9.5.2

488 • CHAPTER 8
TOOLS MENU • 489
The best way to understand the tumbling issue is to see it in action. The goal here is to tilt a cube and
then animate the cube rotating about its Y-axis. It’s not as easy as it sounds!
 Choose File > New to start a new scene.
 Choose Objects > Primitive > Cube to create a cube.
 In the Coordinate manager, under Rotation, set B (bank) to 30° and click
Apply to apply the angle to the cube.
 In the animation toolbar, disable the Position, Scale and Parameter icons so
that only Rotation is active.
 Click Record. Open the Timeline if it isn’t already open and you’ll see that a
new rotation sequence with a key at frame 0 has been created for each rotation
track (H, P and B).
 Drag the time slider to frame 50 and click Record. A new key will be created
for each rotation track.
 Open the Timeline. On the Timeline’s Edit menu, disable the Vector Selection
option. Click on the new key for the Rotation.H track at frame 50 and in the
Attribute manager, set Value to 360°.
 Click Play to view the animation.
Although the cube now rotates, it doesn’t rotate about its local Y-axis. Instead, it’s tumbling. Why?
As mentioned earlier, HPB rotations refer to the object’s parent system. In this case, the cube has no
parent and so instead the HPB rotations refer to the world coordinate system. Thus the cube rotates
based on the world system’s Y-axis rather than its local Y-axis.
So how can you make the tumbling cube rotate about its Y-axis instead?
 Select both of the keys for the Rotation.B track and in the Attribute manager,
set the Value for the keys to 0°.
 Create a Null object. Make the cube a child of the Null object.
 Select the Null object and in the Coordinate manager, set B (Bank) to 30° and
click Apply to tilt the null and its child (i.e. the cube).
 Click Play to view the animation.
The cube now rotates about its Y-axis as desired, thanks to its parent null that provides the necessary
rotation axis.
Rotating multiple objects
When multiple objects are selected, a shared axis system appears in the viewport between the selected
objects. You can rotate the objects using the shared axis system or you can rotate the objects using
any one of their object axis systems (click the origin of the object axis system that you want to use).