The virtual reality Gun controller

A lot of things have happened since the last update. Being the most important one that I achieve to get a job in the augmented reality industry! This has keep me very busy for the last year, but I have effectively managed to learn a lot in the field and also Android, iOS, Unity3D and many… many more. I love it!

Now that my “learning” curve has eased out I finally got time to carry on in my personal projects / hacks. And this time I promise I will put some proper code and tutorials (by the way I have enabled the comments so feel free to comment code in the older entries).

So this first new entry is related to the fact that I just received an Oculus Rift. This HMD is called to push the VR back in the trenches and I wanted to try it first hand… It promises real-time head tracking and perfect 3D vision of the environment with an epic field-of-view. You can move around the scenarios and after 3 minutes you truly believe you are inside. But head tracking is not everything in Virtual Reality and there is still some edges to cut: one of those is solving the problem of “moving around” with some kind of localization and I will talk about that one at some point; but the interesting one today is interacting with the environment, and when I say interacting I mean shooting at things… time for some Virtual Reality FPS.

I want to create a Gun that I could use in a shooter game, kind of the one Nathan has created for Half-Life 2 here. But that gun has some drawbacks (economic drawbacks because he is buyin a custom weapon and a custom tracker) and I want something cheap and nice and custom and hacky and … and … and I want it now. So this and the next posts will talk about creating your very own Gun Controller with tracking and everything for playing in virtual worlds!

Chapter 1: Ripping apart a Nerf Gun and giving it an Arduino brain.

Lets start from the beginning. In this first chapter I will talk about how I opened a plastic gun and closed a electronic one. I will cover how I made the connections from plastic to Arduino inputs and by the end the result will be a gun being able to fire, reload and select alternative fire. Lights/vibration and tracking will come in the next chapters.


The gun: I used a Nerf Gun, the “Alpha Trooper” model has a lot of space inside to maneuver and also looks pretty bad-ass. Actually I bought it to shot foam darts at people at the office… and yes we painted them and everything.

The brain: I have got a Makey Makey, which is basically an Arduino Leonardo. I bought it just to have fun until this project came to my mind! This is not supposed to be a Makey Makey / Arduino tutorial so go to the official forums in case of doubt.

The guts: Some cables, some springs, a solder, a saw, screwdriver and aluminium tape!

Step 1: Unscrew everything

With a star-screwdriver and patience I just simply unscrew all the pieces and carefully removed and organised all the moving-pieces of the gun as you can see in the photo.

I enumerated the pieces and I will use this photo as reference over and over again. Always keeping all the springs I disposed the pieces 13,14 and 15.

Numerated pieces
Numerated pieces
Step 2: Making space for the board

As you may see on the top-right corner of the previous photo, the Makey Makey is not very big but I still have to make some room. The picked place is exactly the center, on top of the magazine, but that position will bring a couple of problems.

“resized” clip

When the ammunition clip is in, it takes almost all the space… so I will cut it with a saw! Avoiding cutting the gap in the side that keeps it hooked to the gun.

This picture compares the resized clip to the board. I also removed all the inner parts such as the springs and the platform that you may see in the previous photo.

“resized” piece

Piece 1 moves using the side rail and when in “firing” mode takes all the space in the center in order to load the bullet. When cutting it, it is important to note the 2 hangers for the rails on each side of the gun need to be intact. And I still wanted to be able to move the piece 4 for realism. So the outcome is cutting to something like this.

1cm cut to serve as slot for the board…

I decided to cut a small slot with a saw where the end of the clip should rest. The next photo will highlight this.Fine! Now I should be able to put the Makey Makey inside, but I still want to be able to remove it sometimes and It must float inside the gun so it does not interfere with the piece 1 moving rails.

Cutting in half the piece 11

Last, the piece 11 which serves as chamber for the foam bullet is also in the way. Show no mercy removing the right side of it. Always keeping in the “right” side the two small legs to attach it to the body.

And now it the gap is big enough the Makey Makey should fit inside and don’t move at all, it is important to note that the piece 1 must be in first, and be sure that its movement is not blocked by the board.

The Arduino board inside the Gun with all pieces
Step 3: Making the triggers talk

The real fun starts now. With some aluminium tape and cables the trigger (piece 3), pump system(piece 2) and the magazine should inform to the Makey Makey of their state.

To do so I followed this principle: moving part should now have any cables but being used to close circuits “printed” in the fixed pieces. How does this apply? Easier than it sounds, simply put aluminium tape in the moving parts that, when in on position will touch other 2 aluminium pieces connected to the board. Let’s see some close ups.

Pump system circuit

This is the edge of the piece 2. Some aluminium tape in the orange part that moves as the very-nice-orange-arrow indicates will connect the red and green areas. It is important to note that the tape must be flat enough to avoid giving too much friction to the moving part. Note how instead of putting directly the cable I allow a big and separated area in the “tape circuit”. This cables should go to ground and a input pin in the board later.

Trigger system circuit

The trigger system works with the same principle but looks sightly different. In top of the trigger piece there are 2 little plastic steps that prevent the moving part to move up and down. With the happy outcome that the second step is only touched by the trigger when pressed! Some tape as in the photo should do it, always remembering to put some tape in the top of the trigger (will be visible in the next photos) and connecting each cable to ground and an input pin in the board.

Reload system circuit

And finally the ammo clip. This one is a bit more trickier, after struggling about how to close a circuit with a piece that feels always so fragile (it moves a lot inside the cabin) I have a great idea while drying my clothes: clothes peg springs.

Two hard metal springs glued strategically in the gun side, so they block partially the clip entrance, but still holds will do it. Always putting some aluminium tape in the clip so it connects both springs which have cables going to the board as always.

Flap to remove in the left side

The final bits include guiding the cables from the tape areas to the board. The Alpha Trooper has enough room behind the trigger to do so. But on the other side of the gun a little flap must be removed.

Removing it will allow some space to guide all the cables through when closing it.

And the very final thing is the USB cable, this step is a bit special, eventually this mod will be wireless with the help of an android phone, but for now an USB connection to the PC is needed. The default cable that comes with the board is a normal mini-usb that won’t fit properly between the board connector and the piece 6 so it is important to get a mini-usb with the mini-head output rotated 90 degrees. This is not easy to find in stores as they come customised directly with some cameras. Lucky me a friend gave me one.

Path for the USB cable

The second part is guiding it out of the Gun, the cable goes the same way behind the trigger but needs to come out from the bottom. With the help of the solder or the saw to make some holes in the plastic the USB should go thought the piece 12, then under the trigger spring, under the trigger connection and finally go over the removed flap in the last step.

In the photo I left in red the places where I made a hole, blue for the x-ray vision on the cable and green for highlighting where I removed the flap (in the other side). Please note that here I am not using the 90 degrees cable but the normal one.

Step 4: Test and close

It is time to seal this mess and give it a try. For doing all that is needed is to simply connect the USB cable to the PC and check if and only if one of the circuits is closed the LED in the board goes green. Pro tip: change the current springs in the gun with those removed from previous pieces in order to have stronger springs in the modified parts.

It is alive!

Now turn to put all the items in and put back the screws.

Final look opened
My next step in the agenda is to do some custom programming to the current Makey Makey script in order to fire the keys for the clip and pump just once when the clip is removed or the or the lever pressed. And also add some AND gates to the trigger so it only shots if there is a clip in position.
Next Step: Programming and LEDs
I would also love to add some funny LEDs arrays behind the piece 7 and animate them when doing actions so stay tuned.

After that another post should come with some info about how to make this all wireless and do some tracking using the gyroscope of an Android phone.