Utility panel > reactor > Havok 1 World/Havok 3 World rollout
This rollout lets you set some general parameters for your simulated world, such as the strength and direction of gravity, the scale of the world, and how easily objects can collide with each other. When Choose Solver is set to Havok 1, the rollout name is Havok 1 World, and when Choose Solver is set to Havok 3, the name is Havok 3 World.
The only difference between the two different versions of the Havok World rollout is that the Havok World 3 rollout contains an extra group of parameters at the end, named Simulation. The following illustration shows the Havok 3 version of the rollout.
Gravity—The acceleration, in world units, the objects in a scene have due to gravity. It is an important value because it affects the overall feeling of scale in a dynamics simulation.
reactor will generate a warning if you specify a non-standard Gravity value compared to World Scale (see following); that is, if you set the value much higher or lower than –9.8 m/s2, where m is World Scale’s representation of one meter. The warnings are provided for guidance and can be safely ignored if you are happy with the behavior of your animation. The default Gravity value reflects "real-world" gravity: –9.8 m/s2 (–386.22 inches/s2) on the Z axis. For more information, see Scale.
World Scale—The distance in 3ds Max world units, that represents one meter in the reactor world, and hence determines the size of every object in your simulation.
Note: Changing the World Scale value can drastically alter simulated objects' behavior. For more information, see Scale.
Col. Tolerance—(Collision Tolerance) One of the tasks that reactor performs at each simulation step is detection of whether any objects in the scene are colliding, and then updating the scene accordingly. If objects are closer together than the Collision Tolerance value, reactor considers them to be colliding. A high Collision Tolerance value results in a stable simulation, but it can also cause gaps between "colliding" objects.
The default value is 1/10th of World Scale (10 cm if you are modeling using real-world sizes), and it is a good rule of thumb to always keep it above 1/40th (4 mm), due to floating point precision limits in the processor. For standard scenes and object sizes, the default parameters for world scale and tolerance should be adequate. If you are simulating very small objects where the tolerance is still to visible, try reducing the World Scale value and the Collision Tolerance and Gravity accordingly. For more information, see Scale.
Add Deactivator—When on, reactor adds a deactivator to the simulation.
The deactivator keeps track of the objects in the simulation and deactivates (stops simulating) objects that it determines are at rest. This keeps reactor from wasting system resources simulating objects that aren't doing anything.
When Add Deactivator is on, you have access to two distance parameters for determining whether an object is moving or not. The reason that there are two properties rather than just one is for bodies that vibrate. It's possible that a body can end up vibrating after a collision or some other occurrence. A vibrating body might vibrate a few millimeters in distance, which would keep it active for a typical Short Frequency test. However, the object is not really moving anywhere, so keeping it active wastes CPU time. However, if it vibrates in place, it fails the Long Frequency test and is deactivated.
-
Short Frequency—The minimum distance, usually in millimeters, that an object must move during each step of a simulation. If an object in a simulation does not move the specified distance in each step, reactor deactivates it.
-
Long Frequency—Also sets a distance, usually larger than the Short Frequency value. Long Frequency checks every few steps simulation rather than at every step. Any object that does not move the required Long Frequency distance is deactivated.
Add Drag Action—When on, ensures that rigid bodies are subject to constant drag. This damps their linear and angular velocities, so they come to rest sooner. This is useful, for example, where rigid bodies are joined with constraints, as it helps the constrained bodies to come to rest despite the forces applied by the constraints.
Do Not Simulate Friction—When on, reactor ignores all Friction values during the simulation, and objects slide easily across each other.
Fracture Penetrations—These parameters let you adjust how reactor simulates Fracture objects. For details, see World rollout > Fracture Penetrations group.
These controls are available only with the Havok 3 engine.
The first lets you choose how reactor computes the simulation:
-
Discrete—reactor checks for collisions only at the beginning and end of each simulation step. This is faster but less accurate.
Continuous—reactor checks for collisions constantly, throughout each step. This is the default choice, and results in slower but highly accurate simulations. This option significantly reduces the chances of missed collisions.
Max Linear Vel.—The assumed maximum linear velocity for all bodies.
This does not set objects' linear velocity. If, later on, a rigid body's velocity significantly exceeds this value, it might tunnel through other objects even if its Quality property is set to Critical.
The default value is 200 meters/second. This value is used during continuous simulations by the collision solver to optimize the simulation, so if it can assume a maximum linear velocity it can discard several cases and get a solution faster.
Stiffness—The hardness of the constraints in the scene.
Use this parameter to configure the dynamics solver. When constraints used in the scene are very hard or stiff, set this to Hard; the Soft or Medium setting works most other cases. Setting Stiffness to Soft can lead to unstable solutions if the constraints are too stiff.
Tip: Another way to reduce the stiffness of the simulation is by lowering the Strength value of constraints, thus relaxing the constraints.