[Figure 8] The two extreme poses for the arm swing. The back positions are keyed at frame 1 and frame 24. The forward position is set at frame 12.

The next step is starting to layer in a few in-between keys. Their position is determined by the distance the arm will have to travel and the amount of acceleration and weight that is desired. Remember, the heavier an object, the more effort it takes to get it to move; therefore, it takes longer to get it moving. For this character, I’ve chosen to place the first set of in-betweens at frame 6 and frame 18. These two positions are a quarter of the way toward their goal in half the time they have to move that direction. The result is an arm that eases out then accelerates quickly to its target.

Along with this relation to distance, I must not forget to keep the keys on the proper arc. They currently lie on a sweeping path from front to back. Minor adjustment might be necessary after future keys are layered in. However, they are positioned at a good starting point.

The current keys have established a basic standard of timing. Their position is creating the proper ease out and acceleration when moving from both front to back and back to front. As I continue to layer in additional in-between keys, it becomes increasingly necessary to concentrate on the path of action the arm is taking. The next few steps are a bit more complex but are needed to create a proper arm swing.

As the arm swings forward, it must continue on a circular path. The arm continues on an upward motion as it breaks back toward the body. This is a big point of confusion for many people. This action starts the first breaking of joints as the limb begins its back swing. The following image shows a sequence of keys that illustrate this point.

A similar arc occurs at the high point of the back swing. The arm makes a small circle as it begins moving back toward the front. Two in-betweens are required to make the tight transition. I’ve placed them at frames 2 and 4.

The arm swing now has all the necessary elements of a believable action. The hand swings along a rounded, organic path and the proper in-betweens give the appearance of weight and acceleration.

Arcs and in-betweens are key fundamentals to keep in mind when animating your scenes. They must be implemented in order to create refined and believable animation. There is little room for shortcuts when entering this level of refinement so you must take control of the software and prevent the computer from making decisions for you. Be conscious of the effort and attention to detail required to produce a believable performance, both physically and emotionally and, of course, the most important rule…make it perfect.

To learn more about character animation, walks, tools of the trade and other topics of interest to animators, check out Inspired 3D Character Animation by Kyle Clark; series edited by Kyle Clark and Michael Ford: Premier Press, 2002. 268 pages with illustrations. ISBN 1-931841-48-9 ($59.99) Read more about all four titles in the Inspired series and check back to VFXWorld frequently to read new excerpts.

Author and series editor Kyle Clark (left) and Series editor Mike Ford (right).

Series editor Kyle Clark is a lead animator at Microsoft's Digital Anvil Studios and co-founder of Animation Foundation. He majored in Film, Video and Computer Animation at USC and has since worked on a number of feature, commercial and game projects. He has also taught at various schools including San Francisco Academy of Art College, San Francisco State University, UCLA School of Design and Texas A&M University.

Series editor and author Michael Ford is a senior technical animator at Sony Pictures Imageworks and co-founder of Animation Foundation. A graduate of UCLA’s School of Design, he has since worked on numerous feature and commercial projects at ILM, Centropolis FX and Digital Magic. He has lectured at the UCLA School of Design, USC, DeAnza College and San Francisco Academy of Art College.