Re: [Torcs-users] Patch for wheel spin velocity traction

[David S. <dsa...@te...>]

----- 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