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FIGURE 38.12

The swivel angle defines the plane along which the joint moves.

The IK Solver Properties rollout also includes Threshold values. These values determine how close the end joint and the goal must be before the solution is pronounced valid. You can set thresholds for Position and Rotation. The Iterations value sets the number of times the solution is tried.

Tip

Setting the Iterations value to a higher number produces smoother (less jerky) results, but it increases the time required to find a solution. •

Displaying IK controls

The IK Display Options rollouts can enable, disable, and set the size of the gizmos used when working with IK solvers. Using this rollout, you can Enable the End Effector, the Goal, the Swivel Angle Manipulator, and the IK solver (which is the line connecting the start and end joints).

Tutorial: Animating a puppet with the HI IK solver

The HI solver is probably the best solver to use for animating characters. This fine fellow made of bones makes a good candidate for trying out the HI solver.

To animate a puppet with the HI IK solver, follow these steps:

1. Open the Dancing puppet.max file from the Chap 38 directory on the CD.

This file is the same file that was created using the bones system.

2. Apply the HI solver to the arm chains by selecting the left upper arm and choosing Animation⇒IK Solvers⇒HI Solver. A dotted line appears in the viewports extending from the selected object. Move the cursor over the left hand object, and click.

3. Repeat Step 2 for the right arm and both leg chains.

4. Click the Auto Key button, and drag the Time Slider to frame 20. Select the goal for the left leg IK chain, click the Select and Move button on the main toolbar (or press the W key), and move the left leg goal upward.

5. Repeat Step 4 for frames 40, 60, 80, and 100, moving the various IK chains in different directions.

6. Move the Time Slider to frame 50, and select all objects by choosing Edit⇒Select All (or by pressing Ctrl+A). Drag all the objects upward a short distance. Drag the Time Slider to frame 100 (or press the End key), and drag all the objects back down again.

7. Click the Play Animation button (or press /) to see the resulting dance.

Figure 38.13 shows one frame of the dancing puppet.

FIGURE 38.13

Moving the goal for each IK chain makes animating a character easy.

History Dependent IK solver

The History Dependent (HD) IK solver takes into account the previous keyframes as it makes a solution. This solver makes having very smooth motion possible, but the cost of time to compute the solution is increased significantly. You also can assign this IK solver to a bones system by specifying the History Dependent solver in the IK Chain Assignment rollout or by choosing Animation⇒IK Solvers⇒HD Solver.

This IK solver shows up as a controller in the Motion panel when the IK chain is selected. The settings are contained in a rollout named IK Controller Parameters, which is visible in the Motion panel if you select one of the end effector gizmos. The end effector gizmo is the object that you move to control the IK chain. It is displayed as a set of crossing axes.

You can access the IK Controller Parameters rollout, shown in Figure 38.14, in the Motion panel. Any parameter changes affect all bones in the current structure. In the Thresholds section, the Position and Rotation values set how close the end effector must be to its destination before the solution is complete. In the Solution section, the Iterations value determines the maximum number of times the solution is attempted. These Thresholds and Iterations values are the same as those in the Preference Settings dialog box, except that they affect only the current linkage. The Start Time and End Time values set the frame range for the IK solution.

FIGURE 38.14

The IK Controller Parameters rollout sets the boundaries of the IK solution.

The Show Initial State option displays the initial state of the linkage and enables you to move it by dragging