A big advantage of the Nerf Vulcan is that no extra servo is needed to fire it. The Arduino can directly be wired to the motor of the gun.
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.