Character Animation

Lecture 4 Excerpt

Principle #9: Arcs

It's important to always be aware of what you are manually animating and what you are allowing the computer to figure out for you. Your computer doesn't know how to animate. It's just a pile of electronics. Therefore, anything you leave up to the computer will inherently be bad animation.

The key difference between hand-drawn animation and computer animation is that with computer animation, you aren't directly responsible for everything that goes into every frame of animation. The computer simplifies things greatly by figuring out how to get smooth interpolation between key frames. This is an important point because it allows you to worry less about what is a difficult technical problem in hand-drawn animation and more about just creating good animation. The problem here is that having the computer figure so much out for you can lead to the assumption that the computer knows what it's doing. But as we know, it really doesn't.

By default, any animation curve is going to move directly from one pose to another, with no deviation from that direct movement. In reality, organic creatures actually move in arcs. Robots move linearly. We don't. Our hands move naturally in arcs when we gesture or when we just swing them at our sides. Our hips move up and down in arcs as we walk.

In this rough sketch I've drawn three poses for a forearm: up, midpoint, down. As you can see, the hand actually moves through an arc as the elbow is rotated down. Fortunately for us, this occurs both with the rotation of a real life elbow and any joint in Maya. This gives us one way of creating built-in natural arcs. Generally, though, the computer will move things in a mechanical linear fashion if left to do most of the work, particularly if you are using inverse kinematics.

Head Arcs

The most basic (and I think one of the most important) examples of body arcs is in the head. Let's take a look at the very simple animation of a head turn that we explored earlier in the course.

Domo Arigato, Mr. Roboto. Click the image to view the movie.

What we have here is a nice smooth ease in/ease out head turn. I set two keyframes and the computer figured out all the rest for me. Problem solved, right? Well, not exactly.

The head is turning smoothly all right, but it turns like a robot. The turn is very linear. Let's see how this shot changes if I simply add a new keyframe in the middle of the shot, dipping the head down.

Much nicer organic motion. Click the image to view the movie.

Just that one little change actually makes the motion look surprisingly more natural. Arcs are fantastic tools in your animation arsenal. If you ever (ever) have a head move that doesn't include an arc, you're missing out on a very easy and important principle.

Embellishing Existing Arcs

Consciously watching for arcs in all parts of the body, and embellishing them, can really enhance the appeal of the motion in your animation. In the ball throw example I used earlier, for instance, I embellished the arc the character's hand made through the air as it swung the ball forward and then arced down and curved back up towards his body.

This simple gesture of an arm moving down, then up, looks kind of linear because all the motion is occurring in the same up and down dimension. The arm is moving through an arc by default, but only in that one dimension.

Simple arcing gesture. Click the image to view the movie.

It doesn't necessarily look bad, but it can certainly look better. If the motion is just embellished a bit by adding a figure eight arc to the path that the hand makes through the air it starts to look a whole lot more interesting and natural.

Embellished Arc. Click the image to view the movie.

It really pays to push your animation beyond just looking "good enough" and trying to find something even better by experimenting with embellishments like this.

Arcs Are Everywhere

As I've mentioned several times, organic characters move entirely in arcs. The image below is a breakdown of a standard walk cycle, which we'll explore in more detail in the next lesson. As you can see, this motion is full of arcs: the up and down motion of the body, the back and forth swing of the arms, even the curve of the feet as they move through the air.

Click to enlarge.

Technique for Improving Arcs

Many animators find it useful to use dry erase markers on their CRT computer screens to trace out the arcs in their characters' bodies and limbs, frame by frame. If you want to try this, be very very careful. Never do this with an LCD screen and only do it with a CRT if you are confident it will come off, and if you wipe it off as soon as possible. If you want to be ultra cautious, you can tape some plastic wrap over your screen and write on that.

Principle #10: Weight

A ball character that starts rolling from a stop with no anticipation, and then stops suddenly without ease, will convey absolutely no sense of weight. A well-portrayed sense of weight is essential for showing that there is effort behind your character's motion and that his motion has an effect on himself, and on his world, in a believable manner. There are a number of separate techniques for creating a good sense of weight.

