Inverse Kinematics with Bones

Inverse Kinematics with Bones

Flash CS4 Tutorial


How to Add Bone Structure to Object for Animation in Flash



Bones are used to drive character animation or fluid motion such as a flag waving in the wind. They can also be used to simulate wind blown grass or the mechanical articulation of an excavator.

Bones are added to objects in multiple ways. It is possible to draw one or more Merge Shape objects, select the entire object, then add the bone structure. For more information on Merge Shapes and adding bones to Merge Shape objects, see topics, Merge Shape and Animating a Flag with Bones.

A second method of adding bones requires that you create your object as a series of Movie Symbols. Once you arrange your Movie Symbols, the bone structure is added with the Bone tool by click-dragging between the symbols. For more information on Movie Symbols, see topic, Movie Symbol. To learn more about creating and animating a Bone structure with Movie Symbols, see topics, Adding Bones to Symbol Objects and Creating a Walk Cycle with Bones.

In this topic we will demonstrate how to create and animate a mechanical arm with the Bone tool. The mechanical arm is built using a series of Movie Symbols.


Step One

Open a new document and add three shapes that create a mechanical arm. You will need a BaseMainSupport, ArmOne and ArmTwo.

Step Two

Select the pieces, one and a time and convert them to Movie Symbols by pressing F8.

Step Three

Position the three Movie Symbols to create the arm mechanism in the rest position.

Step Four

Select the Bone tool (x key), then click the base and drag upward until you are over the second Movie Symbol's rotation point.

Step Five

Click the end of the first Bone and drag to the rotation point of the second arm.

Step Six

Since we want to keep the BaseMainSupport from rotating, choose the Selection tool (v key) and click start of the first Bone. Open the Properties panel.

Step Seven

In the Joint: Rotation section, deselect the Enable checkbox.

Step Eight

We want the base to be able to slide left and right. In the Joint: X Translation section, click the Enable checkbox.

Step Nine

Using the Selection tool (v key), click the workspace, then the object to display the bones.

Step Ten

Click an drag each of the symbols to move the mechanical arm.

 Where is the Original Object Layer?

Once you click and drag from first Movie Symbol to the second, a new Armature layer is added. The symbols are moved to the Armature layer and the original layer becomes empty.

Once all the objects are connected and moved, it is OK to delete the original layer.

Three Types of Bones

The default Bone shape can be clunky to move. To change the Bone preview shape, click the Armature layer name and open the Properties panel. In the Options section, choose Wire, Solid or Line from the Style pull-down menu.

Constraining the Rotation

By selecting a Bone and opening the Properties panel you can limit the rotation at a specific joint. For instance, to limit the rotation of ArmOne, you would select the Bone, open the Properties panel, open the Joint: Rotation section, check Enabled then set the Min and Max values.