Inverse Kinematic Tag

Inverse Kinematic Tag

You can use this tag to specify angle restraints r for the object when using inverse kinematics (IK). For example, a real knee can bend through about 160° only. Angle restrictions can also be useful for preventing objects from intersecting each other.

Specify the restraint by entering Minimum and Maximum values for Heading (H), Pitch (P) and Bank (B). You can also specify a damping factor. The higher you set Damping, the stiffer the joint becomes. Parts of the IK chain with a lower damping factor will move more readily.

Example:

Change into View 2 (XZ plane) and create a Bone object (Objects > Deformation > Bone). Move the view so that the bone object is near the bottom of the view (to move the view, hold down the ‘1’ key and drag within the viewport).

Click the Xaxis icon on the top toolbar to lock the Xaxis. Ctrl-drag from the bone’s orange handle (at the top of the bone) to drag out a new bone. Release the mouse button once the new bone is about the same size as the original bone.

Ctrl-drag a new bone out of the second bone until it is about the same size as the other two. The advantage of dragging out bones in this way is that the hierarchy is created automatically in the Object manager.

Create two nulls (Objects > Null Object). Move one of the nulls along the Zaxis (drag its blue handle) to the end of the bones chain and rename it Handle. Make Handle a child of the last bone in the Object manager. (Open the bone hierarchy by clicking the small plus icons as required.)

Rename the other null Anchor, then make the entire bones chain a child of Anchor. Your chain should look like the picture below.

In the top toolbar, click the Xaxis icon to unlock the Xaxis. Choose Tools > Inverse Kinematics to activate IK mode. In the Object manager, select Handle. Now move the bones around (click and drag somewhere in the viewport, but not directly on the Handle or you may catch the object axes).

The IK mode ensures that all objects maintain the same distance from each other. However, the movement is unrestricted and it is possible to make the bones intersect each other.

In the Object manager, select the first bone. Now Shift-click the remaining bones so that all bones are selected with a bright red color instead of a dull red color (bright red indicates selection while dull red means that a parent is selected. All bones must be bright red). In the Object manager, select CINEMA 4D Tags > Kinematic from the File menu.

Ensure that all three bones are still selected, since we want to change all their parameters at the same time. On the Attribute manager’s Tag page, enable the Heading, Pitch and Bank angles. Leave the Minimum and Maximum parameters at their default values.

In the Object manager, select Handle. Now move the bones around in the viewport once more. Try to make the bones intersect each other. This time, angle restraints make it impossible for the bones to intersect. Otherwise, the bones are still able to move freely.

Now try entering different damping values for the Kinematic tags. Start with 80% for the first bone, 60% for the second bone and 40% for the third bone. You’ll notice that the third bone moves the most readily, while the first bone is the most stubborn. Recall that increasing the damping increases the stiffness.

Use the Figure object for further experimentation. Choose Functions > Make Editable so that you can access the body parts and tags.