Animating IK Attachments

A biped can interact with other objects in the 3ds Max scene. Links between objects are usually static, unless you're using the Link controller. In character studio, such attachments are "animatable" as well; during the course of an animation, the links between the hands, feet, and objects in the scene can change as your character interacts with them.

This capability is useful for:

• Creating freeform motions (without footsteps and gravity) that require that feet or hands be planted with IK, and then released. Examples are climbing a ladder, riding a bike, or rowing a boat.
• Motions that involve the temporary manipulation of objects, such as bouncing or kicking a ball, opening a door, or touching another biped.

An object to which a hand or foot can be attached is called an IK object.

Procedures

To make a hand or foot follow an object:

1. Create the object for the hand or foot to follow.
2. Select the biped's hand or foot.
   Tip: You can select any part of the biped's arm to set keys for the hand, or any part of the leg to set keys for the foot.
3. On the Key Info rollout, expand the IK divider to see the IK section of the rollout.
4. Click (Set Key).

   Once a key is set, the IK Blend value and other IK parameters become available.

5. Click (Select IK Object), and choose the object for the hand or foot to follow.

   The object name appears in the field below the Body and Object radio buttons.

6. On frames where you want the hand or foot to start following the object, set a key, set IK Blend to 1.0 and choose the Object option on the Key Info rollout. You can also click (Set Sliding Key) to set these parameters all at once.
   Note: If Object space is turned on with no IK object specified, the IK constraints will be in World space. In effect, the hand or foot will be attached to the world, and will not move during the time such a key is set.

   Set one key when you want the attachment to begin, and a second key when you want the attachment to stop. This defines an Object space interval, the duration of a temporary attachment.

7. On the frame that defines the end of an attachment interval, set IK Blend to 1.0, choose the Object option, and turn on Join to Prev IK Key. You can also click (Set Planted Key) to set these parameters all at once.
8. On frames where you don't want the hand or foot to follow the object, set a key, set IK Blend to 0.0 and choose the Body option. You can also click (Set Free Key) to set these parameters all at once.

To anchor a hand or foot:

You can use anchoring to temporarily look a hand or foot to a specific point in space while you are animating IK attachments.

1. Move and rotate the hand or foot into the desired posture.
2. On the Keyframing Tools rollout, click the button for the limb you want to anchor: (Anchor Right Arm), (Anchor Left Arm), (Anchor Right Leg), or (Anchor Left Leg).
   Note: The arm or leg you select beforehand does not actually have to be the same as the arm or leg you are anchoring.
3. Set keys for the arm or leg as described in the previous procedure.
   Note: You can also use anchors to hold a foot or hand in position while you render the animation. However, be aware that anchors are turned off when you close the MAX file. If you want to use anchors from one session to the next, you must turn them on again the next time you open the file.