All images from Inspired 3D Character Animation by Kyle Clark, series edited by Kyle Clark and Michael Ford. Reprinted with permission.

This is the next in a number of adaptations from the new Inspired series published by Premier Press. Comprised of four titles and edited by Kyle Clark and Michael Ford, these books are designed to provide animators and curious moviegoers with tips and tricks from Hollywood veterans.

This excerpt focuses on the fundamental and technical aspects of creating effective arcs in your actions. Further discussion on their relationship to actual performance can be found in Chapters 17 and 18 in the book Inspired 3D Character Animation. One must understand both the technical and artistic nature of animation in order to produce quality work.

The fundamental theory regarding arcs took a stronghold in the animation community and became a standard for all traditional 2D and stop-motion artists. Those traditional artists know the importance of maintaining this principle in order to produce quality work. This fundamental remains an important part of the current processes. However, its translation into digital technology hasn’t been an easy one. As you’ll see, managing this important aspect of character movement isn’t that easy.

There is a certain amount of laziness in letting the computer do the work because it is relatively easy to get something to move. If you think in terms of the traditional animator, he does not have this luxury; he must draw every arc needed. There is a lesson to be learned from this approach. I’ve seen both novice computer animators and seasoned industry veterans fail to pay attention to their arcs. To be honest, I’ve done it myself more often than I’d like to admit. Taking a lesson from the traditional animators, I learned to set a few more key frames, because if I fail to pay attention to the arcs that create a natural sense of movement in my characters, the performance suffers.

Different actions have different degrees of arcs in their motions. For example, the swinging of an arm has a fairly noticeable arc between its forward position and rear position. Conversely, a head turning from side to side has a much more subtle degree of an arc as it traverses. I’ll break down some of these exercises in greater detail later in the chapter, and give you some examples of how I use these different types of arcs in my animated characters. First, I’ll show you what arcs are and how they apply to animation.

Arcs
According to Webster’s Dictionary, an arc is simply “a continuous portion of a curved line.” When most people think of an arc, they think of the perfect 180 degree arch on a building, but an arc can also be represented by a figure-eight or just about any other continuous curved line.

The discovery of arcs in human movement can be traced back to the early 16th century and the master artist, scientist, and inventor, Leonardo da Vinci. Through careful dissection, da Vinci was able to uncover the true shapes and internal workings of the human body. More importantly, however (at least for our discussion), Leonardo did not simply observe these structures; he became obsessed with how they worked. This led to the first accurate knowledge of body mechanics and human movement. Because all animation is created with movement, you can see the importance of this work.

By analyzing how the bones attached themselves, the idea of arcs in motion was uncovered. da Vinci observed that the limbs and spine, like any moving object, attached at one end (similar to a pendulum) and moved around the axis of its attachment. Because the joints of the body are attached with a ball and socket (able to rotate on all axes) or hinge joint (only able to rotate along one axis), the resulting path of movement would be curved in nature. The spine is the exception because it derives its movement from a series of specialized joints “compressing” on discs allowing it limited but flexible motion. Another revelation that came out of this tendency toward curves (and one that applies directly to high impact anima-tion) is that these joints were simply unable to make angular, linear motions. Again, LIVING OBJECTS CANNOT PERFORM ANGULAR LINEAR MOVEMENTS.

To illustrate a ball and socket joint, simply stand with your arm fully extended at your side, with your palm facing your thigh. Keeping your arm fully extended, lift your arm perpendicular to your body with your palm facing the ground. If you were to draw a line tracking the movement of the fingertips, you would notice that the path in which your hand traveled can be drawn as a 45-degree arc. For a hinge joint, lay your arm out in front of you with your palm facing up, and bend your elbow toward your shoulder. This motion also creates an arc defining the movement of the hand.

The non-linear path an object takes from one position to another can be defined visually by the representation of an arc. (See Figure 2.) This arc, or curved segment, is present in large movements as well as the slightest motions. From the swaying action of a blade of grass to the sweeping movements of an elephant’s trunk, every character or object that maintains an organic sense of motion incorporates arcs.