Commercial airsoft grenades have to be refilled with CO2 capsules every time they are used. This sound grenade aims to be more economical since it can be used hundreds of times on a single coin cell charge, although you will lose the realistic loud bang and the ability to throw BBs.
It consists of a 3D printed enclosure with electronics inside. There’s a pushbutton at the top plus a buzzer at the bottom. An ATtiny85 microcontroller holds a program that makes the buzzer beep loudly 10s after the button is pressed. It also makes short beeps on each of the last 3s. It’s powered by a 3V coin cell (CR2032), which can easily last hundreds of cycles.
This post will deal with the enclosure, while Part 2 will deal with the electronics inside.
Won’t it break?
The thing with grenades is that they will be thrown around. 3D printed parts don’t like this and break apart easily, usually because of weak layer adhesion. Electronics also have mechanical parts that will break or behave in unexpected ways after hitting the floor one too many times. What do we do? Mostly these two design decisions:
- Notice the two threaded rods in the picture above? They are meant to join the two halves together and keep them compressed so that no external forces manage to pull layers apart. And even if they break, the grenade will remain whole so that you can try to superglue it later at home.
- Choose a good material to print. ABS has worked well for me (for parts of this size, I usually put the extruder 10º higher than normal to improve adhesion). PLA is brittle. Other materials such as nylon or Filaflex might work.
Of course, the throwing style also matters. You should only throw it like a bowling ball: from a low height and rolling along the floor. In fact, that’s the only method approved for any kind of grenade in the fields I play. Otherwise, eventually one would explode on someone’s face.
- Threaded rod (3 mm in diameter, at least 160 mm long)
- 4 x Nuts (3 mm)
- The 3D printed body made of two halves.
3D printing the body
Iterating the design of the sound grenade for a successful 3D print was extremely fun. I even tried my hand at using molds but it was too much work for very little reward.
After many iterations I settled for a simple design which has the round shell but replaces the whole lever plus pin mechanism with a single hole for the pushbutton.
Download it here:
Airsoft Sound Grenade STLs – Download
[canvasio3D width=”320″ height=”250″ border=”1″ borderCol=”#000000″ dropShadow=”0″ backCol=”#FFFFFF” backImg=”…” mouse=”on” rollMode=”off” rollSpeedH=”0″ rollSpeedV=”0″ objPath=”Sonic-Airsoft-Grenade-Top
” objScale=”1.3″ objColor=”#0B6623″ lightSet=”7″ reflection=”off” refVal=”5″ objShadow=”off” floor=”off” floorHeight=”42″ lightRotate=”off” Help=”off”] [/canvasio3D][canvasio3D width=”320″ height=”250″ border=”1″ borderCol=”#000000″ dropShadow=”0″ backCol=”#FFFFFF” backImg=”…” mouse=”on” rollMode=”off” rollSpeedH=”0″ rollSpeedV=”0″ objPath=”Sonic-Airsoft-Grenade-Bottom
” objScale=”1.3″ objColor=”#0B6623″ lightSet=”7″ reflection=”off” refVal=”5″ objShadow=”off” floor=”off” floorHeight=”42″ lightRotate=”off” Help=”off”] [/canvasio3D]
Both are easy to print. Use at least 15% infill and, as I said before, better not use PLA since it is relatively brittle. ABS deals better with impacts, and I suppose Nylon does as well. Layer adhesion is very important here, so I usually print at 10º over the recommended temperature and at standard or lower speeds to prevent warping (luckily it’s not a very big print). No support is needed for any of the pieces.
If you don’t have a 3D printer use a service such as 3Dhubs (it lets you send a design to someone geographically close who has one and he prints it for a fee).
Obviously I recommend forest green for the color, but props to whoever sends a picture of him using a pink one on a real match. Normal green also exists and is also easier to source, but it is very bright for my taste.
Assembly of the sound grenade
Start by inserting two nuts in the lateral holes of the top half. If they don’t fit, tear some plastic with a knife or tweezers. You can use glue, since this nuts will stay here permanently.
Cut two pieces of threaded rod at 76 mm length. Remember to insert a couple nuts before so that, after making the cut, you can screw them off to repair the thread on the extremes. After cutting, insert the rods inside their holes in the top half of the grenade, so that they get screwed into the nuts you lodged before. You can also use glue in this step, since the rods always stay in the top half while it is only the lower half that is removable.
Now you could insert the bottom half and screw the remaining two nuts to make sure that everything fits nicely. However, don’t use glue here since you still have work to do on the electronics front.
For the circuit that actually makes this a functional sound grenade, check out the post:
Sound grenade for Airsoft [Part 2: Electronics]