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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.
In this video, we just want to spend a minute or two digging a little deeper into the rigid body type itself. We want to have a look at the differences found in the three typical rigid body options that are generally made available to us. These are the dynamic, static, and kinematic rigid body types. Sometimes, depending on the software that we are actually using, we may come across slightly different terms such as active, passive, and animated rigid bodies. A dynamic, or active, rigid body object is much like an object in the real world.
It is subject to gravity and other forces present in the scene. It bumps into or collides with objects, effectively pushing them around the 3D environment and it itself can be pushed by these other objects in turn. To create this object interaction, simulation software will assign a piece of geometry in the scene a physical shape or mesh upon its creation as a rigid body type. This in itself is an option that's generally configurable, something that we have a measure of control over.
In MassFX, as in or the systems, the simulation moves this physical representation of the object, the physical shape, and the graphical mesh in the scene--in other words, the geometry that we see in the viewport will be updated or driven from that. A kinematic, or animated rigid body object, is a somewhat different entity. It is not subject to gravity, or indeed any other force that can be found in the scene, although it can collide with and push any dynamic rigid body objects that it encounters.
It, in turn however, cannot be pushed or affected by them. In this particular instance, the graphical mesh--remember, that it is the object that we see in the viewport--is left onto the control of the actual 3D application rather than the simulation engine. Now, this is true whether a Kinematic rigid body is actually animated or not. And so it is the 3D application that will control the transforms of the physical or collision shape or mesh. And remember, that is what calculates the collisions inside the simulation.
The brilliant thing about MassFX in 3ds Max is that an object can start out as a Kinematic rigid body and then switch over to dynamic at any point in the simulation. The object will then behave just like any other dynamic rigid body. It will be subject to the gravity setup in the scene and indeed any of the forces that we may have present in the environment. The Static or Passive rigid body type is somewhat similar to Kinematic, except that it cannot be animated. A Dynamic object can bump into a Static rigid body.
It can bounce off it. But the static rigid body itself will never react in any way. Now static rigid body type is extremely useful for performance optimization, as really all it needs to do is sit in the scene and have other objects collide with it. There is no need to calculate the transforms of that particular object as it is not going to be moving anywhere at all. It is also extremely valuable because it supports concave physical shapes. The fact that we have three different rigid body types to work with in our scenes means that we should fairly easily be able to find a combination to for pretty much any rigid body dynamic scenario that we can come up with.
Sometimes a little careful planning is required to determine which objects need which rigid body type applied to them, but once we've taken a bit of time to get that all figured out, our simulations should turn out very nicely indeed.
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