Modeling and Animating Toothbrush Bristles: Fine Tune Hair Dynamics with Dynamic Interaction Tool

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Instructor Vic Garcia

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Set up Hair Dynamic Parameters for stiff bristles using Dynamic Interaction Tool.

In this lesson, we will use the Dynamics Interaction Tool to give us quick feedback on dynamic simulation of the toothbrush bristles. We will adjust specific Hair parameters to give us stiff looking bristles.



- In this lesson, we'll set up the hair dynamics for the bristles. We use the dynamic interaction tool to preview the hair dynamics in real time. Okay, so let's set up some dynamics for the hair. We're going to go up to simulate, go down to hair options, and we're going to use the dynamics interaction tool for this. We'll pull that out. With this tool we don't have to mess with the timeline or animate the tooth brush in order to fine tune our hair dynamics. We can see instant feedback with this tool. Before we start, let me go into our toothbrush group. We select the hair. We go into the guides tab, and I'm going to drop the amount of guides that I have in the scene. Right now we have 1369, let me drop this to about 200. That way we can speed up the feedback when we start interacting with the hair guides. With this done, I'm going to go up and create a cube. Go ahead and bring this cube up to the front. Then, I'm just going to bring this really close to the bristles, about yea high. I want this cube to come in contact with the bristles around this area right here. This is going to be our proxy collision object. We don't want to bring our teeth in yet. We want to make sure we fine tune everything before we start. Let's go ahead and right click on the cube. Let's go ahead and add a hair collider tag. Once we do that, we can press redraw in our dynamic hair interaction tool. You'll see that our hairs start to fall. If we bring this cube down a bit, you can see it's starting to interact with the guides, and we don't want to work with it way down here. Let's go back up, and we press reset, it'll reset the guides to the initial rest state. There's gravity in the scene, so the guides are going to keep falling even though I press reset over and over again. Let's go ahead and select the hair tab, let's lock this tab down so we don't lose it. Let's go under forces, and let's get rid of the gravity altogether. The gravity isn't helping us, we want these bristles to be as stiff as possible, and now they'll start rising. Let's go ahead and reset the hair. Since there's no more gravity you'll see that the hair just stays straight up until it comes in contact with the collision object. There we go. See it interact. The hair's looking a bit like a sea anemone right now, that's not what we want. Let me go ahead and reset the hair, and let's just into the dynamics tab. In here we have a few parameters. The key ones are going to be hold root stiffness and rest hold. Hold roots will hold the roots as firmly as possible to the growth surface. If we, for instance, set this to zero, then let's go ahead and have this object collide, you'll see that the hairs are no longer held firmly at the base. They're just going to keep spinning around and around. That's not what we want. We can go ahead and increase this to 100. Now, they're going to start rising again and the base is firm. That's good. Let me go ahead and reset the hair. We have the stiffness setting. The stiffness setting, we have it set to 100%. This basically just means that we want this hair to hold as close as possible to the initial state at all times. At 100% you see what we have already if I move this in. It's not that stiff right now. That's okay, we're going to make it stiffer here in a second. Let me go ahead and reset this. Next, we have the rest hold. The rest hold basically says "We want you to be as stiff as possible and hold to the initial state." Right now this is set to zero. If I set this to 100 and go ahead and make these object collide, you'll see that the hair is trying its hardest to stay at its initial state. We're getting some really unpredictable results right now. This isn't what we want. Let me go ahead and reset this. We want to go ahead and drop this down somewhere to about 60%. Now, when I play this through, you'll see that the hair's starting to stay a bit more firm. It's still moving around like it's underwater, but we're getting somewhere now. The hair isn't sticking anymore to the object either, so that's good. I'm going to reset this. One thing we can do to help this further along is to adjust the number of guide segments. Let me go ahead and bring up the picture viewer. In here, I have an example of a guide and a hair. That guide controls the hair. The more can see right here I have three segments for this example. The more segments that this guide has, the softer the guide will be, which means the softer the hair will flow. More segments equals a softer guide and softer hair. Less segments equals stiff hair. These segments, if you can visualize, they're connected by springs. The settings such as rest hold and stiffness and hold roots, they all control these springs and the stiffness of the springs. Let's go into the guides tab. As you can see right now, we have eight segments. We can further see this if we select the hair object and we go up to simulate, hair mode, go down to points, let's move in a little closer. You can actually see the segments here. You can count them, one, two, three, four, five, six, seven, eight segments. Let's drop this down to five. We don't want to go any lower than five for this. Let's see what happens now that we have five. Let me deselect the hair. Let's grab the cube. Let's go ahead and have these interact. Let's see how much this helps. You can see it's already helping. The hair's starting to be stiffer. You go through with the object, the hair's starting to get to its initial rest state a lot faster now. We have some better results, we still need to tune this a little more, but we're getting there. Let me just reset this. Okay, let's keep going with this. Let's go ahead and go into the dynamics tab again. Now, let's go down to the advanced settings. Let's open this up, scroll down, and in here we have a setting called steps. The higher the setting for steps, the better and more accurate our calculations will be. We're going to increase to about 10. Let's see what happens now. Let's go ahead and have these collide. This is looking a lot better. We can move in closer so you can see. As I move this through, you'll see the hair start to really bounce back to their initial state now. They're starting to look like bristles now. Much better. Let me reset this. Next, we have iterations. This iterations setting just helps further enhance and strengthen the tension of those springs just a little bit. You don't want to go too high with iterations because, with a number too high, you won't really see any results. The rule of thumb is basically, you want to set the iterations roughly to the same number as your guide segments. Let's go back to the dynamics tab. Let's go all the way down to iterations. Our segments are set to five. We can actually go just a little bit higher than that, let's go to eight, and let's see what happens now. Let's play this through. That's looking much better. I'm liking that. That's looking pretty stiff. Okay, let me reset this. Once you add motion blur to your animation, any kind of secondary movements that we have left over, you won't really see that with a naked eye. That's looking nice. Let me move around to this angle. Let's go ahead and move this to about right there. Let's move closer. Let's go ahead and render this. You can see that's looking really nice. Let's go up to the hair collider tag on the cube. Let's go ahead and unlock this tab down here, select this hair collider again. Let's set the friction for this to 75 and let's set the bounce down to about 5. That's going to make this look a little better. Let me reset this. Let me go ahead and slide this along. Let's stop about there and let's render this. That's looking nice. If you need to get close for a render, let's say this close, and you need to hair to be a little smoother, you can always jump into the hair tab and you can go ahead and bring this count up for the hair segments themselves to about 15 or so. Let's go ahead and reset this. Let's bring this cube back again. Let's move this forward. Right on there. Let's see what this looks like. So the hair, when the guides are set a little higher for the hair, you'll see that they're smoother. Again, they're different segments. We have hair segments and we have guide segments. We want to leave the guide segments at five and the hair you can just crank up a little bit. I think we had this at 10 before and that looked pretty good. Let's render this again. That looks nice. All right, let me move this cube back. Let's go ahead and try that one more time, I want to go way up here to the front, just want to make sure that everything looks fine. Let's render that. Okay, this is looking great. So I'm happy with the results. I can go ahead and delete the cube, we don't need this anymore. Let's go ahead and close the dynamic interaction tool, we don't need that either. Let's go ahead and do a file, save incremental. By taking advantage of the speed of the dynamics interaction tool, we can get instant feedback on how the bristles will react to the collision object. In the next lesson, we'll animate our toothbrush, brushing across a set of teeth with the assistance of Cappuccino. We'll also fine tune any hair dynamic parameters.
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