[ODE] Damping

[david@csworkbench.com]

One more thing.... Rolling friction can be simulated by only adding
angular damping to those objects that collide with the ground. i.e. check
and see if a geom is the ground during collision detection, and if it is,
add angular drag to the other geom's body.

>
> The following question comes up quite a bit, so I think the answer
> should go into the Wiki FAQ.
>
> --
>
> Q: How do I stop things from rolling off into infinity, or pendulums
> from swinging forever?
>
> A: You can accomplish that pretty well with damping.  It works about
> like this:
>
> 1) Compute the velocity of the object that's supposed to slow down.
>
> 2) Multiply that velocity by a "damping coefficient." This is typically
> a small number, like 0.01 for example.
>
> 3) Change the sign on the velocity vector, and you get your damping
> force.
>
> 4) Apply that force with dBodyAddForce.
>
> Tweak the damping coefficient to get the object to slow down at the rate
> you want.
>
> You can also do the same thing with angular velocity rather than plain
> old linear velocity, and dBodyAddTorque rather than dBodyAddForce.
>
> For air resistance, it would be better to use the cube of the velocity,
> because that's how drag works in reality.  The force should also be
> applied at the objects, aerodynamic center rather than at the body
> location.  The center of the object's cross section would probably be
> close to the aerodynamic center, at least for non-engineering purposes.
>  In any case, dBodyAddForceAtRelPos will allow you to apply the force at
> a specific point in the body's frame of reference.
>
> --
>
> Did I get it right? :-) Any comments before I put this into the FAQ?
>
> --
>
> Nate Waddoups
> Redmond WA USA
> http://www.natew.com
>
>
>
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