Generic Disclaimer: I'm in no way responsible for anything anyone decides to build/create/destroy with anything from this instructable. Don't even try to build anything related to this if you don't know exactly what you are doing. If you are unsure about anything in a build process with compressed air involved, seek help of a qualified individual or just don't attempt it at all. Be responsible and use common sense :)
A little background info.... The idea to make this particular gun design was kind of a spur of the moment idea. I had some small pieces of PVC laying around and an extra sprinkler valve so I decided to go at it with what i had(save some money too). Most of the potato guns I make are usually larger diameter barrels (1" - 4") but this time I wanted to go small with it. The diameter of the barrel I decided to use was 1/2" and the air chamber was 2". I wasn't sure how well this would perform but it seemed worth a try. I will try to be as specific as possible in the build process. If you don't like part of the design or have any feedback, please let me know. I do like to hear peoples opinions, good or bad.
Here's a materials list of the items I used in my version. Depending on the size you wish to build, this list can change dramatically.
This is not a complete list, these are just some of the main parts.
1/2" PVC Pipe
2" PVC Pipe
3" PVC Pipe
2 - 3" PVC Couplers
1 - 3" PVC Cleanout with Plug
1 - 2" PVC Cleanout with Plug
2 - 2" PVC Coupler
1 - 2" to 1"threaded bushing
1 - 1" by 1" threaded pipe
1 - 24 Volt Sprinler valve
1 - 1" threaded to 1/2" slip Coupler
4 - 10" Hose Clamps
2 - 4" Hose Clamps
1 - Cheap Airsoft Gun
1 - SPST Pushbutton Switch
3 - 9 Volt Batteries
4 - 9 Volt Battery Terminals
Miscellaneous Pieces of Wood
You'll also need some pvc cleaner, pvc glue, expanding foam, liquid nails, and miscellaneous building tools.
Also, sorry if some of the pictures are crappy. The best thing I had to take pictures with during the first part of the build was a crappy cell phone.
Step 1: Air Chamber
For the chamber, I used:
1 - 2" PVC Cleanout
2 - 2" Couplers
1 - 2" Slip / 1"Threaded Bushing
There's only one way those parts can be put together so it's a pretty easy step. Make sure to be generous with the cleaner and glue. You want to definitely make sure that you are getting a good air-tight seal on all parts of this project. Always wait the recommended curing time for the glue you are using. I've had caps pop off on parts before and it has the potential to be very dangerous.
The purple on the PVC is the primer in case anyone is wondering.
The next part has to do with the end cap. There can be many different ways and connectors for the end cap but it's all the same basicprinciplee. I decided to use a quick-disconnect fitting on the back of mine. I chose this because this can help with refill times (just keep it connected) and I don't like using tire valves. This is most likely the place where a leak will form in the air chamber. It can be challenging to get a good air tight fit on this. I found a pretty easy way to fix this by heating up the couple part for the inside of the cap to a very hot temperature. It screws on rather loosely (it expanded) but it melts the PVC on the inside and gets a good seal. There are possibly better ways of doing this but this way works for me.
After letting my glue cure it was time to put the cap in place. I didn't use plainTeflonn tape on the threads. I used tape specifically designed to seal gas. This tape is a little thicker and in my opinion has been more durable and reliable than plainTeflonn tape. But I'm sureTeflonn tape will probably work just fine.
At this point, the chamber can be considered done. I would recommend testing it before using it though. You can just put a 1" plug on the other end of the chamber and dunk it in a bucket of water to check for leaks. Be very careful with this also. If the chamber blows up in a bucket of water, it can be a very big explosion. My chamber was good andair tightt. I tested it up to 100psi. So I'm good to move on.
Step 2: Carrier
The first part is to figure out where to cut a hole for the air valve. I'm using a 24Volt sprinkler valve for mine. Depending on the valve you are using, this part can vary or not be needed at all. I didn't worry about making the hole look good since it will be covered up in the final design. The sprinkler valve ended up barely fitting in the 3" pipe. I got lucky this time I guess.
Step 3: The Barrel
Step 4: Combine the "guts" and the Carrier
Step 5: Cover the Valve
Oddly enough this was the hardest part of the build. I just kept having problem after problem of the wood breaking or I cut the wrong spot. Luckily I got it done though and secured. I had built the box a little too big so the hose clamps I had wouldn't fit. Rather than rebuild that demon box I just daisy chained some smaller clamps to make it work. I may go back and change it later.
I didn't secure the box tightly because inside is where the batteries and wire will be contained. That will be put in later on so I just screwed the clamps down enough to keep it from moving around.
Step 6: The Handle
The first part is to get the slide off the gun. This can normally be done by removing a few screws but if all else fails a Dremel will always work. Once the slide is off, you want to reinforce the front part of the gun by gluing something round inside the groove to keep the clamps used to secure it from smashing the gun. I've used wooden dowels, bolts or even the metal weight that sometimes comes in the airsoft gun for this. All of these worked fine.
As for the trigger, I used a SPST momentary pushbutton switch I got from allelectronics.com. It fit perfectly in to the hole left by the orginal trigger. All I did was screw the switch in with the provided screws.
Mounting it is very simple. I used hose clamps again (I like hose clamps) to secure it to the gun. The tip of the airsoft gun went right up to the box covering the valve. This is so I can run the wires though a drilled hole for the switch. It goes straght from the box to the handle without having any exposed wires.
Step 7: Power Supply
Since this is a basic solenoid on the valve, polarity doesn't matter. Just hook one end of the batteries to one side of the switch and the other end to a side of the valve. The of course complete the wiring by hooking the free side of the switch to the free end on the valve. You can attach the batteries on the inside with glue, tape, velcro, zip ties....whatever you want really. You just want to make sure they are secure.
Note: You can use whatever kind of batteries you want for powering the solenoid as long as it works. I've used anywhere from a lot of spare AA's I had to a sealed lead acid battery. As long as it will pull the solenoid it should be fine. Rechargeables are great too. You can even build in a chanrger to the valve cover so you can just plug it in without taking anything off the rifle.
Step 8: Paint
Step 9: Attachments
Step 10: Fin
The good thing about this is that it is scalable. I'm sure a larger version would work much batter but you need to lay down some more money for that. Overall I'm pleased with it. Any questions or comments, please let me know. This was my first instructable so I'm hoping to do more in the future.