Next, you create IK handles
that you’ll later use to pose the arms and legs. The next steps
describe some initial setup you should perform before creating the
To set up the character prior to creating
- Select the root of the hierarchy, back_root,
and then select
Skeleton > Set Preferred Angle.
This sets the current joint angles throughout
the skeleton as the preferred angles. This is a useful step after
you complete a skeleton. Maya thereafter uses the current bend in
the knees and elbows as the preferred initial rotation direction
of these joints during inverse kinematics (IK) posing. This makes
it easier to pose the character with motion that is natural for
a human character.
- Select Jackie in the Outliner and,
from the main menu, select Display > Hide >
(You must select Jackie from the Outliner because Jackie
is a template object.) By hiding Jackie, you’ll lessen scene clutter
as you pose the skeleton in the following steps.
create, pose, and animate IK handles for the legs
Skeleton > IK Handle Tool > .
- In the Tool Settings window,
make sure Current Solver is set to ikRPsolver.
This type of IK solver
has characteristics that work well for this application.
- In the perspective view, click left_hip
This creates an IK handle
that lets you control all joints from left_hip through left_ankle.
The handle’s main manipulator is at the left_ankle.
The IK handle is the
selected object after you create it. If you unintentionally cancel
the selection of the handle, you can select it again by clicking the
left_ankle—the last joint you clicked after using the IK
Handle Tool. Whenever you select a handle, make sure
you do not select joints or other objects along with the handle.
You can check the Outliner to confirm your selection.
- Go to the start of the playback range.
- With the IK handle selected, select
Animate > Set Key to
key the leg’s current position at the first frame.
- Go to frame 12.
- In the side view, use the Move tool
to drag the IK handle up and to the left (see illustration), as
if Jackie were stepping up a staircase. The foot and knee move while
the hip stays in place.
- Set another key for the IK handle.
- Go to frame 24. Move the IK handle back
to its prior position. Set another key.
- Play the animation to see the leg step
up and down during the first 24 frames.
This completes a simple
animation of the leg using an IK handle to control its position.
To practice additional IK techniques
- Go to the start of the animation.
- In a perspective view, practice posing
the leg in various directions by moving the IK handle.
No matter how far you
drag the handle manipulator, the joints of the leg will not stretch
beyond the straight leg position. This is desirable; you do not
want the size of a skeleton to change as you pose it. However, if
you drag a leg joint, the bone hierarchically above that joint will
lengthen. This is why it’s important to check that you haven’t selected
a joint with the IK handle before you move the handle.
As you drag the handle
to some positions, you might notice the leg joints flip abruptly
(see the next figure for an example position). It’s therefore hard
to control the leg positioning in this region.
The default IK handle (IK
Rotate Plane handle) has manipulators you can use to
avoid joint flipping. With the handle selected, select Modify
> Transformation Tools > Show Manipulator Tool.
Move the Pole Vector XYZ manipulator to a slightly different position
(see the following figure).
If this doesn’t solve the problem, rotate
the Twist manipulator to rotate the leg. You can key the Pole Vector
XYZ and Twist attributes to fixed values to avoid the flipping as
the character moves.
A more precise way to avoid joint
flipping, which requires some initial setup, is to use a Pole Vector
Constraint. For more information see
Pole Vector constraints.
- Repeat the preceding steps for the right
leg. (Create an IK handle for the right_hip to right_ankle, then
practice posing and animating the handle.)
you want to move the entire skeleton, group the back_root and all IK
handles under a single node, select the group node, and then use
the Move tool. With this grouping, the motion of the entire skeleton
won’t conflict with the keys you set for the handles.
To create, pose, and animate IK handles
for the arms
Skeleton > IK Handle Tool.
- Click left_shoulder, and then click left_wrist.
This creates an IK handle for the left arm.
Skeleton > IK Handle Tool.
- Click right_shoulder, then click right_wrist.
This creates an IK handle for the right arm.
- Practice posing and animating the handles.