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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.
Having taken the time to examine the importance of forces in our MassFX simulations, it seems only sensible that we take a quick look at how we can work with forces in our mParticle simulations. In our start scene, we have a hopper with a funnel that we have decided will have a stream of objects emitting from it. For demonstration purposes, we will be using cubes, but of course these could be whatever we needed them to be. We can accomplish this effect by using spawned mParticles that collide with both the hopper and stand geometry. The idea is to then apply a force to the particles as they emerge, and we could of course stack forces to apply more then one if necessary.
As a first step, let's set up our collision geometries with the necessary modifiers. Let's select the hopper body and legs and of course the stand itself. Then from the Modifier List in the Command panel, we can apply a PFlow Collision Shape modifier. Now even though technically the modifiers have been instanced, you will notice that with our object still selected, we can actually edit the modifier parameters. However, if we just select one of the objects and then click the Activate button, you can see that as we select the other objects, that parameter change has been applied to all of them.
Well, let's now open up Particle view by pressing the 6 key. Straight away we will need to drag out a MassFX Flow and then just make a few quick changes. The first thing we want to do is replace our Birth Grid with a Birth Stream. Of course adding the Birth Stream operator creates a gizmo in the scene that will determine where our particles will spawn. As we obviously want to align this to our hopper, let's hit H key to bring up the Select From Scene dialog. Firstly, I will just hit the Display All button and then type Birth in the Find field.
As you can see, our birth helper comes to the top of the list, meaning we can now select it. With that done, we can enable the Move tool, come down to the coordinate display area, and enter an X value of -246, Y of -2027, and a Z value of 2700. With our particles spawn in place, let's jump back into Particle view and select the Birth Stream Operator. Over in the parameters section, again we have a few changes we need to make.
For instance we need to set the Emit Stop time to 150, the Rate to 100, our Speed needs to be set at 3000, and the Stream Source Icon size can be set to 680 by 820. Now if we take a look at what we have so far by pressing the Play button down in our animation controls, it is clear that we have a way to go in order to achieve a satisfactory simulation result. One thing that is missing is any kind of collision between our particles and the scene geometry.
To create these we of course need to add a MassFX Collision operator to our Flow. So, from the Depot, let's left- click and drag that in. Because this is a test, we need to make certain that it goes below the MassFX World operator. We can then select it and click on the By list button. Here you will see the four collision meshes listed, so let's select them all and then click the Select button. Now, if you are new to particle flow and are wondering why only the exact meshes that we are looking for seem to get listed here, this is because only valid deflectors show up when we try to add objects to a collision test.
As these are the only objects in the scene with the necessary modifier applied, these are the only ones we see. Of course, at this moment in time our particle geometry is way too large to fit through our funnel, so we need to select Shape operator and set our 3D cube sized to 50 mm. If we press play again, we can see that things are looking pretty good. If we just hit F3 and switch to a wireframe view, you can see that our cubes are interacting nicely with the hopper geometry.
Let's switch back to realistic by, again, hitting F3. Time now to see how we add forces that can be used to influence the behavior and motion of mParticles in the simulation. The first step is to drag a MassFX Force operator into the flow. This time we need to place it above our MassFX World. As a general rule, any non-test MassFX operator needs to go above the MassFX World in an event. This means the MassFX properties defined by the operator are available to the simulation engine before the simulation starts.
Of course, before we can do anything with a Force operator, we need to have a force space warp available in the scene. In the Create tab on the Command panel, let's click the Space Warps button. From the options available, let's grab a Vortex Space Warp, enable AutoGrid, and then click and drag in the viewport to create this just below our funnel. Once I have it at a size I am happy with, I can just right-click to exit creation mode. As one last tweak, with the Move enabled, I'm just going to raise the Vortex Space Warp up a little in the view.
Whilst we have it selected, let's jump over to the Command panel and again perform a couple of quick parameter tweaks. The first thing we want to do is create an on-off effect by setting the on time to frame 35 and in this instance we can leave the off time set to 100. The only other options we will change here are Orbital Speed and Radio Pull, setting them both to a value of 3. To tie everything together we need to jump back to our MassFX Force operator in Particle view and add our Vortex into the Forces list.
We do this by clicking the Add button and selecting the Vortex in the scene. Now, if we run the simulation, once our Space Warp kicks in, we can clearly see the way it influences our mParticles. What we've created here is a simple and straightforward effect. Still, it is enough to help us see the impact that forces can have on the finished result of an mParticle simulation. With forces comes the ability to affect motion inside a simulation in a whole other way. This pushes back the boundaries and opens up the doors regarding the type of dynamic simulation effects that we can produce with 3ds Max and MassFX.
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