   This instructable is a walk-through of how I made my life-sized Turret from the videogame Portal. It turned into a far more involved project than I expected, so be warned: this project is not for the faint of heart.
   When I made this my company, ThinkGeek, was working with Valve to develop a number of licensed products and toys related to the two Portal videogames, so I was already taking a close look at how to recreate these virtual objects in the real world, just not at such an ambitious scale. I had access to some behind the scenes assets, but they weren't nearly as helpful as you'd think - carefully examining screen-captures is best. The Turret proved to be a special challenge since it's so spindly and transforms in ways that leave no room for internal mechanisms.
   This project took me a good 200 hours in my spare time after work over the course of several months and several hundred dollars worth of materials. The entire model is about 48" tall at the top of the egg, with another 10" of antenna above that. I'd guess that it weighs around 20 pounds, but it's such an odd shape that it's impossible to lift in one piece - the front legs tend to fall out.

I'd like to acknowledge some other builders who inspired me to this huge project:
   - Citizen Snips, who started his Turret around the same time as I did, but managed to finish his in a more reasonable amount of time. His is at a different scale, uses other production methods, and contains more electronics. It is a thing of beauty.
   - Voplin props made an amazing Portal gun and every other project on their page is mind-blowing as well.
   - TJ Coffey - This flickr page shows an amazing working Turret with pop-out wings and airsoft guns. He uses a big CNC mill to make molds.
   - Aphius - This flickr page chronicles a valiant effort to make a full scale Turret with papercraft.

   * All photos were taken by me with an iPhone4 except for the hero shot on the blue background, which was done by the ThinkGeek staff photographer, Chris Hoyer.

Step 1: Tools & Materials:

Tools:
- Japanese pull saw
- Click out Olfa knife
- X-acto knife
- Bench-top & handheld jigsaws
- Circular saw
- Oscillating hand sander
- Fein sander / cutter
- Bench-top belt sander
- Surform files
- Metal file
- Needle files
- Sandpaper
- Hot wire cutter
- Quick-grip clamps
- 3/4" conduit bender
- Pipe cutter
- Hobby lathe
- Hand drill & bits / forstner bits
- Dremel & sanding / cutting bits
- Hand plane or spokeshave
- Disposable mixing pots
- Disposable brushes
- Epoxy squeegees
- Plastic sheet drop-cloth
- Eye & ear protection
- Respirator
- Shop-vac

Materials:
- 2" & 3/4" thick pink foam insulation sheets
- 1/2" thick MDF panels
- 1/4" Masonite panels
- Assorted craft wood pieces
- Assorted 3/4" thick lumber
- Assorted dowels
- Drywall screws
- 1/4" thick aluminum plate
- 3/4" steel electrical conduit
- Masking tape & paper
- Woven fiberglass cloth
- West systems epoxy & hardener
- 5 minute epoxy
- Micro-sphere filler powder
- Bondo autobody filler
- Bondo spot-filler
- Super 77 spray glue
- Loctite power grip pressure pack (glue)
- Spray primer (white, gray, & black)
- Spray paint (gloss black)

Step 2: Digital Design:

