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Animation Modes

Most character animators want both Inverse Kinematics ('IK') and Forward Kinematics ('FK') modes at a minimum. Limber also provides a unique mode that we call Free Kinematics ('FreeK'). You can blend smoothly between the different modes, as well as matching a limb’s pose in one mode to another.

Each mode has a group of properties in the Limber effect, and each mode will override the modes above it when you increase it's Blending property: dial FK Blending up to 100%, and FK mode takes over from IK. Increase Free Blending, and FreeK mode takes over from both IK and / or FK, once you've added a FreeK controller.

Inverse Kinematics (IK)

A character on IK will keep it's hands and feet planted to the spot. Unless you disable Stretch and move the body too far away.

IK is what people use Limber for most of the time: you move the two ends of the limb and it kinks or straightens automatically. That makes it much easier to animate characters whose feet need to stay planted to the ground as the body moves - when walking, running or just swaying on the spot.

Limbs on IK will bend out to one side or another - controlled by the Clockwise property. You can also disable Stretch or turn up Anti-pop for limbs on IK. All these properties are covered in more depth in Clockwise, Stretch and Anti-pop.

Forward Kinematics (FK)

Notice how elegant and effective the 'break' in the elbow is. Arcs shown using Arc Checker.

FK makes great arcs. It's a bit like animating with one layer parented to the end of another - when you rotate the parent layer, the child layer follows along. Some moves work better on FK - swinging, kicking or swimming legs, waving arms, cross-body moves, and any time you want to break the joints or do whip or wave motion.

If you have layers parented to your end controller, they won't follow the limb on FK - you'll need to make a Locator and parent them to that instead.

Free Kinematics (FreeK)

The bounce movement of the elbows can be animated by the artist independently of the shoulders and hands. The arms are Finns Leg from the Limb Library with a little added artwork.

Can you place your hand on your desk, not move your shoulder, and still move your elbow? Yes, you can. But how could you possibly animate a movement like that with either IK or FK? You can't. FreeK lifts all the restrictions that traditionally come with rigged 2D characters, and allows you to freely animate a limb’s elbow or knee in ways that are usually impossible with rigged characters in After Effects:

  • When the start and end of the limb need to stay planted but the joint needs to move.
  • To smooth out a bad arc on an IK joint.
  • To make front-facing or isometric walk cycles. Without tearing your hair out.
  • For gesturing hands that move left and right while the elbow stays close to the body

Gestural Elbows

For that last one - try setting FreeK to 50% and turn Clockwise to zero. You'll get a kind of 'magnetic' elbow that naturally follows the movement of the wrist. Thanks to Jared from Backwoods for this idea.