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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.
When working with a complex system such as the MassFX simulation tools inside 3ds Max, we have to remember that there will always be a number of global controls that exercise a great deal of influence over how the system is working. In MassFX these options will impact speed, accuracy, and so ultimately the final quality of our finished dynamics simulations. As these options can be found inside the MassFX Tools dialog, let's once again enable that option from our MassFX toolbar and then just the dock it to the left-hand side of the 3ds Max UI, which is pretty much where I would keep it for the duration of this course.
One of the first choices we will want to make with regard to our simulation setup is whether or not we want to use an object from our scene as a ground collider or can we happily work with the MassFX Use Ground Collision option. This automated system uses an invisible infinite planar static rigid body as a ground object. This is set by default at the height of the 3ds Max home grid, which would be 0 on the world Z axis. As you would expect from any well- thought-out system however, this Height value is indeed editable.
Because this Ground Collision option is on by default, we do need to be careful when working with our object setup. We need to make certain that we don't inadvertently place dynamic objects in a way that causes them to intersect with, or actually sets them below, this ground level. We can undock with our dynamic object behaving in a most bizarre manner if we do. In fact, whenever a simulation behaves in an unexpected manner, this is one of the first problems that I check for. Another extremely important default option in our MassFX simulations would be the settings we use for gravity.
By default, Gravity is both enabled and set to Earth actually MassFX. Now as MassFX uses negative values, this means our Acceleration value will be set to -9.81 m/sec square, assuming of course meters are the units we are currently working with. Don't worry if they are not, because if we just come up to our Customize menu and come down to our Unique setting option, if we just switch over to working with feet and inches for a moment or two, you will notice over in the MassFX controls that it automatically performs the conversion for us; we don't need to really worry about that at all.
Let's just go and set this back to working with meters. These gravity defaults mean that in most simulation--that is, ones that require real-world gravity settings--we really don't need to perform any kind of setup at all, as everything is ready to go out of the box, as it were. However, if our particular simulation requires something other than physically accurate gravity settings, as you can see, we do indeed have options available that will give us control of both the direction and strength of MassFX gravity in the simulation.
However, if our particular simulation requires something other than physically accurate gravity settings, well, as you can see, we do indeed have options available that will give us control over both the direction and the strength of MassFX gravity in the simulation. One interesting and potentially very useful option here is the ability given us to control our global gravity by means of any gravity force object or space warp that we have in our scene. Though if we do use this option, we need to bear in mind that the gravity force object doesn't currently use the same strength, scale, or settings as the default MassFX gravity.
To get the two to correspond--or to match, as it were--we will need to multiply the strength of our force object by 10 and of course use positive rather than negative values. So to set Earth-real gravity in force space warp or a gravity force space warp, we would need to set the Strength value to 98.1 rather than 9.81, as in the MassFX gravity. One obvious benefit of using this particular approach is that we can apply gravity in absolutely any direction that we like.
All we need to do is simply rotate our space warp object in the scene accordingly. We could even disable gravity altogether in our global options and apply different gravity settings to individual objects in the scene by using a number of gravity force objects and applying those at the modifier level rather then globally. In our next video, we will move on from the environmental globals we have looked at here and examine some extremely important options that go a long way towards governing the accuracy of our rigid body simulations, these being the substeps and Solver Iterations options.
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