Here is an overview of how a computer model is animated....
In many ways it is just like traditional stop-motion animation going back to King Kong and the movie monsters of Ray Harryhausen, but with one big difference. Instead of moving the armature incrementally for each frame, the animator plots the movement as key-frames between two points in space and on a timeline. For example, you can set one key-frame with the character’s arm resting at her side, then set another key-frame five seconds along the timeline with the arm raised straight out from her shoulder. The animated element with be a pivot of the armature shoulder joint. Once you have establish the timeline between these two point, the computer will interpolate the points in between. The result will be a smooth movement of an arm being upraised.
Below is an example of a basic keyframe sequence for a single bone in a simple armature. The small diamonds are keyframes, and the graph where they are plotted is called a dope sheet.
When you are animating a complex armature corresponding to the skeletal structure of a character, the dope sheet becomes a pattern of coded movements. The time marker is the blue line. It sweeps from left to right along the timeline
Once the basic movements have been plotted, and the timeline is animated, the character will move, but they will move with a metronomic evenness. This evenness is something you can see in a lot of CGI, especially early CGI. All the movements of the characters and elements within the virtual environment will move as if it is a single clockwork world, which is pretty close to the truth. For the characters to have character each component has to have its own quality of movement with a lot of variation in subtle acceleration and deceleration. One way around this problem is motion capture (MOCAP), where the movements of a live actor are tracked on camera and transferred to the 3D armature. Motion capture is now cheap and easy to do. My personal view is that MOCAP looks good if you are trying to mesh a CGI creation with live action, but it goes down the uncanny valley if you are animating characters that are not attempts at realism, but something painterly and poetic. The characters in this project are not meant to compete with photography, or be invisible within a live film setting. The painterly movement of a 2D Warner Bros. or Disney animation is what I am aspiring to. A "hand drawn” movement done keyframe by keyframe can achieve this, and be like a sketch, expressive and spontaneous.
Achieving this requires understanding and getting a feel for editing F-curves.
F-curve editing works like this: Between each keyframe is a line, a literal time-line, called a function curve, that described the acceleration and deceleration of the animated object along the timeline. There are, depending on the restraints placed on the animated object, F-curve lines representing every axis of movement. You can shape this curves in such a way as to precisely control the subtle acceleration and deceleration of all movement of all elements along timeline
Working the graph editor probably sounds more complicated, and it is, and I will describe and illustrate F-curve editing in greater detail in future posts.