Adding joints to rigid bodies
Video: Adding joints to rigid bodiesWhen we're working with physics, one of the powerful things we can do is to chain objects together. What this will let us do for example, is take this mobile sculpture, and link the pieces together, so it hangs from the ceiling. And when the player knocks into it, it will wobble back and forth. The pieces can rotate, and will move, but are fixed by their rods on that wooden hanger. It's a collection of sphere, and very very small cylinders for the rods. And a roughly modeled series of arcs in wood. WIth a wood base that goes onto the ceiling.
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Interested in game making? Start in Unity—a game engine for mobile and desktop games and real-time simulations. Author Adam Crespi shows techniques used in game development with Unity and introduces the basics of scripting and game functionality. First, learn how to import models and textures, organize your project and hierarchies, and add terrain, water, and foliage. Next, Adam explores how to use lighting to bring the game to life, and add rendering, particles, and interactivity. The end result is a sample game with a lush environment, fully animated characters, and some basic interactive gameplay.
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Adding joints to rigid bodies
When we're working with physics, one of the powerful things we can do is to chain objects together. What this will let us do for example, is take this mobile sculpture, and link the pieces together, so it hangs from the ceiling. And when the player knocks into it, it will wobble back and forth. The pieces can rotate, and will move, but are fixed by their rods on that wooden hanger. It's a collection of sphere, and very very small cylinders for the rods. And a roughly modeled series of arcs in wood. WIth a wood base that goes onto the ceiling.
I've already put in the correct materials. So the eyes are on the spheres. There's chrome, and there's the same dark wood we've used elsewhere. I'm ready to get the colliders on. In this object, I've avoided putting on a mesh collider in the FBX. And so instead I'm going to put on custom sphere and box colliders, so it collides with the rigid bodies correctly. I'll start out by getting the spherical colliders on all the eyes, picking them, choosing Component > Physics and Sphere Collider. Now with the spherical colliders on, I'll get box colliders on the rods.
They're actually five sided cylinders made in Maya and then softened so that they look round. But they're small enough that a box will work nicely. I'll pick the first one, choose component, physics, box collider, and then I'll repeat it with the other three. Finally, I'll get a box collider on the hanger. Although it's actually two boxes that are bent, one big box that work nicely because it is at the same level all the way around roughly. I'll put a box collider on the hanger right at the top and finally one on the top mounting block. Now get rigid bodies on everything. It's simply a matter of going through and picking each one and putting a rigid body component on.
Once all the pieces have a rigid body component on, I can go through and set up the hinges. I also should get a material on. So that they react correctly with the right friction and the right mass. It’s really up to you, what order you'd like to do it in. As long as everything is on, it’ll work nicely. One note here on the top, this mounting block. Although, it’s a box collider, and has that rigid body onto it, I’m going to turn off gravity and freeze the position. This way, it’s fixed at ceiling, and I’ll freeze position on all three axes, and rotation.
Its supposed to stick in place, but let that first hangar rod hang from it correctly. Now I'll get my hinge joints on. I'll start out with the first sphere and I'm going to turn off the lighting so I can see a little better. On this sphere then, I'll choose component, physics and hing joint. We've got a couple different joints here. Hing joints, Fixed joints, spring joints. And then Characters and Configurables. A hinge is one of the simplest ones. It simply allows freedom of movement and rotation on multiple axes, as needed.
Things can be hinged together. A fixed joint, then, joins rigidly, rigid bodies. And finally, a spring, as the name suggests. Is springy and allows objects to snap out and come back. I'll pick Hing joint here and in that Hing joint, we can see it's got an anchor. It's got a spring and a motor. And there's also limits for breaking force. If we need objects to actually break and fly apart, we can put in that force there. Right now, the break force and torque are infinity, meaning it can't be broken.
This way we'll knock into it, but it can't come apart. The Hing joint is noticeable by the small orange arrow and its right up here at the base of the connecting rod. This is where I had set the pivot for that sphere and so it defaults to there until we move it around using the anchor or axis. Now in the connected body in the hinge joint I'll pick that connecting rod. This is IO1, and so it connects to hanger rod 01. I'll click to select, and the only thing that's available in the rigid body section are objects that I put a rigid body on to.
So, I'll pick hanger_rod1. And now there's that connection. Then I'll pick the hanger rod and do the same. Component, physics, Hingd joint. I had put the pivot for this up at the top, and that's where that Hing joint originates. Then I'll pick it's wood hanger as it's connecting piece. I'll repeat this process with the other ones, and then connect in the top hanger. I've added hing joints onto all of the eye's hangars, wood hanger, rods and up to the ceiling base. This way everything should hang, and I'll give it a quick test once I turn back on the building.
And then see what I need to add in my physic materials. I'll pick the master building, and turn on its visibility again. I'll make sure that this is up at the ceiling by selecting that whole sculpture, and pulling it up. Now, I'll press Play and see how it looks. The sculpture bobbles gently. It's already wobbling and the eyes will come over and look around. I may want to start those in a different position. But it looks kind of neat. It works. And when I jump, I can bang into it. And cause them to move around considerably. It does need a little damping.
We can see in here it's getting a little crazy in the motion and that's because those objects really don't have much mass. It's going to sit there and sort of bobble forever and the colliders will freak out a bit and collide with each other. I'll put in some damping. I'll start out with the eyes. Scroll down and look in the rigid body, there is a drag there, and i'll put up the drag to 0.5. I'll add the drag to the other eyes and see how it looks. I've added drag onto all the eyes and I'm ready to add drag and a little bit of resistance on the wood hanger and other connecting rods.
Part of dealing with physic materials then in our rigid bodies is making sure things don't fly around. So I'll put some drag on this hanger too. It's a little heavier so a drag of one should work. I'll give it a test before I put the drag on the chrome hanger rods and I'll see if it behaves any better. It looks better so far. The eyes look around and it's not quite shaking in such a jittery way. I like the way it's looking. And we can just probably bump these as we go by. And they'll knock around a bit without getting too crazy.
We should probably add drag on the other objects, so that they really are kind of A little more stationary, but it looks like the drag is slowing it down nicely. Finally, let's get some physic materials on to complete this. I'll click on the eyes and go into the material in the Sphere collider, and in my physic materials, I'm going to choose rubber. I'll put the rubber material on the other eyes here, and then try this one more time. Finally, before I try it, I'll get a physic material of wood on the hanger. We should really go through and make sure we have materials on anything that really counts here.
These rods are probably okay on their own. Now in a test, my mobile is a little less jittery. I should probably bring up the mass and a few other things, but I like how it's moving. And when I knock into it, it definitely gets a little crazy, but then settles down. So, it's kind of neat to be able to bounce off the art a bit, knock into it accidentally. We can use our physics to add some life to the game. Adding the ability to, fling things. Knock into things, push stuff over, and otherwise affect our world and let the animation happen very naturally.
Being generated by the physics engine.
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