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This chapter is from the book

3D Modeling Tutorials

Topics covered:

Using Extrude
Using Lathe (Closed, Open, and Partial)
Using Sweep (Closed, Open)
Using Skinning
Using Transforms (Move, Scale, Rotate, Taper, Twist, Align)
Using Duplication and Instancing (Mirror, Array)

About the Tutorials

In the following tutorials, you will begin to construct portions of the blimp model. At this point, you should either have tried out the following techniques, or be working with your software manuals to see how your package accomplishes each one of these operations.

If you run into difficulties, review the section of the book that deals with the problem operation, paying particular attention to tips that may help you figure out the problem. The life of a modeler/animator is filled with challenges both artistic and technical, so consider this as part of your training and try to find a creative way around the problem.

NOTE

The tutorial steps presented here are generic and can be adapted to work with nearly any program. However, if you are using one of the more popular 3D packages on the market, including discreet 3ds max 4.2, Alias|Wavefront Maya 4, or NewTek LightWave 7, there are program-specific tutorials and mesh files of the project at various stages on the companion CD-ROM in the back of this book. If you are using one of these packages, I strongly recommend you use the version of the tutorials on the disc rather than the ones in the book.

At the start of the chapter, the basic strategies of planning out a 3D project were presented. For the blimp, the logical overall strategy would be to construct the gas bag first, then add the large video screens. Next would come the other major sub-assemblies, such as the engines and spires. The logos and other details would come last. Unfortunately, the construction of the gas bag is an advanced chapter project, so you'll be doing the monitor screens and engines first. The individual object strategies will become apparent when you do the tutorials.

NOTE

There will probably be several occasions during the course of these tutorials where objects don't materialize in the 3D universe quite where you expect them. Read up on construction grids and planes in your manual to help you build objects where you want them. To help locate and move wayward pieces, use the Zoom All command, which adjusts the viewpoint to show all the mesh in the 3D universe. Most of the time, you'll find "missing" mesh off in the virtual boondocks somewhere. You'll probably use Zoom continually to make the objects large enough to work with.

Using Extrude

NOTE

All units used to specify distances in the tutorials are generic—they don't represent any real-world measurements. Set your software to use generic units and decimal numbers if possible.

Start the tutorials by using a simple extrusion to create the monitor screen for the side of the blimp. Here's the procedure:

  1. Turn on Grids and Snaps. In the right viewport, use lines and arcs to create the 2D monitor shape 575 units wide x 460 units high (see Figure 3.40a).

    If your software requires it, Attach the shapes together and/or Weld their vertices to create a single closed shape. Name it MonSHP01.

  2. If your software doesn't leave the original shape intact when doing an Extrude, copy the shape and move the copy out of the way. You'll need it later on for another operation.

  3. Select the first shape and Extrude it 15 units deep into a thin 3D panel, with one step or segment (see Figure 3.40b). Name the object MonScn01.

  4. Save your file as B_MON01 and close it.

Figure 3.40FIGURE 3.40 Creating an extruded object: (a) Draw the outline of the shape in 2D. (b) Use Extrude to give the shape the desired depth.

Using Lathe (Closed, Open, and Partial)

To try out the different lathe operations, switch over to working on the engines of the blimp, which are called thrusters (see Figure 3.41). The thrusters are enclosed propellers that move the blimp around.

Figure 3.41FIGURE 3.41 The completed thruster assembly. The cylindrical strut the thruster is attached to will rotate to allow the thrusters to operate at different angles.

Creating a Closed Lathe

Here are the steps for creating the nose cone in the center of the prop. Note that this shape could also be created by scaling a 3D hemisphere primitive, but this is a lathe tutorial, so you're going to use a lathe operation instead.

  1. Create a new document. In the front viewport, draw three circles (with radii of 10, 45, and 56 units) to use as a reference in setting the scale of the thruster shroud and nose cone (see Figure 3.42a).

    These lines will not be used to create the 3D objects, but are useful for "roughing out" a shape before modeling. If your software doesn't support the creation of 2D shapes in the 3D environment like this, ignore these references.

  2. In the right viewport, offset the circles from each other by 10 units so that you can see them from this view, then Freeze or Ghost them so that they stay put (see Figure 3.42b).

  3. In the right viewport, create an arc that is the same radius as the small reference circle you drew in the last step, 10 units (thickened here for clarity). Add a polyline that connects to the endpoints of the arc.

