8

668 Chapter 12: Animation
dynamics simulation, and the effect on the link of
such combinations. An asterisk (*) indicates those
combinationsthataremoretypicallyuseful.
Theformatofthislistisasfollows:
X=check box on.
O=check b ox off.
One group of settings is made up of the three Move
check boxes over the three Rotate check boxes.
Here’s an example:
XXO=X and Y Move check boxes on, and Z off.
OXO=Y Rotate check box on, and X and Z off.
1. 1MoveLock:Tu rn on any sing le 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:Tu r n on th re e Moves. ( This
islikeaballjoint,orthetheoretical"pinjoint"
of the statics and dynamics texts, in that it
transmits any force but never transmits any
torque.)
4. 1Move+1Rotate(unique):Turn on any
one Move and any one Rotate, but not in the
same column. (This is like two long pins,
parallel, sliding in a single 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 Rot ate turned on that’s
inthesamecolumnasoneoftheselected
Moves.(Thisisthesameas1Move+1Rotate,
above, except that the pins can no longer slide
vertically in their slot.) If the assembly rotates
so that one pin travels further into the slot, the
other must ride h igher in the slot. This is of
limited application. The possible check box
combinations are: XXO XXO XOX XOX OXX
OXX OXO XOO XOO OOX OOX OXO
6. *2Moves+1Rotate(complementary):
Turn on two Moves, plus one Rotate that’s
not in the same column as any of the selected
Moves. (T his is a sliding universal joint like
the splined output shaft between the automatic
transmission of a rear-drive car and the drive
shaft.) It can transmit torque and constrain
translationintwodirections,bothorthogonal
totheaxisofrotation.Thepossiblecheckbox
combinations are: XOX XXO OXX OXO OOX
XOO
7. 3Moves+1Rotate:Tu r n on t hree Moves plu s
one Rotate. (This is a universal joint without the
sliding.) It’s typical of automotive applications
where the rear axle is located with the trailing
drive shaft. This is an uncommon application.
8. * 1 Move (comple me ntary ) + 2 Rot a t es: Tur n
on one Mov e that’s complementary to two
Rotates.(Thisislikeahockeypuckonice.)The
joint can slide anywhere on a plane, but cannot
fall or tip, and it cannot leave the surface of the
plane. Thepossiblecheckboxcombinations
are: XOO OXO OOX OXX XOX XXO
9. 2Moves(onecomplementary)+2Rotates:
Turn on two Moves, one of which is
complementary to one of the two Rotates that
are selected. (This is like a hockey puck with
a nail through it, and the nail is sliding along
a groove in the ice.) It’s free to travel in one
direction, and to rotate about an orthogonal
axis. One possible check box combination is:
XXO XOX
10. *2Moves+2Rotates(matching):Tur n on
two Mo v es and two matching Rotates. This
results in a sliding axle (a shaft that can both
slide in a nd out of a hole, and rotate with the