Select a rigid body.
For a geometric object to participate in a physics simulation, it must have the MassFX Rigid Body modifier applied. The easiest
way to do this is by selecting the object and then choosing the appropriate rigid body type from the flyout on the MassFX
The modifier interface consists of several rollouts on the Modify panel plus a modifier stack with four sub-object levels.
Most of the controls on this rollout are available only for unbaked rigid bodies and become unavailable once you've baked
an object's motion. To restore the controls, click the Unbake button on the Rigid Body Properties rollout.
The Modify panel rollouts for the Rigid Body Modifier are available for only one object at a time; if multiple rigid bodies
are selected, the rollouts do not appear. However, you can edit multiple selected rigid bodies on the Edit panel
of the MassFX Tools dialog. Most of the Edit panel controls are the same as those on the Modify panel.
Modifier Stack - Sub-Object Levels
- Initial Velocity
This level shows a visualization of the direction of the Initial Velocity
for the rigid body. Use the Rotate tool
to change the direction.
- Initial Spin
This level shows a visualization of the axis and direction of the Initial Spin for the rigid body. Use the Rotate tool to change the axis.
- Center of Mass
This level shows a visualization of the location of the Center of Mass for the rigid body. Use the Move tool to change the location.
- Mesh Transform
This level lets you adjust the position and rotation of a physical mesh for the rigid body. Highlight the physical mesh to
transform in the list on the Physical Meshes rollout; the physical mesh will draw in white wireframe in the viewports. Use the Move and Rotate tools to adjust the physical mesh's relative placement with respect to the rigid body.
Rigid Body Properties rollout
- Rigid Body Type
- Until Frame
When on, MassFX converts the selected kinematic body to a dynamic one at the specified frame. Available only when Rigid Body
Type is set to Kinematic.
This means you can animate an object using standard methods and set Rigid Body Type to Kinematic so it performs as animated
until the designated frame. At that point it becomes a dynamic object and is then subject to the full MassFX simulation forces.
For example, to re-create a baseball game, you might animate the ball leaving the pitcher's hand and flying toward the bat.
Then, using Until Frame, when the bat strikes the ball, MassFX would take over and accurately simulate the action of the batter
hitting a home run (or fouling out).
TipA rigid body need not be animated to take advantage of this feature. For example, you might want to suspend several stationary
bodies and then drop them at different times. To do so, simply set them all to Kinematic and turn on Until Frame, then select
each one in turn and specify the frame at which it should start being subject to gravity.
Converts the simulated motion of the selected rigid body to standard animation keyframes for rendering. Applies only to dynamic
If the selected rigid body is baked, the button label is "Unbake" and clicking it removes the keyframes and restores the body
to Dynamic status.
- Use Gravity
When on and the World panel
Gravity Enabled switch is on, the global gravity settings
apply to the selected rigid body.
- Use High Velocity Collisions
- Start in Sleep Mode
When on, the rigid body starts the simulation in sleep mode, using the global sleep settings
. This means that it will not move until struck by a non-sleeping rigid body. For example, to simulate a domino rally, start
all of the dominos except the first in sleep mode.
- Collide with Rigid Bodies
When on (the default), the rigid body collides with other rigid bodies in the scene.
Physical Material rollout
The Physical Material properties control the the way the rigid body interacts with other elements in the simulation: its mass,
friction, bounciness, and so on. You can set the material properties one at a time, or use a preset to simulate real-world
substances such as cardboard or rubber.
Use the drop-down list to choose the physical mesh of the rigid body for which you are changing the material parameters.
By default, all physical meshes use the common material setting labeled "(Object)". Only physical meshes whose Override Physical Material
check box is on show up in this list.
Choose a preset from the list to specify all Physical Material properties. (The mass of the rigid body is recalculated based
on the value of the density and the volume of the object.) When a preset is chosen the settings are not editable, but when
Preset is set to (None) you can edit the values freely.
To use the settings from a different rigid body in the scene, click and then select a rigid body in the scene.
At the bottom of the list are commands to load and save a preset as a file and to create a new preset.
The density of this rigid body, measured in g/cm3
(grams per cubic centimeter). This is one thousandth of the equivalent measurement in SI units: kg/m3
. Changing this value automatically calculates the correct mass for the object, based on its volume.
The weight of this rigid body, measured in kg (kilograms). Changing this value automatically updates the density of the object,
based on its volume.
- Static Friction
The degree of difficulty for two rigid bodies to start sliding against one another. A value of 0.0 indicates no friction (more
slippery than Teflon); a value of 1.0 indicates full friction (rubber cement on sandpaper).
The effective static friction between two rigid bodies is the product of their static friction values. If one rigid body has
a static friction of 0.0, it doesn't matter how what the value of the other is. (Everything slides on wet ice; even sandpaper.)
Once the two objects start sliding, the dynamic friction (see following) applies instead.
- Dynamic Friction
The degree of difficulty for two rigid bodies to keep sliding against one another. Technically, this parameter is called the
"coefficient of kinematic friction." A value of 0.0 indicates no friction (more slippery than Teflon); a value of 1.0 indicates
full friction (rubber cement on sandpaper).
In the real world, this value should be less than the coefficient of static friction. (It's harder to start pushing a couch
across the floor than it is to keep it moving.) As with static friction, the effective value between two rigid bodies is the
product of their respective values.
