Learn Maya Animation – Bouncing Ball – Part 2

added on Tuesday, April 6th, 2010 at 10:57 am by Geoff Beatty

Learn Maya Animation – Bouncing Ball – Part 2

By Geoff Beatty

In last week’s exciting episode…

Part 1 of this tutorial taught you how to set some basic keyframes on a sphere as a first step in making a bouncing ball. However, we could only go so far in using the timeline for our animation. Instead of a bouncing ball, we got something that looked more like a floating, wavy ball (screenshot). This is obviously not acceptable. If we can put a man on the moon, then we should be able to make a ball look like it’s actually bouncing. To do this, we’ll need to dive into the graph editor.

Graph Editor and Setup

The Graph Editor is one of the most important interfaces for creating animation in Maya. The viewport and the timeline are great tools for quickly interacting with an object or character, but they’re not very good at letting you refine the motion. The Graph Editor, however, allows you to have a very high level of control over your keyframes as well as the interpolation between them. Although it may look confusing, it’s actually a pretty common interface among software packages, and most 3D and 2D animation tools have something very similar. I’m going to assume that you are already familiar with the basics of the graph editor, but if you aren’t, it might be a good time to read through some of the Autodesk documentation to familiarize yourself. I like to work with a viewport on top and the graph editor on the bottom, but you can work with any layout where you can view the object and the graph at the same time.

Working in the Graph Editor

Select the ball in the viewport. You should then see the curves load into the graph editor and a list of the animated attributes on the left (screenshot).
Go to your main menu and choose “Edit>Delete by Type>Static Channels (screenshot)” This eliminates keyframes on any of the attributes that have only one keyframe (in other words, they don’t have any animation on them). This will help weed out unimportant data from the Graph Editor, essentially uncluttering it for us.
Select the Translate X attribute from the list on the left, and then marquee-select all the keys except for the first and the last (screenshot). Delete these keys (screenshot).
Now select the Translate Y attribute and hit the “f” key in the graph to fit the curve to the window. Select the three keyframes at the top of the curve and, in the Graph Editor menu, choose “Tangents>Flat (screenshot).
While we’re at it, let’s use our Move tool (and don’t forget that you need to use your middle mouse button with it – a common thing to forget) to give each of those upper keyframes a descending value, to mimic the way a ball loses altitude with each bounce (screenshot).
Now, let’s select those bottom keyframes, the ones representing the point of contact with the ground. Go to the Graph Editor menu and choose “Keys>Break Tangents (screenshot).” This will allow us to change the in and out tangents of these keyframes separately. You can tell that they’re “broken” because one tangent is brown and the other one is blue.
Using your Move tool (and middle mouse button) to orient the tangents more vertically (screenshot).

Why Did We Do What We Did?

In Step 3, deleting the middle keys gives us a simple linear interpolation between the first and last keyframe. This simple line (as opposed the uneven line before) signifies a constant velocity for the ball as it travels from left to right. If we were to look at some reference, we would see that, until a ball stops bouncing and begins to roll, it retains a fairly constant velocity in whatever direction it was thrown.

In Step 4, we “flattened” the tangents. Just as straight lines define a constant velocity, flattening out the tangents of a curve give us an “ease in” and an “ease out” for a given motion. This mimics the way that a ball gets slower as it approaches the top of its arc, and then accelerates as it approaches the ground.

In Steps 6 and 7, we adjusted the tangents of the contact frames so that they would look more like an actual bounce than the “floating” that was happening in the previous iteration. It’s like the physics of a pool ball – the angle of incidence equals the angle of reflection.

Next Steps

In the next installment of the tutorial, we’ll take a look at some of the refinements you can make to the animation to give it real character. This might be a good time to take some more video or look at more reference footage. You might even start seeing how this applies.

Maya Animation Continued Reading:

Start at the beginning: Part 1: Learn Maya Animation

Read here next: Part 3: Learn Maya Animation

A detailed study: Learning Maya Animation One Step at a Time

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