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Chapter 4. Rigging the Bones > Elbows and Knees

Elbows and Knees

You've got most of the body parts all rigged up: feet, legs, arms, hands, and shoulders. Two of the last parts to rig are the elbows and knees.

You want to be able to make the elbows and knees point in any direction, independently of what the ankles and wrists are doing.

To accomplish this, you'll take advantage of a built-in control for IK chains.

When you experimented with IK chains at the beginning of this chapter, you saw that every IK chain has a swivel angle. You can place a rig control in the scene and use it as a target for the swivel angle. This will enable you to change the swivel angle interactively by moving the target.

TUTORIAL R13: Rigging Elbows and Knees

Set up the Knee Control
1.
Load the file CharRig18.max or continue from the previous tutorial.

2.
In the Top viewport, create a rectangle about 20 by 20 units in size. Make sure you create a rectangle and not a plane.

3.
Name the rectangle CtrlKneeL.

4.
Move the rectangle so it sits in front of the left knee, a short distance from the leg.

5.
Link CtrlKneeL to CtrlFootL.

This will keep the knee control near the character no matter where he goes.

6.
Select the IK chain at the left foot's ankle.

7.
Go to the Motion panel.

8.
In the IK Solver Properties rollout, click the button under Pick Target, and pick CtrlKneeL.

This will cause the joint between the thigh and calf bones to point at CtrlKneeL no matter where you move the control.

Test the Knee Control

It will be much easier to see whether the knee rig is working if you bend the knee first.

1.
Turn on Auto Key.

2.
Go to frame 10, and move CtrlFootL upward to bend the left knee.

3.
Move CtrlKneeL a short distance in the scene.

The knee should point to CtrlKneeL wherever you move it.

4.
Turn off Auto Key.

5.
Create a control for the right knee, and call it CtrlKneeR. Use the same procedure to make it control the right knee.

Set up Elbow Controls
1.
Copy one of the knee controls, and place it behind the left elbow.

2.
Name the control object CtrlElbowL.

3.
Link CtrlElbowL to CtrlWristL.

4.
Select the IK chain at the left wrist.

5.
On the Motion panel, click the button under Pick Target, and pick CtrlElbowL.

6.
Repeat this procedure for the right elbow.

7.
Save the scene as CharRig19.max.

Parameter Collector

The Parameter Collector is a floating dialog in which you can place parameters from the scene. It provides one central location for a group of related parameters that might otherwise be found in many different locations in the user interface. For example, you could put all the foot roll and finger curl parameters in one Parameter Collector dialog. This would allow you to animate the rig's hands and feet without having to select the wrist and foot controls each time.

To open the Parameter Collector, choose Animation > Parameter Collector. To add parameters to the dialog, click Add to New Rollout, and expand the Objects listing in the Track View Pick dialog until you find the parameter(s) you want to add to the dialog. You can organize and rename your rollouts with the Rollouts options in the dialog.

TUTORIAL R14: Finishing the Rig

To complete the rig, you just need to create an overall control for the legs and another for the body, and tidy things up a little.

Create the Control for the Legs
1.
Load the file CharRig19.max, or continue from the previous tutorial.

2.
In the Top viewport, create a circle shape about twice as wide as the character's body. Name the shape CtrlLegs.

TIP

Some riggers prefer to create one control for the spine and another for the legs. This type of rig gives you the ability to rotate the thighs independent of the spine.

3.
Align the shape with BoneSpine01. In the Align dialog, set both Current Object and Target Object to Pivot Point.

4.
Link the thih bones to CtrlLegs.

5.
Unhide the spine control objects.

6.
Link the lowest spine control shape, CtrlSpineBase, to CtrlLegs.

7.
Link the wrist controls to CtrlLegs.

This will cause the arms to move when the spine goes up and down. Some riggers don't like to limit the rig in this way, but I find it easier to work with this arrangement.

Create an Overall Body Control

You need just one last item: A single object that controls the entire body, so you can easily move the entire character at once. This is essential for placing the character at the start of the animation.

1.
In the Top viewport, create a rectangle larger than the CtrlLegs circle. Name the rectangle CtrlBody.

2.
Position the rectangle at the bottom of the character's feet.

Now, the only remaining task is to link up the wrist and shoulder controls.

3.
Link CtrlLegs, CtrlFootL, and CtrlFootR to CtrlBody.

4.
Test the linkage by moving CtrlBody.

When you move CtrlBody, the entire hierarchy should go with it.

Create Named Selection Sets

To prepare the rig for animation, you'll create a named selection set for the controls.

1.
Select all the control objects (all objects beginning with Ctrl).

2.
Create a named selection set called Control Objects.

3.
Select all the IK chains, and create a named selection set called IK Chains.

4.
On frame 0, remove all existing animation keys from control objects. To do this, select all the control objects, and draw a selection region around the keys on the Trackbar. The keys will turn white when selected. Press [Delete] on the keyboard to delete the keys.

5.
Save the scene as CharRig20.max.

There are more controls you could add to this rig, but these will be sufficient for many types of animation. You'll animate with this rig in the Animation section. But before you can do that, you'll need to skin the character with the tools and techniques described in the next chapter.

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