IK Limb Solver

The IK Limb solver is specifically meant for animating the limbs of human characters; for example, the hip to the ankle, or the shoulder to the wrist. Each IK Limb solver affects only two bones in a chain, but multiple solvers can be applied to different parts of the same chain. It is an analytical solver that is very fast and accurate in viewports.

To use the IK Limb solver, a bones system must have at least three bones in the chain. The goal is placed at the pivot point of the bone that is two bones away from the first selected bone.

The IK Limb solver works not only with bone hierarchies, but with any linked hierarchy that has at least three elements, and is set up to model a human limb. The additional requirements are:

The first joint is "spherical." That is, it has three degrees of freedom.
The second joint is "revolute," a robotics term that means it is based on a pin and has one degree of freedom.

The IK Limb solver uses the same controls as the HI Solver, so it allows for mixing periods of forward and inverse kinematics in the same animation period. It does not use the HD Solver methods of damping, precedence, and setting joint limits, instead it has a preferred angle parameter, swivel plane and IK/FK Enabling.

The IK Limb solver can be exported directly to a game engine.

Procedures

To apply a IK limb solver:

Create a chain that has three bones.
Select the root of the chain.
From the Animation menu, choose IK Solvers IK Limb Solver.
In the viewport, move the mouse. You will see a dotted line attached to the cursor as you move the mouse.
Click the third bone in the chain, or any bone after the third bone.
The IK Limb solver displays on the bone chain. The IK Limb solver only affects two bones in the chain, but you need to select the third bone to put it on the other two bones.

To animate an IK limb solver chain:

Apply the IK Limb solver to a two bone chain, with joint limits as described above.
Select the goal.
Move or rotate the goal.

Interface

The Interface for the IK Limb solver is identical to that of the HI Solver.

Select the goal at the end of the chain, and open the Motion panel. Here you will see the controls for the IK Limb solver. (The fourth is available from the Hierarchy IK panel when a bone is selected.)