In this instructable, I will show you how to modify a Nerf Vulcan to automatically aim and fire at targets.  As an added bonus, this gun won't fire at anyone wearing a shirt with the instructables robot on it. I had this project in mind for a long time and finally managed to find the time to bring it to life.

If you've been browsing through my other instructables, you might have noticed that I am obsessed with Nerf guns. So far, I’ve managed to infect just about everyone around me with the Nerf virus. It is really fun to see how these plastic toys turn grown men into small boys!

My main aim was for it to look awesome; which was difficult to achieve without removing the front part of the gun. But, I managed to accomplish this without removing the barrel, and I’m really happy with how it turned out!

A big thanks goes to Bob who authored an awesome write up on how to build a sentry gun.

Please do not attempt this mod unless you are convinced that you will be able to do it; otherwise you might destroy your gun.

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Step 1: Stuff you need

Picture of Stuff you need
Stuff you need

To build the base:
  • Wood: 5 mm, 9 mm, 15 mm plywood
  • 20 x 40 x 45 mm and 20 x 40 x 128 mm rectangular block of wood (you can also use the 1.5 mm plywood)
  • Junior drum throne
  • 2 x ball-bearing (12 x 28 x 8 mm)
  • Axial ball bearing (80 x 105 x 19 mm)
  • 12 mm wooden pole
  • Wood glue
  • Sand paper
  • Wood filler
  • Paint/paint brush
  • 15 x spax/wood screws M4 x 40 mm; 4 x screws M4 x 16 mm
  • 4 x wing nuts: M5
  • 4 x machine screws: M5 x 16 mm
  • 4 x brackets
  • Two component glue

  • Servo for the turn axis: BMS-660DMG+HS
  • Servo for the tilt axis: Hitec HS-805BB
  • Wire
  • Arduino Uno
  • TIP120 transistor
  • 1N4004 diode
  • 1k resistor
  • Pin header

  • Nerf Vulcan (e.g. here)
  • 6 Volt battery pack
  • 5 kg replacement spring for the Vulcan (e.g. here)
  • Optional: Paint and plastic primer for the gun
  • 3 mm lead pearls or something similar as a counter weight
  • 6V 3700mAh battery pack
  • 9.6V 2000mAh battery pack
  • Webcam
  • Laptop 

  • Drill (3, 5, 12, 28 (to fit the bearing) mm drill bits)
  • Sander
  • Scroll saw
  • Soldering iron
  • Claw hammer
  • Phillips Head screw driver
  • Hot glue gun

Things like a scroll saw and a powerful drill are useful, but not a 100% necessary. I finished the whole tilt axis with just a fret saw and a cordless drill which was far too weak to drill the 28mm hole (I used the fret saw instead).
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brett12132 days ago

when I run the program it says the package "org.apache.commons" dose not exist. might be missing a library. please help.

brett12134 days ago

Why is there a yellow wire after the diode. I must be reading it wrong but it seems to lead to no ware nowhere.

brett12135 days ago

Sorry. But what WATT 1k resistor did you use. The pics are to small for me to tell.

brett12135 days ago

Hi I live in the usa and you cant buy wood in metric sizes. If I still use the Axial ball bearing (80 x 105 x 19 mm) but wood in sizes like 1/4" 5/8" and 3/8" Will this work? I am worried the servo will sit too high or low inside the axial bearing. Thank you so much.

I'm considering starting this awesome instructible, but is replacing the spring a must? Would I be able to build the sentry gun while keeping the fire rate normal?

The stonger spring will allow the darts to fly far-er and faster, but no it is not a must. I have seen some people add a few coins and the like behind the spring so as to have the spring be more compressed.

olcraft1 month ago

i can't find m4 40mm and 16 mm screws. It might be better if the screw were m6 instead. Is it ok to replace m4s wtih m6 screws?

jwgottabass2 months ago

I have taken on teaching myself and completing some extremely involved and complicated projects, but this one, whew! I can't wait until I get up to speed on the electronics, then the arduino. The complexity alone isn't the only fantastic characteristic, the instructions seem extremely comprehensive. Once I am, this will be my first project. Amazing!

whitewolf5784 months ago

Is there another place I can get the turn axis servo or maybe a different one would work too? Is there a reason it's a digital servo?

vlre10 months ago

Hello. Could you please give some instructions for using and installing the software?

The thing is that link you provided is not working anymore, and I am stuck on this step... everything is ready, all parts altogether...but there's a problem with this software.

Please help. Thank you.

whitewolf578 vlre4 months ago

Vire, were you able to get the software to work. We're about to start this project but want to make sure we don't get stuck at the end. Thanks!

vlre whitewolf5784 months ago

Yes, I did got it up and running

BrittLiv (author)  vlre10 months ago

Where are you stuck? It has been some time since I build it, so I hope that I am still able to help you. You can still find the page I was referring to, here:

vlre BrittLiv10 months ago


I am stuck with the part where you upload the code to Arduino.