    If your software requires it, Attach the shapes together and/or Weld their vertices to create a single shape (see Figure 3.42c).

  4. Scale the shape 150% along the X-axis (horizontally) to give it a more graceful appearance (see Figure 3.42d).

  5. Save your work as B_THR02.

    In most programs, choosing the Lathe command enables you to define the axis that you want to serve as the centerline of the lathing operation. In some products, however, you may need to define the object's axis in advance.

Figure 3.42FIGURE 3.42 Steps for creating the nose cone shape: (a) Rough out the thruster with circles to establish scale. (b) Offset the circles to see them from the side. (c) Draw a 10 unit arc to serve as a lathe cross-section. (d) Scale the cross-section 150% along the horizontal axis.

  1. Choose Lathe and set the axis along the lower edge of the shape (see Figure 3.43a). This will determine the centerline around which the shape will be spun.

    This is a closed lathe because the axis touches the shape, creating a "solid" result.

  2. Complete the Lathe operation, spinning the shape 360° into a 3D object with 16 segments (see Figure 3.43b).

  3. Examine the results in a Camera or Perspective viewport (see Figure 3.43c). Does the object appear to have the right shape and proportions? If you were experimenting, this would be the point to Undo the operation and adjust the shape before lathing it again.

  4. Render a close-up of the nose cone (see Figure 3.43d).

    Some programs have trouble with lathes like this, and may create odd artifacts near the centerline. Your software may offer a Weld Core command to correct this—if not, doing a Smooth operation (discussed in Chapter 5) should take care of any problems.

  5. Name the object ThrNos01 and save your work as B_THR.

Figure 3.43FIGURE 3.43 Steps for lathing the nose cone object: (a) Set the axis for the lathe. (b) Spin the shape 360 degrees around the axis. (c–d) Examine the resulting object for proper appearance. You may have to apply a smoothing operation to correct artifacts.

Creating an Open Lathe

To create the propeller shroud, use another lathe operation, this time with the axis some distance from the shape. Here are the steps:

  1. Using the reference circles as a guide, create a closed spline cross-section of the shroud 102.5 units long (see Figure 3.44). Use five control points to define the spline.

    You may find it easier to create the rough shape with straight lines first, and then use the Bezier control points to adjust the curves.

Figure 3.44FIGURE 3.44 Use a Bezier spline to create a cross-section of the thruster's engine shroud. Use polylines if your software doesn't support splines.

  1. Choose Lathe (set to 16 steps or segments) and set the axis along the centerline of the nose cone. This will spin the shroud around the same axis as the cone. Complete the Lathe operation, spinning the shape 360° into a 3D object (see Figure 3.45a).

  2. Render the results in a Camera or Perspective viewport (see Figure 3.45b). Name the object ThrShr01.

  3. Save your work as B_THR04.

Figure 3.45FIGURE 3.45 Steps for lathing the engine shroud object. (a) Set the axis for the lathe in the center of the thruster and spin the shape 360 degrees around it. (b) Examine the resulting object for proper appearance.

Creating a Partial Lathe

Next, create the reinforcing bands that partially surround the shroud. Follow this procedure:

  1. In the right viewport, draw a polyline cross-section of the band 11 units wide x 3.25 units high (see Figure 3.46a).

  2. Position the cross-section as shown and set the axis to the same place as the previous lathes—the center of the thruster (see Figure 3.46b).

  3. Lathe the object around the axis, but limit it to 300° rather than the full 360° (see Figure 3.46c).

  4. The result is a partial lathe with a 60° gap starting at the top of the engine. If your software puts the gap on the opposite side, rotate the band around so that it matches the figure. Name the object ThrBnd01 (see Figure 3.46d).

  5. Save your work as B_THR05 and close the file.

Figure 3.46FIGURE 3.46 Doing a partial lathe of the support band: (a) Create a polyline cross-section. (b) Position the cross-section and set the axis. (c) Spin the shape 300° around the axis. (d) Make sure the gap is in the position shown.

Using Sweep (Closed, Open)

This is an opportunity to get experience with two kinds of sweeps: open and closed.

Closed Sweep

To try out a closed sweep, go back to the blimp monitor project and add a frame around it. Here are the steps:

  1. Open the file B_MON01.

  2. Draw a polyline cross-section of the monitor frame 26 units wide x 32 units high (see Figure 3.47a).

  3. If necessary, position the cross-section along the spline MonSHP01 (or its duplicate) that you made earlier.

    Note that some programs may be sensitive to where the object is positioned for an operation like this, whereas others allow you to position it independently when doing the sweep (see Figure 3.47b).

