Introduction: Propane Pop Gun
This fun toy could be customized and decorated to be a prop for a number of different costume ideas. My friends and I made a few of these to play with during a regional Burning Man event in Texas recently. We had a lot of fun with them.
This project uses methylacetylene-propadiene (MAPP), a highly flammable blend of propane gas. I'm not responsible for you or what you do with this. It shoots fire! Be careful. Continually monitor the hose for any hot spots in the hose or the bottle assembly. Shooting it continuously will increase the likelihood of melting but we were shooting ours a lot and had no problems.
From a design stand point, one of the goals in designing this was to come up with a fast and easy to assemble version. The same idea could be used to make something much more elaborate. I'm excited to see what others do with this idea.
I would like to tip my hat to Volcano Al, a fellow that I met at Burning Man this year. His Plasma Popper was my inspiration. Thanks for enduring all my questions, Al. My friends and I are having a blast with this.
As an additional safety concern, don't point this at people, especially the police. Even though there is no projectile, or any real danger unless the person is very close, this pop gun can be loud and threatening. The cops might think to shoot you before finding out that this is harmless. With that said, Have Fun!
Step 1: Supplies
1 Bernzomatic TS4000 torch
1 can of MAPP gas or propane. Be sure you get a can that fits the torch. They are often sold together.
10’ of heavy vinyl tubing with 5/8" or 17mm ID
2 wide mouth plastic bottles (gatorade)
5’ of 2” pvc pipe
50lb 12” zip ties
Heavy duty pruning shears
Step 2: Cut Bottles
Cut a hole in the middle of the bottom of one of the bottles just big enough to push the tubing into it without kinking the tube. The hole should not be a perfect fit but close enough to hold the tubing. Outside air is drawn into to the bottle assembly through the ill fitting seal around the tubing. This is important for getting a good pop. Cut this bottle first. If you mess it up, you can always just cut the bottom off of this one and try again with the other bottle. In my opinion, this may be the hardest step because the plastic is thicker in the center at the bottom. Take your time and be careful not to cut yourself. Don't try to do this with a knife. I used some heavy garden shears.
This step can be simplified by using only one regular plastic soda bottle. It will take a little effort but you can stretch the tubing over the opening of the bottle, then cut a hole in the bottom of the bottle. This option will save you some work but the resulting POP will not be as loud. An example of that can be seen here. https://www.youtube.com/watch?v=8KSHcGHiY0M
Step 3: Build That Nozzle
Care fully line up the mouth of each bottle and tape them together well. Wrap the tape as tight as you can get it, keeping them lined up. I found it easier to have a friend hold them together while I tapped them.
Step 4: Get Ready to Test Fire.
Before you do this step, using caution, try out the torch to get used to using it. Slide the tubing over the tip of the TS4000 about 1” past the beginning of the tip. Don’t secure it with zips just yet.
Step 5: The Tubing Goes Into the Bottle Assembly
Insert and position the tubing so that the end of the tubing is a couple of inches inside the first bottle and as centered as possible.
Step 6: Testing the System.
By this point you should have your bottles cut and assembled and the torch assembled, connected by the length of tubing. Being extra careful not to burn your face off, try it out.
Turn on the gas knob. With one hand, hold the tubing with the bottle assembly away from your body and anything flammable and the TS400 with the other hand. Push the ignition button about ¾ down and count to ten (you will hear the gas) Push the button in the rest of the way. The torch will ignite the gas in the tube and you will see a little blue ball of fire exit the tubing. It will expand in the bottle assembly with a satisfying ‘POP!’ Play around with it, change the depth that the tube goes into the bottle, experiment with timing before firing. Get a feel for how it works and what makes the best results.
Step 7: Secure the Torch to the Pipe.
Make sure the TS4000 is turned off. Zip it to one end of the pipe. Duct tape over the zips to further secure the fuel can to the pipe.
Step 8: Secure the Bottle Assembly
Zip your bottle assembly to the end of the PVC pipe. Notice how I used the grooves in the bottle. You’ll want this to be snug but not tight enough to squish the bottles. The bottle assembly works as a de Laval nozzle. Learn more about that here.
Step 9: Secure the Tubing
Attach tubing to the torch with zip ties. Snug these real tight.
Notice the blue arrow and the circled area in the photo. At the torch tip connection, try to avoid this. Route the tubing so that the fire naturally chases out of the tube without encountering any sharp angles or kinks.
Depending on how you position the rest of the tube, it may cause this connection to bend a little. This can cause a hot spot that could melt. If you see this, fix it by repositioning the rest of the tube. Now secure the tubing to the pipe but don't tighten the zips too tight. No kinks or very narrow spots. You will find that the tubing will want to remain coiled. You can secure it to the pipe to make it go the way you want but I found it easy to get an interesting path using the natural curves. Just make sure that you can get the opposite end of the tubing centered in your bottle assembly.
Step 10: Variation!
Now that you have built a Propane Pop Gun, you can decorate it however you want.
I also made a double barrel pop gun. It has two separate systems made just like the single shot pop gun described in this instructible but mounted together on the same pipe. I wanted it to look more like a weapon so I wrapped the pipe and fuel cans with black tape before assembly. This double model turned out to be much heavier than I expected it to be but looks very impressive with two little fire balls instead of just one. I may put a shoulder strap on it to make it easier to handle.
Step 11: Your Cat Will Not Like This Project
This is a picture of Reynard sitting atop some catnip in a bread pan. He is proof that you can be awesome even if you were not born with a tail.
Remember, while this design is safe, there are some dangerous elements. Be careful. If you decide to make one, please be sure to let me know, especially if you come up with a very cool way to decorate it. This is my first Instructible and I am very happy to have finally done one. Enjoy!