Set center of mass for individual bones

Troubleshooting physics
1

I need some help. I’m not even sure if I can make this work correctly but I was looking for some suggestions. What I’m trying to do is dismember a model and have it basically turn into a bunch of dynamic physics object. The model seems to break apart correctly but the point at which each part pivots/rotates is off. Is there a way to set the center of mass of each bone? Or is there a way to copy each bonerigidbody and create a regular physics rigid body from it? I don’t know jme well enough to come up with any other ideas, but any suggestions are welcome.



Right now I use a kinematicragdollcontrol to dismember the character. I do this for each bone but actually remove the root bone completely from the model so that it does not pull it through the map.

[java]

PhysicsRigidBody prb = ragdoll.getBoneRigidBody(“Head”);

for(Object obj : prb.getJoints().toArray()){

if(obj instanceof PhysicsJoint){

prb.removeJoint((PhysicsJoint)obj);

bullet.getPhysicsSpace().remove(obj);



}

}

[/java]

Just incase I didn’t make it clear what the problem was, I created a short video for example.



Thanks!

2

The center of the object is always its center of mass, move the collision shape and geometry accordingly to move the center of mass relatively.

3

I’m drawing a blank on how I could do that. Can you give me a little more of how to go about this?



Thanks.

4

Bascially like this: https://code.google.com/p/jbullet-jme/wiki/CenterOfMass

5

Awesome, I got the physics part working by adding:

[java]

CompoundCollisionShape compoundCollisionShape=new CompoundCollisionShape();

HullCollisionShape HullCollisionShape = (HullCollisionShape)ragdoll.getBoneRigidBody(“Head”).getCollisionShape();

compoundCollisionShape.addChildShape(HullCollisionShape, new Vector3f(0,-1,0));

prb.setCollisionShape(compoundCollisionShape);

[/java]



I know i’m pretty much having you spoon feed this to me, but how can I grab that portion of the mesh from the ragdoll to move it accordingly?



Thanks again.

6

You have to change the ragdoll for this so it creates the center of the physics objects elsewhere.

7

The ragdoll class or the model i’m using?

8

the class

9

Darn, this sounds like its a little more work than I thought it would be.

10

I ended up just using the ragdoll to figure out the position of each limb then copying it to a rigid body. I didn’t get to keep the texture of each limb but instead just painted it red which still seems fun enough.

Thanks for all you help normen, much appreciated!