  4. Perform the Sweep operation, using the spline MonSHP01 as the path. Set shape segments to 0 and path segments to 1. The resulting sweep object should be centered around the screen. Name it MonFrm01 (see Figure 3.47c).

  5. Render the monitor from a perspective view and check for proper appearance (see Figure 3.47d).

  6. Save your file as B_MON02.

Figure 3.47FIGURE 3.47 Create a closed sweep for the monitor frame: (a) Draw a polyline cross-section. (b) Position the cross-section up against the screen edge if your program requires that. (c) Sweep the object using the monitor shape as the path. (d) Check your results.

Open Sweep

Next, an open sweep is used to create a cable coming off the edge of the screen and connecting to a control box. Here are the steps:

  1. Create a box 200 units wide x 70 units high x 40 units deep and position it on the far side of the object MonPnl01.

    This will be an electrical box for the monitor. Name it MonBox01 (see Figure 3.48a).

  2. To make a cable running from the electrical box to the monitor frame, draw a spline coming out the end of the box, dropping down, then curving back up toward the MonFrm01 object. Create a circular cross-section nearby, with a radius of 5 units (see Figure 3.48b). Make sure the shapes are centered on the box depth-wise by checking the Front viewport.

  3. Create a swept object with the circle, using the spline as a path. Name it MonCab01 (see Figure 3.48c).

  4. Render a perspective view of the box and cable.

    Note that the end of the cable is hanging out in space right now. It will get fixed later on (see Figure 3.48d).

  5. Save your file as B_MON03.

Figure 3.48FIGURE 3.48 Creating an electrical box and cable: (a) Create and position the box. (b) Create an open spline path and circular cross-section. (c) Sweep the circle along the path. (d) Check your work.

At this point, things may start to get a little busy on your screen. Use the Hide command to get unneeded mesh out of the way. Also, remember to use Freeze or Ghost if you need the mesh, but are having trouble selecting the right objects when other mesh is in the way.

Using Skinning

This is a tricky spot, so make sure you understand how your program deals with skinning before you do the tutorial. When you're ready, use skinning to create the bracket where the thruster attaches to the strut:

  1. Open the file B_THR05.

  2. In the Right view, create a closed polyline (50 units square) and two circles (radii 20 and 16 units) that will form the shape of the mounting bracket (see Figure 3.49a).

  3. If your program requires that you use the same number of vertices for each cross-section, add four more vertices to each of the circles. Align the First Vertices of each of the shapes as closely as possible, using Rotate (see Figure 3.49b).

Figure 3.49FIGURE 3.49 Create a skin object by drawing cross-sections: (a) Make sure that the first vertices are aligned now or during the skinning process. (b) If your program requires an equal number of vertices in each cross-section, add additional ones to the circles.

  1. In the Front view, create a straight path 15 units long to define the depth of the skinned object. Position it in the center of the other shapes (see Figure 3.50a).

  2. Using the method outlined by your program, assign the cross-sections to the path. The outermost shape should be used twice, once at the back (the point where the cross-sections reside) of the object and again at the 50% point on the path. The larger circle is used at the 75% and 90% points, and the smaller circle at 100% (see Figure 3.50b).

  3. If the first vertices were properly aligned, the polygons in the object should not appear to be overly twisted (see Figure 3.50c).

  4. Render the object to check for proper appearance. The shape and/or path step settings may have to be adjusted for a smooth result. Name the object ThrMnt01 (see Figure 3.50d).

  5. Save the file as B_THR06.

Figure 3.50FIGURE 3.50 Creating the mounting bracket: (a) Draw a straight path defining the depth of the skinned object. (b) Skin the object by assigning the cross-sections to the appropriate points along the path. (c) Check for overly twisted cross-sections. (d) Check your work.

Move

Here, use Move to reposition the mounting bracket you made in the last tutorial into position on the side of the thruster:

  1. In the Front viewport, select the mounting bracket and Move it to a point midway between the ends of the partially lathed band (see Figure 3.51a).

  2. In the Right view, Move the mounting bracket horizontally until it is positioned as shown (see Figure 3.51b).

  3. Save the file as B_THR07.

Figure 3.51FIGURE 3.51 Moving the mounting bracket: (a) Move the bracket midway between the ends of the partially lathed band created earlier. (b) Adjust the horizontal position of the bracket as shown.