   I've been using SolidWorks for the past 14 years in school and as a professional to make consumer products as an industrial designer, but every project presents new challenges. When I began thinking about the Portal Turret I knew it wouldn't be a simple conversion from a 3d object created using surface or NURBS space to solid or Parametric space. In videogames and movies, almost nothing is designed by an engineer and if a mechanism seems to make sense to the casual observer it's good enough. A good example is the 1980's Transformers toy line - the transformation from vehicle to robot made sense even if the range of motion of the anthropomorphized robots were fudged to make them more human like. This meant that Hasbro could make working toys fairly easily - sticking to realistic toy mechanisms drove the aesthetic of the cartoon. A bad example, on the other hand, is the modern Transformers reboot, where the aesthetic was driven by complex rendering software that is good at pumping out polygons. These robots look more like a magical swirling cloud of spikes than anything hinged or mechanical.
   While the Portal games were created using the same CGI as the modern Transformers movies, the creators wanted to make a world that emphasized realistic physics, as that is the core mechanic of the game. The Turrets are meant to be deadly, but also delicate - hence the spindly legs which are reminiscent of the Striders and Head-crabs from Half-Life, an earlier Valve game.
   The Turrets are basically an Apple-styled lozenge made from glossy white plastic that breaks open into various moving components. In Portal 2 the player makes their way through a factory that builds Turrets, so we get to see a better vision of what the original designer intended. It is fairly obvious that the kneecaps were intended to fill in that gap in the body, but this scene shows that the legs were actually intended to coil and telescope out from the body - something that could never be done in real geometry. The in-game animation is too fast to actually understand how the designers intend the legs to work, but it makes enough sense for something that isn't very critical to the story or gameplay. Another geometric oversight was the range of motion of the wings and guns - to swivel and cover a large portion of the playing area they actually pass through the legs. While the unfolding legs would be impossible to recreate mechanically, the legs and gun-pods could be tweaked a bit so that they really work.
   When I started building my Turret in CAD I used some guesstimates on height & width to give me an internal volume for the mechanisms. From here I could build something that performed the 3 main motions of the wings and gun-pods: extending, rotating side-to-side (yaw), and up & down (pitch). I also needed to transfer the pitch and yaw motions forward to a camera and laser-pointer gimbal. This required putting tiny, high-torque motors on turn-tables with worm gears, belts, and all sorts of complex linkages which explanation is beyond the scope of this Instructable. Suffice it to say the mechanism would be beyond my abilities to create by hand at full-scale and would be impossible as a toy. With access to a good 3d printer, I might be able to build it by printing and then casting parts in more durable materials. Since the mechanism was unrealistic, I decided to forgo tweaking the legs so that the wings could move unimpeded and just made it look right.

The base form of the Portal Turret is a fairly simple set of proportions which can be easily scaled to any size:
   1. The base form has the proportions 100 x 36 x 46 (height x width x depth).
   2. The leg gap is cut using a 61 x 22 ellipse with straight lines 12 degrees off center.
   3. The kneecaps are made from that piece by cutting it side to side and then the front piece is cut front to back.
   4. The wings are cut using the same ellipse as the legs, but this time with lines 20 degrees off center.
   5. The center of the eye is 10 wide and 2 deep with a chamfer 14 wide.
   6. The wing slits are 2.5 x 18 and are 30 from the center.
   7. The center split is 0.25 wide and 0.5 deep.
   8. The legs are too complex to describe, but make the whole thing 136 tall.

   These proportions aren't exact to the in-game geometry, but should be close enough to look right. I couldn't find the overall height of the Turret anywhere, so I used a screen capture with Chell standing next to one. If you assume she's 5'6," the Turret is about 4' tall. Now if you take 48" and plug it into the proportions above: 48" = 136 so 1 = 0.353". While it's much easier to build complex geometry in CAD, anything can be done on paper with enough math. You can also find fairly complete blueprints of the Turret online now.

Step 3: Roughing Out the Base Geometry:

   This figure is a light-weight sculpt primarily made from foam insulation with a fiberglass shell - like a surfboard. I've done some boat-building in the past with different techniques (bent plywood, skin on frame, cold molded plywood, cedar strip) and was very interested in trying this method. Foam is a very cheap & quick way of creating large sculptures.
   In this case, the elliptical, organic form could only be made precisely* by taking a digital model and slicing it into a few dozen layers. I chose to make my slices across the waistline of the Turret since they could all fit onto a sheet of 11x17 paper. In SolidWorks I created the base form by revolving an ellipse and then squishing it to make a lozenge shape that I call the egg. I then used the thickness of my foam to create slices across this shape. I had to remember that each slice should be thinnest part of that area since I would be carving off the extra and not filling in the stair steps that would inevitably develop from the stack. I used thick sheets towards the center, where there is barely any change in the profile across several pieces, and then thinner pieces towards the ends where the profile changes more drastically.
   When laying out the profiles, I started with the largest - tracing out 4 shapes onto pre-cut rectangular blanks (right & left, top & bottom). Once they were traced, I would cut my print-out down to the next smaller profile and trace out another 4 shapes. I think there were 18 total profiles, making 70 foam slices (there were only 2 center pieces, not 4), I used a long-bladed Olfa knife to rough out the slices and then cut them most of the way to their final shape on a small bench-top jigsaw. I then took them down to the outline on a bench-top belt-sander. I would have preferred to use blue buoyancy foam instead of the pink insulation foam since it is less dense and shapes easier. The pink foam is too springy and tends to melt into a black tar when sanded aggressively.
   Once all the parts were cut, I used Super 77 spray glue to build sub-assemblies of the main body. These were as large as my clamps could reach, and I had some trouble with the sections de-laminating across the joints that I didn't clamp. The foam sections were then glued down to sheets of 1/2" MDF. These sheets are large ellipses with the bottom tip cut off and center removed. The tip is removed because on the Portal Turret, there is a large chunk removed where the legs meet the body. The center is cut away just to save weight. In the area where the tip is cut away the slices rest on a thin piece of foam instead of MDF.
   I glued the foam sub-assemblies to the MDF ellipses with PowerGrip glue since it's pretty thick and wouldn't melt the pink foam. Once the glue cured, I started the finish shaping with the Sureforms. It didn't take long to get the whole shape down to a nice smooth surface by just making sure I didn't work any area so much that I carved down below the inner corner of each stair-step. Using a long Sureform and sanding block will keep your final shape convex and very smooth.

