Inverse Kinematics Methods

Inverse kinematics builds on the concepts of hierarchical linking. To understand how IK works, you must first understand the principles of hierarchical linking and forward kinematics. See Animating with Forward Kinematics and Inverse Kinematics (IK).

IK Solvers

IK solvers are specialized controllers that apply IK solutions procedurally across a range of frames.

Four different IK solvers ship with 3ds Max:

• HD (History-Dependent)
• HI (History-Independent)
• IK Limb
• Spline IK

Tip: In order to put an IK solver on a two-bone chain, a third bone is needed. Choose the first bone, then from the Create menu click IK solver, then click the third bone in the viewport.

In general, all IK solvers:

• Work on any hierarchy.
• Work on any hierarchy or bone structure.
• Calculate IK solutions for all frames in real-time as you make changes.
• Allow you to create multiple IK chains within a single hierarchy.
• Allow you to create multiple or overlapping IK chains within a single hierarchy.
• Display active joint axes and joint limits graphically.
• Use a node, goal or an end effector to animate the end of a chain.
• Use an end effector to animate the end of a chain.

An IK solver places keyframes only on the IK goal or end effector, as opposed to forward kinematics (or the non-solver IK methods), which place rotation keyframes on the bones or hierarchical objects themselves.

Other IK Methods

In addition to the IK solvers, 3ds Max provides two non–solver methods of inverse kinematic animation: Interactive IK and Applied IK. These IK methods do not apply an IK solver.

Note: These are older IK methods carried over from the earliest versions of 3ds Max. It is generally recommended that you use IK Solvers in preference to Interactive or Applied IK.

• Interactive IK

  Interactive IK gives you the ability to use IK manipulation on hierarchies without applying an IK solver. You animate your IK structure by activating Interactive IK (found in the IK panel of the Hierarchy panel and on the Hierarchy toolbar) and manually animating the position of end effectors. IK solutions are calculated only for the keyframes you set. All other motion is interpolated as set by the object's controllers. Moving the end of the chain simply adds rotational keys to the objects in the chain. The objects can have joint limits assigned, for additional control. The chain can also be terminated using the tools in the Auto Termination rollout.

• Applied IK

  With Applied IK, you animate follow objects and 3ds Max calculates the solution on every frame of a specified range. The IK solution is applied as standard transform animation keys. Applied IK works with any linked hierarchy of objects except for bones that use the HI Solver or the IK Limb Solver. It can combine forward kinematics with inverse kinematics on the same objects. You can apply it automatically to a range of frames, or interactively to single frames.

  Applied IK is fast and accurate, but it creates keys for every object in the kinematic chain, on every frame. The large number of keys can make it difficult to adjust the animation later. Use Applied IK repeatedly to adjust the animation.