Re: Patch for wheel spin velocity traction

----- BRIAN MARTIN Owner wrote:
> David,
> 
> I tried a couple of your patches and found i liked the original code
> better. Of course, this is completely subjective.
> 
> Tire pressure, the last time i looked, is not implemented in simuv2.
> 
> Changes to the car physics file will get you far more profound changes

Most of these changes are too profound for me.

> in car handling than small sim hacks, especially  changes to mu, clift, 
> wings and brake partitioning. I have attached a sample physics file that works
> very well for me in terms of drifting and just overall fun factor.
> 
> Brian 
>

Thank you very much. I will be trying this file out.
The tire pressure can be changed by changing a value in wheel.cpp
and re-compiling. It does make a difference.

For a few years I changed parameters in the .xml files. Eventually
I decided to look at the code. I have taken into account that
 TORCS car parameters are important.

Some of my concerns are:
- I could not find satisfactory performance by changing the parameters.
- I found that by using 'the golden ratio' in making some empirical
  formulas for TORCS parameters, that I could get a sweet spot.
  (this may show that TORCS has a chaotic function)
- I have been concerned that the operating points for TORCS are
  narrower than in nature.
- I have noticed that the road has abrupt traction differences on either
  side of the racing line that can cause the car to wander similarly to
  loose steering linkage.

>
> ----- Original Message -----
> From: "David Savinkoff"
> To
> Cc: "torcs-users" <[email protected]>
> Sent: Wednesday, April 8, 2015 4:05:20 PM
> Subject: Re: [Torcs-users] Patch for wheel spin velocity traction
> 
> ----- 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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