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In Getting Started with Reactor in 3ds Max, Steve Nelle shows how to create realistic dynamic simulations that have objects recognize, collide and react to coming into contact with each other in 3ds Max animation projects. This course includes a detailed explanation of both rigid and soft body dynamics, reactor's various collection types, using constraints and soft body modifiers, and how to adjust and control a dynamic simulation's accuracy. Four start-to-finish projects are also included in the course, which show practical techniques for breaking objects apart, creating cloth simulations, adding rippling water effects to a scene, and more. Exercise files accompany the course.
Creating a simulation that looks both believable and realistic is obviously of primary concern. In order to assist you in making that happen, Reactor has a series of settings that you can adjust to fine-tune a simulation's accuracy. When Reactor calculates a simulation, it works its magic by moving each object in small steps. The smaller the step, the more accurate the simulation. If when running a sim, you end up with strange little artifacts or abnormalities with the way things move in your scene or interact, you can adjust the number of what are called calculation substeps.
The number of substeps that a calculation uses basically is the number of times per keyframe that Reactor will look at, or evaluate, the scene in doing whatever is necessary to create its animation. The more times Reactor addresses what needs to be calculated, the more likely the simulation will turn out looking accurate. The substeps setting is found under the Preview & Animation tab, in the Command panel's Utility column. The command is formally called Substeps/Key, with the number entered representing the number of times Reactor looks back at the scene at each key interval in order to generate the scene's simulated action.
Reactor defaults the Substeps/Keyframe accuracy value to 10, meaning that the setting divides each keyframe into 10 calculations, increasing that substeps value to let's say 25. So, if a simulation doesn't provide the level of accuracy that you're looking for, the number of substeps per key should be something you ought to look at adjusting. Do know though that the setting does affect your calculation times, so take it up only as high as needed. Most of the times the default setting of 10 will do the job. Something else you need to be aware of when using hard body objects in creating collisions is that if your objects aren't doing a very good job in reacting together, or to each other, you may need to adjust something called Collision Tolerance.
What Collision Tolerance does is control how close or how far apart side-by-side objects need to be in order to detect each other. If a Collision Tolerance number is set too high, objects may unexpectedly explode just moments into a simulation. Let me show you what I mean. This is a file named Collision Tolerance. The scene consists of a bunch of bricks along with a flat cylinder representing a ground plane. Each of the bricks has been assigned a mass of 10. Let's go ahead and select all of the objects, and we'll throw them into a rigid body collection.
I'll window around the entire scene, then Shift+Alt+Right-click to open up the Quad menu. When the dialog opens, in the upper left-hand quadrant, I'll choose Rigid Body Collection. Okay, let's go ahead and run a preview. What happens? It looks kind of neat, but it's not exactly what I'm aiming for. What we'll need to do is adjust the Collision Tolerance value that we're using for our simulation.
Right now, it's probably a little bit too high. In the Utility panel's Reactor commands, we'll open the Havoc 1 World tab. That's where we're going to find the Collision Tolerance setting. All depending on the gaps between your objects, the smaller the Collision Tolerance, the closer your simulated objects can be to each other without unexpectedly interacting. Let's set the Collision Tolerance to 2, and we'll run another preview.
Okay, now this is looking much better, but each brick is still a little bit too sensitive. Let's try a Collision Tolerance value of 1, and we'll preview again. There you go. Things look a good deal better. Now, as with using a higher Keyframe/Substeps value, a lower Collision Tolerance setting does force Reactor to look a little closer things resulting in a longer calculation, so make sure to anticipate that possible delay when adjusting the numbers.
Usually though, by the time you get to adjust in the Collision Tolerance value, you really don't have much choice. You got to take the Collision Tolerance down far enough to get the results you need. Now Reactor certainly has a ton of other adjustments that you can tweak in the hopes of affecting the accuracy of your sim, but I think if you start with the utility's two primary go to controls to tighten things up--the Keyframe/Substeps in the Collision Tolerance-- you are going to be well on your way to getting the accuracy in your simulation that you are aiming to achieve.
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