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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.
One very nice feature of MassFX is the fact that animated characters can participate in simulations as either dynamic or kinematic rag dolls. Using the Dynamic option, a character come both affect and be affected by other objects in the simulation. Using the Kinematic option, a character can affect the simulation, but cannot be affected by it in any way. For example, an animated character could knock down an obstacle on its way-- maybe such as bursting through a prefractured window--but a large box falling on a Kinematic rag doll character would not in any way alter its behavior in the simulation.
To demonstrate how easy it is to create and edit a rag doll and its parameters, we have in our scene, as you can see, a simple character hierarchy created using standard 3ds Max bones. Now, although this is clearly a bipedal character, it does not have to be in order for a rag doll to be applied. We could use any set of linked bones in any kind of character configuration. We could just as easily have used a biped rig here, as the rag doll system will work very nicely with that also.
We cannot, however, currently use rag doll on a cat rig. To apply the rag doll, all we need to do is select any bone on our character, go up to the MassFX toolbar, and from the Ragdoll flyout, invoke either the Create Kinematic or Create Dynamic Ragdoll commands. In this instance, I want to create a dynamic ragdoll. Once the option is chosen, you can see we get an entire system of dynamic rigid bodies and constraints all applied to the bone hierarchy and all set up to generally mimic the range of motion found in the joints of bipedal creatures such as humans.
Straight away of course we can run the simulation. As you can see, our character falls dynamically to the floor. The constraints setup maybe a little off for our particular character setup but as an initial pass, this is not a bad start at all. And of course we can easily go in and refine the set up using all of the modifier and constraint options that we have worked with so far in our course. In this particular case for instance, we might want to get a better fit of our collision meshes of physical shapes to the bones.
We can do this by first of all deselecting what we have as our current selection includes constraints, and then we can switch our Selection filter to the bones and drag a selection around our character. Then, in the Multi-Object Editor, we can set our Physical Mesh Type to Convex instead of the default Capsule. This of course gives us a much better fit of the collision mesh to our bones. If I just switch over to our main camera view by using the C key and selecting that option from the list, you can see if we do at some point need to get back to editing our Ragdoll global properties, that we actually have a Ragdoll icon in the scene.
This was created when we added the ragdoll to our character. This can be selected like any regular 3ds Max object. Of course we will first of all need to alter our selection filter. This time I am just going to set this Helpers. Then when we select the Ragdoll icon, you see, we once again get access to all of our Ragdoll global parameters. With our Selection filter set to Helpers, we could also drag a marquee selection around our character and select all of the constraints in our ragdoll.
This means of course that we can edit all, all groups of them, again inside the Multi-Object Editor. Being able to edit multiple constraints, or indeed rigid body options in this manner can of course be a huge timesaver when we're working with a complex system such as a ragdoll. One thing we may find, if we have to work with a number of ragdolls in our scene, is that our viewport refresh, or frame rates can become a little sluggish. Oftentimes previewing simulations that have lots of constraint helpers constantly being redrawn can do that.
If we find ourselves struggling with this, we might want to disable the display of helpers in our viewport. We can do this of course by coming to the Display tab of our Command panel and using the Hide by Category and Helpers option. As you can see, creating and editing a MassFX ragdoll is a fairly straightforward process. Of course if we're wanting to set up an extremely accurate system, maybe for something like close-up digital double work, then we will need to spend quite a bit of time tweaking constraint settings, along of course with a judicious amount of trial-and-error testing.
But as with everything we've seen so far in MassFX, with good planning and attention to detail, we can get some very nice results from the system inside very acceptable time frames.
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