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Animating the arm

From: After Effects Apprentice 07: Parenting

Video: Animating the arm

Okay, time for the payoff. Animating this anthropomorphic robot arm to go ahead and reach out to each of these titles in time with our video edits. I pressed Home to return to the current time indicator to the very start of the composition. I'm going to enable Rotation for each of the arm pieces. I now need to start moving it into position. Unfortunately with this default parenting setup, you cannot just grab the end of the arm and move into place, because none of the other pieces are going to follow along with it.

Animating the arm

Okay, time for the payoff. Animating this anthropomorphic robot arm to go ahead and reach out to each of these titles in time with our video edits. I pressed Home to return to the current time indicator to the very start of the composition. I'm going to enable Rotation for each of the arm pieces. I now need to start moving it into position. Unfortunately with this default parenting setup, you cannot just grab the end of the arm and move into place, because none of the other pieces are going to follow along with it.

To do that would require something known as Inverse Kinematics. There are scripts available to do that in After Effects, but that's not the default. Instead, you need to build stuff from the bottom up. So say I wanted to setup an initial at-rest position for this arm. I will need to manually scrub first the Big Arm to get it into place. Remember, you can hold Command on Mac or Ctrl on Windows to scrub by minor increments. And let's pull down the Medium Arm to a nice at-rest position like that and then rotate the small piece back up kind of coiled upon itself. Okay.

I would like to go ahead and point out each of these videos at one-second intervals. So boarding at 2, remember our marker. We cut to one skateboarding exercise. At three we cut to another and at four we cut to the skydiving. So I'll go to one second and start rotating these individual arm pieces in a fashion I think might reach up toward the word snowboarding.

Not quite there. I need to straighten out the arm pieces a little bit. I'll go like that and I need to pull the Big Arm up a little bit, maybe around there. And this does require a little bit of work to get it right, but you will get there. The effort is rewarded when you eventually get something into position. So there's my first movement for my at- rest position, reaching out to snowboarding. And I can go head and do a standard reach like that or if I want to have fun I can give a little bit of flare to this animation.

Let's say that I want to add a little arm piece at the end to do a twirl on the way up. I'll just simply go to that keyframe, select its Rotation value, and type +360 on to the end, saying I want you to do another rotation. After Effects will do the math for me. I'll press Enter and now it will do a little unfurl for me as it gets up into position. And that's a more fun animation. I like that. Okay, once I have hit that pose, I want to hold it for a few frames to point out that title.

So let's look at these markers in the music to decide how long to hold. So one of these bass notes that I have marked, it happens at seven frames later in time than that rhythmic chugger I barked out. That might be a good whole duration because then the new bass note will motivate the arm to keep moving. To set another keyframe at the current value, I just need to drag my cursor down at the Add Keyframe switch and there's those keyframes. I'll go to two seconds where the video changes and let's move the arm into another position to then touch vertical ramp.

As I start to scrub, you'll see all parts of the arm move at once. That's because I had to have all the arm pieces selected. Remember to go ahead and select just the piece you want to rotate. So I'll go there, move back to my medium piece, and rotate up my small piece. Not quite there, so let's reach it up a little bit higher, reach back, close. Command or Ctrl for fine increment scrubbing. Down like that and over like that. I'm going to go ahead and preview this animation. That works! Might be a little bit boring after everything else I have done here, so let's go ahead and make the little piece rotate 360 degrees in the other direction to hit this point.

So it will come away, going to a back-rotate like that. So forward-rotate, back-rotate, that's fun. Okay, so let's find another hit point here. Here's another one, seven or eight frames later in time. By the way, a lot of music is structured around factors of two. So if my main chugga's are 30 frames or one second apart, I expect another subdivision to be at 15 frames apart, and another subdivision to be in seven and a half frames apart, between seven and eight.

This time it worked out at seven. I have marked something at eight. You can see how this rhythm is playing out. I'll drag down a keyframe there, go to 3 seconds, and move into a new position to go ahead and point out my other title. I need to fold up a little bit to get to this one. Yeah, I need to come up a little tighter there. And by the way, there is no one right solution to this.

Every time I do this exercise myself, I come up with a slightly different solution. And that's okay. That's where creativity comes in. You have a bit of fun. In honor of keeping that Small Arm interesting, I'll make him rotate 360 forward again. See how that looks. Rotate and hit. That's fun. I'm going to go another seven or eight frames in time just to go ahead and keep the same spacing of my keyframes. Mark those out, and finally go to four seconds and come up with another position for skydiving.

And let's go ahead and put the arm here, maybe bend the medium piece down further, and pull the small piece back. Okay, so I need to pull the large piece up. A kind of visual puzzle here to make this work. Here we go! I'll pull Medium Arm down, rotate the Small Arm over, and now I have got that text hit. And I have got a rhythm going here. So let's go ahead and rotate 360 degrees backwards for the Small Arm.

So it does a little back flip there. Next hit eight frames later. Same rhythm going here. Add Keyframes. And for the very end of my composition, I'm going to press Minus to zoom back in time. I need to come at rest again. Maybe I'll come to rest at this last little rattle right here. Let's say that I want the arm to go back to its at-rest position where it started. That's very simple to do. I'll select its starting keyframe, copy, and then immediately with my time marker in place, do Paste, and it will paste the value I just copied to the current time.

I'll do the same thing for this layer. Select, copy, paste. Select, copy, paste. So now my arm will end up back at rest. And that's kind of a boring movement again, so let's have that funnel arm do one more twirl, +360 Rotate. Bang! Now let's RAM preview. (Whir, whir, whir) That was kind of fun, wasn't that? Now obviously, there's a lot more you can do with this.

And indeed in the Idea Corner chapter that comes next, I'll show you some tweaks I might make to this particular animation. But this gives you the basic idea of how to link together components of an arm, kind of mimicking maybe a human or not quite human chain. And once they've been put together, animating them in a way to go ahead and create these complex movements that only require you doing some simple rotations. Notice that I did not have to animate the positions of any of these arms. They kept the same relationship to each other, once I have set up my parenting chain.

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After Effects Apprentice 07: Parenting

17 video lessons · 7288 viewers

Chris Meyer and Trish Meyer
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