Hi, Just some feedback for those who are interested (if any ;-)
I replaced the test with the land (derived from the biggy script), by a more basic one. I use an ode.body with a ode.GeomSphere paired with a soya.sphere shape. Then I place a GeomPlane. In this case, all work as expected, very bouncy without penetrating. No need for CFM. Jiba, Perphaps this little script could be added to the tutorial to help understand ODE basics ? PS : Making this simplified code help me to find some errors (typo) I made in the previous one. Now I can get the balls bouncing an rolling all over the land, great ! Zack Le Lundi 24 Avril 2006 01:24, Jacques Rebourcier a écrit : > Hi, > > I found some way to tune ode.World behavior (World.ERP, World.CFM, > World.contact_surface_layer, etc). > > I also found out the way to change contact joints properties during > collision (contact.mode activation flags with the binary masks and its > parameters : contact.bounce, contact.CFM, etc). > > When I reduce idler round value to 0.01 (instead of 0.03), add some mass > and add contact.CFM and remove slide efect (mu=infinity) I manage to avoid > penetration. But land seems spongy(sic?) and sticky (like marlemade). > > I cannot get the sphere bounce or roll when I throw it against the land. > Nobody using soya.ODE to explain me what happens ? (I use soya 10.1) > > I will make some test without soya land to see if I get the same > behavior... > > Bye. > Jacques > > Le Samedi 22 Avril 2006 01:03, Jacques Rebourcier a écrit : > > 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 > > > > _______________________________________________ > > Soya-user mailing list > > [email protected] > > https://mail.gna.org/listinfo/soya-user > > _______________________________________________ > Soya-user mailing list > [email protected] > https://mail.gna.org/listinfo/soya-user _______________________________________________ Soya-user mailing list [email protected] https://mail.gna.org/listinfo/soya-user
