Solenoid Driven Nerf Blaster

Motivation

It had been awhile since I'd done an electronics oriented project, and I've always wanted to try making a solenoid driven nerf blaster. More specifically, I wanted to try making a "closed-loop" solenoid by adding limit switches to add feedback. My goal was to get the fastest fire rate possible using a solenoid. While I'm not sure that I quite reached that point, it definitely shoots very quick. I also went with half darts rather than full length darts, since that seems to be what the hobby is leaning towards at least for third party builds.

Prototypes

I began by first creating a proof of concept by actuating the 12V solenoid using a Mosfet and a 5V digital signal. Additionally, I'm "clamping" the solenoid with a regular and zener diode in order to dissipate the magnetic field quicker, resulting in faster actuation. You can find more info about this method here: Texas Instruments Driving Solenoids

From TI Driving Solenoids

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Closed Loop Control

I then added a small limit switch on each end of the solenoid travel. This allowed me to cycle the solenoid quickly and precisely without having to compensate for timing, battery voltage, friction, etc. The resulting actuation is extremely quick (especially when unloaded).

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Trigger Prototype

Instead of a separate triggers for flywheel rev and fire, I wanted to instead integrate the two states into a dual stage trigger. The initial actuation causes the trigger to leave the bottom switch, revving the flywheels. Once the trigger reaches the end of its stroke, it presses the top switch, which causes the solenoid to actuate.

Flywheel Cage

I printed the flywheel cage out of MarkForged Onyx, and then added M3 heat set inserts to allow for mounting. The motors used are OOD High Rpm Loki motors, which achieve about 60k rpm at full speed. The flywheels are Worker Nightingale wheels, due to their concave shape and small profile.

Test Stand

In order to test all of the blaster functions at once, I laser cut some wooden side panels to mount the three main modules: the magwell, solenoid, and flywheel cage. The wiring is a bit of a mess, but the core concept worked! I also tested some 12v UV LEDs to charge the glow in the dark darts I was using. A ball detent holds the magazine in place rather than a traditional mag release.

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Design

This was a good exercise in modeling for aesthetics in addition to function. I've always liked the look of top mounted magazines, so I embraced that idea and aimed for a futuristic sci-fi look. I was heavily inspired by the Cyberpunk 2077 Araska Shingen.

Then main modules of the blaster are held in place by two aluminum plates, which are covered by aesthetic insert plates. The rear of the blaster interfaces with a Bosch 12V drill battery, which I used to power the blaster due to its compact size and ease of swapping in and out

Battery Mount module. Uses a clamping system to hold the tab connectors.

Wiring

The timeline of this project didn't allow me to create a pcb for this project since I couldn't wait for the ~2 week lead time on manufacturing. Instead, I opted to hand solder most of this circuit. The result is pretty messy, but everything actually worked first try!

A buck converter converts the 12V battery voltage to 5V for use by the arduino nano, which captures inputs from the fire select switch, trigger switches, and solenoid feedback switches, and then outputs signals to the two 12V mosfets to control the flywheel motors and solenoid.

All components mounted with leads soldered on

After a couple hours of soldering, everything is connected!. The topmost perfboard distributes 12V power and ground, while the bottom perfborad mounts the arduino nano along with the 2 mosfets.

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All wires somewhat controlled before closing the shell

All closed up. You can hardly tell there's rats nest in there.

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Solenoid action closeup. You can also see the glow tips on the darts being activated by the UV leds.

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Quite pleased with the performance, feeling, and look of this blaster

Final Build

After being gone for 3 months at an amazing internship with Yaskawa America, I returned to this project to add all of the remaining cosmetic parts and implement select fire.

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Reflection

Overall I'm very pleased with how this project turned out. The blaster functions exactly as intended, and I learned a ton about controlling solenoids and motor. The twin aluminum plates give the blaster a very solid feel. No flex, rattling or shaking to be heard. Additionally, the blaster looks fantastic, achieving the futuristic sci-fi look I was shooting for.

However, the blaster construction is quite complex and somewhat bulky. The electronics themselves could have been much smaller if designed with a proper PCB in mind. There are many more parts and fasteners than are necessary mainly to achieve the desired aesthetic. As it stands, this blaster is not one that could be easily mass produced, nor is it the best in performance compared to other existing flywheelers. But as a boutique, one-off blaster I'm super satisfied with the result!

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