Portal Turret Build

Posted: Thursday, May 26, 2011 by Ryan Palser in

So this was a really fun project to build!  I had some major obstacles to overcome, but that was part of what made it so fun.  The first step was to decide how big I wanted this guy to be.  There were a few factors that I considered when making my decision, the first being the overall weight.  Since this guy has very thin legs, I knew that weight was going to be a serious issue in getting the turret to actually stand.  As it gets taller the weight grows exponentially due to the increased surface area.  The second factor was displaying the turret when it was finished.  I didn't want it to take an unrealistic amount of space to display.  After considering all of these factors I finally decided on roughly 36 inches.  This is obviously not full scale, but I found it to be the perfect size to fit my needs.

To make the turrets as light as possible, I decided to make molds and cast the necessary parts.  Slush casting worked perfectly to create a thin plastic shell.  By making molds there's no need to hand make every part that will be in the final turret, since several of them I can just cast twice.  With this decision finalized, it was time to start on the masters.  Lets start with the body:

Phase One:  Making the Masters

I originally started with a foam base that I carved down to the shape of the turret.  I roughed out the general shapes for the various parts, including the arms, eye socket and main body.

Next I coated this with bondo and built up a thick enough layer to be able to sand and shape.  Note, bondo will partially melt the foam if you don't coat it with resin first.  Here is an early shot of the bondo buildup.

This method originally seemed like a good idea.  It wasn't.  After weeks worth of work I just wasn't happy with the shape of the body.  All the sanding had slowly distorted the shape of the body, and for something that needed to be perfectly symmetrical, it just wasn't working.  So I was at a crucial fork in the project...  do I keep working with this body and hope that I will be able to finalize the shape, or do I scrap all the work I had done up to this point and start over.
Start over.  This turned out to be the best decision I could have made.  Since I already had the general dimensions of the turret from the first version of the body, I was able to quickly create a skeleton framework of the body out of MDF.

With the rigid framework, the turret is now perfectly symmetrical with a straight center line.  All I needed to do was fill in the gaps.  With some quick shaping of some foam I was able to rough out the body.  To cover the foam I decided to use Apoxie Sculpt instead of bondo, rolling it out into thin sheets and covering the surface.  After letting it dry I sanded it smooth and in a matter of a week I went from a terrible version 1 body to a near perfect version 2 body.

I left a large hole in the middle if the body to house the electronics.  I'll cover that later on in this write-up.

The eye socket was something that needed to be figured out early on in the project.  I knew I wanted to go with a lens look for the eye, so I found a plastic cover that worked perfectly.  It is actually the cover for a Skil router bit that I picked up from Lowes.  I formed the eye socket of the body around this cover.  The result was spot on.

Next up on the body was many many coats of primer with lots of sanding between each coat.  Slowly working my way to finer and finer grit sandpaper, I had a glassy smooth finish.  The final coat was wet sanding with 1000 grit and then the surface received a coat of wax.

Body ready for its mold.

While I was making the body I was also working on the arm.  Since I will be making a mold of this, only one master arm is required and I'll then cast it twice for the left and right side.  The arm was built using methods from both versions of the body.  I started out with a foam base and attached wooden plates for the 2 flat portions on the inner top and bottom sections.  The outer surface was just covered with lots of bondo and sanded to achieve the curved I needed.

The inside of the arm was formed by creating a template of the arc and using it to form the bondo while it was still malleable.  The hold for the gun box was cut out with a Dremel.

The entire arm then went through the same process as the body, and was primed and sanded until it was glassy smooth and ready for molding.

The same general techniques were used for the remaining parts.  The 4 leg pieces started as blocks of wood and were shaped appropriately.  I found carving these straight from wood was a much faster technique than starting from foam, coating them in resin, and refining the shapes.

I only made one long leg piece to be cast 3 times, with the front two legs cut to length.  I also made a single gun box to be cast twice.

That covers all the main pieces I will need to make a full turret.  By the time I had finished the body, arms, legs and gun box, I lost count of the number of cans of primer I had gone through.  It was seriously a lot of primer.

By this point my garage now has a nice thick layer of dust on absolutely everything!  I'm really looking forward to having to clean it all up at the end of this project.

