Build a potato gun!

Our loyal readers remember how in March 2008 we tested the potato cannon and, having come to it with complete enthusiasm, promised to build a more perfect model in the future. And three years later, we were again drawn to vegetable artillery. Last time, we were satisfied with the accuracy and range, and now we decided to improve the rate of fire. Recall: in order to charge our first classic cannon, it was necessary to unscrew the barrel, blow the breech with a pump, install potatoes in the barrel, apply gas from a spray can and quickly collect weapons.

Shells for loading into the store must be prepared in advance. They are cut from large potatoes using a piece of pipe with a diameter of 63 mm with sharpened edges. In the design of the gun, we used four types of pipes. A 63 mm pipe is used as a barrel. The combustion chamber has a diameter of 90 mm. The arc connecting the breech and tail is made of a 50 mm pipe. A rammer is made from it, which should go into the trunk and push potatoes into it. Finally, the store lintels are cut off from a 25 mm diameter pipe.

On a fully automatic cannon, we have not decided yet. Although such designs exist. They are controlled by a computer controller, and all servos reload all the recharging operations. The potato gun does not give serious returns, the energy of which could be directed to mechanical reloading, so we limited ourselves to reloading a manual but lightweight magazine with six shells, an automatic system for purging and supplying gas to the combustion chamber.

Turbo gun

To reload our gun, the shooter takes the combustion chamber back, holding on to a special handle. At the same time, a purge window is released from under the casing, which is exactly under the fan. The fan automatically turns on and blows the combustion chamber, filling it with air and freeing it from combustion products. At this time, the shooter turns the store, setting another potato opposite the entrance to the trunk.

In the diagram, pipes, angles and tees are shown in gray, and adapter rings in brown. When choosing components, be careful: the catalogs indicate the outer diameters of the pipes and adapter rings. This means that the adapter ring with parameters of 90x63 mm is put on a 63 mm pipe, but does not fit into a 90 mm pipe - only into a suitable tee or coupling with the corresponding inner diameter.

A cylinder with a propane-butane mixture is fixed on the body. A tube is connected to it, the other end of which is fixed exactly above the purge window. At the final stage of charging, the shooter briefly presses the canister button and delivers gas to the combustion chamber. Thanks to the fan, all gas enters the chamber and mixes well with air. Now you need to quickly, until the gas has escaped from the opening of the rammer, push the combustion chamber forward and secure the handle to the locking mechanism. In this case, a rammer attached to the combustion chamber in front will pass through the cylinder of the magazine and push the potato into the trunk. Everything, the gun is ready to fire.

Automation of turning on the fan is very simple. When the combustion chamber is retracted back at full speed, the button installed on it abuts against the housing. In fact, it is the button that serves as a limiter for the breech movement back. The handle plays the same role when moving forward. The most important part of the design is the locking mechanism. It is a corner screwed to the housing, behind which the handle is wound. Without such a lock during a shot, the combustion chamber, instead of sending potatoes along the barrel, will roll back.

The store is the most difficult part of the design. It is made of a transition ring, segments of a 25 mm pipe, six cylinders cut from a 90 mm pipe, and twelve saddles. The design is absolutely reliably assembled on glue. Note that the central adapter ring is fixed on the axis between two of the same couplings. They are also fixed with glue. The diameter of the cylinders significantly exceeds the diameter of the rammer to make it easier to push it toward the barrel. The potato is held in the center of the cylinder by foam pads.

Plumbing Designer

What a blessing that PVC pipes and fittings exist in the world! As a solution for the installation of a water supply system, they are completely not popular, but lovers of technical creativity can build from them everything that your heart desires. Working with PVC pipes resembles a game of constructor: assembly requires a minimum of locksmith work, as from the variety of fittings available on the market, you can choose ready-made "bricks" for almost any design.

