Animation Diagnosis Exercise 2

[robcat2075]

See if you can figure out what has gone wrong here:

 

bouncingBallX.mov

 

Hint: it's about gravity.

 

Don't worry, it's not by anyone from this forum.

[TheSpleen]

First two bounces too high?

[bighop]

The ball seems to have a lot of "hang time", and a little more bounce. Also there should be some squash when the ball hits. In the graph editor you can "peek"(I think that's what you would call it) the keys where the ball hits the ground to make a sharper bounce.

[danf]

It looks to me like the bounce speed changes. It starts way faster and sharper bouncing than at the end.

 

Also, I'd like to contest the notion that "there should be some squash when the ball hits," because not all balls are squashy. If you don't believe me, video tape a golf or billiard ball bouncing off concrete. If there is squash, it's not discernable to our eyes. You have to represent what you're depicting.

[bighop]

It has nothing to do with being squashy, it is an animation principle.

[danf]

This edit is me holding back my beliefs.

[robcat2075]

Now, don't get all riled up guys , it's just a bouncing ball.

[steve392]

I think it needs some squosh and it seem to be in the air a lot,but I would be pleased with it had I done it

[Fuchur]

It behaves like a ballone on some of the bounces... but a ball which would go up that high at the first bounces would lose its power faster or at least would jump much farer per bounce. The weight which is implied by the first bounce is just not there in the other once... so when there is not some antigrave-machine active at the end of its bounces, something is wrong here

 

*Fuchur*

[Walter Baker]

Personally, I thought it looked pretty darn good.

[bighop]

I never get "riled" up, life is too short. I like these post, you get a lot of different views.

[danf]

Alright, since you never get riled up, I'll assume you're open to having your dogmatic stance on the 12 principles of animation pointed out to you. And I'll do it in a way you can understand, in a deference to authority:

 

In Richard Williams' "The Animator's Survival Kit," on page 39, he writes:

 

"The bouncing ball example is often used to show animation 'squash and stretch' - that is, the ball elongates as it falls, flattens on impact with the ground and then returns to its normal shape in the slower part of its arc.

It might squash and stretch this way if it was a very soft ball with not much air in it, but what I've found is that you can get a good enough effect with a rigid coin - provided the spacing of it was right - so this added technique is not always necessary. Certainly a hard golf ball isn't going to bend all over the place. In other words, if you do this squishy squashy thing too much, everything comes out a bit 'sploopy', like it's made of rubber. Life ain't like that. At least most of it ain't."

 

I hope we've all learned something valuable about "rules/laws/principles."

[bighop]

If I wasn't open to feedback on my animations or what post, I wouldn't be here.

 

As you wrote: "so this added technique is not always necessary" I looked at the animation and thought it could use this technique, some did not. It is up the the animator to decide what is right for their project.

 

I think you have to look at what the complete project is. How is the animation being used, who is the audience, how is it going to be displayed, and is the animation a key part of the scene, or just part of the background.

[danf]

I agree. Context is a lot of it.

 

 

I'm changing my guess: I think the third bounce is too fast..?

 

But I'm going to hop on the "I'd be happy if I made it" side of the ship. Is this actually a good bounce and you're trying to throw us off, rob, you sneaky cat??

[itsjustme]

There are a couple of things that bother me about the ball bounce.

 

First, it probably bounces too high on each bounce...unless it's one of those "super ball" type of balls. I would think it would lose more energy on each bounce otherwise.

 

Second, I haven't checked the rate at which it falls, but I'm guessing it doesn't fall at the speed that gravity would actually make it fall. There's a great set of tutorials at animationphysics.com that would apply.

 

Third, it looks like the spin on the ball is incorrect...it is most evident in the part where the ball is rolling on the ground. It looks like the animator set the distance the ball would travel and then didn't adjust the amount of roll, it sort of skids along the ground plane at around the four second mark.

 

I am probably missing another problem, but that's what I think I see with a quick look.

[robcat2075]

It's not a BAD bouncing ball. He's really close on a lot of it.