Rotate

Now, use Rotate to orient the mounting bracket:

  1. In the Front viewport, Rotate the object 120 degrees counter-clockwise around its center until both ends intersect the engine shroud evenly, (see Figure 3.52).

    In the figure, the rotation is made on the Z-axis, but this may be different in your software.

  2. Save the file as B_THR08.

Figure 3.52FIGURE 3.52 Rotate the bracket (around the Z-axis in this example) until both ends intersect the engine shroud equally.

Bend

Returning to the monitor project for a moment, you can take care of that loose cable with a Bend.

  1. Open the file B_MON03.

  2. From the Top view, select the cable object MonCab01 and examine the axis indicator, which is probably centered in the object (see Figure 3.53a).

  3. Use Axis Move or the appropriate command for your software to relocate the axis to the point where the cable meets the box. Because the bend occurs around the axis, it needs to be relocated or both ends of the cable would be affected (see Figure 3.53b).

  4. Apply a Bend to the object until the end of the cable is centered in the monitor frame (see Figure 3.53c–d).

  5. Save the file as B_MON04.

Figure 3.53FIGURE 3.53 Bending the monitor cable: (a) The default position of the axis is the center of the object. (b) Relocate the axis to the end of the cable. (c–d) Apply Bend until the end of the cable is centered in the frame.

Scale

Y'know, that cable looks a little too big (how very convenient). Give Scale a try by re-sizing the monitor cable:

  1. Make sure your software is set to scale along all three axes at once.

  2. Check to make sure the axis of the object MonCab01 is centered along all three axes at the point where the cable meets the box. Scale the object MonCab01 down to 75% of its original size, noting that because the axis was at the end of the cable, it is scaled in that direction rather than toward the center of the object (see Figure 3.54a).

  3. From the Front view, Move the cable horizontally until it is centered in the monitor frame again (see Figure 3.54b).

  4. Save the file as B_MON05 and close it.

Figure 3.54FIGURE 3.54 Scaling the monitor cable: (a) Scale the cable down by 25%. (b) Move it so that the cable is centered in the monitor frame.

Taper

Next, use Taper to create a connector between the mounting base and the reinforcing band:

  1. Open the file B_THR08.

  2. Working near the top of the thruster, draw a polyline slightly larger than the cross-section of the band created earlier (see Figure 3.55a).

  3. Extrude the connector outline until it bridges the gap between the mounting bracket and the band (see Figure 3.55b).

Figure 3.55FIGURE 3.55 Creating the connector: (a) Draw a polyline around the band cross-section. (b) Extrude the polyline to bridge the gap between the bracket and band.

  1. With the object's axis set at the band end of the connector, Taper the opposite end out about 30° along both available axes (see Figure 3.56a–c).

  2. Render the model to check for proper appearance (see Figure 3.56d). Name the object ThrCon01.

  3. Save the file as B_THR09.

Figure 3.56FIGURE 3.56 Tapering the connector: (a–c) Set the pivot point flush with the band end of the connector. Taper the object along both available axes. (d) Compare your result to this image.

Twist

Twist makes heavy demands on the affected faces of the object, so setting the proper mesh resolution is important here. If trouble shows up, you may also want to increase the number of polygons on the object by increasing the number of steps in the propeller object before you extrude it.

NOTE

Some odd things may show up in the tutorial figures when twist is applied. This is because of low mesh resolution, but is unavoidable in this case because the figures would be too confusing and unclear if the mesh were made denser.

To demonstrate Twist, go ahead and make some propellers for the thruster:

  1. In the front view create a cylinder (radius 7.5 units, 10 units deep) in the center of the thruster, behind the nose cone. (Check your placement in the right view.) Name the object ThrPrp01 (see Figure 3.57).

  2. Create a spline outline of a propeller blade (45 units wide x 17 units high) with a total of 4 vertices.

Figure 3.57FIGURE 3.57 Creating the propeller objects: First, make a cylindrical hub for the propeller. Then, create a spline outline of one of the propeller blades.

  1. Move the propeller blade spline out in front of the thruster so it is easier to see and work with (see Figure 3.58a).

  2. Extrude the spline 1 unit to make a thin blade (see Figure 3.58b).

  3. Twist the blade about 30° around the long axis (see Figure 3.58c).

  4. Render the blade and look for smoothing problems. Subdividing or tessellating the object before applying the twist may help (see Figure 3.58d). Save the object as ThrBdA01.

