The Complete Guide to Blender Graphics
Building Destructible Walls

This demonstration is about building barriers or more precisely obstacles which can be demolished such as a stack of boxes or brick walls. For this to be possible the components (boxes or bricks) have to be separate objects.


Creating a Stack


We will build a stack of boxes (cubes) for our obstacle.


Start with the default “Cube' object in the default 3d window. Deselect the cube. In Top Orthographic view add a “Plane” object, scale it up and position it just below the cube.


We will be applying physics to the objects in the scene so they will behave as if in the real world. The “Plane” object will act as the ground on which the stack will sit.


Deselect the plane and select the cube. Make sure it sits just slightly above the plane. We will be applying “Rigid Body” physics to the cubes. The cubes will be stacked on top of each other and if there is a huge gap between lower course of cubes and the ground plane, the stack is likely to collapse before we begin.


You could duplicate the cubes many times and position each duplicate end for end and one on top of the other as if building a real stack. Stacking is a tedious, therefore, we will use “Array Modifiers” to speed up the process.


With the “Cube” selected add an “Array Modifier”. Increase the “Count” value in the array panel to duplicate the cube and create the first course in the wall. By default the “Array Modifier” is set with a “Relative Offset” X axis value of 1.000. Increase the value to 1.030 which produces a gap between each new cube.



Add a second “Array Modifier” maintaining “Relative Offset” but change the X axis value to Z axis and use the same 1.030 value. The complete first course of cubes is replicated on top of the first course. Increase the “Count” value to add courses.



Add a third “Array Modifier” setting the same offset on the Y axis. Increase the “Count” value to produce the stack.




Second Array
Third Array

Separate the Objects


We want all the cubes in the stack to be individual objects.


Select the entire stack. Tab into “Edit” mode. Press the P key and click on “Separate by Lose Parts” in the menu that displays. Every cube will be a separate object but the centre of mass for each cube is located at the centre of the original cube. If physics were applied at this stage the stack would collapse since each cube would rotate due to gravity about it's centre.

To rectify the misplaced centres Tab to Object mode (the whole stack remains selected). In the “Tools Panel”, click on “Set Origin” and select “Origin to Geometry” from the menu. You will see each cube has it's own centre.



Apply Physics


Select a single cube (any cube). Apply “Rigid Body” physics.


Physics is applied to the one selected cube. Box select the stack. In the “Tools Panel”, “Physics” tab, click “Copy from Active to apply physics to all the cubes.


Playing the animation in the “Timeline” window should see the stack settle on the plane and come to rest. It settles since we left gaps between the cubes in the construction process.


If the gaps are too wide or the space between the bottom layer of cubes and the ground plane too great the stack will tumble to pieces.


Providing the stack settles nice ley we can proceed to purposely demolish it.


Create a Wrecking Ball


Go grab the swinging chain created in Supplement 04 (Append).


The chain will do nicely but we need to add a ball on to the swinging end.


Select the last link in the chain (swinging end) and Tab to “Edit” mode. Add a “UV Sphere” object to the scene. Adding in “Edit” mode makes it joined (part of) the selected object.


The physics applied to the link is applied to the whole object (link and sphere). For the ball to have an impact we need to increase the mass. In the “Physics” panel increase “Mass” to 500kg. Be warned if you play the animation the chain will break. Increase the mass of each chain link to 2 kg. Select one link, change the mass value, Box select the whole chain and press “Copy from Active” in the “Tool Panel”, “Physics” tab.


Note: “Copy from Active” has made the physics for each link the same. Remember, the fixed end link had “Dynamic” unchecked to fix it in space. Copying from Active has checked it again.


Select the fixed end link and uncheck “Dynamic” in the “Physics” panel.


Position the Wrecking Ball


Locate the ball and chain such that it swings down and just clears the ground plane and makes contact with the cube stack. Playing the animation will demolish or partially demolish the stack.


Note: You will more than likely have to make adjustments in the preceding set up to achieve the results you want. Consider any rework as part of the learning process. “If at first you don't succeed try and try again”.


Wrecking Ball

Create a Brick Wall


To create a wall begin with the default “Cube” object in the 3D window with a “Plane” positioned for a ground plane.


Scale the cube on the X axis into the shape of a brick and position it above a ground plane.


Add an “Array Modifier” to the brick with an X axis “Relative Offset” value 1.030. Increase the “Count” value to produce the first course of the wall.


Add a second “Array Modifier” with a Z axis “Relative Offset” value 1.030. This places a second course of bricks on top of the first. Reduce the default X axis offset value 1.000 such that it brings the second course back on top of the first course until the gaps between the bricks are positioned mid way over a lower course brick.









Add a third “Array Modifier” with a Z axis offset value 1.000. Increase the “Count” value to build the wall.


Do not be concerned with the alternate bricks in the courses protruding. This can be adjusted later or concealed with another object or simply excluded from “Camera View”.

















Apply the modifiers in the order created and follow the previous procedure for separating the objects and aligning their centres.


Apply “Rigid Body” physics to the bricks and the ground plane per the previous example and you are good to go with the wrecking ball and chain.


Create a Circular Brick Wall (Tower)


Circular brick walls are slightly more complicated but simple when you know how.


Again, start with the default cube in the 3D window. Deselect the cube and add a “Plane” object positioned just below the cube. Scale the “Plane” to form a ground plane on which to build the wall. You may extrude the “Plane” on the Z axis to make it visible when unselected in the 3D window in “Font Orthographic” or “Side Orthographic” view.