Phase Two:  Making the Molds

First things first.  I need to get all of materials I will need to create all the molds.  Luckily I found a place right near where I live that carries Smooth-On products, so I was able to avoid the crazy expensive shipping costs associated with the large quantities I needed for this project.  The boxes can be very heavy.  Due to the size of these molds, I'll be using the hard shell mold technique.  There are a bunch of resources online for different techniques, if you interested in casting and mold making.   I decided to go with Smooth-On Rebound 25 rubber for the molds with a Plasti-Paste shell.

The body and the arm will be cast with hard-shells while the 4 leg pieces will get block molds.  Lets start with the body.  The first step is to create the division line for the first half of the mold.  It actually work out really nicely that a piece of foam core perfectly fits into the center groove of the body.  After adding some registration keys, acorn nuts, and a clay dam around the perimeter, its time for rubber.

The rubber was built up in many coats with registration keys added to help fit the the rubber into the hard-shell.  Looks messy but it got the job done.

The clay dam was moved out and Plasti-Paste was added on top of this to finish up the first side of the mold.  Flip it over and repeat for the other side. 

The same general technique was used for the arm master so I won't bother repeating the process here.  There are photos over on Flickr on the molding of the arm.  On to the legs.  Since all these pieces are much smaller, I'll build block molds instead.  This will be much quicker and only use a minimal amount of extra rubber.

These are poured in halves like the body to create two pieces for each mold.  Finished they look like this:

The holes you see here are spots for the connection point with the body and legs.  From here on out, all the pieces that are created will be part of the final turret which is pretty exciting!  Its time to start casting pieces.

Phase Three: Casting the Parts

I decided to use Smooth-Cast 300 to cast all the pieces.  My original plan was to use this ultra white plastic as the final surface of the turret, with only some clear coat added for extra shine.  After some test casts I determined that wasn't really going to work for a few reasons.  More on that later.  With weight being such an important issue, all pieces relating to the body will be hollow, and all leg pieces solid for extra strength and support.  I'll talk about the body and arm first.

My goal with the hollow pieces was to create a shell that is roughly 1/8" thick.  After doing a few tests with different ways to achieve this, I decided to do each part of the mold separately and then merge the 2 halves to create a final cast.  This helps guarantee that there aren't any spots that are too thin.

And by doing it this way I can add a little extra plastic wherever it might be needed.  This isn't pictured but I added a solid block of wood to the bottom rear of the main body that got sealed in place with more liquid plastic.  This way there is a nice solid block that I will be able to drill to attach the legs.  The rear seam was also reinforced for structural support.

Once I was happy with the overall thickness of the shell, I merged the 2 pieces together.  Leaving a small hole in the center cavity of the molds, I'm able to add additional plastic to seal the seam.  After a few coats (and adequate curing time) I opened the molds:

And the arm.

Its definitely a little more work to do it this way, but the final pulls are lightweight and durable!

There is some clean up work required around the edges of pieces.  The arm on the left side of the image also has had a pass of bondo added to fix a few low spots it the pull.  The body will receive the same treatment to  make the surface as flawless as possible.  Overall the pieces are fairly good and after some love, they are ready to paint.

The last large piece that needs to be cast are the gun boxes that fit inside the arm panels.  One box was shaped out of wood, sanded, and primed- ready for a mold to be made.  Here you can see one in the mold curing, as well as a pulled piece.

There is still some work to be done on these guys.  Holes for the gun barrels as well as the center connection point need to drilled, and the majority of the controls for the turret will be on the rear of one of the gun boxes.  After carefully laying out the pattern, I drilled and cut all the spots, and this is the final result:

Phase Four: Finishing and Paint

Painting is one of those aspects of a project that can completely ruin everything, if you don't take the time to do it right.  It's the difference between a project looking amateur or professional.  I think my plasma rifle is a good example of a paint job done properly.  One thing I've learned is that there are 2 situations spray paint hate more then anything else:  humidity/rain and temperatures below 70.  Both are usually not a problem here in Southern California, it is a desert and all.  Perfect for painting!

Not so much, with an unusually cold and rainy year so far: every night when I would get home from work it was too cold in the garage to paint, and on the weekends it would rain.  This happened like clockwork for 2-3 straight months.  Really slows down your progress.  So I officially recruited my wife to help me get this project finished on time.  She has helped me paint in the past with outstanding results, and I was more then willing to give her the reins.  Being a fine artist and painting from home, she was able to paint pieces for me during the day when the weather was nice.  She did an amazing job!  Each piece has a few coats of primer, several coats of gloss white, and then several coats of high gloss varnish on top of that.  All the while sanding with very fine sandpaper between each coat, to make the surface as glassy as possible.  I don't think I could have done a better job if I tried crazy hard... the final finish is pretty much perfect.  Take a look for yourself:

Phase Five: Electronics

Now here is the fun part of the project!  Essentially bringing the turret to life.  There are a few main elements that I wanted to incorporate into the final turret.  First being the red LEDs for the eye.  Simple enough.  Second is a series of audio clips controlled by a motion sensor.  Third, the ability to play the original Portal theme song.  Now I know the turret shouldn't have the ability to play the theme song, but since this is meant as a display piece, it seemed appropriate to add this extra feature.

