9

690 Chapter 12: Animation
6.
Go to E dit Time display mo de and select all of
the tracks containing keys (or r i ght-click over
the hierarchy, and choose Select All).
7. Double-click any key to select all keys in all
tracks.
8. Click the Reduce Keys button, set the Threshold
to w hat you want, and then click OK.
All selected keys are reduced.
9. Save the reduced version of the scene either
under a new name, or by replacing the original
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 2–500).
The Locks rollout contains three rows of check
boxes affecting the XYZ axes of the three possible
transforms: Move, Rotate, and Scale. The Scale
transforms are ignored, and only the Move and
Rotate locks are used. When a check box is tur ned
on, that axis of the specific transform is locked.
When you manipulate a forward-kinematics
hierarchy directly using the Move or Rotate tools,
you might not bother with the Link Info locks,
because you can specify axis constraints using the
X, Y , Z, and XY buttons in the toolbar. However,
when you use that same hierarchy in a dynamics
simulation, where there are several forces at work
(gravit y, wind, collisions), the only thing t hat
maintains the linkage b etween the objects is the
locks you set in the Link Info > Locks rollout. As a
result, no matter what combination of Move and
Rotate locks you use, you’ll a lways want at least one
Mov e lock in place, or your objects won’t really
be linked.
Thefollowinglistsallofthecombinationsof
Move and Rotate locks that make sense within a
dynamics si mulation, and the effect on the link of
such combinations. An asterisk (*) indicates those
combinationsthataremoretypicallyuseful.
Theformatofthislistisasfollows:
X=check box on.
O=check box off.
One group of settings is made up of the three Move
check b oxes over the three Rotate check boxes.
Here’s an example:
XXO=X and Y Move check b oxes on, and Z off.
OXO=Y Rotate check box on, and X and Z off.
1. 1MoveLock:Tur n on any single Move. ( This
is like a long pin sliding in a loose, long slot.)
The joint can transmit force in one direction
only. The objects can slide with respect to each
other in two directions and rotate freely.
2. 2MoveLocks:Turn on a ny two Moves . ( T his
is like a sliding ball joint; a freely rotating joint
at the end of a sliding shaft, which can slide and
rotateinahole.)
3. *3MoveLocks:Turn on three Moves. (This
islikeaballjoint,orthetheoretical"pinjoint"
of the statics and dynamics texts, in that it
trans mits any force but never tra nsmits any
torque.)
4. 1Move+1Rotate(unique):Turn on any
oneMoveandanyoneRotate,butnotinthe
same column. (This is like two long pins,
parallel, sliding in a sing le long slot.) The joint
can transmit force in one direction only and
restrain rotation about the axis of the "pins."
This combination is of limited application.
5. 2Moves+1Rotate(matching):Tur n on
two Moves, plus one Rotate tu rned on that’s
in the same column as one of the selected
Moves.(Thisisthesameas1Move+1Rotate,
above, except that the pins can no longer slide
vertically in their slot.) If the assembly rotates