The Maya Journal: Modeling the Mech's Arms

In the last edition of the Maya Journal, we modeled the overall structure of the mech's upper torso. To accomplish this, we learned about the differences in world and local space, how to extrude materials, and how to bridge between two edges. These tools and knowledge let us build a set of thrusters, hoses and shoulder guards. We'll continue with modeling the mech's arm, which contains a retractable machine gun, and a set of mechanical claws.

Modeling the Arms

Building a robotic anatomy is obviously much easier that a human one, but for beginners it can still be pretty challenging. Even though our character is a mech, we will still model it like a human body. That is, the arms and legs will have joints on which the upper and lower appendages will rotate. In fact, we will begin by modeling a shoulder joint to be placed directly underneath our shoulder guard. This shoulder joint will take the form of a sphere. Create a polygon primitive sphere and bring it roughly into position under the shoulder guard. Check the orthogonal views to make sure it's seated properly. Make sure to align the sphere's poles (north & south) along the length of the arm. What you're doing is changing their local coordinates. shoulder_sphere We need to keep our polygon count down, so change the sphere's subdivisions (i.e. axis & height) to 12. You can do this in the channel box. It's important to keep polygon counts low, and any hidden objects like this shoulder sphere are great low res candidates. subdivisions


You probably will run into the problem of your sphere being a bit too big to fit comfortably underneath the shoulder guards. Mine penetrated through the back, near the thrusters. Don't worry because there's an easy way to fix this by creating what are called deformers. Essentially, deformers are three-dimension grids you can create around an entire object. You might think of them sort of like hulls around a NURBS surface, or just a larger control surface. Deformers are kind of like cages surrounding an object with handles that let you "deform" it. To create a deformer, first select the entire torso. Then change your menu set to animation. On the main menu, choose the type "lattice" under create deformers, but first go to the lattice options. You will want to adjust the settings to the values below. Finally hit create. lattice_settings Now you should have a lattice work that surrounds the mech torso: lattice Manipulating the lattice is just like any other object. RMB on the lattice and choose lattice point. Then select the set of points closest to where your sphere is penetrating the back of the mech and move them backward. Make sure and select ALL of the points that run through to the other side of the lattice or you will only be deforming part of the torso. lattice_move After you've gotten your torso adjusted, you can delete the lattice in the outliner. Since you've moved the back away from the shoulder guard, you will probably need to deform it, moving it back as well. Just apply the same procedure.

Upper Arm

We can build the upper arm by simply extending it from the sphere. There's no need to add more geometry. We can use what we already have. First select several rows of faces at the end of the sphere. Then choose extrude, but before you move the faces, go into your move tool settings (i.e. click and hold on the move icon) and set the axis to object. This will ensure that your extrusion moves straight down the arm's axis and doesn't spread out at the ends. Finally extrude the faces only a short way down as in the image below. Delete the faces when you're done. extrude_shoulder Building the upper arm now involves creating a polygon cylinder, scaling it, and placing it in position with the last extrusion. Make sure and check your orthogonal views to make sure it's placed properly and is the correct length. upper_arm As you can clearly see above, the cylinder is much smaller and uniformly shaped when compared to the image plane. However, you can model it to fit this shape quite easily. First we'll need more polygons to work with along the cylinder's height. In the channel box, bring the number of subdivisions down along the axis to 12, but increase the subdivisions along the height to 4. Then create two new subdivisions in the cylinder's cap. cylinder_subdiv With the new subdivisions, you can select the edges and scale them out to form the shape of the upper arm. You can select the vertices on the cap (near the shoulder) and scale them out as well. uppera_arm_expand Select the interior circle on the cap to finish the upper arm. Scale it to create a thickness to the upper arm. Next, extrude those faces inward to make to make a hollow section where the elbow joint will sit. Finally delete the faces. You may want to insert some edge loops to tighten up the edges of the upper arm. When you've finished, you should have something resembling this: upper_arm_finished

