MRRF: Mostly Harmless 3D Printed Arms

The Midwest RepRap Festival isn’t just people hanging out with their 3D printers all weekend; There are also people bringing all the things they made with their 3D printers. There was an R2D2 and half of a B1 Battle Droid, a 3D printed quadcopter and of course 3D printed weaponry. [Ryan] and [Kane] from Mostly Harmless Arms brought a collection of their totally not trademark infringing not-Nerf guns.

The guys have a few designs for guns that shoot silicone-tipped extruded foam darts much further than a Nerf gun. There’s a bow, a more traditional spring-powered blaster, and a crossbow. All the designs with the exception of a few pipes and tubes and springs are 3D printed, and all the parts are small enough to fit on an 8″ bed. The darts are made with a dome mold for silicon and insulation foam that’s normally wedged in window and door frames. They’re dusted with cornstarch to prevent sticking, although in the video below there were a few jams. That’s to be expected; there was a camera around.

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Active “Dart-Sensing” Makes Your Nerf Gun Smarter

When choosing weapons to defend yourself in the next zombie apocalypse, dart jamming whilst firing your Nerf Gun can be a deal-breaker. This clogging is an issue with many “semi-automatic” Nerf Guns. When our trigger-happy fingertips attempt to shoot a dart that hasn’t finished loading into the firing chamber, the halfway-loaded dart folds onto itself and jams the chamber from firing any more darts. The solution, as intended by Nerf, would be to open the chamber lid and manually clear the pathway. The solution, according to [Technician Gimmick], however, is active sensing, and the resulting “smart” dart gun is the TR-27 GRYPHON.

To prevent jamming from occurring altogether, [Technician Gimmick] added a trigger-disable until the dart has fully loaded into the firing chamber. An IR LED, harvested from a mouse scroll wheel, returns an analog value to the microcontroller’s analog-to-digital converter, allowing it to determine whether or not a dart is ready for firing. The implementation is simple, but the results are fantastic. No longer will any gun fire a dart until it has completely entered the chamber.

The TR-27 GRYPHON isn’t just a Nerf Gun that enables “smart” dart sensing. [Technician Gimmick] folded a number of other features into the Nerf Gun that makes it a charmer on the shelf. First, a hall-sensor array identifies the current cartridge loaded into the Nerf Gun and it’s carrying capacity. To display this value and decrement appropriately, [Technician Gimmick] added a dual-seven segment display, a trick we’ve seen before. Finally, a whopping 3S LiPo battery replaces the original alkaline batteries, and the voltage-reducing diodes have been cropped, enabling a full 12.6 Volt delivery to the motors at full charge.

We’re glad to see such a simple trick go such a long way as to almost entirely eliminate Nerf dart jams. For all those braving the Humans-Versus-Zombies frontier this season, may this clever trick keep you alive for just a bit longer.

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Supersonic NERF Dart Speedometer

ATtiny Chronograph

[John] was faced with an interesting problem: after he built his own air cannon, how could he tell exactly how fast his NERF darts were moving? Luckily he had some spare parts on hand and hacked together a fully functional projectile speedometer for less than the cost of an Arduino.

A device is essentially two detectors spaced a precise distance apart from one another. When something passes the first detector, a timer is activated which measures how long it takes the object to reach the second detector. From this, the device calculates the speed. [John] used infrared emitter/detector pairs spaced exactly three inches apart and wired them to an ATtiny2313. After a little bit of coding, he now knows just how fast he can fire those squishy ballistic missiles.

The infrared emitter/detector pairs are mounted to a PVC pipe through which the projectile travels. [John] notes that in theory this could be used to measure almost anything that could fit through the pipe, although this particular device might be damaged by muzzle flash or a pressure wave from an actual gun.

We’ve seen other NERF dart air cannons before, and we wonder if maybe there should be some sort of competition to see who can shoot a NERF dart the fastest now that there’s an easy way to measure speed?

 

Upgraded Nerf Gun Keeps Track of your Ammo

[Paul] and his buddy [Jonathan] recently had a zombie themed Larp event to go to, so in the spirit of making the experience more realistic, they decided to upgrade their Nerf N-Strike Stryfe gun.

They started by cracking open the gun and making note of the available space for a few bells and whistles. Luckily, thanks to traditional plastic injection molding practices — there’s lots of room!

Upgrades include a magazine sensor, a jam sensor, a trigger sensor and a voltmeter to make the gun a little bit smarter. A knockoff Arduino Pro Mini takes in all these inputs and outputs it to a 7-segment LED display for easy visibility. Our favorite part is the ammo sensor, which keeps a tally of how many shots you’ve used. It’s simply an IR photo-diode and IR transistor in a Darlington configuration, connected to the GPIO interrupt pin on the fake Arduino.

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