8

Dynamics Utility 667
collide with each other, and assign the gravity
effect to the ball. )
5. UsetheDynamicsutilitytospecifytherangeof
frames to which keys will be generated, and to
calculate the animation and generate the keys.
(Inthecaseofabouncingball,anumberof
position and rotation k eys are generated for the
ball.)
6. Play the animation to see if the effect is what you
were looking for. If one or more objects fly off
into space, or move through objects they should
have bounced off, it’s likely that you need to
increase the Calc Intervals Per Frame value.
To red uce the number of key s generated by the
Dyna mics utility:
When y ou solve a dynamics simulation, Position
andRotationkeysaregeneratedateveryframeof
the specified range for every object affected in the
simulation. Not only does this result in an excess
ofkeysforlaterediting,butitcanincreasethesize
of the
.max file tremendously. The following steps
show how to reduce the number of keys using
Track View.
1. After solving the simulation, check the
animationtomakesureit’swhatyouwant,and
then save that version of the scene.
2. Deselect every object in the scene.
3. In the Dynamics panel > Objects in Simulation
group, click the Select Objects In Sim button.
All objects included in the simulation are
selected.
4. OpenaTrackViewwindow,andthenset
its filter to show Animated Tracks Only and
Selected Objects Only.
5. Right-click the top object in t he Hierarchy list
(Objects), and choose Expand All.
Track View now shows all tracks in the
simulation that have keys.
6. Go to Edit Time display mode and select all of
the tracks containing keys (or rig ht-click over
thehierarchy,andchooseSelectAll).
7. Double-click any key to select all keys in all
tracks.
8. Click the Reduce Ke ys button, set the T hreshold
to what you want, and t hen click OK.
All selected keys are reduced.
9. Save the reduced version of the scene either
under a new name, or by replacing the or iginal
file.
To use link ed hierarchies in a simulation:
When linked hierarchies are included in your
simulation, you must set locks for the children in
the simulation to confine the dynamics results to
specific axes. Do this on the Hierarchy panel >
Link Info >
Locks rollout (page 2–482) .
The Locks rollout contains three rows of check
boxes affecting the XYZ axes of the three possible
transforms: Move, Rotate, and Scale. The Scale
transformsareignored,andonlytheMoveand
Rotate locks are used. When a check b ox is turned
on, that axis of the specific transform is locked.
When you manipulate a forward-kinematics
hierarchydirectlyusingtheMoveorRotatetools,
you might not bother with the Link Info locks,
because you can specif y axis constraints using the
X,Y,Z,andXYbuttonsinthetoolbar.However,
when you use that same hierarchy i n a dynamics
simulation, where there are several forces at work
(gravity, wind, collisions), the only thing that
maintains the linkage between the objects is the
locks you set in the Link Info > Locks rollout. As a
result, no matter what combination of Mov e and
Rotate locks you use, you ’ll always want at least one
Move lock in place, or your objects won’t really
be linked.
The following lists all of the combinations of
Move and Rotate locks that make sense within a