Building a Bones System

In some instances, establishing a hierarchy of objects before linking objects is easier. By building the hierarchy first, you can be sure of the links between objects. One way to build this hierarchy is to use a bones system. A bones system consists of many bone objects that are linked together. These bone objects are normally not rendered, but you can set them to be renderable, like splines. You can also assign an IK Solver to the bones system for controlling their motion.

To create a bones system, select Create Systems Bones IK Chain, click in a viewport to create a root bone, click a short distance away to create another bone, and repeat this a few more times. Each subsequent click creates another bone linked to the previous one. When you're finished adding bones, right-click to exit bone creation mode. In this manner, you can create a long chain of bone objects all linked together.

These bones are actually linked joints. Moving one bone pulls its neighbors in the chain along with it. Bones can also be rotated, scaled, and stretched. Scaling a bones system affects the distance between the bones.

To branch the hierarchy of bones, simply click the bone where you want the branch to start while still in bone creation mode. A new branching bone is created automatically. Click the Bones button again to create a new bone. Then continue to click to add new bones to the branch.

Figure 39.1 shows the rollouts that are available for creating bones.

Figure 39.1: The Bone rollouts lets you specify which bones get assigned an IK Controller.

Assigning an IK Solver

In the IK Chain Assignment rollout (found in the Modify panel when a bone is selected), you can select from four IK Solvers: History Dependent, IKHISolver, IKLimb, and SplineIK Solver. You can assign each of these solver types to children and to the root bone using the available options. You need to select both the Assign to Children and the Assign to Root options to assign the IK Controller to all bones in the system. If the Assign to Children option is deselected, then the Assign to Root option is disabled.

CROSS-REF 

Chapter 40, "Adding Inverse Kinematics," presents details on each of these IK Solvers.

Setting bone parameters

The Bone Parameters rollout (also in the Modify panel) includes parameters for setting the size of each individual bone, including its Width and Height. You can also set the percentage of Taper applied to the bone.

Fins can be displayed on the front, back, and/or sides of each bone. For each fin, you can specify its size and start and end taper values. Including fins on your bones makes correctly positioning and rotating the bone objects easier. Figure 39.2 shows a simple bones system containing two bones. The first bone has fins.

Figure 39.2: This bone includes fins that make understanding its orientation easier.

At the bottom of the Bone Parameters rollout is an option to Generate Mapping Coordinates. Bones are renderable objects, so this option lets you apply texture maps to them.

Tutorial: Creating a bones system for an alligator

To practice creating a bones system, we take a trip to the deep South to gator country. The main movement for this gator is going to be in its tail so we need the most bones there. The front legs are smaller and can be controlled with only two simple bones. We also won't worry about fingers.

To create a bones system for an alligator, follow these steps:

1. Open the  Alligator bones.max file from the Chap 39 directory on the DVD. This file includes an alligator model created by Viewpoint Datalabs.

2. Select Create Systems Bones IK Chain, and in the IK Chain Assignment rollout, select IK Limb from the IK Solver drop-down list. To be able to see the orientation of each bone, enable the Side Fins.

3. In the Top viewport, click the end of the nose, then the base of the head, and continue down the backbone and along the tail. End with a bone at the base of where the arms and legs start. Then right-click to end the bones chain.

4. While still in Bones mode, click the bone just in front of the legs in the Top viewport and drag to the top to form the left arm bone. Continue to click to form the left lower arm. Right-click to end the chain. Repeat to create bones for the opposite arm and the legs.

5. Click the Select Objects button on the main toolbar to exit Bones mode, and select and name each bone object so it can be easily identified later.

Tip 

The Schematic View window is a good interface for quickly labeling bones.

Figure 39.3 shows the completed bones system for the alligator.

Figure 39.3: This bones system for an alligator was easy to create.