Step 10.

When I try to upload the code, it says

backup as not declared in this scope

sketch_feb07a.ino: In function 'void loop()':
sketch_feb07a:222: error: 'backup' was not declared in this scope
sketch_feb07a:227: error: 'restore' was not declared in this scope

You also have a part of the code named "Backup" but there's no mention where to put that piece...

Tnank you

BrittLiv (author)  vlre9 months ago

Hi, I am sorry I totally missed your comment. You will have to open all three files in the Arduino software in order for it to work (hit ctrl+shift+n to open a new tab).

chris13994 months ago
can u make the Nerf Vulcan a CO2less paintball sniper rifle

Excellent, you should make a few of these and sell them online, i'd definitely buy one.

jelimoore5 months ago

Ok, so I am running this code on a 32-bit Processing, with native Raspberry Pi java libraries, and tells me "NullPointerException" on the "camInput.start" line. Nothing pops up inthe debug window, other than "Successfully loaded settings from "settings.txt" Any help appreciated

tymoskov5 months ago

Where do we place backup?

Legomiser15 months ago
Is there any where i can get one?
Legomiser15 months ago

I want to make this but the link for the spring doesn't work please answer. Thank u

BrittLiv (author)  Legomiser15 months ago

I am sorry, it seems like they are not selling it anymore

Legomiser15 months ago

I want to make this but the link for the spring doesn't work please answer. Thank u

jelimoore6 months ago

Does this only work on PC? I have a mac, and when I compile, it throws me this error: Cannot parse error text in:invalid Class-Path header in manifest of jar file: /Users/jmoore/Documents/Processing/Libraries/GenerativeDesign/library/jpen-2.jar

blakelittle6 months ago
Hey can you sell me one I understand how to make it but I don't have the resources

I so want to do this.

ajay50008 months ago

Im having some trouble with the wiring... can someone or @BrittLiv send me some pictures of the breadboard wiring...

BrittLiv (author)  ajay50008 months ago

The first image at step 10 doesn't help?

ajay5000 BrittLiv8 months ago

i cant properly see the connection. when i hooked it up it only fired.. the programs and stuff are working fine. Could you possibly email me a better pic or post one? PLease.. THANKS!

ramsbury8 months ago
Can you make a paintball version or just for nerf
racataca8 months ago

What is the working frequency?

JupiterAvenue8 months ago

Hey! I'm creating this for my last year in university but I'm having some trouble understanding some of the pictures in your guide, I bought my vulcan in the UK and im afraid the internals might be slightly different. I can't figure out where exactly to solder the two wires (the one to the gun servo, and the one to the trigger circuit) because they just look different and the glue in the pics is kinda covering part of the circuit. Could I maybe send you a pic or two of what I did for you to double check? I just don't want it to start puffing smoke when i turn it on lol Any help would be appreciated! And congrats for the guide, and for your painting skills! A warhammer fan maybe?

FWACATA1 year ago
Super impressed.
jlester4 FWACATA8 months ago

she modified this from an existing paintball project

Squidyman10 months ago

I am curious about the tracking abilities given the webcams very close view range and low resolution as well as poor light/dark contrasting abilities. What is the effective range and ability? About 5 years ago or so I used to play with those guns with my friends and they only reached about 30 feet with a lot of gun arching. Do you have any way to compensate for distance using ultrasonic and gun elevation? I have read about squirt guns that shoot squirrels trying to bird food. Same principles apply here I imagine? Looks like even with all its complexities it is just an arduino, a couple servos, a camera, and a laptop. I might just have to give this a try once I find my guns!

And very cool project btw!

(I used to replace the cap of the nerf bullet with a thumb tack so that is stuck into whatever it landed on (including people) (don't try this XD)).

I've seen other builds of this platform track people at over 30 ft. The important thing is that the webcam doesn't have to focus on an object as much as needed for humans. The software that this platform uses only registers blobs of basic colors (red, green, blue) and does so at a very low resolution to reduce processing (it must process every pixel per frame it processes, usually 10+ frames per second. a single meg pixel would is 1,000,000 pixels). This platform isn't designed to calculate trajectory but can using the same webcam and a cheap laser pointer. Google 'webcam laser range finder'. There good for the 30 ft range, but not much beyond. Check out

Hey! Your project was in a article today. Congratulations. Rock on!
BrittLiv (author)  incorrigible packrat8 months ago

Thanks for telling me! It is a really nice write-up.

cr8smthng8 months ago
this is the coolest instructable on the site. I'm definitely making one for "my kids" ;)
jgreat8 months ago

Great tutorial. I'm working on making my own based on your tutorial and others. I have a question about the wiring for the motor. It looks like you are just bypassing the trigger switch with the transistor. So you would still have to use the Nerf battery pack, or wire a battery pack to the existing terminals. Is this correct or am I missing something?

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