Balance

Your character must always be either in balance or moving through unbalanced poses on the way to balanced ones. Your character can't pause or hold in an unbalanced pose. When I talk about balance, I'm referring to the character's center of gravity. Our waist is our center of gravity and we will shift it to maintain balance.

In this example, I show a number of balanced and unbalanced poses:

Click to enlarge.

The character on the left is a prime example of a balanced character. If you stand like this, you'll find yourself in a very sturdy position. Basically, when the neck is roughly centered between the legs or over the leg that is supporting the weight, then it is over your center of gravity and you are balanced.

In the fourth character, his neck is not directly located over the middle of the body but he is still balanced because the neck is directly over the left leg, which is the leg supporting the character's weight. In the image just to its left, the weight appears to be mostly supported by the character's right leg, though the character is centering his neck between his feet so he is slightly off-balance, but not entirely. The character to his left is very off balance because the neck is way out beyond the center of gravity. He's surely about to topple over.

Try standing up straight and slowly shifting your weight over your right foot like the fourth character does. Then continue shifting your weight to the right. Eventually, you'll reach a point at which it becomes difficult to keep your balance, and if you try to go further than that, you'll likely fall over. If you can't do it, your character can't do it either. Any character at rest should be in a balanced pose. It is perfectly fine to move through unbalanced poses on the way to something stable, but you cannot pause very long in an unstable pose.

Below is an exaggerated pose of someone trying to reach something he can't access.

Stretching for that top shelf

This is actually a balanced pose although it is certainly a fairly wobbly pose so he can't hold it for too long. Can you recognize some of this balance behavior in yourself? I bet you stick a leg in the air sometimes, or reach back with an arm, to counterbalance reaching for something that you can't quite walk up to. Or at the very least, if you're walking on an unsteady surface, you'll hold up your arms for better balance.

System of Opposites

The body is essentially a system of opposites. In order to maintain its balance, when one part of the body moves in one direction, another part usually moves in the other direction. This is most clearly evident in the waist and spine.

Here are three poses illustrating this principle to various degrees:

The left guy is in a default pose in which his spine is totally straight. This is pretty unnatural, unless your character is a soldier at attention. Even then, his chest will probably be thrust forward a bit

The middle pose is much better. The big reason for this is that he's actually shifting his weight. Nobody stands with their weight evenly distributed like the guy on the left. We're constantly shifting back and forth to balance on whichever leg is the least tired.

This middle guy's weight is shifted slightly over his left leg. The leg that is acting as weight support will generally be straightened out with the knee locked. This pushes up his left hip, causing the right hip to come down, generally leading to that leg being slightly bent, at rest. In accordance with the system of opposites I was mentioning before, the upper body counter-rotates to the hips by tilting a bit down to the left.

The character on the right gets much more interesting than the other two. He is taking full advantage of the three available rotations for each joint. This is by far the best thing you can do for a character's pose. Give him the full flexibility that the spine allows, to put him in a natural pose. Obviously this is a very exaggerated pose and much more like an acting pose than a resting pose. I spread his legs a bit and pushed his right leg back. This forces his hips to turn. Notice that the hips are rotated to follow the motion of that leg back. His upper body moves in the opposite direction, maintaining the system of opposites.

If you're not quite buying this "system of opposites" nonsense I'm throwing at you, I'll let Michelangelo sell my point. I'm sure you've seen the following sculpture before and have heard that its fame revolves around how "natural" David looks.

Is that a weight shift, a right hip being pushed up and forward by the weight bearing leg, with the opposite reaction occurring in the upper body? Why, yes it is.

In fact, this is one of the factors that made Renaissance art so special. Renaissance art was largely a revival of this technique known as contrapposto, which was established by the artists of Ancient Greece. Before this time period, artists often did not take natural posing into account. Notice how stiff ancient Egyptian sculpture was:

You don't want your animation to look like that!

 

Exercise 4 Excerpt

Start simple with our generic humanoid character (character.mb again—you'll use this a few more times throughout the course), viewed from the waist up, waving from any angle you'd like.

