Creating Frame-by-Frame Animations: The Classic Ball Bounce
The ball bounce is usually the first animation exercise a student undertakes. The reason for this is it uses many of the first principles of animation.
Extremes
Extremes are keyframes that represent the most extreme actions in an animated sequence, generally when the motion changes direction drastically. If you think of a pendulum swinging, the extremes are the points where the pendulum stops and swings the other way. For our ball bounce, it’s when the ball is at it’s highest and lowest points. Here’s an animation of just the extremes:
This is also called blocking or pose-to-pose animation, and is a good first step in planning out a sequence. As well as getting the extremes, you can also lay down the timing, so be sure you leave sufficient space between the keyframes to time your motion.
In-betweens
When doing frame-by-frame animation, once you have the extremes blocked in, you add the in-betweens. You might think that this would mean that you would divide the space evenly between each frame to reach the extremes, but that doesn’t take into account but consider the effect of gravity. As your ball gets closer to the ground, it speeds up until it hits the floor, as it gets higher, it slows down, until it appears to hang for a moment, something like this.
Squash and Stretch
If you were to animate the whole sequence using the technique above, you’d notice that there is something a little unnatural or stiff about it, as if you were bouncing something rigid like a golf or ping pong ball. To get a more classic, cartoony look, you should use squash and stretch. As the ball moves, it “stretches” towards its destination, when it hits the floor it deforms or “squashes” with the impact. The keyframes in squash and stretch look something like this:
This is what it looks like when you put it all together:
Now try to duplicate the above yourself. You can decide how cartoony or soft your ball will be by how much squash and stretch you use.
There are a few tools on the timeline that are going to help you do this. They are located below the timeline, in the center, at the very bottom of the application window, and they look like this:
The first set of buttons, as you might guess, allow you to control playback of the timeline.
In the second set, the red line and square will take you to the center frame when clicked, the curved arrow loops playback.
The third set of icons lets you view and edit multiple frames at a time. These will really help you with your ball!
The first icon in that set turns on “onion skinning” which is a throwback term to when pencil tests were drawn on very thin onion skin paper so that you could see the drawings underneath as you were animating. When you click the onion skin button, you’ll see this appear in the timeline:
The grey area shows you what frames you are viewing, click and drag the left or right edges to increase or decrease the number of frames.
Your stage will now look something like this, with multiple frames showing:
The next button, with the two overlapping white squares, does the same thing, but with outlines, which can be useful when you are animating visually complicated objects:
The next button, with the two solid squares overlapping, allow you to edit multiple frames at a time. Be careful with this button, it’s easy to mess up all your carefully planned out frames if you forget to turn it off! It’s most useful in this exercise to re-align all the circles if they get out of whack vertically.
