When it comes to DIY guns and cannons, while there are certainly many options, there is nothing more quintessential than the potato cannon.
Recently, our manufacturing team set out on a mission to create the perfect potato cannon. We were given the better part of an afternoon to design build and test our cannons with an overall budget of $200 per team. The result of this grand engineering conquest resulted in one triple-barreled eardrum-shattering potato cannon, and another duct taped cannon that was quite the disappointment. Here’s what we did right, what we did wrong, and how you can build the perfect potato cannon.
To design a potato cannon, all that is essentially needed is some PVC parts and a flammable aerosol. You can always over complicate the build and maybe see some minor improvements, but generally, it’s better to stick to the tried and tested methods. I won’t lay out the list of materials needed here, but a quick Google search will yield you plenty of links to guide you along the build. However, there are 2 main components of a potato gun: the combustion chamber and the barrel. The combustion chamber usually has a barbecue lighter to ignite the combustible gasses sprayed inside, and the barrel is essentially a long length of PVC tube. You can develop a cannon of virtually any size using this method, but you want to use a ratio about 2:1 for the combustion chamber volume to barrel ratio. Keeping these components and design criteria in mind, let’s examine our particular designs in their success and failures.
First for the failure. I sit here writing this coming from the team that created the failed cannon. I console myself with the thought that failure is a necessary part of engineering, right? Well, at least that helps me sleep at night. Our team created a single barreled potato cannon that stuck with the classic design. Our combustion chamber was made from 3 inch PVC and the barrel of 1.5 inch PVC. We made some on the fly design choices that ultimately hurt us in overall performance. We opted for a longer barrel and combustion chamber design, assuming that it would help range. However, the longer combustion chamber ultimately resulted in difficulty getting the correct air fuel mixture to ignite. Potato cannons may be easy to build, but to be successful you have to develop a perfect process of getting the air-fuel mixture perfected. The longer barrel also meant that there was more time friction forces were engaged with the potato projectile. This would’ve been okay if we had optimized the ratio of the combustion chamber to barrel, but this was overlooked in the hustle of design. We ultimately got our gun to fire, but only twice, and in a rather disappointing display of range and noise.
Now onto the glaring success of a potato cannon built by the other team. I promise I’m not bitter. This team delivered what was essentially 3 potato cannons strapped together. Rather than spend time creating one system that launched 3 projectiles, they created 3 versions of everything and strapped it together. This resulted in the impressive ability to simultaneously launch three taterjectiles (yes, I did just make that up), hundreds of yards on target. Aside from the fact that this cannon consistently worked, it was about as loud as a real cannon. What ultimately made this cannon so loud was that it was well sealed, the barrel to chamber ratio was near perfect, and the air-fuel mixture was on point. Optimizing all of these design criteria resulted in what I would consider a near perfect potato cannon considering that we only had 4 hours to build them and a limited budget.
Here’s a video we recorded of the triple barrel gun firing. Consequently, it was also recorded on a potato.
So, what can we learn from our failures and successes?
When designing a potato cannon, you need to take into account the volume ratios between the barrel and combustion chamber. You also don’t want your combustion chamber to be too long in order to maintain a proper air-fuel ratio. You can use most aerosols as fuel, but take some time to find one with the widest range of flammability ratios if you are looking for consistency. We found 2 sprays of carburetor spray to work well for us, but it will differ by design. Ultimately, take time to research and design your potato cannon. Select the criteria that are important to you and design around that.