For those interested I am choosing to leave out the functionality of playing the audio clips when the turret is picked up, as well as the related audio clips when the turret is knocked over.  The reason is pretty simple.  This guy is not being built to take the abuse of constant handling or being knocked over all the time.  While the individual parts of the turret are fairly strong,  the assembled turret will be somewhat fragile on those thin spindly legs.  For weight reasons I am also leaving out the ability for the arms to move around like they do in the game.  All of the extra engineering required with components and servos would likely add a good bit of weight to the turret.  It would be cool, but I'm going to stick with a static model.  Same with functioning guns...  it all comes back to the weight.

Alright!  After hours on Mouser and Sparkfun researching components, and much experimentation, I have finally settled on the setup below.  The main components include and arduino uno, mp3 trigger, power regulation board (not shown) and an epir motion sensor.  There are various other smaller components like switches, buttons, LEDs, resistors, the speaker, battery packs and wall jacks.  Here is the main setup:

The programming was all done in the Arduino environment.  Since I would classify myself as a beginning programmer, there were portions of the code that I needed some serious help.  I called on a work buddy of mine, Pedram Javidpour: professional scripter extraordinaire, to help me get this program up and running.  I couldn't have finished it without his help!  Below is the start of the program that controls the turret.

After the program was finished I was ready to start installing all of the electronics into the turret.  I decided to split up the components between the arm and the main body cavity.  The arm would get the battery pack, wall jack, power selector, motion sensor, main power switch, and the button to play the theme song.  Here is what it looks like installed into the arm gun box.  Looks a little messy and confusing, but it all works perfectly.

So electronics in the arm cover power and small components.  The main guts of this guy are located within the body cavity.  In the picture below you can see the arduino on the right side, the mp3 trigger on the bottom, and the speaker on the left.  The cluster of wire at the top link up to the eye.

The eye piece is arguably one of the most important pieces of the turret.  I really wanted it to stand out, taking the time to make sure it came out as best as possible.  After finding a suitable plastic lens I could start on making all of the other necessary pieces.  Here is an image of everything that makes up a finished eye.  The black disks were designed and laser cut to create the groove pattern you see in the final eye.  The translucent disk will help diffuse the red LEDs, and the black rod will create the dot in the center.

After roughly fitting all the pieces together I noticed that the light spill coming down the sides of the lens was really messing with the overall look of the eye.  I resolved this issue by coating the inside of the lens with black electrical tape to prevent any light leak from happening.  This way the only light you will see is coming through the translucent surface of the eye.  The final result is perfect.

 All that's left is to install the eye and connect up the power.  With the electronics finished and installed, all that remains is the detail work.

Phase Six: Finishing the last Details

Let's start with the pipe work on the interior of the body.  This was done by bending black plastic rods with a heat gun.  A small connection point was made for the end of each piece to attach to the main body.  You can also see the location of the speaker in the shot below.  Here is a rough placement of the various pieces for this side of the turret.  They will then be cut down to size, and after the white plate in the center is painted black, they will all be properly installed.

The gun barrels were shaped out of MDF.  I decided this would be quicker, rather than cast them.  They will be cut down to the proper length and attached to the gun boxes after they are finished.

After primer and sanding, they received my special layering of metallic paint.  Throughout various projects I have figured out a great way to simulate metal by layering several different types of metallic spray paint.  I've tried to find a single can that does this, but haven't found anything I like yet.  These guys will receive a small amount of weathering to make them look more like they have been used before being installed.

The final step to be done was probably the scariest part of this project.  Until this point, I have not actually connected the legs.  I still didn't know if the turret would actually stand.

The legs are solid plastic epoxied together to form the main part of each leg.  This connection point is fairly strong, with a peg system that connects them together.  The thin rods of the legs were probably one of the more challenging parts to figure out.  They needed to be as strong as possible, metal, so I went with 3/8" aluminum rods.  These were bent by hand (tough) to form the proper shape.  To achieve this I created a wooden template to bend each rod around.  The ends of each rod had several notches added so the epoxy had a better surface to grip.  They were painted black and then assembled.