How easily and high an object bounces when it hits another rigid body. Technically, this parameter is called the "coefficient
of restitution." A value of 0.0 indicates no bounce (a lump of peanut butter dropped on carpet); a value of 1.0 indicates
that the object will bounce off just about as hard as it hit. The effective bounciness between two rigid bodies is the product
of their bounciness values. A super-bouncy rubber ball landing on peanut butter will not recover.
Physical Meshes rollout
Use this rollout to edit the physical meshes assigned to an object in the simulation. You can use the controls to add and
remove physical meshes, change the mesh type, copy physical meshes between objects, and more. When you run the simulation,
MassFX uses all assigned physical meshes to represent the object's physical presence. For more information, see Rigid Body Overview.
Select a Mesh to Modify group
- Mesh List
Shows each physical mesh added to the rigid body. Highlight a physical mesh in the list to rename it, delete it, copy and
paste it, change its mesh parameters or affect its transform via the Mesh Transform sub-object level.
Add a new physical mesh to the rigid body. This mesh type defaults to Convex, covering the entire graphical mesh. After you
add a mesh, it's highlighted in the list so you can change the mesh type, properties, and so on.
Change the name for the highlighted physical mesh. This name is just for your own use to easily identify multiple physical
Delete the highlighted physical mesh from the rigid body. (The last remaining physical mesh for a rigid body cannot be deleted.)
- Copy Mesh
Copy the highlighted physical mesh to the clipboard for subsequent pasting (see following). Mesh parameters and local transform
of the physical mesh are copied along with the mesh.
- Paste Mesh
Paste a previously copied physical mesh (see preceding) onto the current rigid body.
NoteThe new physical mesh is not an instance; any changes you make to the originally copied physical mesh do not affect the new
physical mesh after pasting.
- Mesh Type
The type of the physical mesh applied to the highlighted mesh in the list at the top of the rollout. The available types are
Sphere, Box, Capsule, Convex, Composite, Original, and Custom. Sphere, Box, and Custom are MassFX primitives and simulate
more quickly than convex/custom hulls. For best performance, use the simplest type you can get away with.
Changing the mesh type generates a new mesh of the chosen type sized to fit around the graphical mesh. The options for the
mesh change depending on the mesh type selected, and are available on the Physical Mesh Parameters rollout (see following).
- Convert to Custom Mesh
Clicking this button creates a new Editable Mesh object in the scene from the highlighted physical mesh and sets the physical
mesh type to Custom. You can use standard mesh-editing tools to adjust the mesh, then update the physical mesh from it. For
more information, see Custom.
- Override Physical Material
By default, every physical mesh in a rigid body uses the material settings set on the Physical Material rollout. However, you might be working with a complex rigid body that comprises many physical meshes, where you want to use different
settings for certain physical meshes. In this case, turn on Override Physical Material. All properties in this section work
as described for the Physical Material rollout, but apply only to the selected physical mesh.
Physical Mesh Parameters Rollout
The contents of this rollout vary, depending on the Mesh Type setting (see preceding). For descriptions of the parameters
for each type, see MassFX Physical Mesh Types.
- Override Collision Overlap
When on, MassFX uses the setting specified here for collision overlap for this rigid body instead of the global setting
- Override Solver Iterations
When on, MassFX uses the setting specified here for solver iterations for this rigid body instead of the global setting
Initial Motion group
This setting applies only to rigid bodies that start out kinematic (typically these are already animated) and then switch
to dynamic at the frame specified by the Until Frame setting on the Rigid Body Properties rollout. Normally, the initial velocity
and initial spin of such bodies are calculated based on the animation for the last frame before they become dynamic. When
this option is set to Absolute, the values of Initial Velocity and Initial Spin (see following) are used instead of the animation-based
values. When set to Relative, the specified values are added to the values calculated from the animation.
- Initial Velocity
The starting direction and speed (in units per second) for the rigid body when it becomes dynamic. The XYZ parameters are
maintained as a normalized vector, which can be difficult to edit or picture. To visualize the Initial Velocity direction
and optionally change it with the Rotate tool
, use the Initial Velocity sub-object level
- Initial Spin
The starting axis and speed (in degrees per second) for the rigid body's rotation when it becomes dynamic. The XYZ parameters
are maintained as a normalized vector, which can be difficult to edit or picture. To visualize the Initial Spin axis and optionally
change it with the Rotate tool
, use the Initial Spin sub-object level
- Calculate at Current Time
Applies to animated, kinematic rigid bodies. Determines the motion values (see preceding) for the animated object at the current
frame and then sets the Initial Velocity and Initial Spin fields to those values.
Use this function to apply initial motion values from a point in the animation of the kinematic body other than those at the
frame at which it becomes dynamic.
- Center of Mass
The point around which real physical objects rotate unless they are constrained in some way. To visualize and adjust this
point graphically for the rigid body, use the Center of Mass sub-object level.
- Calculate from Meshes
Automatically determines an appropriate center of mass for the rigid body.
Damping slows down the rigid bodies. Typical uses include reducing oscillations in a simulation or causing an object to appear
to be traveling through a dense medium.
The amount of force applied to reduce the velocity of moving objects.
The the amount of force applied to reduce the rotational speed of rotating objects.