Re: Adjusting car settings in .xml file

Hi

Depending on the input device you need to switch on ASR/ABS (e.g. when 
using on/off button keys for the accelerator/brake). Brake pressure and 
balance must be adjusted reasonable even for those to work properly.

The robot tutorial contains a section what the various properties 
represent. Usually you can use many values of the real thing, those are 
usually more or less known:
- Geometry (wheel track/base)
- Tire/rim geometry
- Engine curve
- Transmission ratios
- Weight
- Center of gravity
- Drag
- Areas (front, top)
- ...

Guessing/experimentation is usually required for:
- Ground effect
- Tire friction/dynamic properties
- Suspension
- Mass distribution
- ...

Basically I recommend taking a similar existing car as base. Beware, 
there are values which can make the simulation explode (there is no 
validation), e.g. if the fast bump/rebound are set too high, they should 
be usually much lower than the slow damping. The transition point can 
currently not be adjusted, it is fixed at 0.5 m/s IIRC (see susp.cpp), 
but I plan to make this adjustable at some point (from 0.1 to 0.5, real 
products which I have found on the net go from 0.15 to 0.5).

Another trap is if the ride height is set higher than the suspension 
course allows the wheel to expand, then the handling is very bad at low 
speeds (at high speeds the downforce might compresses the suspension 
enough, so it can then expand a bit).

Tire properties are as well very important for the handling, you can 
make a tire very precise, but unforgiving to very unprecise and forgiving.

There are as well two tire properties which are not set in any file so 
far (as far as I know) in any setups, these are "elasticity factor" and 
"pressure", they are just set to the defaults then (see wheel.cpp).

Forgiving is ("swimming"):
- low stiffness
- high dynamic friction
- low mu
- low tire width
- high tire width-height ratio
- low diameter

For fine tuning and balance the suspension and anti rollbars are 
important, the latter especially if the center of gravity is high.

I recommend you just to play with the values, try as well exterme ones, 
such that you get a feeling for it, just keep "working copies" of the 
setup in case you make the simulation explode and just change one thing 
at once, otherwise you cannot know what cause which effect.

Hope this helps at least a bit, have fun.

Bernhard.

On 09/11/2012 10:57 AM, [email protected] wrote:
>
> Admittedly, I'm an amateur, but apart from converting cars to expand my
> private torcs fleet, I'd also like them to be drivable. Unfortunately,
> some of them have insane settings and are like untamed animals beyond my
> grasp. They spin at the slightest acceleration or deceleration and at
> this point are pretty much useless.
>
> Could anybody out there lend a hand in making appropriate changes to the
> xml file, so those wild ones in my garage could also be brought to the
> track? Despite my experimentation, I haven't been able to figure out
> which settings need to be altered and how much to make the car more
> suitable for driving. I guess I missed that mechanics class.
>
> Some might suggest copying the settings from an existing, functional
> car, but then the converted car would lose whatever individual flavor it
> had. And of course, I still wouldn't understand why the original car
> acted so erratically.
>


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