Reactor - Part 1
Rigid Body Physics Simulation - Dominoes
In this tutorial we will be looking at the use of Reactor in 3DS Max. Reactor is no longer a part of 3DS Max in the 2012
version, but the previous versions do still have it. In 2012 this would be done with the Mass FX modifiers, but uses the
same principles in creating rigid body physics simulations.
In order to start let's open a new scene in 3DS Max.
In order to have a physics simulation we need some objects in our scene that can collide and interact with one another.
Let's start with the good old fashioned domino topple.
Create a box in your top viewport that will represent our first domino. Like below:
I have made my domino on the grid with the settings as shown. If your dominoes are too small then you may run in to
trouble later so making them a decent size first off can help you out now.
Next, we'll make a row of copies of our first domino. Get your move tool, hold down the shift key on your keyfboard and
drag along only the arrow pointing towards the front of your domino, in my case it would be the red X axis arrow as
depicted above. You should see the copy being created, don't let go of the mouse button until you have set the domino
close enough to be knocked over by the first domino, but far enough away to give it room to fall. Like the next image.
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Once you have the domino where you want it, let go of your mouse click. The Copy Dialogue settings box should appear.
Make sure that "Copy" is selected from the list, and then give yourself a
number in the "Number of Copies" field. I've made 10 more for this
demonstration.
Once you have made your selections hit the OK button.
You should now have a row of dominoes set evenly spaced apart from one
another.
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Great, now before we get to using reactor, let's give our first domino a bit of a tilt as though we had started pushing it
over to start the action.
Get your rotate tool, select the first domino, and just tilt it forward towards the next one in the line ever so slightly.
Great, now we can get to work in reactor.
If you don't have your reactor panel up already, then right click in the empty space on the main toolbar at the top of the
screen.
Then select reactor from the list.
A pop up menu bar with all the reactor tools should appear.
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Take a minute to scroll over each button and get a feel for what all is included in the reactor tools.
The two tools we will be using for this tutorial are the Create Rigid Body Collection button, and the Create Plane button.
First, click on the Create Plane button, and then click anywhere in your top viewport to create it.
The Reactor plane is going to serve as our ground level. It is an icon that extends a
plane in all directions endlessly, at whatever elevation you place it at. By clicking in our top viewport, it defaults at the
same level as the grid in our perspective view. At 0 on the Z axis.
Next, select everything in your scene. All the dominoes, and the new reactor plane.
Then click on the "Create Rigid Body Collection" button.
It should create an icon on the screen that looks like three stacked boxes. By clicking this
button after we selected all our scene objects, it also automatically adds them to the Rigid Body Collection.
Select the Rigid body icon, and go to your modify tab to see the results.
You should see all 11 boxes in the Rigid Bodies list, and the Plane.
If you missed any in your initial selection, you can always click the add
button and select the missed objects to add them to the list.
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This rigid body collection tells our reactor physics simulator that they are solid objects and should be treated as such.
All that is left now is to create our simulation!
Go to your Utilities tab now. (That's the tab that looks like a hammer!)
Find the reactor button and click on it. The Reactor settings should appear below once you
have turned it on.
<-----Here we can define all the settings for our rigid bodies, as well as generate the animation itself.
First, select all of your dominoes. Be sure to have only the dominoes selected, and not the rigid body collection icon, or
the plane icon.
Then open up the properties rollout menu at the bottom of your reactor settings. The arrow above shows the rollout
title.
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This settings rollout is where we can change the properties of the objects. We
can give them a mass to make them heavier than other objects in the scene to
make our animations seem more realistic.
You can also give them friction which can help if your objects start sliding around
as though they were on ice skates.
Or Elasticity to make them bounce back a bit more like rubber.
The Shell setting is how far away from the surface of the object an invisible shield
is placed. This shield is what actually pushes over the other objects in your scene.
If this is set too high objects will knock each other over without looking as though
they are touching each other. If this is set too low, then the objects will cut
through each other.
The Simulation Geometry is where you can define what the shell will react like.
A convex hull means that your object will be surrounded by the invisible shield.
So models that have openings, holes, etc. won't work well as Convex.
Concave mesh will let the shield follow the object more closely so that meshes
can sit inside another object. Like a Cup, a curved Ramp, or the inside of an open
box.
For the purpose of this tutorial, all we need to change is the mass of our dominoes. I have given them a mass of 5.0 to
start. It really doesn't matter how heavy they are as long as they have some sort of mass. If our objects were all different
and our animation was comprised of different weighted, and sized objects then changing this number will give you
different reactions. Heavier objects will plow through lighter weighted objects, etc.
Once you have given the dominoes a mass, Go back up in your settings and find the" Preview & Animation" rollout.
Click on the "Preview Animation" button to test your simulation.
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A new window will open up for you.
You can press P on the keyboard to play your simulation.
If you are finding that your dominoes just fall straight down and out of view, or they are all jumping up and then falling
over instead of being knocked down one by one, then we have to go back in and move some things around.
Remember when I told you about the shell? The shell is what is actually interacting with things, not the models
themselves.
It isn't perfect, but because this invisible shield exists we have to make sure that the bottom of our dominoes, and the
Reactor Plane we created aren't touching.
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Move the bottom of your dominoes and the rectangular area of the reactor plane apart and then preview your
animation again. Too close and the dominoes will pop up and fall all over instead of the way we want them too, and too
far and the dominoes will fall the distance and probably fall over as well. If the plane is too high your dominoes can fall
straight down and never return.
Adjust the space between as illustrated above and keep previewing until you can find the correct result.
With just enough room to breathe, the simulation will work correctly.
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Once you get a successful preview animation, you can close out the Real Time Preview, and we are ready to create the
actual animation.
Give your animation enough time to work, I found that 150 frames did quite
well.
Then click "Create Animation"
It will take a moment to calculate and then your viewport should show your animation.
Select your dominoes and take a look at the timeline to see what was done. You should have a full timeline of lots and
lots of keyframes. Reactor automatically created them as it simulated your physics animation.
Click here to see the full animation sample: http://animation.diclementi.com/tutorials/dominoes.mov
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