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Wagster
Newbie question
on Jan 2, 2007 at 6:10:10 pm

Is there really no way to edit velocity graphs in Maya, like you might in After Effects? I've been trying to get the right amount of ease on moves and it seems to me that being able to edit only position curves in the graph editor is such a counter-intuitive way of working. Is there a tool I don't know about yet? Or a plug-in?

New York-based Editor-Compositor


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Steve Sayer
Re: Newbie question
on Jan 3, 2007 at 2:47:16 pm

By default, Maya does not calculate velocity for moving objects. Position graphs offer the most precise control, and adjusting the tangents of them allows you to tweak velocity, acceleration, ease, etc.

Do you know about all the curve-editing tools in the Graph Editor, including weighted and unlocked tangents? I must confess I've never found the level of control with these tools to be a problem.

If you really want to tweak velocities you could turn objects into rigid bodies, and keyframe velocities just as you describe... but I don't really see it being a productive workflow.

-Steve


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Wagster
Re: Newbie question
on Jan 3, 2007 at 7:47:28 pm

Thanks, Steve. I think I understand the curve controls on the graph editor reasonably well. Maybe this is a case of my being used to what I'm used to, but I'm doing the simplest animation exercise - the bouncing ball - and having a hard time getting the ease at the top of the bounce to be exactly how I'd like it. This ease depends on both the X and Y curves, and what makes it more of a headache is that editing those curves also changes the path of the object. Do you see why I might prefer a velocity graph?

Anyhow thanks for your response. I'll try the rigid body technique, just as a learning experience. Also, if I put the ball on a path, is there any way of putting the value of the UV position on the graph editor? If that's possible, that might give me the control I want.


New York-based Editor-Compositor


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Steve Sayer
Re: Newbie question
on Jan 4, 2007 at 6:14:51 am

Hmmm, the problem may be that you're making the situation more complicated than it needs to be.

In a former life I studied some physics, and that background has helped out more than once with animation. In this case, the real-world motion of a bouncing ball will exhibit parabolic motion in Y (the diminishing-arches pattern we associate with cartoon bouncing balls), but purely linear motion in X. In other words, for an 'accurate to real life' simulation, the X animation curve should be a nice smooth slope; no curves or sharp points.

(A super-realistic version would probably introduce a little bit of variation since the ball would slow down a bit with every impact, but while it's in the air its horizontal motion should remain quite constant.)

Try starting with that approach and see if you can obtain results you're happy with. Really, at that point the only thing to tweak is the weight of the peak keyframes on the translate-Y curve, and I can't imagine that giving you too much trouble if you know your way around the graph editor.

Could you post a playblast of your results, or even a screenshot of your animation curves?

The rigid body approach is really probably overkill, but let me know if you come up with anything interesting.

-Steve


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Wagster
Re: Newbie question
on Jan 4, 2007 at 4:14:26 pm

The X curve is straight! I didn't quite believe you, but I checked one of those multiple-exposure photos of a bouncing ball and you're right.

I still might prefer other controls, but I guess I should just get over it and get used to a different way of working.

Happy New Year!

- W.

New York-based Editor-Compositor


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Steve Sayer
Re: Newbie question
on Jan 4, 2007 at 5:11:42 pm

[Wagster] "I didn't quite believe you, but I checked one of those multiple-exposure photos of a bouncing ball and you're right."

:)

This is one of those counter-intuitive delights that the universe likes to throw at us. Here's another one for you: if you increase the amount of mass on a pendulum, will it take more or less time to complete each swing? Answer: neither! The mass doesn't affect the timing at all... the only factor that matters is the pendulum's length. Strange but true--try it!

Anyway, back on topic... of course there are two fundamentally different approaches to animating something like this: you are either going for a realistic simulation or a cartoony imitation. The realistic simulation would have a velocity graph that looked like a sawtooth function; a jagged row of sharp peaks. The acceleration graph would be a constant (flat) line with a few one-frame spikes. Of course, for a more cartoony feel, you can adjust hangtime and acceleration to taste, perhaps making the ball stay at its peak a little longer than normal for an extra bit of bounce and character.

In either case, though, I think the position graph is the most detailed and the best choice for tweaking the animation:

Mathematically, the position graph contains all of the information contained in the velocity and acceleration graphs (its slope indicates the velocity at any point, and its curvature indicates the acceleration). However, the reverse is not true: the velocity and acceleration graphs are missing information about position, and the information they do display is not very visually intuitive.

Visually, the position graph of a bouncing ball looks like the path of a bouncing ball; the velocity and acceleration graphs do not. It would be difficult to picture how tweaks to such graphs would affect the final animation of the object.

You will probably find that with a bit of practice, you become much more comfortable animating position (i.e. translation) curves. If you're having trouble achieving a specific effect, post again; you can post or email a playblast or scene file if you want more detailed feedback.

-Steve


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