howitzer potato cannon

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http://www.instructables.com/id/Howitzer-Potato-Cannon/

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Howitzer Potato Cannonby Flagella on March 19, 2011

Table of Contents

Howitzer Potato Cannon ........................................................................................................

Intro: Howitzer Potato Cannon .................................................................................................

Step 1: Principles / Concepts of Cannon .........................................................................................

Step 2: Barrel .............................................................................................................

Step 3: Combustion Chamber .................................................................................................

Step 4: Metering System .....................................................................................................

Step 5: Ignition System ......................................................................................................

Step 6: Final Construction .................................................................................................... 1

Step 7: Howitzer Design ..................................................................................................... 1

Step 8: Wheels/ Axle + Base .................................................................................................. 1

Step 9: Mount Trail ......................................................................................................... 1

Step 10: Cannon Cradle ..................................................................................................... 1

Step 11: Final Construction ................................................................................................... 1

Step 12: Operation ......................................................................................................... 1

Related Instructables ........................................................................................................ 1
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Intro: Howitzer Potato CannonThis is a two part Instructable designed to demonstrate how to construct 1) A hybrid potato cannon capable of accelerating a projectile to supersonic speeds and 2) Acannon mount that resembles a WWII Howitzer field piece.

I found most of the parts for the cannon at a plumbing supply store in town and the rest at Home Depot. Then I pieced together the mount from parts I had laying aroumy home.

The whole cannon can be made with no welding experience as all the parts can either be screwed together are epoxied together. The only difficulty that comes with this that you have to fix a lot of leaks before you can operate the cannon. But this is not hard to do.

Image Notes1. Hybrid Cannon2. Howitzer mount

Image Notes1. Cradle support2. Trail

Image Notes1. Your childhood spudgun

Step 1:Principles / Concepts of Cannon A regular potato gun that every serious DIYer has built utilizes just a regular combustion of gases at atmospheric pressure. This is the most basic of potato gunand usually the least powerful. The next most powerful type of gun is a pneumatic cannon that uses pressurized air to launch a projectile. After that comes the hybridpotato cannon which is a combination of the other two (hence "hybrid"). A hybrid is powered by the combustion of pressurized gases. This allows for much more fuel and oxidizer to react inside the combustion chamber and it willproduce much higher pressures than the other two types of potato guns. More information can be found at http://en.wikipedia.org/wiki/Spud_gun .

There are 4 major components to a hybrid potato cannon:- Barrel- Combustion Chamber- Metering System- Ignition System

Operation: The potato gun is first fueled via the metering system which injects just the right mixtures of fuel and air into the combustion chamber. The fuel mixture is tignited by two spark plugs connected to a stun gun. The resulting combustion produces enough pressure to break the burst disk holding the gases inside of thecombustion chamber and to shoot the projectile out at high speeds
http://en.wikipedia.org/wiki/Spud_gun


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The next step will demonstrate how to build the barrel.

Step 2:BarrelThe barrel is made out of a 2 1/2" SCH 40 steel pipe that is 63 inches long and that encloses approximately 300 cubic inches. This was threaded on one end andattached to one end of a steel union pictured below.

Image Notes1. Attached to barrel

Image Notes1. Steel two and one half inch union


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Step 3:Combustion ChamberThe combustion chamber was made of 5 pieces:

- A 34 inch long piece of 4 inch SCH 40 steel pipe which is threaded on both ends.- One 4 inch pipe cap- A 4 inch to 2 1/2 inch pipe reducer- A 2 1/2 inch steel nipple- The other half of the union

Image Notes1. Steel two and one half inch union


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Image Notes1. Brass Saddle2. Support block

Step 4:Metering SystemThe purpose of the metering system is to inject the correct ratios of fuel to oxidizer into the combustion chamber. The simplest way to do this is to pressurize the gaseinside of a pipe and then inject them into the chamber.

When using threaded parts, it is useful to know that there are many different classifications of thread types.

This design of a metering system uses a

The parts list is as follows:- A 4 inch to 3/4 inch brass saddle- 3/4" 90 degree elbow

- 3/4" 2 inch nipple- 3/4" Ball valves (2)- 3/4" 24 inch pipe threaded on both ends- 3/4" brass nipple

- 3/4" to 1/2" Pipe reducing coupling- 1/2" brass nipple- 1/2" to 1/4" Pipe reducing coupling- 1/4" brass nipple (3)- 1/4" brass tee (2)- 1/4" Pressure gauge (MIP)- 1/4" Schrader valve (FIP)

- 1/4" FIP to MIP adapter- 1/4" Pressure regulator with gauge- 1/4" Compression connector with MIP insert

- 5 foot 1/4" vinyl tube- 1/4" Compression connector- Propane pencil torch head

Assemble the parts as shown in the pictures below.

The whole metering system screws into the brass saddle which fits around the combustion chamber.

Image Notes


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1. Metering pipe2. Propane bottle with modified torch head.

Image Notes1. Torch Head with nozzle removed and a hole drilled into the tip for better flow.

