3ds Max 2012 Bible - Kelly L. Murdock [413]
If the Iterations value is reached without a valid solution, Max uses the last calculated iteration. •
The Use Secondary Threshold option provides a backup method for determining whether Max should continue to look for a valid solution. This method should be used if you want Max to bail out of a particularly difficult situation rather than to continue to look for a solution. If you are working with very small thresholds, you want to enable this option.
The Always Transform Children of the World option enables you to move the root object when it is selected by itself, but constrains its movement when any of its children are moved.
Tutorial: Animating a simple IK propeller system
Machines are good examples of kinematics systems. In this example, you animate a simple gear-and-propeller system using the Applied IK method.
To animate an inverse kinematics system with a propeller, follow these steps:
1. Open the Gear and prop.max file from the Chap 38 directory on the CD.
This file includes a simple handle-and-prop system.
2. To accomplish the first task—linking the model—click the Select and Link button on the main toolbar, and drag from each child object to its parent. Connect the propeller to the shaft, the shaft to the gear, and the gear to the handle.
3. Open the Hierarchy panel, and click the IK button. Constrain the motions of the parts by selecting the handle object. All Sliding Joints can be deactivated, and only the Z Axis Rotational Joint needs to be activated. To do this, make sure that a check mark is next to the Active option. When this is set for the handle object, click the Copy button for both joint types, select the gear object, and click Paste to copy these constraints. Then select the shaft object, click both Paste buttons again, and repeat this process for the propeller.
4. Enable the Auto Key button (or press the N key), drag the Time Slider to frame 100 (or press the End key), and click the Interactive IK button in the Inverse Kinematics rollout of the Hierarchy panel. Select the Select and Rotate button (or press E), and drag in the Left viewport to rotate the handle about its Z-axis.
Figure 38.10 shows the propeller system.
Applied IK
Applied IK applies a solution over a range of frames, computing the keys for every frame. This task is accomplished by binding the IK system to an object that it follows. This method is more precise than the interactive IK method, but it creates lots of keys. Because keys are set for every object and every transform, this solution sets lots of keys, which increases the size and complexity of the scene. Each frame has its own set of keys, which could result in jerky, non-smooth results.
FIGURE 38.10
The propeller rotates by turning the handle and using IK.
To animate using the Applied IK method, you need to bind one or more parts of the system to a follow object, which can be a dummy object or an object in the scene. You do so by clicking the Bind button in the Object Parameters rollout of the Hierarchy panel and selecting an object in one of the viewports. After the system has a bound follow object, select an object in the system. Open the Hierarchy panel; in the Inverse Kinematics rollout, click the Apply IK button. Max computes the keys for every frame between the Start and End frames specified in the rollout. Click the Apply IK button to start the computation process that sets all the animation keys for the range of frames indicated.
History Independent IK solver
The History Independent (HI) IK solver looks at each keyframe independently when making its solution. You can animate linked chains with this IK solver applied by positioning the goal object; the solver then inserts a keyframe at the pivot point of the last object in the chain to match the goal object.
You can apply IK solvers to any hierarchy of objects. IK solvers are applied automatically to a bones system when you create the system. You also can choose Animation⇒IK Solvers to select an IK solver.
When you choose Animation⇒IK Solver, a dotted line appears from the selected