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Over the years of teaching, I've seen the same sort of issues crop up again and again with my students who are just beginning in 3D animation. One of these is improper usage of the Scale tool. I've reverted back to this very simple example of a robot arm because I think it's a better illustration of what the problem is. That problem is if you non-uniformly scale an object, if you stretch it in one direction with the Scale tool and then link it up to other objects, you're going to get some very, very ugly skewing problems that are a direct consequence of the fact that you've non-uniformly scaled objects.
As I kind of mentioned earlier on in the course, scaling is problematic, or to put it even more bluntly, scaling is evil if you don't know exactly what you're doing. So here's an example. I've got a box down here. That's going to be part of my robot arm, but it's not tall enough. So if I didn't know any better, I would just scale the box up. So let's try that. Grab the Scale tool and scale it up in Z until it's about 400% of its original size.
You can see at the bottom of my screen in Z, we're getting some numbers going by. So if I set that to about 400, then that's approximately 400% or 4 times its original height. So I think that's fine and everything is beautiful. Then I go and link all of my parts together. Just do that quickly, Link, Link. I want to check that in the Schematic view really quick to make sure that it is what I think it is. It looks good to me. Then I'll test it.
I'll grab my Rotate tool and maybe turn that wrist. Okay, that's fine. That's doing fine. Let's try this one. Whoa! Hello! Okay, so this is exactly what I was talking about. This is symptomatic of improper usage of the Scale tool. So let me undo that, Ctrl+Z, and take a little bit closer look at this. If I select an object and go to the Scale tool, I can actually right-click and get a little pop-up dialog here that's giving me more information about the scale of the selected object.
So this one as we see has been scaled up 400%. If we select the next child in the chain, you'll see, hey, wait a minute! This one is no longer at 100% scale. It's now got a Y scale of about 25%. Now, I did not change the scale of this object, but 3ds Max actually went behind my back and scaled this object to 25%, because scale is inherited by children. So what happened here is I scaled this one up to 4 times and then 3ds Max actually went and scaled this one down to scale of one-forth, so that it would maintain the same shape and I wouldn't see it suddenly jump to being much taller.
If this were at a value of 100%, then all of the subsequent children would be stretched out. 3ds Max thinks that it was doing me a favor by setting this to about 25%. That's fine until I start to rotate stuff. So if you then rotate things then it starts skewing and doing evil things, and the reason that's happening is because there's an internal order of operations to the transforms in 3ds Max. So under the hood, there's an order of position, rotation, and scale, and you can't change that.
What's happening here is that it's being rotated and then scaled. But it's being scaled relative to its parent. So it's a bit messy and you don't really need to have a full, firm, technical grasp as exactly why this is happening, but you do need to understand that you can't scale things non- uniformly, and if you do, then you're going to have problems with the hierarchy. So how do we solve this? I'm going to hit Ctrl+Z and undo, and there's a couple of different ways around this.
One would be to reset the scale. So currently, this has got a scale of 400 and this has got a scale of 25. If I select those, I can go into the Hierarchy panel and scrolling down a little bit, Adjust Transform, you'll see there is a Reset button here. So I can reset the scale. So if I click on that and then reselect these objects, aha! Now, this is at 100 and this is at 100 and change. Let's reset that again.
So you'll see here now that I've restored everything back to sort of neutral scale. In fact, all of the objects in your scene really should have a scale of 100, 100, 100, in order to prevent any of these problems from coming up. So if I try rotating this now, everything is fine. So that's one possible solution to the problem is resetting the scale. But there are better solutions. I'm going to reopen the scene from scratch to show you in this case a much better solution would be to simply change the parameters of the box. Select that box.
Go into the Modify panel. In fact, I have the ability to change the height here directly by just typing in a value or by adjusting the spinner or what have you. So the point here is that if I make changes inside the modifier stack, then that does not affect the transforms. The transforms are what are giving me grief here. So just to verify, if I go to my Scale tool, you'll see the scale is 100, 100, 100. So I won't incur any of those problems. So that's fine if you've got a procedural primitive object like a box and you can just plug-in the height that you want, but let's say you don't have a procedural primitive.
Let's say it's been converted to Editable and you don't have any parameters. So I can right-click and convert this to Editable Poly to illustrate that. Now what do I do? If I want to scale this up, well there's a couple of things I can do. In this case because it's just a simple box, I could actually select this top polygon here and just move it up. Done! I grab my Scale tool and you'll see everything is at 100. So perfect! That's a great solution. I didn't scale it at the object level.
I didn't have the ability to change any parameters, but I just changed the shape by moving a polygon. Finally, there is one last way to do this. This is probably the way that you'll need to do it if you've got a more complex shape. That is to scale at the sub-object level. So if I go into any sub-object or component level like a polygon and select all those parts, I can scale that up and down however I want.
That's not going to affect the Object Transforms, because it's happening inside the shape of the object or inside the modifier stack. So the modifier stack is separate from the Transforms. So if I do it in this manner, then I won't have any issues. So in fact, let's say I scale it all the way down, exit out of here, and I'm looking at the scale at the object level and it's still at 100. Go back to Polygon mode, scale it up in sub-object mode, exit, and you'll see it's still at 100, 100, 100 in the object Scale Transforms. So there you go! Don't scale things non-uniformly unless you're doing it at the sub-object level, and certainly don't link any objects that have non-uniform scale to one another.
Otherwise, your animation is going to break.
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