Rigid Body Properties

Mass—A rigid body’s mass governs how the object interacts with other objects. When its mass is set to 0.0 (the default value), the object remains fixed in space during the simulation, although other objects will be able to collide with it. For example, you could use a fixed rigid body to create a slope for other objects to roll down. Other values allow the object to move during the simulation, depending on other circumstances. A valid value for Mass is greater than or equal to 0.0.

Friction—The coefficient of friction for the object’s surface. This affects how smoothly the rigid body moves relative to surfaces it’s in contact with. The friction values for both objects combine to produce a coefficient for the interaction. To achieve realistic results, use values between 0.0 and 1.0. However, values up to 5.0 are accepted.

Elasticity—This value governs the effect collisions have on the velocities of the rigid body; in other words, how "bouncy" the object is. Like Friction, this is a pair-wise coefficient: When two objects collide, their elasticity values combine to produce a coefficient for the interaction. To achieve realistic results, use values between 0.0 and 1.0. However, values up to 5.0 are accepted.

Inactive—When on, the rigid body starts the simulation in an inactive state. This means it requires interaction with another object or system, or the mouse, before it becomes active in the simulation. For example, if you place an object in midair, give it a mass and set it to Inactive, when the simulation starts it sits in midair until something interacts with it. Inactive objects require less computation during simulation.

Disable All Collisions—When on, the object doesn’t collide with other objects in the scene; it simply passes through them.

Unyielding—When on, the rigid body takes its motion from the animation it already has in 3ds Max, rather than the physical simulation. Other objects in the simulation can collide with it and react to its motion, but its motion is governed solely by the current animation in 3ds Max, and reactor will not create keyframes for it.

Phantom—A phantom object has no physical presence in the simulation. Like an object with Disable All Collisions on, it simply passes through other objects. Unlike an object with disabled collisions, however, a phantom maintains collision information about any objects that it passes through during the simulation. You can then use this collision information, for instance, to trigger sounds or other effects. You can find out how to access collision data in the Storing and Accessing Collisions.

Shell—The radius of an extra "shell" around convex shapes, which reactor uses as the shape's surface for collision-detection purposes. The simulation tries to ensure that the distance between this shell and other objects is always more than zero; in other words, that the distance between the original convex shape and other objects is always more than the combined radii of the objects. Default=0.05.

Important: Applies to Havok 3 only.

Adding a shell to an object can improve performance. The core convex-convex collision-detection algorithm is fast when objects are not interpenetrating, and slower when they are. Adding a shell makes it less likely that the shapes themselves will interpenetrate, thus reducing the likelihood of using the slower algorithm. Using a shell is thus faster in situations that involve the risk of shapes interpenetrating; for instance, when an object is settling or sliding on a surface, when there is a stack of objects, or when many objects are jostling together.

Penet.—(Penetration) The amount of penetration reactor permits.

To avoid trying to solve insoluble physical problems, the Havok 3 engine allows penetration between objects even if continuous physics is enabled. Default=0.05.

Important: Applies to Havok 3 only.

Quality—Lets you set individual settings for each object based on the desired level of interaction. Default=Moving.

Important: Applies to Havok 3 only.

The available Quality settings are:

Lets you specify the physical representation of your object that will be used in the Havok simulation.

reactor supports substituting one object for another in two different ways: geometry proxies and display proxies.

Geometry proxies allow you to specify a different body’s geometry as the simulation geometry for an object. For example, you can have a complex object displayed on-screen, but replaced for simulation purposes by a box, which is much easier and faster for reactor to simulate. The box governs the movement of the object, and dictates how it collides, its position, and orientation. However, on-screen you can see the complex object in full detail. Geometry proxies are applied per object.

Display proxies replace a rigid body’s display body with that of another object. Therefore, they affect display only during the real-time preview and do not affect animation. They are applied per rigid body, rather than per object. This means that you can create a compound rigid body of several objects and simulate these, but display an alternative mesh for the body during the preview. You can find out how to specify a display proxy in the Display section.

A rigid body primitive is defined as convex if, given any two points inside the object, you can always go in a straight line from one to the other without leaving the object. Convex objects include spheres, cylinders, and boxes. For example, a sphere is convex but a golf ball is concave because of the concavities (dimples) in its surface. Also, by definition, non-closed meshes (planes, hollow hemispheres) are always concave.

Convex objects are faster to simulate than concave objects. Because of this, you should aim to use convex objects as often as possible for simulation. Treating concave objects as convex for simulation purposes allows you to take advantage of their faster processing time. This is the default setting for an object’s simulation geometry (Mesh Convex Hull). If you are unsure whether an object is convex or concave, you can perform a convexity test on it. With the object selected, open the reactor - Utilities menu and select Convexity Test.

You can specify one of the following simulation geometry options to define how your object will be represented in the physical simulation. To view the simulation geometry for your objects in the preview, as in the following examples, select Sim Edges from the Display menu in the Preview Window.

Bounding Box—The object is simulated as a box whose extents are determined by the object’s dimensions.

Bounding Sphere—The object is simulated as an implicit sphere. The sphere is centered on the object’s pivot point and then minimally encloses the object’s geometry.

Mesh Convex Hull—This is the default option. The object’s geometry is passed through an algorithm that creates a convex geometry using the geometry’s vertices, completely enclosing the geometry’s vertices. To visualize this, imagine shrink-wrapping a teapot: The teapot is concave but its shrink-wrap forms a convex hull.

Proxy Convex Hull—The convex hull of another object is used as the physical representation of the object in the simulation. For instance, you could use the convex hull of a low-poly teapot to simulate a high-poly teapot. The proxy object’s pivot point is aligned with that of the rigid body.

Concave Mesh—The actual mesh of the object is used for simulation. Although the convex hull of an object and the object’s actual mesh may be exactly the same shape, using the convex hull simulates much more quickly, as reactor can make certain assumptions for convex objects. If you try to use Concave Mesh for a convex object you will get a warning. Not heeding such warnings could dramatically reduce the speed of your simulation. In some cases, though, you might want to ignore that warning. If, for example, you want to place objects inside a convex object, and make them collide with the internal faces of that object, you should simulate it as concave instead of convex.

Note: If you are using a standard 3ds Max plane as a rigid body (as opposed to the special reactor Plane object), you must set its simulation geometry to Concave Mesh.

Proxy Concave Mesh—Another object’s concave mesh is used as the physical representation of the object. For example, you can use a low-poly teapot to animate a highly tessellated teapot. The proxy object’s pivot point is aligned with that of the rigid body.

Not Shared—This option is active only when multiple objects with different Simulation Geometry settings are selected, and cannot be chosen by the user.

Use Display Proxy—When on and you specify a proxy object by clicking the Proxy button, reactor displays the specified proxy In the Preview Window in place of the object.