Compressed Air Gun

Imagine building your own gun (It shoots ping pong balls, so it is ok by the way). That's basically my project: A compressed air gun that propels a small projectile. This project was inspired by LoneSoulSurfer's Compressed Air Blow Gun and was created by me, Mithil Srungarapu, for my Principles of Engineering class taught by Ms. Berbawy. Special thanks to Nathan Lintu for helping me design the propulsion mechanism and Ms. Berbawy for funding and guiding me through this project!

If you are interested in this project and want to create your own version, feel free to follow along! You can copy my approach completely or tinker with it to satisfy your needs! It's all up to you! This project is beginner-friendly and inexpensive, so I highly suggest it for any ability level. This project features Computer-Aided Design (CAD) in Fusion 360, 3d-printing on a Prusa (feel free to use an alternative 3d printer), basic circuitry & soldering, and best of all: the opportunity to work with power tools.

Materials:

• 1/2 inch PVC pipe
• Solenoid valve
• Electric bike pump (Comes with swim ring nozzle, required for regulating pressure)
• Micro lever switch
• 2 x 3/4 inch female thread to 3/4 inch coupling (Make sure you choose the 0.75-inch option)
• Electrical wire
• 3/4 PVC socket cap
• 9-volt battery
• 9-volt battery holder
• Paint (I prefer white, light blue, or black)
• 3/4 inch ping pong balls

Tools & Assembly:

• (Hack) Saw
• Sandpaper
• Drill
• Paint Brush
• PVC Glue
• Hot Glue Gun
• Super Glue
• Dial Caliper
• Pliers
• USB
• Wire Stripper
• Wire Cutter
• Soldering Kit
• 3d Printing Access
• CAD Software (Fusion 360 recommended)
• 3d Printer (Prusa recommended)
• 3d Printer Filament

That's a great question! If you are interested in knowing the answer, read this section. If you want to go straight to the project, do just that! This step is optional!

The Compressed Air Gun is broken into 3 parts: the barrel, the pressure chamber, and everything else. The projectile, or ping pong ball in this case, resides in the barrel. There is no force pushing the ball, so it stays still at the back of the barrel. The goal is to generate force in the pressure chamber and release it into the barrel, propelling the ball outside the barrel and into the air!

That brings us to 2 important questions: How would we generate force in the pressure chamber and how would we "push" this force into the barrel?

Generating Force

An electric bike pump will be inserted into the pressure chamber and push air inside so that inside the pressure chamber, there will be lots and lots and lots of air. Since there is so much air inside a small amount of space, the air will want to spread out and expand. However, the pressure chamber will be completely airtight, so the air won't be able to leave, creating an intense pressure inside the chamber. If a hole was to be made in the pressure chamber, the air would immediately release with a great force. This is the force that will push the ping pong ball. However, that still brings the question of how is the pressure released into the barrel if the pressure chamber is completely air-tight?

Applying Force Onto Projectile

For this project to work, it is really, really important that no air leaks from the pressure chamber because if this happens, the pressure chamber will not be pressurized and will be unable to generate any force onto the projectile. So this begs the question: How can we release the pressure from the pressure chamber into the barrel if we need it to be completely airtight? To solve this problem, we can use a Solenoid Valve.

A solenoid valve can be thought of as a door. It has the ability to open and close, which will allow us to direct air through it, allowing the pressure from the pressure chamber to as a force, propelling the barrel. If you want more information on solenoid valves and how they work, check out this amazing article!

The solenoid valve or "door" as we can think of it, will be placed between the barrel and air chamber, opening and releasing the pressure when the circuit is activated. How does this circuit activate, you may ask. This will be covered in the electronics and circuits section of the Instructables. Let's get started with the project now!

For this project, we will make a barrel and pressure chamber out of PVC pipes. Take the 1/2 inch PVC Pipe and place marks on it at the 4.5-inch and 10-inch marks, so that you can cut sections of that size. I suggest using a pencil and rotating across the entire PVC pipe, so the mark can be seen from any view of the PVC pipe.

Now, for the fun part! Take your saw and cut the PVC pipe into the parts based on the markings. I recommend using a Hack Saw if possible but any saw will do the job. Additionally, it will be significantly easier to cut if you have a clamp to hold the PVC pipe in place while you cut. It is important for you to cut the PVC in a straight line but don't worry if it's not perfectly straight because after cutting, sand down the ends of the PVC sections until they are flat.

