Intro: High Velocity Vortex Cannon
In this Instructable I'll show how to make a high velocity vortex cannon that runs on propane. I built this project as an upgrade to one of my earlier vortex cannons which was significantly harder to make, and required a more complex procedure to fire as it used a burst disc to help build pressure in the chamber. This new cannon uses a propane torch as it's fuel source, which mixes the fuel and air in the perfect ratio to be highly combustible such that it does not require a burst disc to provide back pressure during combustion. This cannon can be fired quickly and easily.
There is a video tutorial covering the entire process to build this cannon which you can watch above!
When building this cannon I had it in mind that it would be an excellent device for such tasks as shooting frisbees out of trees, as I have a small disc golf course in my backyard. A vortex cannon fires only a slug of air, so there is no solid projectile that will come back down to earth and potentially land on a neighbor's head.
Parts used in this project:
- Plastic Landscaping Trim (AKA Terrace Board)
- Bernzomatic TS8000 or an equivalent trigger start torch
- 3" Sch.40 PVC Pipe
- 1/2" Sch.40 PVC Pipe
- 1/2"x1 1/2" PVC Adapter
- 1 1/2"x3" PVC Adapter
- 2"x3" PVC Adapter
- Plastic Funnel
- Duct Tape
- Fiberglass Reinforced Tape
Step 1: Preparing Terrace Board for the Cannon Barrel
If you've seen a vortex cannon in science class you're probably expecting a garbage can with a hole cut in the bottom and a diaphragm on the back. While you can make low velocity vortex rings this way, to make a really high power slug of air a cone shaped barrel is the way to go. Making such a barrel can be a difficult task. In previous iterations of this cannon I used fiberglass to form a cone over a paper mold; a messy process that is likely to have you breathing toxic resin fumes and spending quite a bit of money on materials.
For my new design we'll be using a roll of plastic terrace board, 4" wide by 40' long. Terrace board is sold in slightly smaller rolls which I have found work just as well. The 40' roll might be overkill but I decided I may as well go big for the tutorial.
To make a cone from this roll of plastic the first step is to secure the outside layer so it won't unravel once the straps are cut that bundle it together on the store shelves. We need the outside layer secured, but the inner portion of the coil free to be pulled out. To do this the simplest method is to wrap the roll in fiberglass reinforced tape, but an even more secure method is plastic welding.
There are only a few types of plastic that can be safely welded without giving off horrible chemicals, and fortunately HDPE, high density polyethylene is one of them. HDPE is a close relative to paraffin candle wax, and when burned the similarity is apparent as it smells just like a blown out candle.
Using a torch on low heat we can melt the outer edge of the roll until the plastic pools and begins to merge into the layer beneath. To make sure we only melt the very edge of the roll a piece of thick metal (I used a wrench) should be placed where we would like the melting to stop. Once the plastic has been sufficiently melted together and cooled it should be strong enough that we can cut the straps on the roll without it unraveling.
Safety note: Though HDPE burns cleanly compared to other plastics, it is still wise to weld in an area with a lot of ventilation. It's best to avoid breathing smoke from even the cleanest forms of combustion. If the smoke stinks like a burning tire or is marked with something other than "HDPE" or "LDPE" it's not a safe plastic to weld and you should use a different method to secure the roll.
Step 2: Pulling the Cone
With the roll of plastic welded or bound by tape, it now needs to be suspended in the air from it's outside layer. I did this by using fiberglass tape to form straps, then hung the roll from my ceiling with a chain. I'm aiming to turn this roll into a cone that expands at roughly a 14 degree angle, similar in shape to my original cannon barrel seen in the image above.
It can be difficult to start expanding the cone because of friction between layers of the plastic roll, but using a pair of pliers to twist up the center slightly can provide relief and allow it to go more smoothly.
By eyeballing the spacing between each layer of the cone as it's expanded downward we can make the incline of the cone consistent from top to bottom. It's not terribly important to be precise in this process, so long as we get somewhat close to a 14 degree angle of expansion.
Step 3: Securing the Final Shape of the Barrel
Once the shape of the cone looks adequate to operate as the barrel for the vortex cannon it can be secured permanently by heating nails red hot, and pressing them through each layer of the plastic into the one beneath. This is done in three rows evenly spaced around the circumference barrel. Doing so should keep the cone very rigid, and the nails poking through the inside wall do not seem to hinder the formation of the vortex.
To bring the cone to a smaller point the end is first trimmed if there is any part of the roll protruding from where it was pulled into shape, and then a section of a plastic funnel is fitted over the opening to give a smooth transition from barrel to what will be the chamber. This section of funnel should narrow to about a 1.5" opening, and be secured to the cone with duct tape.
Step 4: Mounting the Barrel
As an optional step, I secured my barrel to a sturdy tripod using bolts and a spare quick release plate. This will allow the cannon to be aimed without my having to hold it.
Step 5: Building the Combustion Chamber
The fuel source of my cannon will be propane from a TS8000 torch, with an auto igniting trigger that will also serve as the ignition for the vortex cannon.
To attach this torch to my chamber and then to my cannon I use a series of PVC parts. The nozzle of the torch fits inside 1/2" PVC pipe, so I use a series of PVC adapters to reduce a 3" diameter pipe to a 1/2" opening. The above image shows all parts assembled. A series of adapters reducing an 8" long section of 3" diameter pipe to the 1/2" opening on the left, and a 3"x2" adapter reducing the other end of the chamber to a size that will fit over the end of the newly made cannon barrel.
With these parts held together with PVC primer and cement, the 1/2" opening slips over the end of the torch and the chamber is ready for use. This completes all necessary components of our cannon.
Step 6: Firing the Cannon
To fire a vortex from our cannon the chamber is slipped over the end of the barrel. It requires only light pressure to hold it in place, as this cannon does not get up to significantly high pressures when fired. Much of the acceleration of the vortex occurs in the barrel rather than the chamber. By holding the trigger of the torch down partially gas will begin flowing into the chamber and barrel of the cannon. This should be done for 5 seconds to provide enough fuel, at which point the trigger of the torch can be fully pressed to spark the igniter. A vortex should be formed from the resulting combustion which will travel at a great velocity and stay coherent enough to knock over objects over 100 feet away.
Safety notes: This cannon is LOUD! Ear protection is required. It is also wise to wear safety glasses in case of dust or sparks being thrown around. I did not wear glasses in the above images and that was foolish. Do not follow my example in that way. Also note that there is a small risk of starting a fire with this cannon. The flash of fire is very brief and not capable of igniting most flammable objects, but caution is still advisable not to use in dry environments.
Step 7: Making Vortex Rings Visible
Vortex rings are usually invisible, and as such this cannon does not put on much of a show by default except in how it effects the target. As an extra upgrade to this cannon a fog machine can be piped into the barrel so that the vortex rings carry fog along with them. This sends out high velocity smoke rings which are great fun to watch.
Even more interesting is to use a laser line module to broadcast a narrow beam of light across the flight path of the vortex. This enhances the visibility and puts on a surprisingly good show.
Safety note: High power lasers are extremely dangerous to your eyesight. Use caution and note that lasers from disreputable suppliers can be higher power and more dangerous than advertised.
Step 8: Conclusion
I am very satisfied with the outcome in building this new vortex cannon. The ease of use could not be better, and the results using a fog machine and laser are incredible. I hope you have enjoyed this project, and please be sure to watch the full video tutorial to see it in action.