[ODE] Resistance on bodys.

Jon Watte (ODE) hplus-ode at mindcontrol.org
Thu Jun 15 07:33:57 MST 2006

The documentation (and FAQ) clearly states that rolling friction is not 
modeled, so no, there's no simple flag you can turn on.

What I do is apply a slight counter-force and slight counter-torque to 
each body each step to dampen the system. This also models rolling 
friction. In C++ terms:

  Vector3 lVel = body->LinearVelocity();
  Vector3 aVel = body->AngularVelocity();
  float mass = body->MassScalar();
  body->AddForce(-mass * LINEAR_DAMPENING * lVel);
  body->AddTorque(-mass * ANGULAR_DAMPENING * aVel);

Values for LINEAR_DAMPENING in the 0.002 to 0.02 range seem to work 
well, as do values for ANUGLAR_DAMPENING in the range 0.005 to 0.05, but 
it all comes down to your simulation constants and step size.


          / h+

Russell Bartley wrote:
> Hi,
>     I have a body with 1 spherical geom that rolls down a hill, then 
> continues rolling along forever. I'd like to add some resistance to 
> the simulation so the ball has some sort of resistance applised to it 
> so it slows down and comes to an eventual stop. I have read a bit 
> about AMotors, and think I could probably achieve what I'm after with 
> these, but they seem a bit of overkill. Am I missing some parameter in 
> the contact joints I'm creating that can suffice? Do I have to put in 
> an AMotor to slow it down? What would I do for air resistance, where 
> there are no contacts?
>     thanks
>     Russ
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