   * I later realized that a good way of creating an approximately oval base shape would be to cut an ellipse in the shape of the side view of the Turret in a heavy piece of MDF on top of a large air-tight box and then laying a hot sheet of styrene over it. It should droop into that hole and could be pulled further into the box with a light vacuum pressure. You can't control the profile perfectly, but I've heard this technique used before to make domes for R2-D2 robots and the Mythbusters used a similar principle to shape sheetmetal in their 'Torpedo Tastic' episode.

Step 4: Carving Up the 'Egg' and Glassing the Foam:

   Once I had the clean “egg” halves, I used a hot-wire cutter to cut off the wings. This ended up being kind of a disaster* - the wire was too short and not hot enough to cut through 12"+ of foam. My plan was to gracefully guide the wire across a form in front and behind the egg, but in reality I ended up sawing the wire back and forth for an hour. The wire also bowed back significantly as I pressed it into the foam, so when I got to the area with a sharp corner, I had to pull it tight and hope that it would melt its way into that area. Another problem was that many of my foam slices were only stuck to one another near the MDF core, so when I cut them away they just fell apart.
   After I glued the broken wing parts back together, I cut off the leg notch areas very easily with a Japanese pull saw. The “scrap” from the leg notch is actually re-used to create the Turret's kneecaps. You need to cut each scrap piece in half, glue 2 together to create the back kneecap, and then also fill in the concave areas with more foam.

   Now that all the parts were created in foam, all I had to do was fiberglass over them. Foolishly, I decided to cheap-out on fiberglass and re-use my scraps for the in-between reinforcing layers. This lead to a really lumpy and bubble-filled surface that took FOREVER to fix. I'm sure I spent at least half of my time fussing over the surface imperfections and voids in the fiberglass. If I had just used larger pieces and been more careful when laying them down, things would have gone much smoother. (Pun!)
   This method for applying fiberglass is a little different than how you would do it in a female mold. With a mold, the neatness of the layers is less important because the outer surface of your finished piece is pressed up against the mold and the back side will show any changes in thickness or lumps. Typically a mold is treated with an anti-stick coating, then the fiberglass is laid in, making sure that everything is thoroughly 'wetted' with epoxy poured and applied with disposable paint brushes. Then the fiberglass is covered in 'peel & ply,' a cotton batting like 'breather' layer, and sealed inside a bag that is loose enough to not tear as it is drawn into all the nooks & crannies of the mold by a vacuum compressor. This is a good method for two reasons: first, it presses the fiberglass into all the details of the mold; second, the peel & ply will help draw out extra epoxy, leading to a lighter & stronger part. When fiberglassing over a positive core you can't vacuum bag without distorting the parts and it's very hard to keep the layers pressed down.
   I was only able to fiberglass about 2 major surfaces a night simply because I didn't have enough room to store all the parts as they cured, so doing all the parts took a long time. I started with the main body halves and the outside of the wings. I needed to wait until the main body was cured and somewhat smooth before I could shape the inside of the wings where they would need to sit flush with the surface.
   On the outside of the wings is a small slit, which I believe is intended by the game designers to be used as a carrying handle. Before I glassed the outside of the wings, I carved a small trench and made sure to cut pleated holes in the fiberglass so it could fold into the trench. I also took a few strips of foam core poster board wrapped in saran warp and jammed them in the slit to help shape the edges of the hole as the epoxy cured. This turned out better than I expected even though I had to pick out scraps of plastic that got folded over and trapped in the glue.
   On the sides of the main body, there are two large square recesses where the mechanical guts & wires of the Turret would be exposed when the wings are extended. To create this feature I cut through the fiberglass and foam and punched out that section before slicing off 3/4" from the backside and then glued it back in place. The sharp edge that this created turned into a nightmare of bubbled fiberglass that I kept breaking through as I did the finish sanding. I think it would have been better to line the edges with stops of plastic or pre-cured fiberglass and then just strengthen the corner areas.
   Another major piece of the Portal Turret were the gun-pods. I glued up foam and carved it to match the profile of the front and back frames I made from thin strips of craft wood. I then spread a couple whole sheets of fiberglass over this and trimmed it along the wooden edge. These relatively simple boxes were easy to create, but I probably didn't need to use fiberglass and foam - I should have used the same wooden frames, but then covered the in-between area with a sheet of bent styrene or sheetmetal.
   The foam kneecap parts were in pretty rough shape due to the extreme stair-stepping in that area of the original form and the fact that they are made from several tiny pieces of foam. I covered the main faces with fiberglass and waited until the wooden legs and metal tubes were attached before finishing off the rest.