Image Notes1. Vinyl tube connecting propane to metering system

Image Notes1. Pressure regulator used to control the flow of propane precisely.

Image Notes1. 3"

Image Notes1. 2 - half inch spark plugs

Image Notes1. Quarter-inch Pressure gauge


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Image Notes1. Torch head with nozzle removed


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Image Notes1. Propane


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Step 5:Ignition SystemMultiple ignition sourcesThe simplest way to create multiple sparks inside the chamber is to use a high voltage source such as the one found in a stun gun.The stun gun is connected to two sparks plugs which are epoxied into holes drilled into the combustion chamber. If the wiring is right, there should be two large sparksinside of the combustion chamber

I just taped the whole wiring/ stun gun assembly on the outside, but I do plan on making a more permanent solution.

Image Notes1. 2 - half inch spark plugs


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Step 6:Final ConstructionSince all of the parts are threaded, you can screw them all together using either teflon tape or a yellow gas line tape as a sealant.

Once all the parts are screwed together (except the end cap), you will need to connect the metering system to the combustion chamber via the brass saddle. To do thyou will need to drill a 3/4 inch hole where you want to connect the saddle. Then epoxy and tighten the saddle around the hole using a liquid gasket silicon to seal arouthe hole.A wooden block is recommended to support the other end of the meter.

Next you will have to drill and tap two holes for the spark plugs. Drill the holes using a 7/16 inch bit and tap using a 1/2 inch, course thread tap. Then epoxy and screwspark plugs in.

Wire the two spark plugs together on the inside and to the stun gun on the outside.

Now, once everything on the inside of the chamber is taken care of, you can screw the end cap on.

When the whole cannon is constructed, you can check for leaks by pressurizing the system and spraying some sort of cleaner on all of the joints. If a part is leaking,bubbles should start to form.

A burst disk can be between the two halves of the union to seal of the chamber. The easiest and cheapest way to make a burst disk is to just fold a sheet of tin foil into10 layers.

Image Notes1. Brass Saddle2. Support block


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Step 7:Howitzer DesignThe howitzer mount is both designed with practicality and style in mind. Really, for any cannon this big you will need some sort of mount to support it and take the streoff of the join connecting the chamber to the barrel.

The mount is able to do 4 principle things:- Support the cannon for firing- Supply a method for controlling the elevation of the gun- Afford a means of transportation- Keep the cannon from moving too much from recoil

I made the mount from spare wood and parts I found laying around my home, so it cost me little to no money.


Step 8:Wheels/ Axle + BaseWheels: The wheels were just two old spare tires I found laying around my yard. Old wheel barrow wheels will probably work as well.I had to screw a piece of wood on both sides of the wheel and then drill a hole into the center of it (Figure 2). This allowed a 1 1/2 inch pipe to fit snugly through the tire

Axle: The axle was made of a 1 1/2 inch steel pipe that was capped on the ends by two pipe tighteners.

Spacers : Two spacers were made of 3" long sections ABS pipe to separate the wheel from the base.

Base: The base is the wooden frame that fits on the axle and supports the cannon. This part is important to make strong as it will be taking a lot of weight. The base wmade from 2 by 8 boards and screwed together to make a base two feet wide and two feet tall as shown in Figure 1.

Image Notes1. Figure 1


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Image Notes1. Figure 2

Step 9:Mount TrailThe trails will balance and support the mount when apart, and allow the mount to be towed when closed together. The trails are made of boards 6 1/2 feet long attach

to a door hinge.


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Step 10:Cannon CradleThe cradle is critical to make accurately since it will be directly holding the cannon. The main section is two 6 1/2 foot sections of board screwed together to form a 'V'.Then spacers for the different section of the cannon are screwed in at different intervals.

The spacers must be thick enough to support the different sized barrel and chamber. It will take some time to form them to the right thickness.


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Image Notes1. Boards for cradle support

Step 11:Final ConstructionFirst, screw the trails onto either side of the base. Then construct a support for the cradle that can fit into a pipe running along the top of the base. Finally, get either twlengths of rope or two cargo straps and put one on either side of the base connecting the main axle to the cradle. this will provide a way of controlling elevation. You jutighten one and loosen the other to change the elevation.

Then, put some sort of cap on the cradle to prevent the cannon from sliding out and bunjee cord the cannon into the cradle


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Image Notes1. Cradle support2. Trail

Image Notes1. Boards for cradle support



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Step 12:OperationFirst, set up the mount and fix an elevation. Then attach the cannon to the mount and make sure it is secure. Insert a burst disk made of tin foil into the steel union.

To operate the cannon, first open the propane valve and measure a certain pressure into the meter. Release this into the chamber and use an air compressor to add acertain pressure of air into the chamber. For more information see http://www.spudfiles.com/spud_wiki/index.php?title=Stoichiometric

Then stand aside, turn the stun gun on, press the button, and listen to the boom.

Image Notes1. Cradle support

2. Trail

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