3ds Max 2012 Bible - Kelly L. Murdock [411]
Binding objects
When using applied IK, you need to bind an object in the IK system to a follow object. The IK joint that is bound to the follow object then follows the follow object around the scene. The bind controls are located in the Hierarchy panel under the Object Parameters rollout. To bind an object to a follow object, click the Bind button in the Object Parameters rollout and select the follow object.
In addition to binding to a follow object, IK joints also can be bound to the world for each axis by position and orientation. This causes the object to be locked in its current position so it won't move or rotate along the axis that is selected. You also can assign a Weight value. When the IK computations determine that two objects need to move in opposite directions, the solution favors the object with the largest Weight value.
The Unbind button eliminates the binding.
Understanding precedence
When Max computes an IK solution, the order in which the joints are solved determines the end result. The Precedence value (located in the Object Parameters rollout) lets you set the order in which joints are solved. To set the precedence for an object, select the object and enter a value in the Precedence value setting. Max computes the object with a higher precedence value first.
The default joint precedence for all objects is 0. This assumes that the objects farthest down the linkage move the most. The Object Parameters rollout also includes two default precedence settings. The Child to Parent button sets the precedence value for the root object to 0 and increments the precedence of each level under the root by 10. The Parent to Child button sets the opposite precedence, with the root object having a value of 0 and the precedence value of each successive object decreasing by 10.
Tutorial: Controlling a backhoe
As an example of a kinematics system, you start with a backhoe, which is a simple linkage system with tracks that can move forward, a chair housing that can rotate independently, and an arm and bucket that can rotate about a pivot. When you're finished with this tutorial, you can take the backhoe out and dig a hole for a swimming pool. I think you deserve it.
To create an inverse kinematics system for a backhoe, follow these steps:
1. Open the Backhoe.max file from the Chap 38 directory on the CD.
2. Open the Schematic View window with the Graph Editors⇒New Schematic View menu. Click the Connect button, and connect the tracks to the base plate, the base plate and the housing to the base cylinder, the bucket to the arm, and the arm to the housing. The connections should look like those in Figure 38.7.
Cross-Reference
You can learn more about the Schematic View window in Chapter 25, “Building Complex Scenes with Containers, XRefs, and the Schematic View.” •
FIGURE 38.7
The Schematic View window is helpful for linking hierarchies.
3. Next, you need to define the pivots for the objects that can rotate. Select the housing, and notice that its pivot is already located in the center of the base cylinder where it should be. Then select the arm, open the Hierarchy panel, and click the Pivot button. Click the Affect Pivot Only button, and move the pivot to the center of the cylinder that connects it to the housing. Then do the same for the bucket. Click the Affect Pivot Only button again to exit pivot-editing mode.
4. The next step is to define the joint constraints for the system. Open the Hierarchy panel, and click the IK button. In the Object Parameters rollout, select the base cylinder and enable the Terminator, Bind Position, and Bind Orientation options; doing so prevents the base cylinder from moving anywhere. In the Rotational Joint rollout, deactivate all the axes.
5. Select the housing object, and enable the Bind Position