Be sure to animate more than just the arm. The body and head are going to move a little in reaction to the arm. When the arm waves to the left, for instance, it will tend to push the body a bit to the left a few frames later, causing the head to lag a bit and then sway to the left as well. Act it out and pay attention to what your body does. Does it act as I've described? Don't forget to:

	Include follow through in the fingers and head. Include lots of overlap in the body, arm, and fingers. Shape the fingers into a natural curl. Don't leave them stiff and straight. Use all three dimensions for a more natural look.

Feel free to be creative, within the requirements of the assignment. The character could look up, see someone, and wave. Or he could do an excited wave with both arms. The wave could be a salute, an excited wave, a calm greeting wave, a wave to try to get someone's attention, and so on...

These are just some possible suggestions to make the project more fun; you can add a creative touch depending on your ambition and skills thus far. Just make sure that you act out the wave and pay attention to the details to make it work, if you'd like to try something more ambitious. Also, keep in mind that you will not need IK for this wave—just the default FK is the way to go since this hand won't be locked to something.

The finger controls aren't entirely intuitive, based on what we know about working with this rig. Select one of the character's finger controls—the finger controls are the long lollipop shapes at the knuckles. You can rotate one of these controls to rotate an entire finger. You can even translate it for fine tuning, though I don't suggest pushing this too far. To rotate the other joints in the finger, you'll want to use the "Middle Joint" and "Last Joint" attributes that show up in the Channel Box. You can click on one of these attributes and then MMB drag in your view window to adjust the rotation. Try this out to see what I mean. You can also drag a selection of both of these attributes in the Channel Box, by clicking and holding on "Middle Joint" and dragging down to "Last Joint." Now if you MMB drag in the view window, you can rotate both joints at once. In fact, if you select all of the character's fingers at once, and select the two finger joints in the Channel Box, you can move all of the fingers at once.

Save your file as character_wave.mb so you don't overwrite the main character file, which you'll use again later in the course.

Part 2: The Turn

Animate a turn and weight shift motion similar to the one I animated in the weight section of the lesson. I know this is a boring exercise to do but it will force you to get the hang of a concept that will be incredibly useful for almost everything you'll be animating in the future.

Refer back to that section of the lesson for full details on how to animate it, but don't just copy what I did. Be sure to act it out yourself and pay attention to what your body does. Here's a recap of the steps you'll need:

	1. Act out the weight shift that you would like to animate. 2. Using the perspective view, animate just the side to side motion of the character. 3. Play through and adjust your poses and timing to get them working correctly. Make Playblasts if necessary. 4. Move on to the up and down motion of the character. Be sure to remove all existing keyframes from the Translate Y channel before starting, and to keyframe only that channel as you work. 5. Animate the twist in the shoulders and hips. 6. Add follow through on the head and upper body. 7. Animate the fine detail of the feet. 8. Animate the follow through and overlap of the arms and fingers

Important: The most important control in this assignment is the big yellow control around the hips. You will be mainly translating this control. Some rotation is nice too, but the key is to show the entire body clearly moving back and forth.

You are free to be creative with this exercise as well, as long as your character performs a turn and weight shift. The character could do a little dance step or jump to the side. But only do this if you feel so comfortable with the material that extra work won't hold you back.

Save this character as character_weight.mb.

This lesson will probably require a minimum of two to four hours of work per exercise.

Grading Criteria: What your instructor expects you to do:   Animate a creative hand wave in which the entire body (from the waist up) is affected by the wave, moving the arm and body in all three dimensions to create a natural appearance. Demonstrate a strong ability to use arcs, overlap, and follow through, paying specific attention to the arm and fingers in the wave. Animate a turn and weight shift demonstrating attention to balance, the system of opposites, contrapposto posing, and arcs. How to Post: Now it's time to submit your work. For this exercise I'll just need to see your Playblasts, named character_wave and character_weight. At this point you should be far enough along as an animator to have strong keyframing techniques. Go to Dropbox 4 and attach your Playblasts. Feel free to add any comments, particularly if you have attempted to do something creative with these exercises and would like to clarify the action. As always, feel free to email me with any questions or concerns regarding the lesson or the exercise, at any time. I look forward to seeing your work!