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.
Step 1: 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
- 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
- Drill (3, 5, 12, 28 (to fit the bearing) mm drill bits)
- 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).
Step 2: Take the Vulcan Apart
- Start by taking the handle off. You won't have to loosen any screws. Just hold the gun down and pull it to the side, as shown in the first picture.
- Remove the screws from the belt retainer and take out the plastic inserts. Afterwards you can just pull it off.
Step 3: Take the Vulcan Apart
- Use a claw hammer, to pry off the bolt head.
- Remove the battery tray cover, as well as the battery tray.
- Depending on the age of your Vulcan, there might be a sticker.
- If there is a sticker, you will then have to cut it in half.
- You don’t need to take the screws off which hold the barrel together unless you plan on painting the blaster.
Step 4: Optional: Replace the Spring
In my opinion, a 5 kg spring works best (the original one is a two kilo spring). I tried a 7 kilo spring in one, and although it was strong, it resulted in a lot of mis-firing.
To replace the spring, follow these steps:
- Start by removing the orange plastic piece on the plunger.
- Remove the 10 screws marked in the first picture of this step.
- Then take off the casing.
- Unhook the spring.
I tried to remove the air restrictor, too but noticed no difference in the firing speed, so I just left it where it was originally
Step 5: Rewiring
To wire the Arduino to the Motor:
- First solder one wire to the positive side of the motor - as shown in the first picture.
- Then solder a second wire to the switch - as shown in the second picture.
Either unscrew the mechanism, or use pliers to place the wire underneath it, as shown in the third picture. Now all that is left to do is to secure the wires with hot glue, as shown in the fourth picture of this step. I simply connected the two wires; But you can also add a switch, to also enable firing by pulling the trigger.
If you are planning on painting the gun, be sure to avoid painting the plunger head and the internal parts. The paint will only disturb the function and be scraped off after a time.
I've uploaded a picture to help you reassemble the Nerf gun. Be cautious so you don’t snap or break any pieces.
Step 6: Turn Axis
I originally wanted to use the base plate of the chair, but noticed that it was quite shabby. So after cutting off the cushion I replaced it with a 20x20x1.5 cm plywood plate, as shown in the pictures.
Cut a slot into the other 20x20x1.5 cm plywood plate, to fit the servo. Make sure that the axis is perfectly centered!
Now you will have to cut a hole into each of the 0.5 cm plywood or MDF plates, in order to fit the axial ball bearing (take a look at step 1 for the measurements). Glue one to plate holding the servo and the other one to the third plate. Drill a hole into the center of the third plat, which has to be big enough to allow you to screw the servo arm to the servo.
Step 7: Turn Axis
Glue the sides to the bottom plate of the box, as shown in the first picture. The piece in the front was supposed to hold the webcam. But after using the gun for the first time, I noticed that even though the base is really sturdy it moves a bit when the gun stops, which results in false detections. So I just decided to place the camera on the floor in front of the gun until I'll be able to find the time to build a tripod for the camera.
Before you paint the pieces, you should fill the holes and prime them. Next. , make sure that everything fits and screw the servo in place. In my experience the best way to position the servo arm is to screw it to the servo and to use two component glue to attach it to the top piece. Before you do so, make sure that the angle the servo can turn in both directions is the same. After the glue is set, unscrew the arm from the servo and take the plate off. Now you can screw the servo arm to the plate, to give the connection better strength.
Step 8: Tilt Axis
Before attaching the pole as shown in this step, I wanted build a platform. The platform should make attaching and removing the Vulcan as easy as possible; but I noticed that it didn't work. The main reason for this was that even though the center of gravity of the back and the front was pretty well balanced, the top and bottom really wasn't. So the servo didn’t have enough power to move the gun.
I decided that the best way to attach the wooden pole would be through an existing screw hole. Since the gun should be attached in its center of gravity, I had to use counterweights later on (I didn't want to take the front of the gun off, since I thought it looked good). Otherwise the center of gravity interferes with the ammo belt.
Drill a hole to fit the wooden pole through the screw hole marked in the first picture. Cut a disc with a 6 cm diameter from the 1.5 cm plywood and drill a 12 mm hole into its center. Paint the disc and place the pole through the hole. Secure it with a screw, as shown in the pictures. I suggest that you paint the pole after you've placed it in the bearings, otherwise it might not fit. Place the pole through the Nerf gun and glue the wooden disc to the plastic. Use two more screws to secure it.
Step 9: Tilt Axis
Cut a wooden disc to fit the arm of the Hitec HS805BB servo. Secure it with the provided screws and screw it to the servo. Cut all the pieces from the 9 mm plywood that are shown in the second step. Be sure to round the top edges of one side, as shown in the last picture. If you don’t, your ammo belt might get stuck. Place the two ball bearings into the two identical side pieces and paint them after filling and priming. Cut a hole into the third piece to fit the servo. It’s very important that the axis is perfectly centered. You should really spend some time on this step, since it will greatly affect how well your gun will work.
Place the wooden pole holding the Nerf Vulcan between the two pieces with the bearings. Now use the 128 mm rectangular block of wood as a spacer (the lower end of the plates has to face the back of the gun). At first I tried to secure the spacer with glue, but the connection was just not strong enough. So I used M4 x 40mm wood screws, to secure it in place. It also makes it easier to take the gun apart later should it be necessary.
Glue the 45 mm rectangular block of wood to the bottom of one of the panels and cut the wooden pole to the correct length in order for it to perfectly fit into the wooden disc which you've build before. Attach the servo and screw the wooden disc to the pole, as well as the servo plate to the spacer.
Then use the brackets, screws and wing nuts to attach the base, as shown in the pictures. Using the wing nuts allows an easy disassembly of the gun and therefore assures easy transportation.
Use the lead pearls or something similar as a counter weight, until the gun is perfectly in balance. Hot glue works great to hold the pearls in place.
Step 10: Electronics
The voltage of the battery pack connected to your gun motor controls the firing rate. If you want your gun to shoot faster feel free to use a second battery pack, or one with a higher voltage rate.
Thanks a lot lo Bob Rudolph for writing the awesome code for the sentry gun (you can also download it here). Just upload the files to your Arduino. Make sure to adjust the servo positions to your gun!
PSG Arduino code:
Step 11: Processing IDE
Create a folder named "Processing" and copy the files provided with this step into it. Furthermore you will have to copy the files in the "copy these into processing root or system32" folder to your root system.
You can find a detailed description on how the software works on the project sentry gun page here. The only major new thing is the surf classifier to detect the instructables robot. It can be controlled with these lines:
<pre>public boolean use_surf = true; public int surf_sensivity = 3; public String surfRefFile = "D:/Sentry/robot_live2.jpg";
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