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774 Chapter 13: reactor
rollout. This value can be as low as –1.0,
but –0.1 should suffice in most cases. This
scales the Collision Tolerance (page 2–808) for
pieces of a fracture object. A negative Scale
Tolerance value effec tively shrinks the object
as it is perceived by the collision-detection
system. Pieces that were snug against each
other now have a comfortable safety zone
wherenocollisionstakeplace. Thisistied
to the Collision Tolerance value, so changing
Collision Tolerance changes the effective
tolerance used when fracture pieces collide with
other fracture pieces. It dramatically reduces
unstable oscil lations. This is the most effective
thing to try when you wish to avoid explosions.
• Manua lly offset the pieces from each other,
leaving a physical gap b etween al l pieces. The
gap should be as big as Collision Tolerance *
Scale Tolerance.
• Increase the Energy Loss value on the Fracture
object’s Properties rollout. This is the percent of
energythatcanbe"lost"inthefractureeventby
transferring momentum f rom the broken piece
totheunbrokenFractureobject.Increasingit
increases the relative velocity between the newly
fracturedpieceandtheremainingunfractured
pieces. Ultimately this reduces the chances of a
chain-reaction of unstable oscillations.
• IncreasetheSeparationTimevalueand/or
decrease the Velocity C ap in the Fracture
Pe netrations (page 2–773) group of the World
rollout. This controls how aggressively
reactor pushes the pieces out of a state of
interpenetration. After doing this you may
notice visible interpenetrations.
• Slice up your object in a different configuration.
Avoid c reating very small pieces, especially if
theyarerightnexttoverylargepieces.
• Turn on the Use Connectivity check box on the
Properties rollout of the Fracture helper. When
connectivity is enabled, clumps of pieces that
are disconnected from other clumps but still
internally glued to each other are set f ree to
move independent of the other clumps. This
ser ves to create gaps between fractured pieces
earlier, so unstable oscillations won’t happen.
Storing and Accessing Collisions
Utility panel > reactor > Collisions rollout
reactor lets you store information about all rigid
body collisions that occur during the simulation.
You can access this information via MAXScript
or sa v e it to a text file. The information includes
the objects involved, the point of collision, and the
relative velocity during collision. You can then
use it to generate particles or other effects in your
animation when objects collide, trigger sounds,
and s o on.
You can activate and configure collision storing
using the reactor utility’s Collisions rollout (page
2–810).
Interfa ce
Store Collisions group