    By using letters as part of the object name, you can keep a "01" designation for all the blades in the first thruster.

  5. Save the file as B_THR10.

Figure 3.58FIGURE 3.58 Twisting the propeller blade: (a) Move the spline away from the thruster. (b) Extrude it to create a thin blade. (c) Twist it 30 degrees around the long axis. (d) Examine the result for flaws.

Mirror

NOTE

Normally, it's a good idea to apply mapping coordinates and texture to a single object before duplicating it, because it saves you time later on. Unfortunately, it would be disruptive to the tutorial to get into mapping issues at this point. You may, however, want to look over the mapping coordinate section of Chapter 6, "Texture Mapping," and do that work at this point.

For this tutorial, use Mirror to generate a reversed copy of the connector built earlier:

  1. Select the connector (object ThrCon01) and Mirror copy it along the appropriate axis so that a reversed version appears (see Figure 3.59a).

    You may need to use a Shift key or other modifier to make Mirror create a copy rather than just reverse the original.

  2. Set the connector copy to use the center of the thruster as the rotation axis. Rotate the copy counterclockwise about 55° into position on the opposite side of the mounting bracket (see Figure 3.59b).

  3. Save the file as B_THR11.

Figure 3.59FIGURE 3.59 Mirroring the connector: (a) Mirror copy the connector. (b) Rotate it into position on the opposite side of the mounting bracket.

Copy

At this point, balance things out by copying the band and connectors:

  1. Select the band and connectors (see Figure 3.60a).

  2. Use the modifier key (usually Shift) for your software to do a Move-Copy operation. Drag the copy about 20 units into the position shown (see Figure 3.60b). Name the new object ThrBdA01 (ThrusterBandAssembly01).

  3. Save the file as B_THR12.

Figure 3.60FIGURE 3.60 Copying the band and connectors: (a) Select all three objects. (b) Use a Move command with the correct modifier key (check your manual) to create a copy and position it as shown.

Align

Getting back to the propeller blades, use Align to position the first blade on the thruster model:

  1. In the Top viewport, select the blade, ThrBdA01. Choose Align, and then select the prop object ThrPrp01 (see Figure 3.61a).

  2. Choose the appropriate Align options to center the blade on the hub along the thruster's central axis (see Figure 3.61b).

  3. Save the file as B_THR13.

Figure 3.61FIGURE 3.61 Aligning the blade: (a) Choose the blade, then Align. Select the prop hub object as the destination. (b) Set the Align options to center the blade as shown.

Arrays

Next, use a radial array to make the rest of the propeller blades:

  1. From the Front viewport, select the propeller blade ThrBdA01, and make sure the pivot point is set to the center of the prop hub, ThrPrp01 (see Figure 3.62a).

  2. Choose Array and set the rotation angle to 60°, the number of duplicates to 5, and the type of duplicate to "instanced." The result should be a radial array of six blades (see Figure 3.62b–c).

NOTE

If your software doesn't allow instanced objects, work around this by transforming one blade, then using it as the basis for a new propeller array.

  1. Render the model and observe the results. You may notice oddities in the blades now that you are seeing them from different angles (see Figure 3.62d).

  2. Save the file as B_THR14.

Figure 3.62FIGURE 3.62 Using Array to create the rest of the propeller: (a) Choose the blade and check that the pivot point is aligned with the center of the hub. (b–c) Use Array to make 5 more instanced duplicates rotated 60°. (d) Check the results to see whether any new anomalies have shown up in the blades.

Adjusting Instanced Objects

In the last tutorial, you created a radial array, using instanced objects, so that any adjustments made to any one of the blades are made to them all. To demonstrate this, adjust the pitch (angle) of the blades in the thruster model:

  1. In the Top view, select one of the blades and increase the Twist setting (or apply an additional one), to increase it by another 30° (see Figure 3.63a).

  2. Render and examine the results. Looks a lot more high-tech now, doesn't it (see Figure 3.63b)?

  3. Save your work as B_THR15 and close the file.

Figure 3.63FIGURE 3.63 Adjusting the blade pitch with instanced objects: (a) Select a blade and increase the Twist to a total of 60 degrees. All the blades are twisted by the same amount, because they are instance objects. (b) Render the result.

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