Watch the Double Ball Bounce lecture
The Double Ball bounce is an add-on assignment to the Perpetual Ball Bounce.
By adding the second ball you are creating an overlapping action. Overlapping action can be defined simply as: not everything happens at the same time. We're going to delay the actions of the second ball a bit.
The very first question you need to ask yourself is: What is the second ball made of? How stretchy is it? How does it react to the initial ball bounce? Before you decide to animate something, you need to know how it's going to do what you want it to do and whether or not it actually can or should do what you plan to make it do.
Once you have decided on it's physical properties, you can then start to visualize what it's going to do.
We also need to figure out which drawing to star with. In the Perpetual Ball Bounce, we started with drawing 1, where the ball was at it's high point. This was our first Key Pose. Then we did the lowest point where it had contacted the ground and was in the squished position. This was our second Key Pose.
With overlapping action we want the second ball to react to the actions of the first ball. We could just guess as to what the second ball would look like on drawing 1 but it would be better to go with a drawing that we could be absolutely sure as to what it would be doing. That drawing would be #5 of the ball at it's maximum rate going down.
If the bottom ball is falling and we want the top ball to be a little more flexible, it would most likely be in a stretched position, being pulled by the bottom ball. Here's how I decided to draw it:
From this point on, I did the remaining drawings as straight ahead animation, simply asking myself, "What would happen to the ball on top next?"
6 would also be stretched. The bottom ball is impacting on the surface and being squished but the top ball is delayed as it is still coming down.
Drawing 7 has the ball beginning to move back up. This is the favor out of drawing 6. I have the top ball being squished over top of the bottom one. I gave it the "jelly bean shape" so it would show the force of the bottom ball moving back up while the sides of the top ball are still going down.
In drawing 8 the bottom ball is stretching up and so I have the top ball being compressed over even more.
In drawings 9, 10, 11, and back into 1 the top ball recovers.
In drawings 2, 3, and 4, as the bottom ball begins to drop, I've kept the top of the upper ball pinned to the same point, while the bottom gets stretched. This gives it the similar action that you find in the Roadrunner/Coyote cartoons, when the Coyote goes over the edge of the cliff. As soon as he becomes aware that he's defying gravity, his body falls off screen, leaving his head hovering in mid-air. Then his head zips off screen.
By keeping the upper part of the top ball stationary, it creates a slightly different type of overlapping action... remember, not everything has to happen at the same time.
The action then cycles back into #5 and loops.
Here is a pencil test of the Double Ball Bounce action shot on 2s:
Here is a pencil test of the Double Ball Bounce action shot on 3s:
Here is the pencil test of the Double Ball with the tail:
Here's a quick piece of animation that I did in class after the lecture that applies the exact same principles that are used in the "Double Ball with the Tail". This version is shot on 2s.
This version is shot on 3s.
Here it is cleaned up and in color with inbetweens and shot on ones and twos... and with the tail added on.
Here are some variations to the double ball bounce: