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axes and the X and Y Orientation axes. Then disable the X and Y Rotation axes. Select the arm object, and enable all the Bind Position axes and the X and Z Orientation axes. Then disable the X and Z Rotational axes. Click the Copy button for the Rotational joint type in the Object Parameters rollout, select the bucket object, and click the Paste button. This copies the joint constraints from the arm object to the bucket object.

6. To test the system, select the Interactive IK button in the Inverse Kinematics rollout and select and move the bucket.

As the bucket is moved, the arm rotates and the housing spins about its axis, just as you'd expect.

Figure 38.8 shows the bucket moving. With the Interactive IK mode disabled, any object can be moved and/or rotated, and only the links are enforced.

FIGURE 38.8

The objects in this scene are part of an inverse kinematics system.

Using the Various Inverse Kinematics Methods

After you create a linked hierarchy chain, you need to apply an IK method to the chain before you can animate it. Max includes several methods for animating using IK. The traditional methods of Interactive and Applied IK are now joined with IK solvers. The Interactive and Applied IK methods are applied using the Hierarchy panel; the IK solvers can be applied to a bones system, or you can use the Animation⇒IK Solvers menu.

An IK solver is a specialized controller that computes an IK solution. This solution is used to automatically set all the required keys needed for the animation. Max offers four IK solvers: History Dependent (HD) IK, History Independent (HI) IK, IK Limb, and Spline IK solvers.

Interactive IK

Interactive IK is the method that lets you position a linked hierarchy of objects at different frames. Max then interpolates all the keyframes between the various keys. This method isn't as precise, but it uses a minimum number of keys and is useful for an animation sequence involving many frames. Interactive IK interpolates positions between the two different keys, whereas Applied IK computes positions for every key. Because the motions are simple interpolations between two keys, the result may not be accurate, but the motion is smooth.

Caution

Be aware that Interactive IK is not available for all IK Solvers. •

After your IK system is established, animating using the Interactive IK method is simple. First, you need to enable the Auto Key button and select the Interactive IK button in the IK rollout of the Hierarchy panel. Enabling this button places you in Interactive IK mode, causing the system to move together as a hierarchy. Then reposition the system in a different frame; Max automatically interpolates between the two positions and creates the animation keys. To exit Interactive IK mode, simply click the Interactive IK button again.

The IK rollout includes several options. The Apply Only to Keys option forces Max to solve IK positions for only those frames that currently have keys. The Update Viewports option shows the animation solutions in the viewports as it progresses, and the Clear Keys option removes any existing keys as the solution is calculated. The Start and End values mark the frames to include in the solution.

IK Preference settings

The required accuracy of the IK solution can be set using the Inverse Kinematics panel in the Preference Settings dialog box, shown in Figure 38.9. You can open this dialog box by choosing Customize⇒Preferences. For the Interactive and Applied IK methods, you can set Position and Rotation Thresholds. These Threshold values determine how close the moving object must be to the defined position for the solution to be valid.

FIGURE 38.9

The Inverse Kinematics panel of the Preference Settings dialog box lets you set the global Threshold values.

You also can set an Iterations limit for both methods. The Iterations value is the maximum number of times the calculations are performed. This value limits the time that Max spends looking for a valid solution. The Iterations settings control the speed and accuracy of each IK solution.

Note