reference materialsRigid IK
by Nathanael Fuller		  
   

Rigid-IK is a variation of normal inverse kinematics in which bones are used to drive the motion of a single object. Rigid-IK uses multiples objects (or object layers) in the IK chain without using bones at all. This technique is useful for animating machinery, robots, and anything else with mechanical motion. The major drawback to using rigid-IK is the more complex hierarchy of objects in a scene. Since rigid-IK uses separate layers, the list of objects can quickly expand. Another potential drawback is having to manually move pivot points to joint areas in Modeler. This can add quite a bit of time to the setup phase of animation.

Note: You should be at least somewhat familiar with using IK before starting this tutorial. You must also download the Snake.lwo file before beginning.


Figure 1
 
1.) Open Layout and add the snake.lwo to the scene. You will notice that the pivot points of the object layers have been moved to correspond with the joint areas of the snake. Also note that parenting has already been set up for you (If this is not the case, everything should be parented in order to the Snake:Tail section of the object). [Figure 1]
   
2.) Select the Snake:Head layer and open its Motion Options by pressing m.
Figure 2
 
3.) Assign limits to Heading (0, 0, 1.0), Pitch (0, 0, 1.0), and Bank (-24, 42, 1.0). [Figure 2]
 

4.) Change the Bank Controller dropbox to Inverse Kinematics.

5.) Repeat steps 3 and 4 for every layer of the Snake object.

6.) Add a null object to the scene named "Head Control".

7.) Select the Snake:Head layer again and click on the IK and Modifiers tab in the Motion Options window.

   
8.) Select Head Control as the Goal Object; assign a Goal Strength of 100.0; and make sure that Full-time IK, Match Goal Orientation, and Keep Goal Within Reach are checked. [Figure 3]








Figure 3
   
9.) Select the Head Control null and move it around to see the results. For this tutorial, I moved the null to -1.1m on the X-axis and 3.5m on the Y-axis and created a keyframe at 30. [Figure 4]








Figure 4
   
 
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