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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.
If the ability to use forces in 3ds Max as part of a MassFX dynamic simulation is not something that we see as a particularly big deal, hopefully this video will redirect our thinking a little and show us just why this functionality is an extremely important and indeed powerful part of the simulation process. As we look at the two objects we have present in our scene, which of course are just rough representations of a feather and a brick, we may instantly have certain expectations about how they ought to behave if dropped from their current position.
Most of us will be well aware that a brick or a large stone when dropped tends to travel pretty quickly. By comparison, a feather or something equivalent in mass such as a small piece of paper seems to almost meander its way to the ground, taking much more time to get there then our brick or stone. In an environment subject to gravity, these two objects should fall at exactly the same rate. And indeed, if I run the simulation, you can see this is exactly what happens in MassFX. Of course, whilst this may be technically correct, to our eyes this just looks all wrong.
Now we may be wondering whether or not the problem is being caused by poor setup of our object's physical properties in the simulation. Could it be that we just need to accurately set the mass and density values in our modifier options? Let's try doing that and see if it makes a difference. First of all, let's select our brick and in the physical material rollout, let's set its Mass to a volume of 2.75 kg. This is a mass of standard UK house brick. Then, if we select our feather, we can set its Mass to a value of 0.01 kg.
Now, this of course is somewhat higher than a feather typically would be, but it gives us a nice simple value with which to work, and of course the setting is still way below the mass that we have applied to or brick. With that done, let's runs the simulation again. As you can see, our objects still fall at exactly the same rate. The problem is that our scene lacks any kind of atmospheric friction or drag, which is of course always present in the real world. Because air has density, it creates friction.
So, if we want realism in our simulations, if we want our objects to fall in a believable manner, we need to re-create this real-world occurrence. This then, is where the addition of forces to the MassFX toolset becomes extremely important. Let's add some drag to our environment by coming across to the Command panel. In the Create tab we need to navigate to the Space Warp section. Here we gain access to a collection of Space Warp forces. Now, if we don't see forces by default, we can just access this dropdown and choose Forces from the list.
To re-create our atmospheric friction let's select the Drag Space Warp and then with AutoGrid enabled, we can click and drag to create the space warp in the viewport. Now, generally speaking, it is not really important where we place our space warp icon, but I'm just going to drag it up in the view so as to avoid any potential problems due to it intersecting with our rigid body object. Next, of course we need to set up our Space Warp's parameters so as to get the desired effect in our simulation. Let's set the X and Y Linear Damping values to 0.
The up axis really is the only one that we need to apply drag to for this particular example. If we run the simulation now, you can see we get no change in our objects behavior. This is because we need to create an association between the drag force and the objects we are simulating. To do that we can select our brick and then over in the modifier properties scroll down until we reach the Forces rollout. And here we can click the Add button, select the Drag Space Warp in the scene, and we have now created a connection between these two.
We naturally need to follow the same steps for our feather. If we see run the simulation now, you can see we are clearly getting a reaction, but it would seem that our Z axis strength value is too high. Let's select the Space Warp then and set the Z axis linear damping value to 0.005. If we run the simulation again, you can see things are looking much more promising now.
To art direct matters a little here, we could make our feather heavier so as to have it settle in the view if we want. To do that, let's select it and in the physical material rollout, set its Mass to a somewhat unrealistic value of 200 grams. This would be 0.20. This of course will force it to move downward more than across. If we run the simulation now, you see what we get is looking pretty nice indeed. Without a doubt, creating believable simulations of real-world objects in MassFX is a complex mix involving a whole range of settings and parameters.
This can include creating accurately scaled models; applying realistic volume, mass, and density settings; applying appropriate physical properties, such as bounciness; and of course the addition of forces to our scenes to mimic real- world environmental effects such as drag.
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