Place the 3D window in “Top Orthographic” view. Tab into “Edit Mode”. Using the manipulator widget, drag the cube's vertices along the Y axis. The exact distance is immaterial. Tab back to “Object” mode and deselect the cube.



In performing the above you have relocated the cube's vertices away from it's centre. The centre remains at the centre of the scene. The 3D window cursor is also at the centre of the scene. Leave this in position, aligned with the centre of the cube.


Note: Do NOT change the shape of the cube in “Object” mode after it has been translated away from the centre.


Add an “Empty” object to the scene. Use a “Plain Axis” type. The “Empty” object will be located at the location of the 3D window cursor which is the centre for the “Cube” object. Deselect the “Empty” and select the “Cube”.


Add an “Array Modifier” to the “Cube”. Uncheck “Relative Offset” and check “Object Offset”. Enter “Empty” as the offset object.

Note: Using an “Object Offset Modifier” usually produces an array of the original object offset, from the original by the distance between the original and the object itself. In this case both the original (Cube) and the offset object (Empty) are located in the exact same position (Centre of the Scene). We will be using the rotation of the “Empty” object in this scenario.


Deselect the “Cube”. Select the “Empty”. Position the mouse cursor a fair way away from the “Empty” and press the R key to rotate the “Empty”. Slowly rotate until the duplicate of the cube is positioned as shown in the diagram (intersecting edges in the centres).



Deselect the “Empty” and select the “Cube”.


Increase the “Count” value in the modifier panel to approximately form a circle of cubes.


You may fine tune the arrangement by selecting  the “Empty” and rotating  carefully.


To accurately form a circle of cubes evenly spaced, divide 360° by the count number (the number of cubes). This gives the precise Z axis rotation of the “Empty” object. For example: for 18 cubes, 360° divided by 18 = 20°. To enter this value, select the “Empty” object and go to the “Properties” window. “Object” buttons, “Transform” tab. Enter 20° in the Z axis “Rotation” panel.


Select the original cube and tab to “Edit” mode. Select the edges of the cube in turn as shown in the diagram and rotate aligning with the centre.



Note: When selecting edges make sure “Limit Selection to Visible” is OFF.



Select the outer and inner edges and scale to fit. Ensure there is a gap between the segments.


Note: When scaling the outer and inner edges be sure to confine the scale to the X axis.


Note: Without a gap the bricks (Cubes) will fly apart when physics is applied.



To create a second course of bricks Tab to “Object” mode and have the complete array selected in “Front Orthographic” view. Add a second “Array Modifier” this time with a “Relative Offset” Z axis value 1.030 (.030 produces a gap).


Note: The vertical gaps between the bricks in the second course line up with the first course.


To stagger the gaps we will have to rotate the second course and to do so we have to separate the bricks into individual objects.


Before separating apply the “Array Modifiers” in the order created. “Array Modifier” 1 then “Array Modifier” 2 (Click on “Apply” in the modifiier panel).


With both arrays in the 3D window selected Tab to “Edit” mode and press the P key. Select “Separate by Loose Parts” from the menu that displays. Each brick will be a separate object BUT the centre of each brick is located at the centre of the original brick (Cube). To correct this Tab to “Object” mode and in the “Tools Panel” click on “Select to Origin” then select “Origin to Geometry” (Alternatively click “Object” in the 3D window header, select “Transform” then “Origin to Geometry”). Each brick will have it's own centre located at its centre of mass.


In “Front Orthographic” view select the upper course of bricks and rotate about the Z axis to stagger the bricks.


To Build a Tower


Select all the bricks in both layers and press “Join” in the “Tools” panel. Before selecting delete the “Empty” object. If you inadvertently select the “Empty” with the bricks you will find the “Join” button inactive or missing.


Note: Before selecting, delete the “Empty” object. If you box select the bricks you will also select the “Empty” and you will find the “Join” function missing in the “Tools” panel.


Add a new “Array Modifier” with “Relative Offset” value 1.030 on the Z axis. Increase the “Count” value to build the tower.


With a completed tower we will have to again separate.


Apply the modifier. Tab to “Edit” mode. Press the P key. Select “Separate by Loose Parts”. Tab to “Object” mode and in the “Tools” panel press “Transform” and select “Origin to Geometry”.


The tower is complete and every brick is a separate object.


You may duplicate alternate bricks in the top layer and castellate the top of the tower.


Warning: Sometimes the unexpected happens. I appear to have a few windows in my tower.



Apply Physics


Our objective has been to create a destructible wall therefore apply physics as previously described.


You are ready to destroy your creation. Use the wrecking ball or animate a “Sphere” object in the scene to fire into the tower. You may even create a cannon to blast the wall to smithereens.


With a completed tower we will have to again separate.


Apply the modifier. Tab to “Edit” mode. Press the P key. Select “Separate by Loose Parts”. Tab to “Object” mode and in the “Tools” panel press “Transform” and select “Origin to Geometry”.


The tower is complete and every brick is a separate object.


You may duplicate alternate bricks in the top layer and castellate the top of the tower.


Warning: Sometimes the unexpected happens. I appear to have a few windows in my tower.


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At this point you have created an array of an array of an array. To proceed further you have to apply the arrays. To do this simply click the “Apply” button in each “Array Panel” but be sure to apply in the order in which the arrays were created (First to Last).