Apocalypse sentry system

by MOAM Industries

In honour of the supposed apocalypse we decided to throw a party! (and let our mortgage lapse, a mistake in hindsight).

To greet our guests at the door as they came in we decided to greet them with a Nerf sentry gun. We had simple requirements for this system, it cannot involve permanent modification to the guns (a present from Mel) and had to fire automatically, no remote control.

This is the result

Twin Nerf vulcan cannons trained on our front door

Twin Nerf vulcan cannons trained on our front door

This is a perfect application for an Arduino and in our opinion the core of an arduinos usefulness; quick short term projects that can be completed in a few hours. Easy to prototype and quick to program. To facilitate automated firing of the vulcan cannons we inserted a PCB in series with the battery pack to interupt the current flow. Then we secured the trigger on using a cable tie. With this technique we could control the firing with a relay instead of complicated servos to pull the trigger.

To make contact with the battery we attached a wire to a cut down prototype of our eagle reference board, applying a generous ammount of solder to the traces

To make contact with the battery we attached a wire to a cut down prototype of our eagle reference board, applying a generous amount of solder to the traces

Flying lead connection to the other side of the isolating PCB. Simply wire wrapped around the sprung  battery terminal

Flying lead connection to the other side of the isolating PCB. Simply wire wrapped around the sprung battery terminal

Assembled with batteried reinstalled.

Assembled with batteries reinstalled.

Firing control relay to complete the Nerf power circuit. These little relays are great with the coil rated at 5v & 40ma they can be driven directly by the microcontroller and can switch up to 5A at 250VAC

Firing control relay to complete the Nerf power circuit. These little relays are great with the coil rated at 5v & 40ma they can be driven directly by the microcontroller and can switch up to 5A at 250VAC

Trigger cable tied into the fire position. Thankfully the Vulcan cannon is fully automatic and not semi-automatic.

Trigger cable tied into the fire position. Thankfully the Vulcan canon is fully automatic and not semi-automatic.

These modifications now ensure the Nerf gun can fire automatically and has not involved any permanent damage or modification to the guns.

The next step is the automation of firing and control. We had a spare PIR sensor available which makes for a nice plug and play sensor we could use to detect guests.

Simple PIR sensor

Simple PIR sensor

We decided to take mercy on our guests and at least give them a warning of the impending rain of soft foam darts. A buzzer from our stock for the Reflow controllers was added to a small piece of strip board with headers for the arduino connection. Of course with any automated weapons system we also included a missile switch for fire control, allowing the system to be armed and disarmed so we didn’t have to spend all night picking up little foam darts before Moose ate them.

Gheto strip board arduino shield, it's not fancy but it's cheap. side mounted buzzer for warning and missile switch for firing control. The 2.1mm barrel jacks provide connectivity to firing relays.

Ghetto strip board arduino shield, it’s not fancy but it’s cheap. Side mounted buzzer for warning and missile switch for firing control. The 2.1mm barrel jacks provide connectivity to firing relays.

Finally half an hour spent coding had the guns firing nicely in alternating single shot bursts. Unfortunately the PIR sensor had a minimum pulse of 3 seconds on detection so firing was not totally accurate on movement. We also included a 9 second cool down after 6 shots to give our guests a chance to get past and again so we did not spend all nigh reloading the bandolier.

Vulcan Sentry guns, now with full automation!

Vulcan Sentry guns, now with full automation!

We have also uploaded a small video detailing the build and demonstrating the guns in action.

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