It was time for the moment of truth... I connected the legs and cautiously turned the turret right side up.  It didn't collapse!  It's definitely top heavy, but it stands.  It was truly nerve racking to know that this project could have completely failed at the very end.

Phase Seven: Taking Sexy Pictures

Well all that's left is taking pictures that make your project look unbelievable!  There are a few things I do here to get the best documentation possible.  The first thing is to set up a proper photo shoot.  Luckily for me, the building I work in has a nice large space with no windows, and some really nice box lights.  They provide great soft lighting, and are part of the reason my photos come out looking so polished.  The second thing I do is to have my wife take all the pictures!  She has a much better sense for photography than I do, and she's always taking these amazing photos.  I'm sure it comes from the fine art background, and she always does an amazing job.
If you're interested, check out her work here:

After a few minor adjustments in photoshop, the project is officially done... hope you all enjoy it as much as I enjoyed making it!


  1. Dave says:


    Wow! Outstanding! I can see a lot of work went into this.

    Haven't had the time to read through it all yet, but it looks like you've got some thorough documentation the build process too!

  1. Anonymous says:

    you should make the guns shoot or make them flash or somthing and make it panic when you pick it up

  1. Damn that is pretty! I chanced across your blog \cause I'm actually in the process of making a Portal Turret as a mid year exam in interactivity! Unfortunately mine isn't nearly as pretty, my coding is stronger (and better equipped) than my model building abilities!

    Tell me, seeing as this is a cast item, would you be able to cast more with relative ease? I'm asking as I may be keen to pay you for one to stick all of my peripherals and coding into! Too late for my assignment, but a flippen cool way to keep my exam coding going to waste!

  1. Hey Tim

    I'd love to see an example of your code in action. There were several features I left out of my design due to the fragility of the project. I knew I wasn't going to be able to make something this big that could be knocked over without breaking for example.

    The casts unfortunately take a fair amount of time to make and require several days of cleanup work on top of the fact that they use about a gallon of smooth-on liquid plastic which isn't cheap. I have several other projects I have moved onto and just don't have the time to spend making any more casts. Not enough hours in the day.

  1. Hey again!

    I'll be sure to contact you once I have some videos put together!

    I'm not sure if you are familiar with Max/MSP? I've written the patch in max, and the code will be available on the university website after my exams, so you're gonna be welcome to try it out!

    A pity! I'll have to make a plan when I myself have a few more hours in the day!

  1. Anonymous says:

    Excellent work. You've gotten me interested in casting and prop making. Now the question is: Half-life Gravity Gun or MassEffect Geth-head desklamp?...on second thought I'll let you try those and start off smaller. lol

  1. Anonymous says:

    That's AWESOME!!!!!!! I want one!

  1. Eric says:

    Beautiful work! My 7 year old and I are embarking on a project to make a sentry, thanks for sharing this! Ours will probably end up being made from paper mache and macaroni:)

  1. Anonymous says:

    Katie says:

    Awesome work I just might make one :D

  1. Thought you might be keen to see a short video of my coding in action!


  1. YingYing says:

    is there any video preview of this?

  1. Yes there is a video over on my flickr page. Link below


  1. Anthony says:

    Hey can you put the codes for the programming in the blog too? I want to try to make this! If you could it would be great!

  1. Very nice. You did a great job with it.

    I was just wondering, what sort of machining stuff do you have to do the work on this? It looks like the gun barrels might have been turned on a lathe, while the MDF frame seems like it might have been either laser cut or done on a CNC router (I suppose you might be able to do it on a manual router as well, but the curves involved would be difficult.)

  1. @Anthony - Send me an email at kronosprops@gmail.com

    @FenixPheonix - My shop is fairly simple. The framework for the turret was done on a bandsaw and a belt sander. While I don't have one currently, a lathe is on my list of tools to acquire. My current list of tools is as follows. Bandsaw, belt sander, small drill press, router, hand drill, chop saw, and a dremel. I could probably work much faster will better tools but I try and work with what I have. Maybe I'll put up a picture of my shop.