Lower Arm

Before we construct the forearm, we need to build a ball joint to connect it with the upper arm. Build the ball joint out of a polygon sphere. Position the sphere within the end of the upper arm. Don't align the poles of the sphere with the entire arm as we did with the shoulder. Rather, slightly rotate the elbow joint so that its poles have the same angle as the end of the upper arm. Then decrease the axis and height subdivisions to 12. If you want, you can extrude two lines of faces orbiting the sphere's center and pull them inward to create a groove that runs around the elbow sphere. This is just for adding detail. ball_joint_elbow Now we can build the lower arm (forearm) with a cylinder. Scale it up and change the axis and height subdivisions to 12 and 4 respectively. Then shape the cylinder using the front and side orthogonal views, roughly positioning it at the ball joint. The forearm's shape is tapered, getting larger as you move toward the claws. You can select the vertices along each height subdivision to them scale up to get the correct tapered shape. lower_arm Now that we've got the forearm size scaled correctly, we want to place the arm somewhere out of the way because we've got a lot more detail to add. Sometimes it's best to position an object back at its creation origin (0,0,0) to isolate it for further manipulation. Instead of trying to manually move the forearm, you can simply zero-out its translate and rotate values. Don't zero-out the scale, as that would change it's shape! lower_arm_reset We will be working mostly on the larger end of the forearm, which will have a gun that telescopes inside and out. However, begin at the smaller end and select the faces, extrude them to create thickness, extrude them inward and finally delete the faces. This is the exact procedure we followed for the ends of the upper arm. Again, we're just making a hole for the ball joint to set in. The lower part of the forearm, however, will take a few more steps. Creating it will be very similar to how we made the thrusters. First select all of the end faces (i.e. the cap) and extrude scale them inward to create a similar thickness to the smaller end you just did. But don't deselect the faces just yet. end_cap_extrude With the faces still selected, hit the G key and extrude the faces once again, but a little thicker now than the outer lip. What you're going for here is a stair stepped shape. cap_extrude2 Finally extrude the same selected faces upward and delete. I've selected the four faces in the image below just to help show the this stair stepping look. cap_extrude 3 Now we're going to thicken the bigger end of the forearm and create a wristband by extruding the exterior ring of bottom faces outwards. After selecting the entire ring of faces, duplicated (Ctrl+D) this selection, which will make an independent object. If you've got your outliner open, you can find the duplicated ring easily. Just make sure it's the only object selected. lower_arm_duplication Extrude these faces outward uniformly until they're about the same thickness as the first inner ring we just created. Now we've formed the wristband. bottom_extrude We can now create some detail by selecting the end faces of the wristband. Again, make sure it's the only object select. Use your outliner to find it if you need to. On the bottom end of the wristband select two adjacent faces, then skip two adjacent faces, then select two, and so on. Your selection should look like this: wristband_selection Next, make sure you're in the world axis and extrude these three sets of faces straight downwards a little ways. end_extrude The basic shape of the lower arm is now complete. You will want to insert some edge loops along the bottom of the wrist band, the top of the forearm, and any where else you want to tighten up an edge. Use the 3 key to switch to a smoothed version of your forearm to check and see if your edges are as tight as you want them. This is what mine looked like smoothed after inserting some edge loops. forearm_smoothed

Creating the Telescoping Gun

The telescoping gun will fit into our lower forearm and is made up of three distinct parts. Each part will fit inside of each other. The first one we will construct from a polygon pipe. Go to main menu and create>polygon primitive>pipe. We're already at the origin, so the pipe should appear exactly where it needs to be within the lower arm. Scale the pipe's thickness and height. Make sure it's diameter is big enough to fit just inside the lower arm opening. Remember, these parts need to retract back inside the arm. Also, none of these three components of the telescoping gun need to extend up into the entire length of the lower arm. Just make them go up inside enough to hide their ends. pipe For the second component of the gun we'll create a cylinder, which again will appear at the origin. Scale its diameter width so that it sits just inside the pipe. Make its height so that it extends a good ways outside the pipe's opening. Insert one subdivision for its cap and select that inner circle of faces. Then scale them outwards, creating thickness, and move them downward to create a beveled, tapered edge. Keep your faces selected. inner_cylinder Finally, extrude the faces inward to create thickness, extrude inward and delete the faces. inner_cylinder2 The final piece of the telescoping gun is the actual barrel, which we'll create out of another cylinder. Follow the same procedure to create the barrel, but keep its diameter much smaller then the inside of the last cylinder. That's because we're going to create a larger head on the barrel, which should fit just inside the other cylinder. Add some subdivisions to the barrel's height. barrel To form the head of the barrel, just select the bottom set of faces (excluding the cap) and extrude them outward. You may also want to taper the ends to make it look like an actual barrel. Finally select the faces on the cap, extrude scale them for thickness, extrude them inward, and delete. Again, make sure the barrel head fits just inside the previous cylinder. barrel_final Now you have a telescoping gun which can be animated to extend outwards. telescoped inwards, the entire lower arm should look something like this: gun final

