Creating mouths that move with a head turn

So now, at this point we have the mouth connected to a slider, and everything attached to the head. So let's go ahead and add in the expressions that are going to allow those mouths to move with the head turn. So the first thing I want to do is create an animation. I'm going to go ahead and zoom in to my head here so we can see what we're doing, and I want to create an animation of my head turning. And I'm going to match my new mouths to the old mouths of that head, and that way I'll have some numbers that I can work with to actually create the expressions.

The first thing I'm going to do is go ahead and zoom in on my Timeline, make sure I'm at 0 here, and I want to zoom in enough so I can get to Frame 10 and Frame 20 pretty easily. So now we're going to animate a HEAD TURN of this HEAD So I'm going to set my slider to 0, move to Frame 0, and set a keyframe. Go to Frame 10, set that slider to 10, set another keyframe. And we're going to do same for Frame 20. So now you can see what we've done here; we've just created -- it moves one increment per frame.

So let's go ahead and move down to Frame 10, and we're going to start matching the animation of mouths to this underlying guide. So I'm going to take my new MOUTHS, make sure I've it selected. Select the key for Position, Scale, Rotation. Then I'm going to move to the extreme at Frame 0, and let's go ahead and move this over. Now remember, in the original animation we scaled this down and rotated it.

So to make things easier I'm just going to type in the numbers here. I remember I scaled it down to 90% and I rotated it by 8 degrees. So let's go ahead and fine-tune that positioning here; and there we go. So now we've got the first half. So let's go ahead and do the second half, and again, let's just start with Rotation and Scale. So we rotat it the opposite direction, -8, and 90% again, and then let's just go ahead and position this. There we go. So now I should have a pretty good animation.

Now I want to use this as reference, okay. So the only reason I animated that was to get some numbers. Now let's just start from the bottom here; rotation goes from 8, through 0, to -8. Scale goes from 90, up to 100, and then back down to 90. So remember these numbers here. Now the other one is Position. We have two values; one for X, and one for Y. X is left to right, so from left to right it's moving from -119 to 169.

On the Y side, it's moving from 46 down to 58 -- now remember in Y, higher numbers are lower on the screen -- and then back up to 46 again. So let's go ahead and use these numbers to do some animation. Now I want to start with the X position. Now, because this just moves linearly, you can just figure out what each increment is, and it makes it pretty simple. So here at Frame 10, you can see I've it at 40, and at Frame 11 it's at 53.

So it's moving somewhere around 13 units per frame. So let's go ahead and add in the expression. So the first thing I want to do is just delete the animation, because we're going to replace it with expressions. So the first thing we need to do is separate out X and Y, because we're going to be using different expressions for each. So I'm going to select Position, right- click over it, and do Separate Dimensions. And what that does is it separates out each X and Y, so now I can put separate expressions on each.

So I'm going to select my X Position, Animation > Add Expression. What I need to do is figure out which changing variable I'll use to create my X Position. In this case, I want to use the frame number of my HEAD, so I'm going to use my Time Remap number. So I'm going to start by taking my Pick Whip, and going Time Remap. With just that open, you can see that not much is happening, because this is just going from 0 all the way up to 0.7. And that's because, even though I'm displaying frames, it's actually spitting out seconds, so we need to do some conversions here.

So the first thing I'm going to do is say, a Equals, and then just that same expression: thisComp, layer, HEAD, timeRemap, semicolon, and then I want to add in a function called timeToFrames of a. When I do that, notice how this is now going from 0 to 20. And also notice how the mouth is actually moving left and right just a little bit; not too bad. But now I need to multiply that by how much the old mouth was moving on each frame, and in this case I remembered, from my numbers, I could actually calculate that, that it was a little bit over 13 units per frame.

So what I can do is create another variable, b is equal to that frame number, or timeToFrames, and then we can say the actual output is going to be b times, and then the number I had was actually 13.5. And when I do that, you'll see that it pretty much moves along with the head, at least in the horizontal direction, but I'm a little bit off. But that's easy to fix. This is why I added in this additional Null layer here.

So what I can do is I can take this Null layer, and just use this to position that mouth at the right place. So now once I do that, this is kind of like my offset control. Let's go ahead and make sure that that's right there. Okay, so now once I have that, you can see that my left and right motion is pretty much dead on, but I still need to add in all the other motions. I need to add in Y, as well as Scale, and Rotation. Now at this point, let's go ahead and add in the expression for Rotation.

I'm going to skip Y Position, and Scale, because those require slightly more complex expressions, and we'll get to those in the next video. But let's go ahead and add in an expression for Rotation, and the expression that we use is going to be almost identical to the one that we used for X Position. I'm going to open up the expression for X Position, select everything in it, Copy, scroll down to Rotation and then just Paste that in. Now the Rotation is not going to be the number of frames times 13, obviously; it's going to be slightly different.

So let's just go ahead and see what happens when we put in just that frame number. So what we've got is is we've got it starting to rotate, but it's starting from a positive position. So what we need to do is to bring it positive at the beginning, and negative at the end. So what I'm going to do is I'm going to type in 10 Minus b, and let's see how this works. It actually gets it pretty close. You see we're kind of rotating along the right axis at least.

Let's just go through this. So at Frame 0, b is 0, because that's what my slider is here, because I've animated that slider. So when my Time Remap is 0, b is 0, and so 10 Minus 0 is 10. When I go up to 20, my Time Remap is 20, so 10 Minus 20 is -10. So what this does is it gives me pretty close, but what I need to do is instead of going from 10 to -10, I need to go from 8 to -8, but that's pretty easy.

All I have to do is multiply this, so times 0.8, and that should do it. So now I've got my MOUTHS rotating the proper way, and moving along the X the proper way. So to refresh, what we've done is we've tied the X Position, and Rotation, to the value of the Time Remap, and as that increases or decreases, the MOUTHS will move along with the HEAD.