Bones That Compress

One way to use bones with the biped is to use the Select And Link tool on the 3ds Max toolbar to link the root of the bone to one part of the biped and have the bone End Effector follow another part of the biped. As the biped moves these bones compress and expand.

In the image of the mechanical leg, piston objects are linked to the bones. As the bones compress and expand, they also animate the linked piston assembly. As the bones compress and expand in the abdominal area in the bottom image, the envelopes created by Physique for the bones compress and expand to animate this area on the mesh.

IK Solution

In the IK Controller Parameters rollout, you specify the accuracy of the IK solution and the frame duration of the solution. For bones that compress, you generally want an accurate solution to ensure that the bone follows the end effector perfectly, without any drift. In the image of the rollout Position has a value of 0, the least amount of allowable distance (Rotation is at its default value of 1, the Rotation End Effector is not used in this example). Iterations is set high, ensuring that that the solution is accurate, even if the character is scaled down a great deal. Start and End Time should span the animation.

There are many ways to use bones with the biped. You could automatically animate the bending of a hose that is attached to a character’s shoulder and mouth when the biped head rotates, for example. Bones attached to the biped create links and envelopes when Physique is applied; these extra Physique links offer localized skin control if necessary.

Procedures

To make compressible bones (bones with end effectors):

1. Create a bones system with end effectors.
2. Link the root of the bone to the appropriate biped object.
3. On the Motion Panel, specify an End Effector Parent.
4. Select another part of the bones system.
5. On the Motion Panel, set the Position Threshold to 0.
6. On the Hierarchy panel IK Sliding Joints rollout, turn on all the sliding parameters.
7. Animate the bones system.

   The bones expand and compress with the motion of the character.

To add a bone after Physique is applied using Reinitialize:

1. Turn on (Figure Mode).
2. Add a bone where it is needed.
3. Link the root node of the bone to the biped.
4. On the Physique rollout, click (Reinitialize).
5. On the Physique Initialization dialog, click Initial Skeleton Pose and then click Include New Bones.

   Vertex Link Assignment turns on also.

6. Click Initialize.
7. Adjust envelopes in Sub-Object Envelope.
8. Turn off (Figure Mode).

   If you want the end of the bone to follow the biped, select the bone and delete the bone end effector in the Motion Panel

To add a bone after Physique is applied using Add (Add Bone):

1. Turn on (Figure Mode).
2. Add a bone where it is needed.
3. Link the root node of the bone to the biped.
4. On the Physique Floating Bones rollout, click Add.
5. In the viewports, click a bone.

   Repeat until all bones are added.

6. Adjust envelopes.
7. Turn off (Figure Mode).