Edit: Youtube Series on the way! Check out my Channel.

After finally having gotten around to building a 3d printer of my own, and being inspired by youtube videos I thought about making a “real” HL2 turret/Sentry Gun. And by real I mean the turret body should rotate side to side about 90 degrees, the machine gun part should move up and down and be able to point the gun and body towards a face. The gun will only probably be an led or something safe like a pellet gun . Edit: Oh my God, not a pellet gun! I thought they’re something else. Definitely not a pellet gun.

I will be using a Raspberry Pi for the brains of the operation. The basic idea is to have the Pi connected to either a webcam or a Pi camera mounted in the body of the turret and with a little image recognition identify the height and angle of body rotation at which a face is found and then via the serial port command and arduino to move the servos, change LED colors and so on. Of course, it will be able to play the turret sound from the game.

But how does one get started on such a project anyway? Well I did some googling and I couldn’t find any 3d models which I could use as a basis for my 3d printable, functional model, and the pictures I could find online with the turret were all isometric views which I couldn’t exactly use as a reference.

After a bit more searching, I stumbled over a paper craft model. There are a lot of these models available. After downloading it (I can’t find the link but I’m hosting it on google drive), I saw it had a *.pdo extension. What is that? Well, apparently it is a pepakura model and it can be opened with Pepakura Viewer which you can find here. I opened it, and guess what? It’s perfect for the scope of this project. On the left side of the screen you get a 3d view of the paper model and on the right you have the unfolded printable version of it. The 3d view will be perfect for taking snapshots of the model to insert onto sketching planes when creating the robotic version. Not only that, but you can click on the various parts and they’ll be isolated to increase visibility on that part.

So now I’ve got a good starting point. But what about scale? Well it sure won’t be 1:1 because that would be a bit too much to print, but what I did was to create a block shape the size of the raspberry pi, the brains of the operation and then scale the image of the turret until it fit into the body. Then, one by one I started sketching out the parts and assembling them. I started the project in Solidworks 2010 but I wanted to try out Autodesk Fusion 360 because it’s free so I transitioned to it by outputting the Solidworks assembly to a .STEP file and importing it into Fusion. It worked great.

One important issue with the functionality of the turret is that the panel on which the back leg is mounted interferes with the body when in search mode so it would be impossible for the turret to rotate when assembled. The front legs are a bit easier because they mount on a plate which is positioned directly under the body and would make a great axis of rotation. So for the back leg I decided it would be easiest to just extend the plate downwards until it can be solvent welded with acetone to the front legs plate.

After some deliberation I decided to use two bearings on 8mm threaded rod to enable the body to rotate and then used a mini or micro servo as an actuator. I’m a bit worried about using a small servo for the rotation of the turret because the movement should be smooth and I’m not sure how much torque will be required once the entire thing is assembled. Although right now, the bearings seem to be really easy to rotate. I’ve also printed some servo “horns” and I used a 2mm steel wire to connect the two (not pictured). It should be enough for only 90 degrees of rotation. Another possibility I considered was using a small stepper motor and belt drive, but I’ll leave that as plan B in case I get issues with the servo.

The bearing holder will be solvent welded to one of the base halves and the other half has two recesses in order to support the turrets weight once both halves are mounted.

Also, to get the back leg plate to fit onto my print bed I cut it in half and It will be solvent welded during assembly.

I there is interest in this subject I will make the CAD available for free. I think a Youtube series would also be nice.