Creating a control object for an IK system

Using the IK Handle to pose an IK chain is generally not a good practice. The IK Handle can be challenging to select in the scene view, especially when it’s grouped into a hierarchy that includes a skeleton and other surface components. A better practice is to create a control object.

You create a control object to select and manipulate an IK system instead of directly using the IK Handle. You can create a control object with a curve or a locator, which are often used because they don’t appear in the rendered image.

The control object controls the movement of the IK Handle using a constraint. You can constrain the position, orientation, or scale of an object to other objects using constraints.

To create a control object:

To create a control object using a locator

  1. From the main menu, select Create > Locator.

    A three-dimensional cross is created at the origin in the scene view.

  2. Select the Move Tool from the Toolbox.
  3. In the side view, reposition the locator slightly above and in front of the end of the mechanical arm as shown in the image below.

To easily identify the locator as a control object in the Hypergraph, rename the locator.

To rename the control object using the Hypergraph

  1. In the Hypergraph, right-click the node named locator1. Choose Rename from the pop-up menu that appears.

    The locator1 name is highlighted on the node.

  2. Type the name ArmControl and press Enter to save the name for the locator.

Before you constrain the IK handle to the control object, you need to freeze the transformations for the control object. Freeze Transformations zeros the transformations for an object without changing the position of the object. This is another good practice; If it becomes necessary to reset the arm to its default position, you can set the transformation on the control object to zero, and the arm will return to this default pose.

To freeze the transformations for the control object

  1. In the Hypergraph, select the node named ArmControl.

    The control object is selected in the scene view.

  2. In the main menu, select Modify > Freeze Transformations > .
  3. In the Freeze Transformation Options window do the following:
    • Select Edit > Reset Settings to set the tool to its default settings.
    • Click Freeze Transform.

    The transformations for ArmControl are set to zero. From this point onwards, you can reset its position to this location by zeroing its translations in the Channel Box.

To easily identify the locator as the control object in the scene view, label the control object using an annotation. An annotation is a text label that can be set to point at the labeled item. Annotations are useful because they always face the viewer, regardless of the orientation of the model in the scene view.

To label the control object in the scene view

  1. In the Hypergraph, select the ArmControl node.
  2. In the main menu, select Create > Annotation.

    A input window appears.

  3. Type ArmControl and click OK.

    In the scene view, the word ArmControl appears near the locator/control object. In the Hypergraph, two new nodes appear in a hierarchy beneath ArmControl.

  4. With the annotation still selected, select the Move Tool.
  5. In the side view, drag only the annotation so it appears slightly offset from the locator object as shown below.

    The annotation displays in any scene view so you can easily identify the control object for selection.

To simplify the display of the Arm Control node

  1. In the Hypergraph, right-click the ArmControl node. Choose Collapse from the pop-up menu. (You can also double-click a node to collapse or expand the hierarchy below it.)

    The ArmControl node appears as a single node instead of the previous three node hierarchy. The small arrowhead on the lower left-hand corner of the node indicates that the node is collapsed.

The control object must be linked to the IK Handle to control the IK Handle.