[ODE] Boxes floating in a plane

Jon Watte (ODE) hplus-ode at mindcontrol.org
Mon Nov 6 13:26:18 MST 2006

This is just an artifact of the way that the simulation works. 
Simplified, I believe this is what happens: The gravity will pull the 
object into a surface; the surface will generate a force that's 
proportional to the penetration; the higher the gravity force is, the 
farther the penetration will be before they achieve equilibrium.

When you are using floating point values for ODE simulation, the 
recommendation is to stay close to the 1.0 range for masses. Thus, I 
would scale my masses (and forces) so that they are in the range of 0.1 
through 100 or so. Often, you cannot model, say, a coke can, and a car, 
at the same relative mass, while retaining stable simulation, in 
floating point. For this reason, I often use sqrt(mass) instead of 
actual mass, for the "mass" property. It gives a convincing enough 
result for gameplay.


          / h+

Christoph Beyer wrote:
> *Kyle Hubert wrote:*
>> I just bumped the mass up really high, that's all.
> Yes you're right. It happens with all heavy objects.
> It happens with all kind of geom: heavy objects
> ( affected by gravity, or other forces/velocities ) are floating into 
> other objects!
> It seems to be a "bug" of the correction-forces.
> disabling soft_cfm and incrementing the soft_erp value reduces this problem,
> but it is never solved.
> I hope, that someone has an idea how to solve this.
> Because i need cfm to avoid jittering (i.e. in boxstacks),
> but high cfm makes small objects with more than 5000 mass 
> floating/bouncing into walls.
> christoph
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