Body Inertia

Without any inertia, the body of a skeleton will react immediately to the motion of the effectors. If the effectors are controlling extremeties (like feet and hands) it may be desirable to delay the effect of their motion on the body to give it a better sense of weight.

Smoothing the body motion approximates the tendency of creatures to spare energy by not moving their core mass any more than is necesssary.

Inertia is a feature available on all Power IK nodes.

Smooth Damping Based Inertia

This is the most typical (default) type of inertia.

This delays the body's reaction to the motion of the effectors. This effect will not "wobble" and overshoot. It simply "catches up" to the effector motion in a gradual, dampened and non-linear way.

To enable "Smooth" inertia:

  1. Find the "Body Inertia" section of the Solver settings.
  2. Set "Apply Inertia To Body" to true.
  3. Tune the Smooth Factor value.

Smooth Factor: The Smooth Factor determines how much the body motion is smoothed when the effectors positions are modified. Typical values range from 1 to 20, which higher numbers smoothing the motion more and causing a longer delay between the effector motion and the body's reaction.

Spring Based Inertia

The Smooth Factor has a few desirable properties. It is unconditionally stable and will not "overshoot" the target body location.

In some cases though, it may be desirable to give the body a "springy" behavior. This can be achieved by:

  1. Find the "Body Inertia" section of the Solver settings.
  2. Set "Apply Inertia To Body" to true.
  3. Set "Use Spring" to true.
  4. Tune "Spring Strength" and "Spring Damping" as described below.

Spring Strength: Typical values range from 10 to 300. Determines how quickly the body is pulled towards the effectors when they are moved.

Spring Damping: Typical values range from 0.01 to 0.5. Dampens the spring motion. Higher values cause the spring motion to settle sooner.