Intro: PVC Compressed Air Cannon
Earlier this year I decided to make an air cannon that incorporated an electrical launching system. I did some research and I had a bold plan. I wrote a list of what I needed and went off to Bunnings. I spent an hour with a Store Manager and two other staff who were unsure of what I was going to make with all the PVC pipes and parts but with their help, we eventually sourced everything I needed. The total cost of the materials was around $70 which was good value. I then used some parts I had at home to make my air cannon. I decided to do an instructables to share how I did it. I'm sorry I have no photos of the process but I've taken a'lot of photos of the parts and tools I've used as well as made a simple circuit design which you can follow. I will not be held responsible if you decide to build this and something goes wrong.
Build at you're own risk and be responsible. Check everything before use. Do your research before building this air cannon. Always use the correct pressure piping and glue. Wear safety glasses while firing and bringing up to pressure. Maximum pressure I would recommend is 50 psi. If you live in Australia do not use as a spud gun as it's illegal. Check if this is legal in you're country. Only use soft balls and home made paper or card board rockets. MAKE SURE YOU CAN CLEARLY SEE THE AREA YOU ARE LAUNCHING INTO IS CLEAR AND SAFE.
Step 1: What You Need
You will need:
(AU Links Only)
x1 Case Enclosure (Recommend you buy from a store)
x1 Small 3 connector Junction Box
x1 25mm solenoid
x2 50mm Pressure Pipe (AU- Class 9 / US-schedule 40)
x1 40mm Pressure Pipe
x2 50mm right angle joiner (Pressure joint)
x2 50mm End cap (Pressure Joint)
x1 40mm PVC coupling (Pressure Joint)
x1 50mm to 40mm reducing bush
x2 40mm to 25mm reducing bush
2x 25mm to 1" Valve Socket
1x PVC Priming Fluid
1x PVC Pressure Cement Solvent
x1 Tire valve insert
x3 Wire Screw Connector
x1 Pressure Gauge
x1 Red Momentary Switch
x1 On/Off Switch
x1 DC Power Jack Input (Make sure you buy one that suits your DC jack)
x1 Red Signal Lamp (Recommended)
x1 Piezo Buzzer (Recommended)
2x 9 volt batterys
2x 9 volt battery clips
1x Long extention cord wire
1x Large Plank of wood raised either side
x8 Cable ties
x1 Old 16-24v power plug
Spray Paint (Optional)
Step 2: Assembly
Get both of your 50mm Pressure Pipes and check that they are 1 metre long. Mark a line 70cm from the end of both pipes. Then get your hacksaw and cut down the line of both pipes. Use some sandpaper to clean up the ends of the cuts. Before you assemble the base you need to add the tyre valve. To do this you need to drill a hole just big enough for it to come through the inside of the T joiner. Angle your T joiner up and drill the hole in the correct position (Refer to photo above). Then feed your tyre valve inside the T joiner and make sure it's faced the right way when you put it through the pre-drilled hole. Then pull through tightly until you can see it is in the right position. Now you need to test assemble the base. Make sure the shortest pipes are between the cap and the right angle connector and the longer ends are fitted between the T joiner and the right angle connector. If you have trouble understanding refer to the design image above. Get your 50mm to 40mm and 40mm to 25mm reducer bushings as well as your 25mm to 1" valve socket and test fit them into the angled T joiner. Now you need to prepare the barrel. If you want to make the 40mm PVC barrel shorter you can but I left it as it was (1m). Get your 40mm PVC coupling and place it on the end of the barrel. Then get your 40mm to 25mm reducer bushing as well as your 25mm to 1" valve socket and give it a test fit. Make sure you keep your base and barrel separate.
Now you need to take the joins apart and prime the insides of each connection. Once they are all primed you can begin to glue the base. Start with both of the caps and slowly make your way towards the T. Once you've got both sides glued you then need to angle your T joiner up and put both sides of the base into the T. Then glue the adaptors onto the top of the T joiner. Make sure the base is level then you can move onto the Barrel. Glue all the parts together and leave the barrel and the base separate to set overnight.
Once its set use some teflon tape to screw on the solenoid as well as the barrel and make sure it has a good seal.
(MAKE SURE ALL YOUR FITTINGS AND PIPES ARE CLASS 9 OR ABOVE)
Step 3: Pressure Gauge
You now have the choice spray paint it but I recommend that you are careful because mine had air bubbles all over it. Once that's done you can now attach you're Pressure Gauge. To do this you need to find a place where its easily in site when you fill it with air. For this step I failed because I angled it straight up, so when you do this make sure it's angled back enough to be visible. My pressure gauge had its threads at the bottom but most of the ones I saw online had their threads on the back so make sure you fit it to its specific orientation. So now you can drill the hole. Measure the circumference of the threaded valve and drill it at least 2mm smaller. Before I screwed it in I got a file and filed out a little notch to help it screw in. Once you've done that use a fair bit of force and screw it in. Once its going in without a lot of effort unscrew the gauge and wrap the valve with teflon tape then re-insert it.
Step 4: Electrical
Before you start on the electrical get a board put two rises either side and use cable ties to hold the air cannon down onto the board. Now you need to set up the electrical circuit for the launching mechanism. If you want to only rely on the batteries I suggest you use the circuit without the light and buzzer to save power. But if you want to use the batteries sometimes but rely on the dc power as well as have a safety light and buzzer I would use the circuit with the light and buzzer (that was the one I used). I didn't lay it out great but the wire between the junction box and the main circuit will be the extension cord which can be as long as you want. The Blue wire is Ground which will go to the solenoid and the light, the brown wire is the launch power to the solenoid and the yellow/green wire is the power that goes to the light and is activated when the first switch is turned on. The buzzer will sit in the electrical box and will connect to the wire screw cap between the switch and button and the negative wire will go in the negative wire screw cap. Make sure you have a diode on the positive lead of the battery to stop power going from the dc jack into the battery. The small junction box will be mounted on the board and the light will need to go in the middle of the board. Drill two holes between the light and the junction box and thread through the positive and negative wires for the light as shown in some of the photos above. Put all the electrical components and wires into the electrical box then make a hole for the extension cord wire to go to the junction box. You may need to do some filing to shape some of the holes. Drill two holes and mount the switch and button and make a hole for the dc jack. I needed to use a file to shape the dc jack hole and finished it off with some glue to hold it in. I was able to find a 15v power plug off an old drill charger but if you don't have one go to an electric shop and buy one. Screw the light and junction box down and you're ready to test without air. If it works you've done everything right but if something is wrong have a look around and if I've done something wrong in the circuit leave a comment. Hope you like this instructable tutorial and if you do make this do your research and be responsible.