Learn an intuitive workflow to creating complex rigid-body simulations and realistic effects with practical projects and examples. Contains over three hours of project-based training for artists learning rigid body tools in Houdini. Popular highlights include: Rigid Body Setup; Dynamic Operator Networks; Physical Properties; Initial States; Deforming Rigid Bodies; Forces; Constraints; Groups; Rigid Body Creation; Cookie Shatter; Fracture and Glue Objects; Animation to Simulation Switch; DOP Expressions. Software required: Houdini 9.1 and up.
Introduction and Project Overview Hello and welcome to the Fundamentals of Rigid Body Dynamics in Houdini, presented by Digital-Tutors, a Houdini training partner. My name is Sunder, and I'll be your instructor in this course guiding you through the necessary processes of harnessing Houdini's rigid body dynamic system. Rigid body dynamics is the process of simulating physical motions based on forces and collisions. This is very useful for pulling off various effects and reducing tedious animations. So during the next few hours, we're going to learn how to set up rigid body dynamic networks and how to adjust different physical properties of our objects like mass, friction, elasticity and so on. We're also going to learn about the different dynamic operators like RBD state, RBD solver, and RBD auto freeze to name a few. We'll also learn about different constraints, forces, and rigid body types. We're also going to study different ways of making multiple rigid bodies with duplication, creation expressions, and copy point techniques. Finally we're going to learn DOP expressions to trigger certain actions based on collisions. There's a lot of content to be covered, so let's begin by looking at basic rigid body setup. Once you have your project files copied to a writable location, pull up an instance of Houdini and open up 01_Tray. Inside of this particular scene file, we have a couple of objects, we have an apple and a tray, and we're going to learn the basics of rigid body dynamic simulations with the help of falling apples. We'll set it up so that the apple can fall down and collide with the tray over here. So to do that we'll need to create a dynamics operator network. You cannot basically create dynamics or rigid body solutions at geometry or inside of a geometry node. We need to use a separate kind of network which is a DOP network or a dynamics operator network. Fortunately for us, setting these up is quite simple with the help of the rigid body shelf. It's inside of the dynamic shelf area all you have to do is left click to access it and we have all the necessary commands in here that we can use to create rigid body simulations. So if you want to make the apple descend, for example, all we have to do is select it, and with it selected click on the RBD object button or the rigid body dynamics button. Once we left click it here like so, it'll add an auto DOP network, which is nothing but a normal dynamics operator network, or DOP network, and inside of it it'll add a bunch of nodes in that'll make this simulation possible. Basically, it'll take our object, connect it into a rigid body solver, and have that be effected by a force like gravity. Once we hit the play button, the apple will descend very nicely like so. And that's the beauty of rigid body simulations, they're just a way of creating animations in our 3D scenes using physical properties such as collisions and forces to create the different motions. So because we have gravity in here and the gravity has a force of negative 9. 8 in the y direction, the apple is falling down. Well, it's falling down but it's not colliding with the tray here. So the way we can make it, make the tray collide-able is by making it a rigid body object as well, that way it can be included in the auto DOP network. Now if we do make this a rigid body object, keep in mind that it's going to descend with the apple as well. Well, if we don't want this object to be effected by forces or the collision of the apple here, we can actually set the tray up as a static object and not a rigid body dynamic object. A static object is basically like the name suggests, static. It cannot be moved by forces or collisions. So if you want to do that, select the tray and click on the static object button which is symbolized by a wall that's being struck with a ball. So once we left click it, it'll go ahead and create that. If you enter the auto DOP network you'll see that the tray has been connected into a static solver which is not part of the dynamics network. At any time you can hit the L key to rearrange what we have in here. Now if we hit rewind and play, the apple falls down and collides very nicely with the tray here. So now they're both set up as part of our dynamic simulation. Now what happens if we want to set this up so that it's static at one point in time and dynamic later on? Well, the way we can do that is by actually making it a rigid body dynamic object, but we'll need to deactivate it and ensure that forces and collisions don't act upon it by making sure that it's passive. We're going to learn more about this in the next lesson. We're going to learn how to remove the object from the simulation so we can change it from being static to dynamic.