Firing potatoes 500 feet on a budget
The cannon in action
Since we had no final exam in AP Physics this year, my teacher made the (poorly informed) decision to let us all design and build our own final projects. The rules were simple, and we only had two main parameters to follow:
- Must have data to analyze
- Don’t do anything too dangerous
Obviously the latter was soon thrown out the window as me and my roommate decided to build a potato cannon. Our design was very simple, consisting of three main parts:
- A combustion chamber: Where the fuel would be ignited
- A grill igniter: Connected through a handle to the top of the combustion chamber, which would set off the fuel
- A barrel: Airtight to the potato, allowing for it to build up momentum before exiting the cannon
We started by creating a basic diagram of all the parts and ordering everything online and taking a trip to home depot.
| Quantity | Name | Notes | Price |
|---|---|---|---|
| 1 | 1-1/2” PVC pipe 24” long | $5.76 | |
| 1 | 3/4” PVC pipe 24” long | $3.16 | |
| 1 | 1-1/2” PVC pipe 4-6” long | $5.99 | |
| 1 | 3” PVC pipe 4-6” long | $4.71 | |
| 1 | 3” PVC threaded clean-out plug | $3.97 | |
| 1 | 3” PVC Spigot FIP adapter | $3.78 | |
| 1 | 3”x3”x1-1/2” PVC Sanitary Tee | $5.66 | |
| 1 | 3”x2” PVC bell reducer | $5.94 | |
| 1 | 1-1/2” PVC Street 90 | $3.59 | |
| 1 | 1-1/2” PVC glue cap | $1.65 | |
| 2 | 3/4” PVC glue caps | $0.82 | |
| 1 | Aqua Net hair spray | any high butane aerosol should, but aqua net gave us the best results | $3.19 |
| 1 | Sack of potatoes | relatively small; ~3in diameter MAX, will be cut down to 2in by barrel | $2.20 |
| 1 | Barbeque grill igniter replacement kit | $2.89 | |
| 1 | 2” long stainless steel screw | Free |
After assembling we initially used a spray deoderant, but were effectively unable to get the potato out of the barrell. We at first attributed this to a problem with the lighter, and decided to drill a hole in the bottom of the combustion chamber, and stick a normal butane lighter in the bottom. This setup ended up incredibly janky and, of course, didn’t work.
After this, to test the different methods we all “put on respirators”, filled the combustion chamber with fuel, and stuck the lighter in. After the boom was somewhat underwhelming we realized that the issue was likely the fuel, and covered the hole we had drilled after ordering a replacement. I’d read online that aqua net was really the one to beat, so we decided on that and came back later that day to launch some taters, this time with an added blast shield.
PS: Here’s the presentation for anyone who wants to look at the data