 

I don't mark him off for not using squetch. The first assignment you get in animation school is to do a bouncing ball with no squetch and that may very well be the intention here. It's hard to make the contact with the ground look solid without squash but there are certain objects like bowling balls and coconuts that you'll need to drop on some one someday and they never squash even in the floppiest of universes.

 

So we won't worry about squash.

 

 

Several of you are on the right track with comments about the speed of the bounces or "hang time" or the gravity going away. Any one of those bounces from one contact to the next might be an OK motion for a ball to travel thru. We have no idea about the scale of the ball or the distance it's dropping.

 

But if we count frames on these bounces we find some things that just can't be.

 

To simplify, I counted the frames it took for the ball to drop from the peak of each arc to the ground and came up with these

 

6 6 5 5 5 5 4 4 3 3 3 3 2 1

 

(btw, the time going up should equal the time going down in each arc)

 

So we have quite a few drops that are taking the exact same length of time to happen.

 

For example drops 3, 4, 5, and 6 all take 5 frames to hit the ground. They are falling from progressively lower distances and yet take the same amount of time to reach the ground. In fact, drop 6 falls from 1/3 the height that drop 3 fell from.

It's as if gravity is reducing for each bounce. That starts to look weird after a bounce or two even if you don't count frames.

 

One solution would be to have the ball bounce height decay much less so the ball was rising to and falling from about the same height each time.

 

But if he wants to decay the bounce as much as he does, the lower bounces will need to happen faster than they do. Which means he's going to run out of bounce much sooner. Which means he might want to start from a much higher height so he has more time on that first bounce to shave frames from on the later bounces.

 

Somewhat related, there are several brief stretches where the balls speed is rather linear... it's moving the same distance from one frame to another, particularly as it nears or leaves the ground. That can't be. A ball falling will cover more and more vertical distance on succeeding frames and a ball rising after a bounce will always cover less and less distance on succeeding frames.

 

On the plus side, he's got the horizontal motion of the pretty well down. It moves steadily forward regardless of how fast the ball is rising or falling. A lot of people will have the ball slowing in mid air at the top of the arc. And the arcs seem to be pretty good parabolas. The beginnings and ends might be a little straightish but it's hard to tell when the distance covered in each bounce is so small.

 

The spin of the ball is an issue. It looks OK initially but in the last few bounces it doesn't seem related to the ground contacts. But you'd really want to get the basic bouncing motion of the ball right before you tried to fix the spin. (Real balls can spin in an unintuitive manner. A superball can actually reverse spin on a bounce if you toss it right)

 

Now these may seem like very small points, but small points are all that "bouncing ball" has. There's no story, or dialog or posing, or staging issues. You just need to get the basic physics right, and if you can't do it on a bouncing ball you probably won't get it on all the bounce-like things a character has to do like walking or running or falling down or tossing something or just dropping their hands to their side.

 

Mastering the basic physics of falling or bouncing objects goes a long way to making your characters seem to have real weight when they move.

 

Thanks for all your participation and comments!

[danf]

I can't believe I was too lazy to count frames! That should've been the second step after just watching it!

 

You sold me, I'll work on the bouncing ball next.

 

Oh, and if the bouncing ball is the first lesson in an animation class- what's the second? And third? Actually, if you could just write out a series of exercises which would cover all of the necessary skills in character animation, that'd be great.

 

But seriously, thanks for the Diagnosis exercises. These are cool.

[robcat2075]

Oh, and if the bouncing ball is the first lesson in an animation class- what's the second? And third?

 

Here's the third one, squetchy bouncing ball... with anticipation!

 

anticbounce0001MP4.mov

 

 

Actually I've been meaning to do a tut on bouncing ball because I have yet to see one that made good sense in terms of what we do in CG.

 

So much to do... so little enthusiasm to do it.

[danf]

So for that tut. we'd imagine the ball is a squetchy character, bouncing around freely? That's a pretty liberating exercise!

 

I really need a second A:M instance, b/c I'll be rendering into next week at this rate...