3D Print a Half-Life 2 Turret/Sentry Gun That Can Shoot Mini Marshmallows

If you’re even a casual gamer, you’re likely at least somewhat familiar with Half-Life 2, even if you haven’t played it yourself. The first-person shooter game was released in 2004 to much acclaim from both critics and fans, and it’s remained wildly popular. As gamers and 3D printing enthusiasts frequently intersect, it’s no surprise that the Internet is full of instructions on how to print elements from video games, including HL2.

A recent blog post documents the making of an HL2 Turret/Sentry Gun, explaining what this kind of gun is and how exactly one begins to design a 3D printed version of it. A Sentry Gun is one that has a turret body that can rotate side to side about 90 degrees, with the machine gun part designed with the ability to both move up and down and point the gun and body toward the face.

The way that this 3D printed gun will be able to rotate is by using a Raspberry Pi for the operation’s brains. The Pi is connected to either a webcam or Pi camera that is mounted in the body of the turret. Image recognition will identify the height and angle of the gun’s body rotation, allowing it to find a face, and then use a “serial port command and Arduino to move the servos” and change LED colors.

The designer, who goes by Istimat — and found that drinking tea during projects is even more delightful when a 3D printed accessory helps make the perfect cuppa — searched for a model online until he discovered a paper craft “pepakura” model that can be opened using a Pepakura Viewer found here. Then, once the model was located, the following steps were taken:

“…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 major design issue here is that to allow the turret to rotate when assembled, the plate that the front legs are mounted on has to be extended downward “until it can be solvent welded with acetone to the front legs plate.” Two bearings on 8mm-threaded rod are used to allow the gun’s body to rotate, and then a micro or mini servo can be used as an actuator. Blogger Istimat explains his misgivings about this turret design:

“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.”

While the design and 3D printing of the gun is still a work in progress, you can see the thoughtful design process Istimat describes and the progress he’s made already on the printed parts. There’s also talk on Reddit of having the gun shoot mini marshmallows or 3D printed ones that are hollow, so the fun with this project hasn’t even begun. Stay tuned! Discuss in the 3D Printed Turret Gun forum over at 3DPB.com.