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Using expressions to control the arm

From: After Effects: Rigging a Character Arm for Animation

Video: Using expressions to control the arm

In this movie we're going to use expression controllers to make this thing work a little bit easier. We're going to make the arm move and bend and then grip with just three simple little controllers. So the first thing we need to do is create a null object. We can right-click in the blank spot here in the Timeline panel and create a New > Null Object. I prefer using the keyboard shortcut, Command+Option+Shift+Y, so basically all the modifier keys, plus the letter Y; on a PC that would be Ctrl+Alt+Shift+Y. Now, a null layer is just a nothing layer, nothing on it whatsoever.

Using expressions to control the arm

In this movie we're going to use expression controllers to make this thing work a little bit easier. We're going to make the arm move and bend and then grip with just three simple little controllers. So the first thing we need to do is create a null object. We can right-click in the blank spot here in the Timeline panel and create a New > Null Object. I prefer using the keyboard shortcut, Command+Option+Shift+Y, so basically all the modifier keys, plus the letter Y; on a PC that would be Ctrl+Alt+Shift+Y. Now, a null layer is just a nothing layer, nothing on it whatsoever.

And expression controllers, or expression controls as they're called here in the Effects & Presets panel--if we just open this up we can see these--they are applied as effects, and as such, they need to be applied to a layer. And just so I know where things are, so I don't get mixed up, I like to apply these to a null layer. And I could go ahead and rename this just by hitting the Enter key. I'm going to call this CONTROLLER. Maybe even I'll call it ARM CONTROLLER, even better. And what I'm going to do is I'm going to apply an expression controller.

Now, there are a few different things. So for example, the checkbox control, which you can check on and off and animate that or whatever. I find myself using the slider control quite a bit. But what we're going to be doing here is we're going to be controlling the rotation of certain properties--the fingers, the arms--and so we want something that's the most like rotation, which is the angle control. So I'm going to call this Angle Control. And again, I'm going to hit the Enter key and I'm going to rename this GRIP CONTROL.

Now, because we've already set up the parenting, if I click on this layer right here, which is pinky 1, hit R for rotation, if I rotate this, then the pinky, the entire pinky rotates. So what I want to do is I want to link up all of the fingers to be controlled by this controller here, by this GRIP CONTROL. So what I'm going to do is I'm going to create a simple expression. And this is so, so, so easy, so don't be frightened if you're intimidated by expressions.

I'm going to open up ARM CONTROLLER here in the Timeline panel, open up Effects, open up GRIP CONTROL, Angle. I want to be able to see this property. So that way when I go here to, let's say for example, pinky 2, and I press R for eotation, and then I Option+Click, or on the PC I'd Alt+Click that stopwatch to create an expression--don't type anything here, don't touch anything, just grab this pick whip, and drag this to Angle. And then click anywhere on these blank areas here to go ahead and accept the expression. Now, what you want to do is do this for all of these layers here.

So Option+Click, drag the pick whip to Angle, and click to deselect. And I'm going to do that really quick here, and we'll speed through, through the magic of editing so you don't have to sit here all bored while I'm doing this. So zip through it. Okay. With all of that done, we go back up to our GRIP CONTROL here, and now when I move the angle, I'm basically going to be rotating all of these fingers, which does this.

Pretty cool! Now, what I want to do is actually make this grip though, because these fingers are kind of like swaying in the breeze a little bit, and we're losing the magic of the opposable thumb. That's what makes it so great to be a human being. And so what I'm going to do is I'm going to go over to thumb 1, down here to this expression. I'm going to modify it a little bit. I'm just going to click at the end, put my cursor at the end of the expression. And what I want this to do is move in the opposite direction as the other one.

So as we move that angle controller, I want these things, these fingers, to go in, and I want this one to go in as well and not go off in the other direction. So I'm just going to multiply this, which I'm going to put the asterisk, times -1. And so basically as these numbers go to a negative, like -7, this will be a positive 7. So when I go to Angle and I move this, look at that. That's great! And actually, I realized I need to do that to thumb 2 as well.

So let's go ahead and select the thumb 2 layer. I'm going to type E two times fast to open up the expression, and we will multiply this times -1 as well. Now, as I play with this, this looks really cool, but it does kind of look like the whole arm is--or the whole hand-- is gripping something. The whole hand is gripping, and I actually want it to be more of like a pinch motion. Because what's going to happen is this arm is going to come down and it's going to pinch that little movie camera to pick it up. So I don't want the whole arm to grip necessarily, even though that looks pretty freaking sweet actually.

So what I'm going to do is I'm going to change the value on these different layers here. So for example, let's go down to index 1, press EE to reveal its expression. If I play with this a little bit-- let's say, for example, I type *1.5, so that will make that move a little bit differently here, so it will basically move a little faster. And what I might want to do is also subtract, let's say for example, subtract 3, so it's not moving quite as much.

And I could play around with the rotation of all of these. It kind of looks like he is going to a little tea party with his pinky extended a little bit like that. So we might want to fiddle around with that on each layer. I don't want to take the time to do that now though. Really what we need to do is go down to the fingertips. So for example, the index 2 layer here, I want to go down and fiddle with that. And let's say that this is just -3, so basically it's this value minus 3.

And if I do that to all of the points here--so I could go here, that's * -1 and then just -3 there--it's not going to move as much. And actually with the thumb, I think because it's a negative value, it went the opposite way, so I need to go to thumb 2 and then do +3. There we go! And then same thing with these other points here. I want these to come in a little bit without having to close the hand, and that's going to make things look a little better here.

So if we go to Angle and we move that here, now we have a little bit more of a pinch because these fingers don't close up quite as much, so a dainty little pinch there instead of gripping the entire hand. Now, what I could do, I don't have to do this, but what I could do to make things a little bit easier, add a couple of more angle control effects. Snd I can control the other parts of the arm with these as well. So I'm going to close up these other layers. And actually I could do that by clicking one, Shift+Clicking the bottom, and pressing Shift+Tilde to close those up.

And then what I want to do is--I'm not going to worry about the palm actually, just the upper arm and the forearm. So I'm going to go to this angle control and I'm going to press Return or Enter to rename this. I'm going to call this ELBOW CONTROL, and then I'll call this next one ARM CONTROL. And I will select the forearm layer. I don't know why I'm talking like that for. I'm going to press Option+Click to create an expression there, drag the pick whip to the angle of the ELBOW CONTROL on the forearm layer, and do the same thing for the upper arm, except do the ARM CONTROL. Option+Click your expression, drag a pick whip to Angle.

And now, the magic here is that I've got tons of layers with tons of properties, and it's all confusing, but I could control it all with this simple layer, just with this expression controller. So I could raise the arm, I could bend the elbow, and I could make the grip. And I realize that this is a lot of extra work, that you could have easily just set keyframes and animated those principles here, but this is so much more flexible. If you wanted to change things later, it's so easy just to go in there and open up the hand, rather than going to each one of these fingers and changing its rotation value and then the elbow.

So if your client said, "Oh, actually I want the hand to come down later, or move more like this, or bend at the elbow more," it's just so much easier once you have a rigged set up like this. Teally easy, thanks to expression controllers. And as we see in the next move, when we talk about picking up objects, it's going to be so much easier, more flexible down the road as well to be able to do things that way. So this is all about efficiency and doing things the best way. And also kind of, isn't this the funnest thing in the world to be able to, like, drag this little slider and have this little monster hand, which is really just a bunch of shape layers, just a bunch of like triangles and rectangles? But we've kind of brought it to life with this one little slider here.

Love it!

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