2009

can also simulate a rigid body made up of more than one primitive. To do
this, you need to group objects together using the 3ds Max Group menu. You
can then add the group to the collection, and the objects in the group then
become the primitives that make up the rigid body.
Creating such compound rigid bodies can be useful, as it is much faster to
simulate a rigid body made up of convex pieces than to simulate a more
complex concave shape. In addition, the primitives that make up a compound
rigid body can have different masses, so you can create rigid bodies that have
nonuniform mass distribution. For example, you can create a hand axe where
the head is heavier than the handle, so that if you toss the axe it spins around
its head.
You can do this because the Mass property on the Rigid Body Properties dialog
is assigned to a specific primitive rather than an entire rigid body, unlike most
of the other properties in this dialog. For single-primitive rigid bodies, this
distinction is unimportant. However, in the case of a compound rigid body,
the group parent is the rigid body and cannot have a Mass value assigned:
Mass can be assigned only to its children, the primitives.
Simulation geometry is also defined at a primitive level, so you can combine
concave and convex hull geometries in a single rigid body.
Procedures
To create a compound rigid body:
1 Arrange the objects to use to make up your compound rigid body.
2 Select all of the objects.
3 From the Group menu, choose Group.
Compound Rigid Bodies | 3921