Modeling the Claws 

The final feature to our mech's arm is a three-pronged claw. Each claw will sit within the three lowered sections of the arm piece be built earlier. But we don't want to have to build all three parts of the claw. Instead we can model one and use Maya's duplicate feature to form two exact copies. Duplicating will be made simpler if we begin with the lowered section that aligns itself with an axis. That way our calculations for positioning the other duplicates will be much easier. So choose the lowered section that is aligned with an X or Z axis along the grid. In the image below you can see that I've chosen the section aligning itself with the Z (blue arrow) axis. claw1 Create a cube and center it in this lowered section. Scale its length, width, and height to form the shape of your first claw section. The top end only needs to extends a little ways into the lowered section. Something like this: claw2 Add some subdivisions along the height and width then taper its end to a point. claw3 Translate the claw so that it's angled inward. Don't be afraid to experiment with the shape. You can use the side view to thicken the base or any other part if you wish. What ever looks good to you. Just give the claw this basic angled shape: claw4 To give the claw some detail you can select its center faces and extrude them them outwards. claw5 Smoothed, the claw will probably appear too rounded, so add insert some edge loops along its height and width to sharpen the corners. This is what mine looked like in the smoothed view (3 key): claw6 We need to also move the claw's pivot point where we want it to rotate back and forth. This will be at the top where the claw enters the arm. To move the pivot point, select the claw and choose the move tool. Then hold down the D key and move the pivot point near the top. Now when we rotate the claw it should pivot at this point. claw7 We're now ready to create two duplicates of the claw that will sit in the other two lower sections. Before we duplicate, we need to create a group of all of the claws. Hit Ctrl+G to group and you should see the claw formed under a new group within your outliner. You can label the group "ClawGRP" and the claw itself "ClawBASE". You will also notice that with the ClawGRP selected that your object's point of origin returns to 0,0,0. claw8 Duplicating the claw requires us to create what's called an instance. To do this select the claw group, NOT the individual claw. Find "duplicate special" under the edit menu and open the options for it. Set the duplicate special options to the values below. We want an instance, NOT a copy. We want to instance the claw along the Y axis 120 degrees (i.e. 360/3), and we want number of copies to be 2. Finally, hit duplicate special. Now if you select the claw base we initially built and rotate it in and out along the pivot point, the other two claws should also rotate simultaneously. claw9

Organizing Objects in the Outliner

The final step for completing the arm is to organize all of these various parts into a whole. We want all of arm's constituent parts to be grouped together so we can move them all at once. This means selecting all of those parts in the outliner and hitting Ctrl+G, but before doing that choose the forearm pieces we built first. You can find them in your outliner. Select both, and hit Shift+P to ungroup them. They should now appear below your claw groups. claw10 With both still selected, go to the edit menu and delete their history. This will remove both the transform node and the entire group from the outliner. Now, you're ready to group all of the arm's parts together. You can label the new group "Lower Arm". claw11 Now move the entire arm into its position on the mech's body. You can use the side and front orthogonal views to place it just right. Here is the final image: final image In this installment of the Maya Journal, we've successfully built an upper and lower arm. We've also learned how to scale and extrude objects to create detail as well as moving pivot points for animation down the pipeline. Most importantly, we've given the mech a deadly forearm complete with telescoping machine gun and some nasty looking claws for grasping its victims. The mech is really starting to come together at this point. In our next installment we will be completing the Maya Journal project by modeling the mech's leg and mirroring it along with the arm to the other side of the body. Please let me know if you have any questions by leaving comments below.