Nerf Gun Demo - Using FRDM K64F

[#1]

Demo

 

This was a super fun project to work on and is popular around the office and on the road.  Now I have two of these for a truly amazing barrage of Nerf darts!  It's also always a lot of fun to tear things down and the Nerf gun had some cool plastic work and the shooting mechanism is more simple than what I originally guess.  But I digress, this post is about how you can build one of these yourself.  Please leave any questions or comments in the section below and I will try to answer and make refinements to this guide as we go.

The shopping list (aka Bill of Materials or BOM)

If you shop around you might be able to find better prices or substitute parts.

Type	Part	Qty	Price	URL
UBEC	HKU5	1	$             5.33	http://www.hobbyking.com/hobbyking/store/__16663__HobbyKing_HKU5_5V_5A_UBEC.html
LiPo	TURNIGY 2200mAh 3S 20C	1	$             7.89	http://www.hobbyking.com/hobbyking/store/__8932__Turnigy_2200mAh_3S_20C_Lipo_Pack.html
Servo	S5030DX	1	$           28.63	http://www.hobbyking.com/hobbyking/store/__18862__Hobbyking_S5030DX_Digital_MG_Servo_X_Large_HV_164g...
Servo	HK15138	1	$             3.12	http://www.hobbyking.com/hobbyking/store/__16269__HK15138_Standard_Analog_Servo_38g_4_3kg_0_17s.html
Relay PCB	COM-11041	1	$             3.95	https://www.sparkfun.com/products/11041
Relay Components	Various	1	$             3.00	https://www.sparkfun.com/wish_lists/36307
Nerf Gun	Nerf Dart Tag Swarmfire Blaster	1	$           44.99	http://www.toysrus.com/product/index.jsp?productId=11267568
Controller	FRDM-K64F	1	$           29.00	FRDM-K64F | mbed
Servo Arm	Double Servo Arm X-Long	1	$             3.20	http://www.hobbyking.com/hobbyking/store/__19468__CNC_Alloy_Double_Servo_Arm_X_Long_Futaba_.html
Servo Arm	Heavy Duty Alloy Arm	1	$             5.63	http://www.hobbyking.com/hobbyking/store/__18350__Heavy_Duty_Alloy_1in_Servo_Arm_Futaba_Red_.html
Servo Linkage	Alloy Pushrod with Ball-Link 65mm	1	$             2.10	http://www.hobbyking.com/hobbyking/store/__25834__Alloy_Pushrod_with_Ball_Link_65mm.html
Lazy Susan	Shepherd 6 in. Lazy-Susan Turntable	1	$             4.49	http://www.homedepot.com/p/Shepherd-6-in-Lazy-Susan-Turntable-9548/100180572#.UYk5UqLql8E
Metal Rod	3/8 in. x 36 in. Zinc Threaded Rod	1	$             2.87	http://www.homedepot.com/p/3-8-in-x-36-in-Zinc-Threaded-Rod-17340/202183465#.UYk5pqLql8E
Frame	1/2 MDF 2ftx4ft	1	$           10.45	http://www.homedepot.com/p/1-2-in-x-2-ft-x-4-ft-Medium-Density-Fiberboard-Handy-Panel-1508108/202089...

The build

Two main pieces to construct in this phase.  The base turret and the actual hacking of the Nerf gun.

All your base..

The base of the turret is pretty rudimentary, lot's of room for improvement here.  I used 1/2 MDF and some carpentry skills.  Here is some instruction on how to build a MDF box.  Atop the box is a lazy Susan (ball bearing ring) so that the top-plate can rotate smoothly.  We considered leaving this element out, but worried that it would put to much strain on the servo.

On the subject of servos, a few tidbits of wisdom for you as you build this thing.  First, the left/right servo needs to be dead center of the lazy susan, if your off too much things will start to bind which is not good for your servo.  Second, I used large higher torque servos which cost a bit more, they might be overkill, but it certainly performs well.

I did a quick dimensionally accurate rendering of the design in Sketchup. Files are here.

Hacking the Nerf

Now for the fun stuff.

There is no shortage of screws with this Nerf Gun.  So get out your Phillips screwdriver and go to town.

There are two electrical systems in the Nerf that we are going to tap into.  One is the power switch and the other is the electrical trigger.

This is the electrical trigger.  The trigger goes to our relay, which is either on or off.  We did try at first to use a 7.2V R/C car battery, but the Nerf draws too much power and didn't fire.  Going up to a 11.1V LiPo fixed that right up.

This is the power switch.

In Nerfinator 1.0 everything was hardwired together, which prevented us from completely pulling the Nerf from the base and made repairs difficult to say the least.  Nerfinator 2.0 we put this handy connector which allowed us to completely and easily remove the Nerf from the base.  Shipping this thing around the country will take a toll on it!  On that subject, Nerf 1.0, stopped cycling to the next position for us at the Austin Mini Maker Faire.  After a through inspection of the operational mechanics inside the Nerf (really cool BTW) it was a little bitty spring that was causing the piston not to fully retract.  We replaced the spring with 1/2 a ballpoint pin spring and to our surprise it all worked again.

Electrical Connection Diagram

Added High-Level Block Diagram.  Need to add pinouts.  You'll have to read the code for now to figure it out.

Code

Mbed was the programming tool of choice for this build.

Receive Side (RX) - The receiver is the base side.  This one takes input from the remote and controls the servo movement.

NerfGun_nRF24L01P_RX - a mercurial repository | mbed

Transmit Side (TX) - The transmitter is the remote side.  This one senses the users movement (accelerometer) and sends that data to the base station.

NerfGun_nRF24L01P_TX - a mercurial repository | mbed

Finishing Touches

In the first passes of this build we just used a bare development board as the remote control.  We found that when given the remote they would not orientate it properly, so

3D Printed Controller STL files

Development Team

John McLellan - Amplification/Motivation

Clark Jarvis - Software/Hardware

Iain Galloway and Angus Galloway - Design and print of controller

• FRDM_case_sunday_PART_REV_001.STL.zip

[laurenpercy]

This is so cool.

I want one.

[danielhadad]

You should have it track people !!http://makezine.com/2015/02/16/foamland-security-sibling-proof-your-stuff-with-a-nerf-sentry-gun/

[michaelball]

LOL  Reminds me of my project where I strapped a nerf dart gun on an autonomous penguin...

[echoyang]

that's great！