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This course introduces basic physics simulation principles in Autodesk 3ds Max using MassFX, a system that makes it cost effective to animate rigid body objects, cloth, and particle systems. Author Brian Bradley introduces basic concepts such as gravity, drag, volume, and density, and how Newton's Laws of Motion can help you understand the interaction of objects with these unseen forces. Using the purpose built scene, Brian walks through the tools and features of the MassFX (PhysX) system, applying the principles discussed as he goes. Along the way, discover how to combine rigid bodies and constraints, mCloth fabrics, and mParticles geometry to create fairground-style effects.
We have already noted that one of the big complaints in connection with the removal of Reactor in 3ds Max was the fact that users no longer have the means to create simple rope objects that could be used in dynamic simulations. In this video, we're going to step through the process of creating a simple rope object using the mCloth modifier. Before we get started here, it is important to note that this particular option for creating a rope object, whilst potentially very useful for our background or distance objects, does have some, or at least one, very serious limitation which we will demonstrate as we move along.
As you can see, our style scene once again consists of a number of suspended cylinders, although this time we do have something a little different in the form of an animated collider object in the scene. If I just press the Play button in our animation controls, you see our box simply travels across the screen, moving from right to left. To get started on our rope object, let's first of all select one of the cylinders and apply an mCloth modifier to it. If we straight away run the simulation without animation, you can see we do get some very strange behavior coming from our newly created cloth object.
Rather than falling down and crumpling in a heap as a piece of cloth probably should, we get this long pause and then a long, slow, very rough-looking collapse. What we are seeing is essentially a geometry problem, or to be more specific, a lack of geometry problem. If we just jump into the modifier stack and come down to the cylinder level, you can see we are working with a low level of geometric detail. We can alter this by setting our Height segment to a value of 55.
If we run the simulation again, you see that we get something much more cloth-like in behavior. However, we do also immediately see the serious drawback of mCloth for this particular use, namely its complete lack of volume preservation in the mesh. The one mCloth feature that we may instantly think about trying is the ability to set an internal pressure for a soft body object. Or, to use MassFX speak, we may try enabling the Balloon Behavior feature.
In fact, let's do this by scrolling down to the Volume Properties rollout and putting a check in the Enable Balloon Behavior checkbox. Let's then set the Pressure value to 1 and see what happens if we again run our simulation. As you can see, enabling this option doesn't appear to preserve our rope object's volume in any useful way, certainly not on this type of simulated motion. Although, if with the simulation still running, I just bump the Pressure value up to 6, you can see we do somewhat get an effect that looks a little like a hose filling with air or water maybe.
Be that as it may however, a rope object created with mCloth is clearly not suited to creating a falling rope that coils on the floor. But it can in some instances serve very well, especially as background motion in a shot, maybe as a hanging object that needs to interact with rigid bodies in the scene such as our box collider. To get our rope object to interact with this collider, we do once again need to make use of mCloth's pin constraint. Let's jump to vertex level in our mCloth modifier.
Now, if I just hit the C key and switch over to my Main_View camera, you see we're now able to select the top, or top couple, of the text rows. Then we can come over and use the Make Group function, give our group a name, and then click OK. Now, of course, we're ready to apply our pin constraint to the group. With that done, let's come out of subobject mode and switch back to our Target_CloseUp camera. Of course, the rope object won't interact with our collider just yet because we haven't set our collider up as a kinematic rigid body.
So, let's select it, and from the flyout on the MassFX toolbar, let's apply a Kinematic Rigid Body. And if we run the simulation now, you see our rope object interacts very nicely with the box, swinging to and fro in a very rope-like manner. Now while it's clearly not the highest quality, nor the most flexible option available for creating a rope object in MassFX, we hopefully can see how using mCloth could give us a very quick, easy, and usable option for certain types of shots or motions that we may be called upon to create.
Although in this particular case mCloth's Balloon Behavior feature didn't really help us out much, in our next video, we will take a look at how it can help us create a usable soft toy object for our simulations.
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