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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 seen how we can easily set up a basic rigid constraint in MassFX and make it breakable, we are now going to move on to something a little more visually interesting. One brilliant thing about constraints in MassFX is that they can help us create some very interesting, even complex- looking background or ambient motions as I like to call them, without having to hand-animate everything. In this video we will see how we can take some simple seesaw keyframe animations and use them to create dynamic moving targets.
We will also demonstrate an alternative workflow from the ones we have used so far. In fact, what we will do is create our rigid body modifiers, constraints, and set up the proper parent-child relationship in just a few short steps. Let's go ahead then and select the two objects that we want to constrain together. The actual order in which we pick them here is important as the object we select first will become the parent in the constraint relationship, whilst the second object selected becomes the child.
Let's left-mouse-click on one of our board or seesaw object to set it as the parent and then, holding down the Ctrl key, we can left click to select its corresponding target object, setting it as the child. With the selection made, we can come to the Constraint options on the MassFX toolbar, left-mouse-click, and hold until we get the flyout and then select the slide constraint. As with the rigid constraint, we are straight away reminded that our objects need rigid body modifiers applying to them, so let's click Yes to apply them.
Then of course we can set the size of our constraint helper objects in the scene. We do this by sliding our mouse either toward or away from the parent object. Once we have the size set how we want, we can just left-mouse-click to complete the operation. And because of a slight glitch in current MassFX versions, we may have to manually align the constraint slide axis in order for our setup to work correctly. Here our constraint helper is being created at somewhat of an offset angle from the board object itself.
In fact, if I just switch to a top view by using the T keyboard shortcut and then switch to Y frame mode by using F3, you will be able to see just what I mean. This thin white line, or guide, shows us the direct in which our object will currently slide, which is clearly not what we are wanting here. To fix things, I am just going to disable Angle Snap, select our Rotate tool, and then simply rotate our constraint into alignment.
Once this is done, we can hit the C key to switch back to our Targets camera, selecting it from the list, and then use F3 to switch back to a shaded view. Of course we don't want our target to slide too far. We need to set a limit on the constraint to a value that works for our current setup. With the helper still selected then, if we just come over to the Command panel and to the Translation Limits rollout, we can set the Limit Radius value to something around about 22, which should work nicely for our setup.
Again, our constraint guide, our thin white line, is giving you some nice visual feedback regarding just where our constraint or our slide will end. Before we test our simulation, before we run it, we need to set our seesaw's rigid body modifier type to kinematic. These are animated objects. With that done, we can come and run the simulation. As you can see, once our seesaw animation gets going, our slide constraint is working very nicely. Now, as with our rigid constraint, the slide constraint can be made breakable.
If I just select the constraint helper, I could right-click in the Command panel and jump to Advance rollout, where we can enable that option. We need to make certain our Max Force value is set at 100, and we can change our Max Torque settings to 1500. And if we just run the simulation again, you can see that at first, our breakable limits that we have set are not passed, our slide just continues on its way, but then once the tolerances are exceeded, MassFX breaks the constraint and down she comes.
As you can imagine, once we have applied the same setup to all of the target objects in the scene, we will have some complex background motion going on. Hand-keyframing this level of motion and interactivity would certainly take quite a bit more time than the quick MassFX setup that we have used here. In our next video, we will move on to a slightly different type of motion, as we make use of the MassFX hinge constraint.
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