   * Assuming that cutting off the wing areas would be simple was the first of several tasks that were more difficult that I had originally planned because I was thinking about doing things in the real world like they were a CAD program. Making an extrude cut or cut with a surface in SolidWorks is just a couple of mouse clicks, but in the real world you have to worry about the blade thickness, flexing, not cutting perfectly straight, etc. Cutting the pockets in the sides of the main body was another situation where I assumed I could cut through something, push it aside by an inch and then re-glue it. Now I'm positive there are better ways.

Step 5: Filling and Surface Finish:

   Every surface of the model was covered in a liberal amount of Bondo auto-body filler. This was for 2 reasons: to fill in the texture created by the woven fiberglass and to hide the dents and uneven areas that were created by using scraps of fiberglass instead of whole sheets. I must have Bondo'ed and sanded the entire thing at least 5 times to get the surface to the point where you couldn't see any flat spots or weird texture showing through. There were weeks where it looked like I was baking a Portal Turret cake covered in ugly brown frosting.
   Bondo has an interesting property in that it goes from runny reddish goo to hard plastic in about an hour, but for some of the time while it's curing, you can carve it like it's warm chocolate. It's best to remember to knock off the worst of the bumps with a Sureform in this critical window, otherwise you'll spend many extra hours working on it with 60 grit sandpaper.
   I worked on all the parts in different phases as some areas were easier to finish than others, and some parts, like the inside of the wings, needed to meet cleanly with other parts. The outer surface of the wings and main body were my primary focus since they are the largest surface that you look at. The gun-pods were very easy as I had learned to avoid re-using scraps of fiberglass. The insides of the wings were particularly difficult due to the fact that they are large, gently concave surfaces and the hot-wire cutter did such a terrible job of cutting. The center of each of these faces had a large hole in the fiberglass and shallow pocket in the foam which would hold the gun-pods with a friction fit. The edges of this hole were a little rough due to the fact that I nearly ran out of fiberglass.

   Once I felt like the surfaces were getting pretty close to finished I sprayed them all down with a thick coat of white primer. At this stage you feel like things are really coming together, but once it's dry and you can take a closer look, you realize just how much work is left to do. White paint is especially unforgiving as it reflects the most light and even the smallest imperfection will be clearly visible. From this point on I was doing Bondo & spot filler, and painting every chance I could get. There were also large areas like the pockets on the main body, which were several weeks behind the rest of the parts, and I was trying to think of ways to smooth out these areas without bothering with Bondo. I could have used some sheet styrene, but for some dumb reason I just did it all with Bondo. I also had a hard time making the bottom of the wing slits very smooth, so I poured in epoxy resin and let it cure on a level surface instead of trying to fill every little dent on that recessed surface.
   Eventually I had to accept that there would always be more detail work to do on something so large, so I gave myself a deadline to finish the project and stop worrying about every little pinhole in the paint. The “final” product is still covered in white primer albeit a very clean coat of white primer. The gun-pods are grey primer, and legs are gloss black.

