6.10.2 Rotating Skin wound Bones

The purpose of this example is to demonstrate and clarify the purpose of the secondary skeleton required by the general skeleton method, and how it can be used for rotating target objects around the primary skeleton.

1. Create a freeform tube by rotating a curve around a horizontal axis (Create/Freeform/Rotate). Stretch the tube so that the cross-section of it is ellipse. This helps you to visualize the animation when it will be played.

2. Make the freeform tube mesh the current level and subdivide its control polygon to sub-groups horizontally (each sub-group should be an ellipse around the axis of the tube).

3. Create a SKELETON method to control the sub-groups (so put it to the same hierarchy level with them).

4. Create the primary skeleton curve, following the axis of the tube, under the method.

5. Create the secondary skeleton by using the function Create/Controls/Axis; draw the axis perpendicular to the primary skeleton.

6. Select the menu Animate/Control/Refresh so REAL 3D matches the targets with the skeletons.

7. Now, bend the primary skeleton curve and refresh the animation system. The freeform tube is bent accordingly.

8. Swap the orientation of the View window so you look along the primary skeleton, select the secondary skeleton and apply the function Animate/Create/Rotate to it. This makes the secondary skeleton rotate around the primary skeleton, making the "skin" (= the tube surface) also rotate accordingly around the "bones" (= the primary skeleton).

Play the animation; try rotating the View window so you can see how the freeform tube rotates around its "elastic axis".

Let us leave the SKELETON method now and enter the next example section which demonstrates the use of INVERSE KINEMATICS.