  1. Anonymous says:

    SEX!!! Ok if you're reading this then i got your attention. Um hello my name is Kyler Graves. I am a 15 year old highschool student. I was wondering if you might be able to make me one of these portal turrets for my 7 year old little brother. He is a Portal fanatic and he saw your pictures of this and wanted one but got depressed when he found out he would have to make it himself and knew he couldn't because we don't have the tools or the know how. His birthday is coming up so I just thought that this would be a nice gift for him. I'm willing to pay you. If you can find it in your heart to help me out I would be oh so grateful. Please e-mail me at "Kylergraves@hotmail.com" if you are willing to help.

  1. Kay says:


    What a fantastic turret gun! I am attempting to build my own and had a quick question for you: what brand/types of primer and bondo did you use? I've attempted to use bondo before, but I think I got the wrong kind because it looked NOTHING like the color or texture of the tutorial I was following. It also didn't work as well as I needed it to and I was forced to scrap the project.

    Thanks for the great write-up on your process!

  1. @Kay

    The spray paint is Valspar or Rustoleum. Nothing special about it. I just pick up the standard stuff available at home depot. The Bondo is just plain old name brand Bondo I get at Auto Zone. The important thing with Bondo is to make sure you get the ratio of hardener correct. If you use too much or too little, it will not set properly. I recommend doing a bunch of tests until you get the proportions right. You'll know when you do. Best of Luck


  1. talon says:

    I am currently starting what is essentially a complete clone of your project, however I am going to attempt to implement articulating side-casings and a moveable (aimable) body. Also, an airsoft gearbox for each "arm". I will have much to squeeze into that case! Any thoughts or advice to give from your project? By the way, congratulations on the build, I have seen it all over the net! I am also looking forward to your write-up.

  1. talon says:

    I have one more question that I'd like to ask--What was the approximate cost of this build?

  1. LANDWERLIN Adrien says:

    First i woold like to congratz you for this amazing and great job.

    I'm a french guy, and i really would like to get one.
    I would give you arround 1500$ for one.

    Please contact me at Landwerlin.adrien@orange.fr

  1. DisaFear says:

    Nicely done man, nicely done

  1. DisaFear says:

    Someone mentioned making Geth from Mass Effect, that would be totally amazing :D

  1. Anonymous says:

    Quick question, sorry if's already been answered. Can the barrels for the guns slide in and out?

  1. I'm speechless. This is a masterpiece and you are a maestro.
    You deserve a cake, sir.

  1. jale says:

    I agree to kitten cake4U ! :D

    This turret is SO amazing. I'll try to build it by my own :D you could shure make lots of money with these :o

    Do you know how much the material will cost? '~'

  1. I don't have an exact number but it was in the neighborhood of $500-700 for all needed materials. The rebound 25 is quite expensive at $184 a gallon and the smoothcast 300 is $86 a gallon. The electronics were about $130.

  1. John Alvarez says:

    Wow, this is simply amazing, i would to have a portal turret ):

    Just asking, do you have blue prints for this? i would to make one for my Solid Works school project, but i need the blue prints in order to make it.

    Where can i get them?

    Tx for your attention.

  1. talon says:

    Thank you very much for getting back to me on the price. Still in the "collecting research and planning" phase. Good luck on your next two guns (GoW & HL2)!

  1. Abtin says:

    Dude, you are my hero! I'd love to make one like this.


  1. bdcooper says:

    WOW that is all i can say! (clap), (clap), (clap). i wish i had the skill, talent, and money! wow i would love to know how much the finished product came out to be. i would love to have one of thees but i don't have the skill talent money and things needed! i cant stress how good this is! to make one of these i would have to wait a longgggg time i only have like $50 for projects, and a plan on spending them on a real potato GLaDOS, a stuffed companion cube, and a plush turret! i don't have allot of money in my portal 2 fund! lol and again you did a great job on this!

  1. Anonymous says:

    This is awesome, I can tell a lot of work went into this. One suggestion though, the grove down the middle of the turret should be painted black. Not only does it matched the game, it also adds a nice contrast to the fully white. :D

  1. Isaac says:

    Cool maybe I'll make one but without the electronics.

  1. I haven't necessary tools, or materials, or space in my apartament, but I wil try to make one. I need to use an easy, and cheap way. I will make the body from foam, I will cover it wit some silicone and i will paint it. I will not make the song system, but I will try to do the glowing eye.
    Excuse my English!

  1. Wow man...this is simply awesome! Cave Johnson would be proud of you dear.
    Now I feel bad if I show you what I did >o< But i will anyway, hope you think mine's is at least 1/3 of your awesomeness :p