Painting your craft is optional. Apply 2 thick layers of an oil-based paint over the PVC so that any markings or smudges cannot be seen. Paint any designs or shapes on the PVC sections. This is your project so you get to choose how it looks, so go crazy and have fun!

Before starting this step, please download Fusion 360 (or an alternative CAD software) and PrusaSlicer (or an alternative CAD software). Please ensure that you have access to a 3d-printer.

For this step, you will create 2 of the same custom adapter to connect the PVC bodies together. Specifically, each adapter will connect from the coupling to the solenoid valve. Since we need extremely precise measurements and a custom fitting, we will 3d-print these. I have attached pictures of how it looks as well as the STL file that you can take a look at. I highly suggest that you attempt to CAD it yourself by using a dial caliper and measuring each of the parts that it connects to, so you can gain real experience in CAD. However, this is optional and all up to you!

The adapter has 3 parts: The connection to the solenoid valve, the connection to the coupling, and the connection between the 2 connectors. Take a look at the various pictures to get a better idea of what it looks like.

After you finish the CAD for the adapter, export it and place it into a slicing application. Each CAD program has a separate method of exporting the file, so search it up if you have difficulty. For this tutorial, I will be using Fusion 360, and you can take a look at Fusion 360 exports on this link.

Open your slicing software and complete the introduction information. Import the adapter CAD into your slicing software. Set the presets in the first picture. Once you are satisfied, click "Slice now". Use your USB to export the G-code of the sliced adapter CAD. Plug the USB into your 3d-printer and click "Start print".

After a few hours, your adapter should be complete. This adapter will act as a test print for you to know whether everything worked out properly. Use pliers to remove the supports from the print and test if it fits snuggly into the solenoid valve and coupling. If everything works properly, continue on to the next part. Otherwise, try tinkering with the CAD file or slicing settings until you get the desired result.

For the final print, import 2 adapters onto the slicing software and ensure that they are close by but not in contact with one another. Similar to the first time, ensure that the slicing settings are accurate. Use the 3rd picture for reference. The only difference is that in the final print, we will be using Prusament PETG instead of Generic PETG. Use the same techniques from the test print to get the final print started.

Once it is complete, use pliers to remove the supports and test to see if it fits.

Use the (hack) saw to cut the swim ring nozzle and insert it inside the PVC air chamber. Drill a hole into the PVC air chamber. Insert the swim ring nozzle from the inside of the air chamber upwards until it pokes outward. Use hot-glue to ensure that the air is pumped into the air chamber with no leakage and that the pump is attached to the air chamber.

Now, connect all of the parts together. Get the tool that can be found inside the PVC glue tin can. This is what we will use to apply PVC glue. Apply a small layer around the end of the air chamber PVC. Immediately place the coupling over and allow it to dry. Repeat this process for the barrel and coupling as well. That was the easy part! Next, we will do the same thing to the adapter but be very careful because the threads will make it hard to stick. Apply PVC glue around each of the threads and then connect the ends to the coupling and solenoid valve. Make sure to do each connection and gluing separately instead of gluing all 4 ends.

As talked about in the introduction section, the opening of the solenoid valve allows air to flow through. But how does the solenoid valve open? This will be solved with circuitry. A micro lever switch will act as a trigger, opening and closing the solenoid valve, propelling the ball with simply a click. Take a look at the third image to understand how all the electronics are connected. There is a battery that powers the system and the connected wires will send electrical currents from the switch to the solenoid valve.

For the wiring, make sure to use a wire stripper and cutter to get wires of your desired length. The switch has 3 numbered silver extensions. This is where you will connect your wires and solder them. Additionally, the red connected wires should be soldered as well. This will ensure that the wires are permanently connected.

Next, hot glue the battery pack and trigger onto the air pump as shown in the 2nd photo. Make sure to place the 9-volt battery inside the battery pack and ensure that the air pump is fully charged.

With that completed, start testing the trigger and see if the solenoid valve opens and closes. It will be very difficult to detect this visually, so listen closely to the opening sound.

Place your ping pong ball at the end of the barrel and pressurize the air chamber to 12 psi.

For the fun part, press the trigger and the ball will shoot out! I hope you liked this tutorial. I had a lot of fun building this project and writing instructions for people like you to make it yourself. Feel free to comment on this Instructable if you have any questions, want advice, want to show off your version of this project, have a funny joke, or anything!