   * All of the photos from this phase blend together, but I wanted to show them to demonstrate how frustratingly repetitive making smooth surfaces can be.

Step 6: Detail - Gun Pods:

The Portal Turret is a pretty minimalist object but it still has a number of complex details. The Guns on the original version vary greatly from those on the Turrets in Portal 2. I chose to stick with the simpler and more iconic design of the Portal 1 Turret, which has a stubby cylindrical gun above a longer, more pointy gun. At this point I had completely given up on making the gun-pods pop out, even though I had somewhat figured out how to make them retract into the body. In the end I just turned some sections of dowels on a hobby lathe and attached them with friction fit pegs. The same product could probably be created using a belt-sander and hand drill, but use whatever is easiest.
At one point I had planned on mounting disposable camera flash components inside the barrels of the guns to give the effect that they were actually shooting, but the final product is almost entirely devoid of electronics.

Step 7: Detail - Legs:

   The legs are made from laminated planks of 3/4" thick pine wood. On the two front legs, the plank on the flat side extends 4 or 5" further than the curved edge so that there is something for the kneecap to hold onto. The back leg is made from 3 planks, where the center one is longer. The legs are more freehand than the rest of the Turret because they are very organic when compared to the body. There is a straight section which turns into a gentle curve down to the point and on the back side of the legs there is a similar, shorter curve that leads down to a flat area. If you were to look at a section view of the leg it would look like a quarter circle with a flat section on the edge which I carved down with a hand-plane. There are other details and edges that I created as I was carving the legs, but most of it is invisible because it's painted black and is so far down on the figure. The best way to make sure that the right and left front legs are symmetrical is to carve them at the same time, while stuck together with double sided tape.
   The metal tube part of the legs are made from 3/4" steel electrical conduit which is bent to a 12" diameter using a contractors conduit bender. The front legs are are bent a bit less than 180 degrees while the back leg is more than 200 degrees, which is further than the bender is designed for. This means that I had to work the pipe into a bit of a helix, which I tried to flatten out, but it didn't really work. Once the metal is bent it becomes much harder and becomes impossible to adjust. I cut the part of the pipe that connects to the kneecaps right at the end of the bend. The other end has a few inches of straight pipe that allows the legs to fit into holes in the body.
   In order to attach the wooden legs and metal tube parts to the kneecaps I carved pocket for the leg tenon to fit into. Remember to put the kneecap and legs together in what seems like opposite pairs - the left leg goes on the right kneecap so that the flat side faces out. It's glued in with a thick slurry of epoxy and micro-spheres. For the metal tubes I drilled & dremeled out a round hole for it to fit into. It took a lot of tweaking and jig setup to make sure that everything set up in the correct position. I also drilled 2 holes near the end of the tubes and put drywall screws through them to create more of an anchor in the foam & epoxy. Once all the epoxy had cured I finished covering the kneecaps in fiberglass.
   I attached the legs to the body by fitting them into 3/4" holes in the bottom of the main body. The 2 front leg holes are a little distorted as they are projected onto a curved surface. The back leg hole comes out of the main body at a bit of an angle, so I needed to make a short "J" shaped trench on each side of the MDF. Each of the holes is capped with a bit of MDF to make sure the holes don't widen and make the legs fit too loosely. There's nothing that holds the legs in - they stay in place due to the weight of the upper body.

Step 8: Detail - Support Arm:

The wing and gun-pods are attached to the body with a length of 1" wooden dowel. The dowel is held inside the main body in a circular drum with a hole cut through it. The drum is made from a bunch of 3/4" thick strips of wood cut at a 45 degree angle arranged in a circle and then glued and screwed to 1/4" thick masonite circles. Once the drum was assembled I cleaned up the octagonal edge on the belt-sander until it was round. When finished I filled, sanded, and painted the whole thing white.
The drum is held between the main body halves in a semi-circular pocket about 3" tall. There's a hole to the outside that has angled edges which limit the rotation of the drum to 45 degrees forward and 45 degrees back.

