I would advise researching what is known as vehicle "SIDESLIP".
This is the direction of travel of the car against it's yaw orientation. The effect of Sideslip is often called Oversteer.
It is calculated as atan2(car longtitude velocity, car lateral velocity )
or atan(car longtitude velocity / car lateral velocity )
I think DB uses atanfull instead of atan2. I'm not a user of the db language.
atan gives +- 180 degrees ( +- pi radians )
The order, (long , lat) might be reversed, im typing from memory at present with no access to code to verify.
The longtitude and lateral velocities of the car are in local car coordinates and not world frame coordinates.
The car might be travelling positevly in x world coordinates but pointing along the positive z axis, thus making it slide sideways at 90 degrees. This would give a sideslip value of 90 degrees.
longtitude velocity of 0 and a lateral velocity of >0 in local car frame coordinates.
Once the sideslip of the car is calculated, you can then calculate the force produced by the tires, which in turn provides a yaw force (torque) on the car in order to turn it back to neutrol. Any amount of sideslip the car is experiencing will have the effect of forcing the car back into a straight line. Slowing it's angular momentum until sideslip = 0.
To calculate the tire force in order to turn the car, i would advise using the famous Magic Pacejka Formula. The formula is available via the racer free open project as c source code, just a relatively small function which should be easy to port.
Incidentally, the racer site is an excellent place for car physics resources and also the forums at racesimcentral are invaluable for help from other car physics coders.
So to recap,
calculate the sideslip of the car
calculate the tire force with sideslip as your input
turn car by resulting force (slowing its angular (yaw) momentum)
This is the method most commercial car games use. Using a physics engine for general physics interactions and collisions and handling the car physics via your own code. This i have also done myself.
You can, for instance, simply make a cube in your physics engine with no ground friction. Apply force in its longtitude direction, which would push it forward ie, acceleration, add a yaw force via the steering which would give it angular momentum, then process your car physics code, which would apply a yaw force to slow down the yaw momentum of the car via it's current sideslip.
Even if you dont decide to go this route, i would still advise researching the method if only to get a better understanding of how a real car behaves.
Hope that sheds a bit more light on a pretty tricky subject.
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