid[index] =  s;
> > because s is correct, and never exceeds 1.0f (100% slip).
> >
> > removed:
> >   stmp = MIN(s, 1.5f);
> >
> > Magic formula uses 's' instead of 'stmp'
> >
> >
> >
> > Sincerely,
> > David Savinkoff
> >
> > ----- David Savinkoff wrote:
> >> 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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