# The Maya Journal: Modeling Thrusters, Hoses and Shoulder Guards

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In the last installment of the Maya Journal, we modeled the basic shape of the mech's torso. We used nurbs surfaces to build a windshield and polygon primitives to build the torso's basic shape. In this article we will continue modeling the torso by adding some rocket thursters on the mech's back (he's got to be able to fly!), some hoses that fuel the thrusters, and finally a shoulder guard. During our modeling process, we will learn the difference between world and local spaces and how to use the extrude and bridge functions to help fill in gaps in our models. These functions can help you save valuable time and effort.

#### World and Local Axes

At this point in our mech project, you should be familiar with the world space within Maya and the x,y,y coordinates that correspond to width, height and depth. World space within Maya is the virtual space that mimics a real world three-dimensional coordinate system. However, there's another type of space that's important when modeling objects. It's called local space and it bases its directional coordinates on selected objects. It's an important distinction 2D artists need to understand to successfully translate objects in a virtual world. A finished model is usually made from multiple objects. For example an object like a bicycle would be made out of at least two wheels, a frame, and handle bars. All of these separate objects would then make up the larger object, the bicycle. Easy enough, but we must understand that these smaller objects also have their own local space. If we were going to animate this hypothetical bicycle, we would need the wheels to rotate on a central point along the X axis (horizontal) just like a real wheel rotates on a horizontal axle. The bike's frame would then move smoothly along one direction as the wheels rotated forward. Here, the wheels' rotation exists in local space while the entire bike moves in one direction within world space (along world coordinates). Therefore, both the wheel and the bike need different spaces as references for their movement. The handle bars would also have its own local space because it would need to rotate left and right along the Y axis. As you've probably guessed both the handle bars and the wheels would also need to rotate identically along this Y axis. When you rotate the handle bars left, the wheel turns left, and so on. You must keep this in mind when working with such an object, whether it's moving, rotating or scaling it. I'll provide a more relevant example using a 3D sphere in Maya. In the image below, I've created a basic polygon primitive sphere and selected 6 of its faces to extrude (i.e. extend). I will do this within both the world and local space to illustrate the difference results. First I will extrude along the local axis. Notice how the faces (which are already at an angle) have extended at an angle upwards and out. This is because extruding them in local space means Maya is using the actual object (i.e. the sphere) as a reference point for what direction and size to take these 6 faces. It's calculating based on where the faces are placed on the object itself. Now I will extrude the same 6 faces, but this time use the world space coordinates. Now the extrusion moves straight out from the sphere. That's because it's following the world x,y,z coordinate system. That is, the same system as the grid itself follows. This is why it's so important to know in which space you're moving. Your changes can have very different results. In this installment of the Maya Journal, I will be switching between local and world coordinates at times as I use the extrude function, so the implications of this should become a little clearer. But first, let's talk a little more about extruding.

#### Extruding

When we extrude components like vertices, edges and faces (usually faces), we're basically telling 3D programs to build surfaces based upon the size and shape of what we've selected. For example, if I select a face and extrude it along the X, Y or Z axis, Maya will move that face long the axis while also building surfaces that connect it to its previous position. To extrude a component select it and go to edit mesh>extrude command under the appropriate component (i.e. face, edge, vertex). You can switch between world and local spaces in the viewport. Maya provides an on screen switch near your manipulator that lets you cycle through both. Not only can you extrude objects outward or inward as in the sphere example, but you can scale them through extrusion. Basically, this brings a face inward or outward, making it smaller or larger accordingly. We will be using scale extrusion when building the mech's rocket thrusters.

#### Modeling the Thrusters

Let's start getting our extrusion on! Now that we've got the basic torso shape for the front of the mech modeled, it's time to build some rocket thrusters for the back. We'll do this by extruding faces. First, we'll select two columns of faces on the top of the Mech's torso. Start at the front and work your way to about the middle of the back. Second, engage the extrude faces function (edit mesh>extrude faces). You should see that your manipulator has changed in appearance. Third, change the local space to a world space by clicking on the switch. Your manipulator should have changed position, reflecting the orientation of the world coordinates. Next, grab the y-axis arrow (not the cube) and drag upward. You should see the entire selection move straight upward along the y world axis. It's helpful to switch to the side orthographic view so that you can translate this extrusion to fit the source image. Now that we've extruded and formed this ridge line on the mech's shoulder, we can build the thrusters through a similar extrusion process. For this you will want to select a collection of faces on the back mesh that you can extrude to form the actual rocket thrusters. Forming the thrusters also requires scaling extrusions inward. But the process is basically the same. Something very handy in extrusion and manipulating objects in general is the G key, which is a hot key that selects the last tool or function you've used. For example, after extruding the thruster faces outwards, you can hit the G key and quickly begin to extrude/scale them from the last point you stopped. This is a work flow that's helpful in modeling the thrusters. We can now select the extruded faces that will form the thrusters. However, we only want to select the two side squares and not the connecting part in between them as in the image below. Using the extrude faces command, you can select the cube on the manipulator and scale the faces inward to create the thickness of the box. Hit G key again to repeat and make the walls a little more thick. Then repeat, but this time you want to move the faces inward to create the opening in the box. Remember that when you're making corners, as we are here, the more edges you have closer to each other, the sharper your corner will be. A corner made of only one edge will be very rounded, but a corner with three will be much sharper. You want the thrusters' corner to be pretty sharp to appear "boxy". To add more edges around your corners, you can use the "Insert Edge Loop" tool under the edit mesh menu. This let's you add lines that loop all the way around you model. This saves a lot of time. Below you can see how I'm inserting an edge loop around the outside of a thruster. After pushing the thruster faces in flush with the back, you can duplicate them and extrude those faces outward past the original box edge. What your going to be forming is another box inside your original one. You may need to do some minor adjustments like rotating the faces to get them to look just right. But don't be too critical at this point in the results. Finally, you can model those faces in the exact way you did the original box, scaling inward, forming tight edges and finally pushing faces back inward. The result should look something like the image below. Note that only the right thruster has the interior box. This is what my thrusters looked like after finishing and switching from a low quality display (number 1 key) to a high quality one (number 3 key). I've added some other details in the final image, yours may not look exactly the same. That's okay. As long as you've got the basic shape here, the model will look fine. We now need to create some thickness around the mech's shoulders. Select the section of faces at the edge of the shoulders and extrude them along the z-axis. Make sure that you include in your selection the bottom of the upper torso as in the image below. After extruding, the shoulders should have a much tighter, more beveled look to them. Here's the finished torso with the thrusters and shoulder thickness added. Next, is the addition of some hoses that run from the upper front of the mech torso and connect to the thrusters. They're essentially like fuel lines that run along the top of the shoulders on both sides. There will be a set of two for each side. To model them, we will be using nurbs curves and surfaces.