Moving the IK Target Up the Limb

Traditionally the IK target sits at the end of the limb, but sometimes a different location is necessary. For example, for a crawling character, the IK target should be positioned at the knee. You can animate the IK target up and down the limb with the Num IK Bones setting.

Num IK Bones allows you to slide the IK target up and down the limb. The Num IK Bones value ranges from 0.0 to the number of bones on the limb, including the palm. For example, with a typical leg setup of two leg bones and an ankle, the range goes from 0.0 to 3.0.

Lowering the Num IK Bones value moves the IK target (for example, the Footplatform) up the limb, bone by bone. On a typical leg, the value 1.0 places the IK target at the knee, while a value of 0.0 places it at the top of the leg: the pelvis.

As the value changes, the limb is pulled down through the IK target. This is normal. The part of the limb that is beyond the IK target is in FK.

Num IK Bones=1.0

At this setting the lower leg can be rotated in FK.

Procedures

To access to the Limb Animation rollout:

• The IK controls for the limb are available for all limb bones. Select the limb and go to the Motion panel Limb Animation rollout.

To blend a limb seamlessly from IK to FK:

1. Make sure an Absolute layer and Animation mode are active.
2. Go to the frame at which to start the blend.

   This should be an IK frame, meaning the IK/FK value is 0.0.

3. Turn on (Auto Key).
4. Click the Match IK And FK button.
   
5. Tweak the IK/FK slider to create a keyframe.
6. Go to the time at which to end the blend.
7. Move the IK/FK slider to 1.0.

To blend from FK to IK:

As you decrease the IK/FK value, the limb remains in the same place but is ready to animate in IK.

1. Make sure an Absolute layer and Animation mode are active.
2. Go to the frame at which to start the blend.

   This should be an FK frame, meaning the IK/FK value is 1.0.

3. Click the Move IK Target To Palm button.
   
4. Turn on (Auto Key).
5. Tweak the IK/FK slider to create a keyframe.
6. Go to the time at which to end the blend.
7. Set IK/FK to 0.0.

Interface

The Limb Animation rollout provides access to the IK and FK settings for the limb.

Create IK Target

By default, a rig arm has no IK target. To animate in IK, first use the Create IK Target function. This creates a special point helper that serves as the IK target for the arm.

The IK target for a leg is the FootPlatform.

Select IK Target

Selects the IK target for the selected palm or ankle without having to search for it in the scene.

NoteMoving the IK target affects the limb only when the IK/FK value (see following in this topic) is less than the maximum 1.0. Also, when the IK target is selected, the function and name of this button switch to Select Limb End.

Move IKTarget to Palm

Centers the IK target at the end of the palm. Use this function when you have been animating in FK mode, leaving the IK target behind, and you want to blend back to IK.

Match IK and FK

Creates a seamless blend between IK and FK modes. Click this button with Auto Key on before you blend to or from IK.

IK/FK

Blends between IK and FK on the limb, with 0.0 being IK and 1.0 being FK.

TipNormally, you would not leave the value between 0.0 and 1.0 while animating. The interim values are intended mainly for blending between IK and FK.

Display FK Limb in IK

When on, and the limb is in IK, displays a ghost/wireframe image of the position the limb would be if using FK. This option is useful when you are animating to see quickly what the FK solution is doing when in IK, in case you are having issues with the IK solver bending in the wrong direction.

As you slide the IK/FK slider to the right, the limb gradually assumes the ghost position.

Left: Limb in IK, with Display FK Limb In IK on

Right: Limb in FK

Num IK Bones

Slides the IK target up and down the limb.

The value ranges from 0.0 to the number of bones on the limb, including the palm. For example, with a typical leg setup of two leg bones and an ankle, the range is 0.0 to 3.0.

Retargeting

This slider blends CAT's Retargeting for the selected limb. At 0.0, retargeting is off, and a value of 1.0 means retargeting is fully on.