When choosing a set of pipes and fittings, you need to remember the following. First, you should choose pipes for pressurized water supply, and not for sewage. The latter are not designed to work under pressure, so a gun made from them can explode. Secondly, do not confuse PVC pipes with more common polyethylene pipes, for the connection of which a special welding machine is needed. PVC pipes and fittings are designed for adhesive bonding. It is important to remember that PVC glue causes irritation of the mucous membrane of the eyes and respiratory tract, so you need to work with it in a respirator, in a well-ventilated area.

Finally, when choosing adapter rings for connecting pipes of different diameters, you should be very careful not to confuse the inner and outer diameters. Looking at the diagram, you might think that in the design of our gun there are too many extra parts, those transition rings. This is due precisely to the desire to select elements of matching diameters so that they can be easily assembled without any locksmith refinement.

Two long self-tapping screws screwed into the pipe at an angle to each other form an excellent ignition system. Self-tapping screws are better than screws, because they do not loosen and have a pointed end, which favorably affects the formation of a spark. By turning them in one direction or another, you can adjust the gap between them. A feature of this design is a “tightly” sealed combustion chamber. Therefore, before gluing the plug to the pipe, make sure that the ignition system is assembled and working, and that the handle is screwed securely and is not going to loose. Repairing a sealed combustion chamber in the event of a breakdown will be problematic. For a similar reason, do not use low-quality fuel: hair spray or deodorant. This will quickly lead to contamination of the electrodes, which can no longer be cleaned.

We could not do without locksmithing at all. The fact is that our gun involves a number of movable joints, and not one of the standard fittings is designed for through passage of the pipe through it. On the contrary, all adapter rings have coupling joints - special stops that secure the fitting to the end of the pipe for ease of installation. We had to grind these stops with a drill.

In addition to the PVC pipes and fittings that the circuit will help you to choose, for the construction of the gun you will need an 8-cm computer fan, a 9-volt battery, a piezoelectric kitchen lighter, several metal corners and mounting profiles, as well as a can of propane-butane mixture for tourist burners, which can be purchased at a sports store.

We were very lucky with the gas supply system. On one of the cans of paint lying around in the editorial office there was a button with a spray gun, the diameter of which corresponded exactly to the thickness of the aquarium hose, which also had been idle since time immemorial. It remains only to put the hose on the button, and the button on the cylinder with the propane-butane mixture.

Funny gas

The air-fuel mixture is a moody thing. Learning to supply exactly as much gas as necessary to the combustion chamber is the main skill of the potato shooter. Too lean a mixture cannot ignite, too rich a mixture cannot. I would like to urge all experimenters to be careful, admitting for example in their own sloppiness. Exercising in single shooting, we pretty much overcooked the mixture. Desperate to set it on fire, we left the gun with the shutter closed. Returning a little later, they tried to click the lighter again. During this time, the excess gas weathered, the mixture in the combustion chamber mixed well. As a result, the cannon fluttered so that half of the employees on the floor still rang in their ears for another half day. So we found out not without joy that our gun is capable of firing with much greater force than we thought, and also that you can never shoot indoors even at idle. Yes, and on the street we now always use headphones or ear plugs.

Most computer coolers are rated for 12V, but they work fine with a 9-volt battery. Do not be afraid that four wires come out of the fan. To make it work, the black wire must be connected to the negative terminal of the battery, and the yellow wire to the positive terminal. The fan is turned on by a button that is mounted on the combustion chamber. When the breech is retracted to recharge, the button abuts the body, starting the purge process.

When collecting the gun, we expected that paying for the convenience of reloading would have to be long-range. A multicharged gun is structurally more complicated than the classical one, and in its design there is a “bottleneck” in the literal sense of the word: this is a rammer, the diameter of which is less than the diameter of the barrel. In addition, the purge window and the same rammer are places of potential leakage of working gases. That is why we strongly discourage the use of handguns.

Our forecasts turned out to be erroneous. Through-blowing with a fan provided better filling of the combustion chamber with oxygen and better mixing of air with gas. Therefore, the pressure in the chamber during combustion of the mixture increased, and with it increased the firing range. So we can safely recommend you to repeat our experience. Go for it, but be careful!

The article “Harsh Samopal” was published in the journal Popular Mechanics (No. 8, August 2011).


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