Step #1: Safety WarningPrevNext
This should really go without saying, but POTATO CANNONS ARE NOT SAFE! If you do not handle them properly, they can seriously injure or kill you. They can also cause great damage to property. Mixing chemicals in a closed container can create high pressures that can cause the container to explode. Build this project at your own risk. Please be safe. Have responsible adults nearby at all times. Don't do anything stupid.
Also, it may not be legal to fire a potato cannon in your area. Be aware of your local laws.
Step #2: The Baking Soda and Vinegar ReactionPrevNext
- Vinegar is a weak solution of acetic acid (usually 5 percent). Baking soda is powdered sodium bicarbonate. When one molecule of acetic acid reacts with one molecule of sodium bicarbonate, it produces one molecule of sodium acetate, one molecule of water and one molecule of carbon dioxide. The carbon dioxide is what produces the characteristic foaming and bubbling. In a closed container, the carbon dioxide that is produced builds up pressure inside the container. This pressure can be used to send a potato flying through the air.
- The ideal ratio of vinegar to baking soda is 14 milliliters of 5 percent vinegar for every 1 gram of baking soda. This can be approximated to about 1 cup of vinegar for every tablespoon of baking soda.
- All these chemicals are generally considered to be non-toxic and safe (in small quantities). To clean up, everything can be safely poured down the sink. Although it is always a good idea to dilute any chemical that you are disposing of.
Step #4: Cut the PipePrevNext
- The reaction chamber is made from a 2' long piece of 4" diameter pipe. The Barrel is made from a 2' long piece of 2" diameter pipe. There are also 2 small pieces of 2" diameter pipe that connect the reducers to the ball valves that are each about 3" long. These dimensions do not have to be exact. Feel free to modify them — larger reaction chambers and barrels will give you more power, but they take up more space and can make the cannon difficult to handle.
- I used a hack saw to cut the pipe to the appropriate lengths. I recommend clamping the pipe to a table to keep it from moving while you are cutting. Some hardware stores may cut the pipe for you when you buy it.
Step #5: Dry Fit the Pieces TogetherPrevNext
Before gluing anything, you want to fit all the pieces together to make sure that the spacing works. This will also give you an idea of where you want to place the pressure gauge. If any pieces get stuck together and don't want to come apart, you can use a rubber mallet to gently separate them.
Step #6: Glue the Pieces TogetherPrevNext
- Pieces of PVC pipe are fixed together in a process called solvent welding. The 2 pieces of PVC are essentially chemically melted and cemented together. This process should be done outside or in a very well ventilated area.
- First make sure that all the surfaces are clean and dry. Then apply a coat of purple PVC primer to all the surfaces that will be connected. Follow the instructions for the primary that you are using. You may need to apply a second coat of primary to some areas.
- Then apply a coat of PVC pipe cement to all surfaces that will be connected. Again, follow the instructions for your PVC cement. You may need to apply a second coat to some areas. After applying, the cement quickly sticks the 2 parts together. Once the pieces are inserted all the way, turn them 1/4 turn. Hold the 2 pieces together for 30 seconds. After assembling all the pieces, let it sit until it is fully cured.
Step #7: Connect the Pressure GaugePrevNext
- The pressure gauge can be mounted to any point on the reaction chamber. I recommend mounting it at one end near the ball valve.
- Start by drilling a small hole through the side of the PVC pipe. Then re-drill the hole with larger bits until the hole is just smaller than the fitting on the pressure gauge. You want the pressure gauge to fit tightly in place so that it doesn't blow out when the tank is pressurized. You may need to smooth out the sides of the hole with a file. Then apply plumber's tape all around the threads of the pressure gauge. Using a wrench, screw the pressure gauge into the hole until the threads are just sticking out of the top.
Step #10: Load in the Baking SodaPrevNext
- As soon as the baking soda comes in contact with the vinegar it will start to react, so you want to add the baking soda as quickly as possible. The best way that I have found to do this is to make a small packet of baking soda by wrapping it in a thin napkin.
- Take 1/4 cup of baking soda and place it in the center of a napkin. Then lift up the sides and gently twist them so that the baking soda is wrapped into a small packet that is about 1" in diameter. Tear off any excess napkin on the end.
- Open the ball valve on the back of the reaction chamber and insert the whole baking soda packet into the tank. As soon as the baking soda is inside, quickly close the ball valve to seal the chamber.
Step #11: Gently Shake the Chamber to Help the Reactants MixPrevNext
- The reaction will happen most slowly if all the baking soda stays in one big chunk. So gently rock the chamber back and forth to help break it up and mix better. As you do this keep an eye on the pressure gauge. Once the pressure stops going up, the reaction should be mostly complete. It should get up to about 20 PSI.
- Never let the pressure get too high. I recommend keeping the pressure below 1/2 of the capacity of the lowest rated component. In this case, the weakest component was rated for 80 PSI, so I always kept the pressure below 40 PSI.
Step #12: Fire the CannonPrevNext
- Clear the firing range. Aim the cannon at your target. Grip the cannon tightly, then quickly open the front ball valve to fire the cannon. If everything performed properly, the potato should fly more than 100 feet. The final range will depend on the pressure in your tank, the size of the reaction chamber, the size of the barrel, the size of the potato, and the wind.
- The potato will also be accompanied by a large blast of liquid, smoke and foam.
Step #13: Clean the CannonPrevNext
- After each use, you need to clean out the cannon; you don't want any reactants left in the barrel or the reaction chamber, which can cause problems for the shot. Also, it is not good to let vinegar sit in the cannon, as this can lead to the parts wearing out prematurely.
- I dumped the remaining contents of the reaction chamber into a large bucket and rinsed out the whole thing with a garden hose. After cleaning out the cannon, you should be ready to load it and fire it again.