[ODE] Yet Another Car Simulation With Problems

[Jon Watte]

> 1) Chassis mass = 1000 kg, wheel mass = 20 kg; is there any 
> inherent problem with these values if I keep everything 

If the simulation is stable, then the numbers are OK. The magnitude 
of the numbers affect the stability more than they affect things 
like feel/behavior.

> 2) Damping - I've seen damping used several times; is it to 
> stabilize the simulation or to simulate aerodynamic drag?

Both.

> 3) Progressive steering? Right now I'm using "digital" steering, 

Yes, you need this. Note that, when you turn the wheel of the 
car, it actually turns against the ground. This induces torque 
on the chassis itself. I don't know if this is enough to cause 
the skid that you're getting, but it's quite possibly one of 
the reasons.

> 4) Collision model - I tried using a slip model for the wheels 
> but I couldn't find a good set of { surface_mu, tyre_mu, 
> tyre_slip } that didn't either make the terrain as an ice 
> surface or made the car tip over easily (which it didn't before 
> since the CoG is at the same height as the wheels).

CoG needs to be the same height as the GROUND (i e, as the 
contacts between wheels and surface) to eliminate most flips.

Btw: if you use more than two boxes for the chassis, I'd 
suggest using a coarse trimesh instead. It'll probably be more 
efficient, AND you get a better fit to the chassis.

Last, I made a similar app, with the simulation source file 
included, available at: 
http://www.speakeasy.net/~hplus/carworld-040730.zip
Feel free to read it for inspiration, or tweak the tweakable 
parameters.

I've also found that making sure the "inner" wheel twists more 
than the "outer" wheel actually make steering better -- this is 
not part of the archive on the web page.

That being said, I'm not so sure that using sphere for wheels 
is actually good enough... I'm debating whether to keep going 
this way, or to turn to box + four rays (which is what most real 
car games use), or try my luck with the cylinder collider. 
Box + 4 rays is easier to get to behave well, but it's much 
harder to get the wheels to affect the environment when you do 
it that way :-(

Cheers,

			/ h+