Hi,
I try to understand ODE bindings with buggy.py script in tutorial.
I replaced the car by a simple rigid body a sphere, wich is rendered with a
soya sphere volume. A removed all the group of joints for the car. I also
removed all the keyboard controler stuff to move the car. So the sphere is
just falling to the land. I expect to see my sphere bounces and roll on the
land.
When the sphere enters in collision the land, it is blocked for a short time,
then continue to be "pulled" by its gravity through the land, after some
resistance and slow penetration, the sphere finally traverse completly the
land and continue its fall.
I tried to change, the mass value of the body or the gravity of the ode world.
Without success. I have seen an explanation in ode manual, but I don't know
how to set these parameters with this soya binding.
[
Sometimes when rigid bodies collide without restitution, they appear to
inter-penetrate slightly and then get pushed apart so that they only just
touch. The problem gets worse as the time step gets larger. What is going on?
The contact joint constraint is only applied after the collision is detected.
If a fixed time step is being used, it is likely that the bodies have already
penetrated when this happens. The error reduction mechanism will push the
bodies apart, but this can take a few time steps (depending on the value of
the ERP parameter).
This penetration and pushing apart sometimes makes the bodies look like they
are bouncing, although it is completely independent of whether restitution is
on or not.
Some other simulators have individual rigid bodies take variable sized
timesteps to make sure bodies never penetrate much. However ODE takes fixed
size steps, as automatically choosing a non-penetrating step size is
problematic for an articulated rigid body simulator (the entire ARB structure
must be stepped to account for the first penetration, which may result in
very small steps).
There are three fixes for this problem:
* Take smaller time steps.
* Increase ERP to make the problem less visible.
* Do your own variable sized time stepping somehow.
]
Someone can help me ?
PS : Sorry for my bad English, not my first language (i am french)
Good WE
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