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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.
The physical properties we assign to objects inside any kind of simulation will always play a big part in determining the behavior and believability of those objects as they simulate. Before we get into lots of micro-tweaking regarding other aspects of an mCloth, or indeed any MassFX simulation, we do need to spend some time considering and then setting up the physical properties of our objects. In this video we will take a quick overview of the mCloth physical property options available to us.
Let's select our mCloth object then and come over to the Command panel. If we scroll down a little in our mCloth modifier properties, you can see we have a Physical Fabric Properties rollout. The first option, Gravity Scale, is a multiplayer for the gravitational force in the scene, assuming of course that we do have global gravity enabled. This is a value we would increase if we, for instance, needed to simulate something like the effect of wet or heavy cloth. Typically though, we will leave this value set at 1.0.
Density is the weight of our Cloth object measured in grams per square centimeter. Now it is important that we take note of that fact, that this measurement is in grams per square centimeter. Now, the value we set here takes effect mainly when a cloth object collides with other dynamic bodies in the simulation. The ratio of our mCloth object's mass compared to that of the body it collides with will determine the extent to which our mCloth object affects the other dynamic object's motion inside the simulation.
In this instance we want our cloth to behave as if it has a cotton weight off 250 g. This means we will need to set our Density value to 0.0250. Remember, this particular field uses values in grams per square centimeter, whereas fabric in the metric system is measured per square meter. That's why we need to just do that little shift in decimal places. Our next two object properties really do speak for themselves, in terms of describing what it is that they do.
Stretchiness controls how easily our cloth will stretch, and Bendiness determines how easily our cloth will bend, or perhaps fold would be a more accurate description. The Ortho Bending option gives us really an alternative method for calculating cloth bend. This method can be more accurate inside a simulation, but oftentimes it will take longer to simulate. For this reason we may want to do a little testing with this option both enabled and disabled to determine which will suit our current simulation needs.
Damping controls the springiness of our cloth, affecting the time it will take it to come back to a resting position when it has gone through a flapping or snapping motion. Friction determines the extent of course to which our cloth resists sliding when it collides either with itself or with other objects. And finally, our two compression controls really determine the behavior of our cloth edges. Limit controls the extent to which cloth edges can compress or crumple. Stiffness determines the extent to which our cloth edges will resist compression or crumpling.
Now that we have an idea of what the physical properties options are about and with that simple change to our physical properties applied, it's time to put our final tweak in place that will really mean our hammock is ready for work. With Cloth objects, we generally want to let them settle into a usable shape and then capture that shape to be used as the starting point of a simulation, or in a simulation. As you can see, a straight or flat geometric plane does not make a believable cloth object as the simulation starts.
To get this set up we will make use of a piece of MassFX functionality that we have already looked at. This would be our start simulation without animation option. Now if we just enable that and then let our simulation run until the cloth settles down and is relatively still, we can then stop the simulation and coming over to the Command panel, we can come into our Capture States rollout and just click the Capture Initial State button. This of course captures the current state of our selected piece of geometry and sets this as the default or starting point inside the simulation for it.
Of course if we want to back up and start again, we can just use the Reset Initial State button and our Cloth object returns to its original unsimulated shape. If we now just run our simulation again, this time of course with animation enabled, we do still get a bit of a drop as the simulation kicks in, so we will need to allow for that in any timing that we set up as the simulation get started. But I am sure you'll agree that as a starting point for a Cloth object, what we have here is much more usable than a perfectly flat geometric plane.
With the physical properties set up then, we will need to move on to determining just how our mCloth object will interact both with itself and other dynamic objects inside the simulation. In our next video we will do this by taking a look at the parameters available inside the mCLoth Interaction rollout. With the physical properties set, we would next need to move on to determining just how our mCloth object will interact, both with itself and other dynamic objects inside the simulation.
In our next video we will do this by taking a look at the parameters available inside the mCloth Interaction rollout.
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