Step 9: Detail - Seam and Eye Pocket:

Another important feature on the Turret is the seam the goes along the center of the main body. To build this seam I just cut an ellipse 1/4" smaller than the MDF panels from 1/4" masonite and glued it to one side. Something I noticed at this point was that the main body halves had warped slightly and the consistent 1/4" wide seam I was hoping to create was noticeably wider at the top and bottom. I tried to fix this by adding thin wedges of craft wood to the most bendy side and fairing them in with rest of the MDF.
While I'm talking about the center seam I should comment on the eye pocket. The eye is an interesting piece of geometry - it's not exactly a cone and if you make the mistake of assuming it is one it will end up looking too narrow. The best way to create it is to cut a 3 inch hole while both halves are assembled and then draw a circle 1" outside that. Measure up from the bottom of the hole and draw a line around the inside of the hole. If you measure from the top of the hole, the line will not be flat. Now cut down to both lines in a radial pattern using a saw and dermal. I ran into some problems getting this surface smooth the first time around and ended up cutting out significant parts of the foam in that area and replacing it with an epoxy/micro-sphere mixture. You should try your best to make this part look good as it's the focal point of the whole figure.

Step 10: Detail - Antenna:

I wanted the antenna to be unnaturally angular so it was cut from a 3" wide, 1/4" thick aluminum plate using a hand-held circular saw. This was an extremely tricky and dangerous operation which I hope to never repeat. It would have been much better to use a bandsaw or jigsaw, but the aluminum I had was far too tough to cut easily that way. I cut nearly all the way to the interior corners and then finished the cut with a hacksaw. Filing down the edges took a lot of elbow grease, but the result was worth it. I tried to use the belt-sander as little as possible since the aluminum heats up very quickly from friction. Before painting the metal, I sanded down the surfaces and softened the edges a bit.
Laying out the holes for attaching the antenna was pretty difficult. In order to make sure they didn't go all cockeyed, I taped them firmly to a piece of cardboard so they would act as a single piece until it was secured to the main body. Laying out the square holes projected onto a curved surface was a very interesting experience - they turned into weirdly distorted diamonds. I made sure to cut the top hole first and then slide in the first leg of the antenna before cutting the other hole. Once the holes were cut to the proper depth, I used small slivers of wood to wedge the metal rods in place and cut them off flush with the surface of the body. I didn't want to use glue in case I ever needed to crate up and transport the figure.

Step 11: Detail - Eye:

The last detail to create was the eye. I made a simple radial pattern in Adobe Illustrator and printed it out on regular paper which I then adhered to an empty masking tape roll. I wanted to make a simple back-light for the eye, so I shopped around until I found a clip-on LED bike reflector. The reflector's battery pack was off to one side, so I had to cut a couple small strips out of the plastic for the leads on the LED to pass through. I then bent the whole battery pack behind the reflector and tucked it inside the tape roll. It's an adequate solution, but the batteries will only last about an hour.

Step 12: Final Assembly:

   When everything is finished and the paint is dry there are 10 major parts with 7 detail pieces. I had an idea to make a crate for the parts that matches the box for the Turret as seen in Portal 2, but I doubt it will need to travel anywhere. The 2 halves of the main body are connected with tapered pegs that are cut in half and glued into holes in the opposite faces. My intent was to drill through each pair of half-pegs and use a locking pin to keep them in position, but a friction fit proved to be strong enough.
   To assemble the figure, you first center the arm support rod in the axle barrel and place it between the 2 halves of the main body. You then insert the rear leg and close up the main body. Now you can tilt it back and insert the front legs, making sure that they are positioned correctly. The gun-pods attach to the wings with a friction fit and the slip onto the ends of the support rod. The guns themselves are attached to the gun-pods with 1/4" pegs and the eye rests inside it's socket with a little bit of double sided tape.

   *If you wanted to skip all the messy fiberglassing and bondo, I think this would be a very good project for a theater or cosplay prop. It can be made even easier by building a closed Turret with carved or painted wing seam lines. I'm not sure what would be best to use as filler if you make any mistakes in the foam carving stage, but latex house paint shouldn't melt this type of foam. The legs will always be a very difficult since they're so spindly, but the more weight you remove from the top, the less strong the legs need to be. If you can find a way to heat the tubes evenly, you might be able to make them from PVC plumbers pipe.