Center of Mass (Rig)


The Center of Mass is a unique point that characterizes movement of an object (or a group of objects) as a whole. When a linear force is applied to the center of mass, it causes linear acceleration without angular acceleration.

A Center of Mass is required for Physic Tools to work properly.
More about this here.

Creating Centers of Mass

To create a center of mass:

1. Switch to the Rig mode:

2. Select one or several Rigid Bodies.

3. Go to the Rigging Tools panel.

4. Open the Main actions panel:

5. In the Prototype center of mass section, click Add:

Keep in mind that creating a new Center of Mass causes a couple of issues.

First, Direction Controllers won’t work properly.

This can be fixed by connecting them to the Center of Mass:

1. Switch to the Rigging Mode.

2. Select Direction Controllers.

3. Select the Center of Mass.

4. Connect them by selecting CenterOfMass → Connect with dir controllers from the Commands menu:

Second, Ballistic Ghosts won’t render with a newly created Center of Mass. To fix this, you’ll need to snap the mesh to it:

1. Switch to the Mesh Mode.

2. Select every mesh that makes up your character.

3. Switch to the Point Controller Mode.

4. Select the Center of Mass.

5. Use Commands → CenterOfMass → Snap mesh to the center of mass:

After you take care of these two issues, everything should work as intended.

Multiple Centers of Mass

A character might have more than one Center of Mass.

Here, we have a center of mass for the character and another one for the sword the character is holding.

In cases you have two or more CoMs, you might want to add a composite Center of Mass for the entire character.
For example, if you have two characters interacting, a composite center of mass can be used to monitor the characteristics of their interaction.

To create a composite Center of Mass:

1. Switch to the Rigging Mode.

2. Select every Center of Mass.

3. Use Commands → CenterOfMass → Create composite:

The composite Center of Mass, like a regular one, should be connected to the meshes and Direction Controllers, as described above.


See Also

Center of Mass (Physics Tools)

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