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Reactor is an excellent tool for getting realistic object movement with very little effort. However, many wish to combine the ease of reactor with keyframed animation. 3dKingdom already has a great tutorial on how to do this with a brick wall and a ball. Please, refer to it as it has several helpful items. Through this tutorial I will show you a few tricks on how to combine reactor rope and keyframed animation. The end result will be a simple wrecking ball that can be used to demolish other reactor objects.

This will be a step-by-step tutorial, so please reset your copy of 3ds Max or higher. Then make sure you have loaded the reactor toolbar (go to “Customize” / “Customize User Interface / Select the toolbars option and load a reactor toolbar). Activate angle snaps.

Step 1: Create the scene

The Arm

In the top view create a 10 x 10 x 100 box with 1 width segment, 1 length segment, and 4 height segments. Since this will be the arm of our crane name this box “Arm”

By right clicking the move command in the main toolbar, move the arm to (0,0,0).

Go to the left view and select rotate from the main tool bar. Selecting the outermost ring, rotate the arm -35 degrees.

Now in the modify panel, apply an edit mesh modifier and enter vertex mode. Select the top eight (four you can’t see in this view) vertices of the arm. Rotate these the same way as the arm until they are parallel to the ground.

After rotating the top vertices you may wish to move the away from the rest of the arm so that the arm isn’t so bent.

Also, you may wish to move the left most vertices toward the arm.

Much more detail can be given to the arm but we’re focusing on reactor, so let’s move on.

This part is quite simple. Return to the top view and create a cone (standard primitive) with radius 1 at 30, radius 2 at 20, and height at 10. The number of segments aren’t important for this simulation, but more detail can be added if you like. Name this figure “Base.”

Right clicking the move command in the main tool bar, move the newly created base to (0,0,0).

This is equally simple. In the left view port, create a sphere with radius 8 near the crane arm. Lets name this “Ball”.

Right clicking the move command in the main tool bar, move the sphere to (0, 80, 30).

The Rope

In the left view, create a line (Create, spline) from the center of the crane head, to the center of the ball. Just keep the line type to corner and use only one click. Again using the move command move the line to (0, 70, 50). Name this rope.

You scene should look like this.

Putting it all Together

Pay close attention here!!! The main key to reactor is that any movement you intend to show must be done BEFORE any reactor simulations are run. Since we intend to swing this crane, we need to go ahead and keyframe that now.

First select the Ball. Link this to the rope. Link the rope to the arm, and link the arm to the base.

Slide the frame slider to frame 100 and press auto key. Now chose rotate from the main tool bar and select the base object in the top view. Rotate the base 180 degrees. Turn off auto key. You may want to go ahead and play the animation just to make sure that all the parts are connected and moving properly.

That’s it with the basic setup. Now we shall move on to the more interesting parts of reactor

Step 2: Setting up the rope

For this part, it will probably be best to work in a maximized left view port.

Select the rope object and open the modify panel.

Choose the Normalize Spline modifier. This modifier breaks our line up into segments of equal length. In the panel set the segment length to 2. This should allow sufficient vertices for the rope to simulate properly.

Choose the Spline Select modifier. The default setting for this is in vertex mode so use a box to select all of the vertices of the rope. This allows us to apply the next modifier in the stack to only the selected vertices.

Choose the Reactor Roper modifier. Since all of the vertices have been selected, this will turn the entire line into rope. In the panel be sure to set the rope type to constraint. Otherwise, your rope will stretch too much and do other odd things.

Chose the Spline Select modifier again. This time select only those vertices that are inside the arm. There should only be 3 or 4 vertices inside.

Chose the Reactor Attach to RB modifier. This will attach only the selected vertices to a Rigid Body that we will chose. In the properties rollout click the box under “Rigid Body” that says “None.” Now select the arm. While in the properties rollout, uncheck the boxes “Ignore Collisions” & “Do not affect RB.”

Chose the Spline Select modifier again. Now select the vertices inside the ball.

Chose the Reactor Attach to RB modifier again. This time you will not need to uncheck the boxes, but you will still need to click the none button and set the ball as the rigid body.

Your modifier stack for the rope should look like the following.

To finish off this section, select line at the bottom of the modifier stack. Open the rendering rollout. Check “Renderable” and “Display render mesh.” You may increase you line thickness here if you like.

Step 3: Getting Reactor Ready

Before starting this next step it would be a good idea to save you scene. Here all the basics are set up and if mistakes are made later, reloading from here will save much time. Also, make sure that you have loaded the reactor toolbar from the customize menu.

From the reactor toolbar, add a Rigid Body Collection to the scene. This can be placed anywhere since it will not be rendered. In the RB Collection Properties rollout click add and select the arm, base, and ball. This has only added those object to the reactor simulation. It has not yet assigned them any properties. We’ll handle that later.

From the reactor toolbar, add a Rope Collection to the scene. Again, this will not render. As before, under the properties rollout, click the add button and select the rope object.

Now click on the Utilities tab (it’s the picture of a hammer). You should see a list of utilities with reactor in it. Click reactor and open the properties rollout.

With the properties rollout open select the ball. At the top of the rollout you’ll see a box that says “Mass.” Set this to something around 50. Below that you’ll see a heading that says “Convex.” Move the dot so that “Bounding Sphere” is selected. That’s it for the ball.

Now select the rope object. Notice that the properties have changed. Why this isn’t part of the reactor rope modifier, I have no clue. But this is where the properties of the rope are set. The only change that need to be made is we need to give the rope mass. Set the mass to about 100. The lower the number, the more the rope tends to stretch, so keep the number high.

Now, here is the key to the whole effect. Select the arm object. We do not need to change the mass of this object as it would cause gravity to make the object fall. However, go ahead and set convex setting to “Use Bounding Box.” Here’s the important part. Look down slightly in the properties box and Check Unyielding. Without checking this box, the rope would just hang where it was in space while the arm rotates. Now the rope will follow the arm as we want.

Step 4: Animating

Now for the easy part. Switch to the “Perspective” view to get a better look at things. Also, you may want to select the Rigid Body & Rope Collect and hide them using the quad menu. In the reactor panel, open the “Animation & Export” rollout. Click “Perform Simulation.” After a few seconds the wrecking ball should be ready. Press Play!

For added fun, refer to the tutorial on smashing a wall of bricks. Combing the two to actually demolish a wall with a wrecking ball is kind of fun!