# [ODE] High density sphere passes into plane?

Anna-Beth Fox anna_beth_fox at yahoo.com.au
Mon Aug 7 17:41:43 MST 2006

```Yeah, I did set the sphere's position at (0, 8, 0). Forgot to mention that. Sorry. Any ideas?

Elijah Taylor <eatmailinglists at gmail.com> wrote: Oops, meant to send this to the list...

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Aside from the usual response of fiddling with CFM and ERP values so that only a particular amount of penetration is allowed, I beleve that there's an different solution to your problem.

Since you're creating the sphere geom/body without setting its position, it's likely created at the origin, and thus immediately penetrating the plane (in fact, the plane would split it in half).  Try setting the geom position to some positive height (greater than the radius) and see if that works.

Also, to set the sphere's mass by value rather than by density, use dMassSetSphereTotal, the *Total versions of these functions accept total mass as an argument.

-Elijah

On 8/7/06, Anna-Beth Fox <anna_beth_fox at yahoo.com.au> wrote: Hello again all,

I have setup a simple ODE test bed for experiments and the like and when I create a plane (for the floor/ground representation) and a sphere, the sphere "sinks" into the plane under gravity. For example:

...
dMass m;

my_world = dWorldCreate();
my_space = dHashSpaceCreate(NULL);
contact_group = dJointGroupCreate(0);
dWorldSetGravity(my_world, 0.0f, - 9.81f, 0.0f);
dWorldSetCFM(my_world, 0.0001f);
dWorldSetContactMaxCorrectingVel(my_world, 0.1f);
dWorldSetContactSurfaceLayer(my_world, 0.0001f);
dCreatePlane(my_space, 0.0f, 1.0f, 0.0f, 0.0f); // Floor

the_ball.body = dBodyCreate(my_world);
the_ball.geom = dCreateSphere(my_space, 0.5f);
dGeomSetBody(the_ball.geom, the_ball.body);

dMassSetZero(&m);
dMassSetSphere(&m, 5.0f, 0.5f); // Really any density greater than 2.0!!!
dBodySetMass(the_ball.body, &m);

What's the issue here? What am I missing or stuffed up? And how do I set the mass of the sphere to be like 21Kg.

TIA peeps.

Anna-Beth
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