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Using convex meshes

A convex object can use several of the options found in the Physical Meshes rollout, including Sphere, Box, Capsule, and Convex. Use the shape that best fits the mesh you are working with.

The properties for the mesh types are listed in the Physical Mesh Parameters rollout. When an object type is applied to an object, the Convex mesh type is applied by default, because it generally works for all objects. The Convex mesh type is created from a Geosphere object represented by 32 vertices. If you reduce the number of vertices—or switch to a Sphere, Box, or Capsule mesh type—you can speed up the simulation calculations.

Using the Inflation value, you can increase or decrease the size of the collision mesh. Additional settings are available in the Physical Mesh Parameters rollout for each type. For example, the Sphere mesh type has a Radius value and the Box mesh type has Length, Height, and Width values. If you make changes to the Convex mesh type that don't work, you can always regenerate the mesh using the Regenerate from Original button.

If the collision mesh shape is right, but its position is off, then you can choose the Mesh Transform subobject mode in the Modifier Stack and change the mesh's position and orientation.

Using concave meshes

If you have a concave object that you want to use in the simulation, you should first try to use a convex collision mesh if possible, but if you can't (such as with the bowl in the preceding example), the best option is the Composite mesh type. For example, a doughnut-shaped object bouncing in a scene could easily use a flat sphere shaped convex collision mesh because it isn't likely that a smaller object will go through the doughnut's center. However, if you are dealing with a basketball rim, then enabling a convex mesh won't work because objects will be going through the rim's center, so a concave collision mesh is required.

This Composite option lets you specify the number of vertices and several other settings and includes a Generate button to automatically create the collision mesh based on the object's geometry. Once generated, the number hulls and vertices included in the collision mesh are displayed. If these numbers are still too high, you can change the Max Vertices, Split Levels, or Size Difference values and try the Generate button again. Remember that more vertices means better accuracy in the simulation, but also more time to complete.

The Original option works well for concave objects that are set to static and won't move during the simulation. It uses the actual mesh as the collision mesh.

The Custom option lets you create a collision mesh based on selected piece of geometry in the scene. It includes buttons for picking the source object and extracting a mesh from the source object. The proxy mesh should be a low-resolution version of an object used here for collision detection.

Caution

Custom collision meshes are limited to objects with 256 vertices or less. •

Setting initial motion

Every dynamic object has an initial motion setting that you can control to start the object in motion. This works whether gravity is enabled or disabled. The Initial Motion values are located in the Advanced rollout and can be set to an Absolute or Relative value. If a kinematic object is in motion when it is converted to a dynamic object using the Until Frame setting and it has an initial motion value, then the Absolute setting uses only the initial motion value and the Relative option adds the initial motion value to the existing keyframed motion that the object already has. The X, Y, and Z value denote a direction, and Speed sets how fast the object is moving. A setting for the initial spin of the object is available as well.

The Damping values are used to slow down the motion (Linear) and the rotation (Angular) of objects in motion with higher values causing the objects to rapidly decrease their speed.

Under the MassFX Rigid Body modifier that is applied to the selected object, you can select the