Build a Gear Rig with Expressions in After Effects

Joey Korenman : What's up Joey here at School of Motion and welcome to day three of 30 days of after effects. Today, we're going to talk about one of my favorite topics, expressions. It's also one of the dorkiest things that a grown man can talk about today. We're going to take a look at how to animate some gears because they're kind of a perfect example of something that moves in a mathematical way. And that's something that you don't want to necessarily have to key frame, especially if you have tons and tons of gears to animate, I'm going to show you some strategies on how to deal with multiple gears. And also don't forget to sign up for a free student account. So you can grab the project files from this lesson and the expressions as well as assets from any other lesson on the site. Now let's dive into after effects and get started.
Joey Korenman : So more expressions for you guys, and those of you who have not watched intro to after effects expressions, you should probably watch that one first because that's going to let this tutorial make a whole lot more sense for you. Um, I'll link to that in the description for this tutorial. So what I want to show you, um, is just another cool way to use expressions. Um, and this is actually going to get slightly advanced just because when I started building this thing out, um, you know, as happened so often you, you think that this is a simple problem to solve and it ends up being more complicated than you thought. So what I want to show you guys is specifically how to create a system of interlocking gears that really work like real gears. They actually turn correctly and accurately, and they don't intersect. Um, and you can control exactly how fast they're turning and they all turn you know together.
Joey Korenman : Um, so let's dive right in and get started here. So I have a, here's what I did. I, um, I went into illustrator and I made four gears, right. So I made this one and then a little bit smaller, a little bit smaller and a little bit smaller. All right. Um, and so let's bring those into a comp and take a look at them. So I'm just gonna make a new comp, we're going to call this, uh, gear vid. Um, and I am going to just make this a light colored background so we can take a look at it. All right. So let's just drag all these in there, one by one. So you got gear one, like you're two or three and gear four. Okay. So when I started out, um, creating this tutorial, what I thought I would do is just sort eyeball, you know, the speed of these gears and come up with a, an expression rig that would let me just kind of keep nudging and adjusting the speed of each gear until it looked right.
Joey Korenman : And it turns out that's actually very tricky. Um, because if this gear, let's say this big one spins around six times, then this little one has to spin the exact correct. Number of times, otherwise the teeth are going to start intersecting with each other and that's not what I wanted. So, uh, I kinda beat my head against my desk for awhile, and I did some Googling. And what I found out is that the right way to do this is a, you have to make sure that all of the teeth of these gears are the same size. And what I mean by that is even though this little guy is much smaller than this big guy, if you look at the actual size of the teeth, right. They're the same. Okay. So when I made these in illustrator, I just made sure, um, to use the exact same size and I can get into exactly how I did that in a different tutorial, if anyone's curious about how I made the gears.
Joey Korenman : Um, so now that I've got them set up so that they can actually work like real gears, I had to figure out the math involved, uh, in making gears work together. And it actually wasn't as complicated as I thought. So let me start building this rig. And then I'll get into the math behind the way gears work. Um, and I hate that there's so much math in my tutorials, but unfortunately motion design is really full of, of math and kind of sneaky ways. So let's start out by making a Knoll and this is going to be the gear controller. Okay. So this is actually going to have the property on it that I will key frame to rotate these gears. So to do that, I'm going to add an expression control, uh, specifically an angle control. All right. And so what I want is to be able to rotate this and have all of the gears rotate correctly.