Applying IK to a skeleton hierarchy

IK allows you to control the joint rotations in a skeleton using an IK handle. You pose the skeleton by positioning the IK handle (usually located at the end extremity of the skeleton) and having the rotations for the other joints calculated automatically by the IK solver. In the steps that follow, you apply IK to the skeletal hierarchy.

To create an IK handle for the mechanical arm

1. From the main menu, select Skeleton > IK Handle Tool > .

   The IK Handle Tool Settings window appears. When the mouse pointer is in the orthographic view its appearance changes to the tool's cross hair cursor .

2. In the IK Handle Tool Settings window, do the following:
   • Click Reset Tool to set the tool to its default settings.
   • In the IK Handle Settings, set Current Solver: ikSCsolver.

   The ikSCsolver setting selects the IK Single Chain Solver. This solver ensures that the joints in the skeleton will lie along a single plane. This solver is well suited for the mechanical arm, because the arm doesn’t need to twist, unlike a real arm.

3. Working in the side view, starting from the base of the mechanical arm, do the following:
   • Click on the skeleton joint at the base of the mechanical arm.
   • Click on the skeleton joint at the tip of the mechanical arm. (The IK Tool is designed to attach to the joints closest to your selection point.)
     

   In the side view, the IK handle is drawn as a line from the start and end joints of the IK chain.

4. In the Hypergraph menu, select View > Frame All.

   In the Hypergraph, two new nodes appear in the hierarchy that represent the IK chain: an IK Handle node and an end effector node.

   
5. In the Hypergraph, select the node named ikHandle1.

   The IK Handle (in combination with the end effector) is used by the IK solver to calculate the rotation of the joints in the IK chain. By default, the IK Handle is located at the last joint of the IK chain in the scene view.

6. Select the Move Tool from the Toolbox, and drag the Move Tool’s Z axis manipulator (blue arrow) to reposition the mechanical arm.

   When you drag the manipulator, the skeleton and mechanical arm model are repositioned.

7. Reset the mechanical arm to its previous position by selecting Edit > Undo until the mechanical arm is positioned into its previous orientation.
   Note

   When using the Undo feature, do not undo so many times that you inadvertently undo the IK handle you’ve just created.

The next steps describe how to manipulate the IK Handle using a control object.