GnK-90: Top loading, Solenoid powered, Brushless Nerf Blaster

UPDATES:

18/06/2024

• Made the Rear.stl walls slightly thiccer by 0.75mm.

• Spring guide in the Mag Base.stl is now taller, this will prevent the mag spring from tangling and prevent the follower from going further down than it needs to, which also tangles the spring.

• Changes reflected in .STEP file.

04/02/2024

• Added a new Mag Securing Block built into the Riser, this will help push mags down into the correct position and acts as a guide for mag insertion, held in place with a new Top Rail. Requires a new Compression Spring, 5.5mm OD, 35mm Length (Same one in the Mag Ejector)

• Rack has been made slightly beefier, with a shorter front end to prevent it striking the turnaround extension spring as much.

• 1.5mm fillet added to cage to prevent extension spring sticking to the side of the cage (hand filing the side of the cage will also help clear this)

• Changes reflected in .STEP file.

28/12/2023

• Adjusted Dart Lock, Mag Feed and Follower magazine prints to print easier and work slightly better with 38mm long and older darts. Preferred dart is still Worker Gen 2 HEs.

30/11/2023 

• Added stock.stl and stock alt.stl

27/11/2023

• Updated hardware list and wiring diagram with MOSFET information

25/11/2023

• Published

This is my attempt at creating a top loading P90-esque Nerf blaster, the GnK-90!

GnK-90 features 2x 2004/2104 size brushless motors and 40mm wheels, hitting around 190fps from my testing on 1g Worker HE darts, solenoid control using either a generic 35mm solenoid or FTW Hyperdrive, with added select fire. There are 2 select switches located behind the foregrip for select fire or select RPM, allowing presets for how fast you want the motors to spin. Also included is a 19mm OD barrel, which allows fitment of Worker faux muzzles. 

I opted to adapt Worker Talon mags to feed them at a 90 degree angle and have them turn around inside the blaster into the flywheels, so I designed a few adapter pieces that slot onto the mags, no shell cutting needed and its completely reversable. Using straight talons allows for an 18 dart capacity, and angled talons allows for 21 darts!

I chronoed this blaster to approximately 190fps, this may be higher or lower depending on your build quality and motor setup, but I managed this through the 2104 3000kv motors, fresh 1g Worker HE darts, on a fully charged 4s Lipo. This was also using the included Rifled Muzzle, which will drop FPS by about 5 or 10, but significantly improve accuracy. Default settings in the arduino sketch are for low RPM, 130FPS, and Max RPM. This may change dependent on your motor selection once again.

GnK-90 fits the lipo in the rear, there is a MASSIVE amount of battery space, I can fit in a 4500mah 4s LiHV with ease. Running on 4s is essential for the solenoid having enough power to work the turnaround mechanism, even with the FTW Hyperdrive solenoid. 

Firmware is included, I will admit this is not the prettest, but it works to get the blaster working at a minimum. You are welcome to use your own firmware, different microcontroller, add a screen, whatever you like with this! I would love to see what others can do with this shell. 

This project is licensed under the terms of the Creative Commons Non-Commercial Attribution Share Alike 4.0 license, which means you can print it, remix it, share it, and if you do and give myself credit. You cannot sell this without permission from myself. 

Pinout/Wiring Diagram for Arduino Nano:

• D2 = Rev Switch

• D3 = Trigger Switch

• D4 = Left RPM Switch 1

• D5 = Right RPM Switch 2

• D6 = Left Select Switch 1

• D7 = Right Select Switch 2

• D8 = Solenoid MOSFET

• D9 = ESC 1

• D10 = ESC 2

Hardware:

• 23x M3 Heat Insert, 5mm OD, 4mm Height

• 1x M3x4mm Bolts

• 6x M3x6mm Bolts

• 14x M3x8mm Bolts

• 1x M3x10mm Bolts

• 1x M3x18mm Bolts

• 1x M3 Thumbscrew

• 6x M4x6mm Bolts (4x if using FTW Hyperdrive)

• 4x M2x8mm Bolts (For switch mounting)

• 1x Extension Spring, 5mm OD, 20.5mm length

• 1x Compression Spring, 5.5mm OD, 20mm Length (For Trigger)

• 2x Compression Spring, 5.5mm OD, 35mm Length (For Mag ejector and Mag Securing Block)

• 1x Compression Spring, 7mm OD, 19mm Length (For Mag release)

• 1x Compression Spring, 7mm OD, 12.5mm Length (For Mags)

• 8x M2x6mm Bolts (For motor and flywheel mounting, HIGHLY recommend they are button head bolts for minimum height clearance)

• 8x M2 Washers (Optional but highly recommended for the motor mounting, saves the bolt drilling into the flywheel cage too far)

• 1x F683zz flanged bearing

• 1x M3 Washer

• 2x 35A BLheli_32 ESCs

• 2x T Motor F2004 3000kv / RCinpower GTS V3 2104T Light 3000kv 

• 1x FTW Hyperdrive Solenoid / Generic 35mm Solenoid (With upgrades springs)

• 1x IRFZ44N MOSFET with 10k resistor and 1N5400 diode (Or suitable MOSFET board)

• 1x Arduino Nano

• 1x Buck converter/BEC

• 2x 3 Pos switches (SS-23D32G6)

• 1x Subminiature Microswitch

• 1x 10A Microswitch

• 1x 4s Lipo/LiHV, 32x66x144mm max size

• 16 AWG power wires

• 22 AWG signal wires

• Lube for moving parts

Below is also my preferred BLHeli_32 settings, this has worked for me, you can adjust as you like:

You can switch out and use your own electronics if needed, if you want to use different motors, make sure to double check the measurements on the flywheels and motor mounts to see if they will fit. 

Turnaround Assembly:

• The turnaround assembly may require work to get it operating smoothly, this really depends on your print settings and your willingness to troubleshoot friction points and sand down parts, be prepared!

• Remember to grease/lube the moving parts well, this will significantly aid in operation.

• Add loctite to any bolts so they do not come loose and ensure a consistent operation. 

• Not all solenoids are built the same! I have found the plunger rod is sometimes bent, if the rack.stl is rubbing, rotate the plunger slightly, and this will change how the rack sits on the cage.

• You may need to adjust/cut down the extension spring, you can do this with snips, cutting down a coil and then twisting it to the desired angle so it can fit onto the spring block/turnaround bolts. Make sure it isn't too tight otherwise it will squeeze the rack inbetween the turnaround and spring block, causing it to stick. 

• A F683zz flanged bearing fits inside the turnaround and is mounted into place with an M3 bolt, I would recommend an M3 washer underneath the turnaround as well to ensure enough clearance. 

• You will need strong return springs on the solenoids, I used a cut down retaliator spring on my FTW Hyperdrive solenoid, trial and error will be needed for this. 

• Remeber to test each part individually before fully assembling, this will seriously aid in troubleshooting and knowing which parts may need adjustment. 

• Refer to the .step file for fitment, if necessary scale up/down parts for tolerances. 

Other Build Notes:

• I'd highly recommend printing the cage in PETG or any other heat resistant material, and the flywheels in ABS. I have tested PLA flywheels and they worked well enough, but you may have a different experience. 

• Loctite your bolts into the motors, or at least periodically check they are screwed in. I have found that using the M2 Washers for the motor mount bolts have helped significantly in keeping the motors secure without cracking the flywheel cage.

• Some parts may need supports when printing, I will leave that up to you for support placement.