SpudFiles Wiki - User contributions [en]

Chamber

2012-05-14T17:08:18Z

DYI:

The '''chamber''' or '''reservoir''' is the power source of a spudgun. It is, along with the [[barrel]], the only component found in all launchers.

In [[combustion cannon]]s, the chamber contains the flammable [[fuel]]/air mixture. When this mixture is [[combustion process|ignited]], its temperature increases, raising the [[pressure]] in the chamber.

In a [[pneumatic cannon]] the chamber contains compressed gas. The chamber is connected to the barrel through a [[valve]]; when the valve opens the pressure expels the projectile.

The chamber is often the part of the launcher that is subjected to the highest stress, and it's important that it is well [[Cannon construction|constructed]] and offers a high enough pressure rating. It is also the part where the most accessories are connected, especially in combustion launchers; they can have multiple holes to accommodate [[spark gap]]s, [[chamber fan]]s, [[fuel meter]]s and for [[venting]].

[[Category:Components]]

Hybrid cannon

2012-05-14T17:05:18Z

DYI:

[[Image:hybrid.jpg|right|thumb|300px| A very well built hybrid, although it is not safe for handheld operation due to its use of a PVC chamber]]
A '''hybrid''' is a type of spudgun that combines principles of the [[combustion cannon|combustion]] and [[pneumatic cannon|pneumatic]] spudgun. It uses a pressurized mixture of [[fuel]] and air to get more power out of a given chamber volume than a normal combustion or pneumatic gun could.
The hybrid is capable of higher velocities than a combustion or pneumatic spudgun; projectiles fired by a hybrid have reached almost 1000 m/s. This is possible because of the higher [[pressure]] gases generated by a hybrid [[combustion process|combustion]].

A hybrid launcher consists of seven basic elements:

*High pressure combustion [[chamber]]
*Pressure-triggered main [[valve]] (usually a [[burst disk]], see below)
*[[Barrel]]
*Fuel system (usually [[fuel meter|metered propane]])
*Inlet port for propellant mix with a connection for attaching fueling line(s)(usually [[schrader valve|schrader]] or [[quick disconnect|quick connect]])
*High-voltage [[Ignition source]]
*One or more [[pressure gauge]]s

==Operation theory==
A hybrid is first injected with a measured amount of fuel - much more than would be used in a regular combustion. However, without adequate oxygen, the mixture would be far too rich to ignite, so the chamber is then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a [[stoichiometric]] fuel/air ratio in the chamber.

A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, pressure gauges and fuel [[fuel meter|meters]] are used for this.

The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered [[ignition source]] such as a [[stungun]], [[flyback circuit]], or other high-voltage source; [[BBQ ignitor|grill igniters]] may be unreliable and require a very small [[spark gap]](typically 1mm or less) to work correctly in pressurized fuel/air environments.

The gases resulting from the combustion of the fuel/air mixture are released to the barrel via a self-operating valve of some sort, most commonly a [[burst disk]] because of it's simplicity and reliability, although self-venting [[piston valve|piston]]/[[diaphragm valve|diaphragm]] valves have been used. The valve is required to contain the pressure of the mixture pre-ignition, in other words, to prevent the pressurized fuel/air mixture from exiting out the barrel before ignition. Upon ignition of the fuel-air mix, the pressure rises and the valve opens.

===Safety===
A hybrid is one of the more dangerous types of launchers to build, apart from high pressure pneumatics. It is advised to only attempt to build one with pipe that can handle the high pressure environment (300+ [[Pressure gauge|PSI]]), generally SCH 40 steel or better. SCH 80 PVC has been used, but is not safe due to recurring fatiguing problems that have been observed in PVC hybrids and multiple failures even at low mixes. As with any launcher, the entire chamber is only rated to the spec of the lowest-rated part, so care must be taken when constructing the chamber of a hybrid. [[Remotely_activated_valve |Remote ignition]] is a must if PVC is used as a construction material, and is strongly advised for the initial testing of any hybrid. Although it was originally thought that mixes higher than 4x posed an unacceptable risk of [[DDT]] (deflagration to detonation transition), further calculations have revealed that the increased temperature of higher mixes barely counters the decreased burn rate caused by higher pre-ignition pressures, and that even a 20x mix will only burn a few m/s faster than a 1x mix. If DDT of all or most of the fuel load did occur, it would produce an extremely violent shock and pressure spike, which would cause any PVC chamber to rupture, and damage steel or copper components which were not highly overbuilt. The standard for hybrid construction is currently SCH 40 [[Steel Pipe|steel pipe]] and fittings, which have been tested in 2" sizes at mixes of up to 20x, repeatedly without failure. Theoretical burst pressure of SCH 40 2" steel pipe is >4kpsi (ignoring threaded sections and end effects), and there is no recorded incidence of ruptures occurring in SCH 40 steel hybrid chambers. Copper tube barrels have burst and/or bulged due to what is thought to be localized DDT.

Hybrid cannon

2012-04-17T20:32:41Z

DYI: /* Safety */

[[Image:hybrid.jpg|right|thumb|300px| A very well built hybrid, although it is not safe for handheld operation due to its use of a PVC chamber]]
A '''hybrid''' is a type of spudgun that combines principles of the [[combustion cannon|combustion]] and [[pneumatic cannon|pneumatic]] spudgun. It uses a pressurized mixture of [[fuel]] and air to get more power out of a given chamber volume than a normal combustion or pneumatic gun could.
The hybrid is capable of higher velocities than a combustion or pneumatic spudgun; projectiles fired by a hybrid have broken the sound barrier. This is possible because of the higher [[pressure]] and temperature gases generated by a hybrid [[combustion process|combustion]].

A hybrid launcher consists of seven basic elements:

*High pressure combustion [[chamber]]
*Pressure-triggered main [[valve]] (usually a [[burst disk]], see below)
*[[Barrel]]
*Fuel system (usually [[fuel meter|metered propane]])
*Air injection valve (usually [[schrader valve|schrader]] or [[quick disconnect|quick connect]])
*High-voltage [[Ignition source]]
*One or more [[pressure gauge]]s

==Operation theory==
A hybrid is first injected with a measured amount of fuel - much more than would be used in a regular combustion. However, without adequate oxygen, the mixture would be far too rich to ignite, so the chamber is then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a [[stoichiometric]] fuel/air ratio in the chamber.

A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, pressure gauges and fuel [[fuel meter|meters]] are used for this.

The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered [[ignition source]] such as a [[stungun]], [[flyback circuit]], or other high-voltage source; [[BBQ ignitor|grill igniters]] may be unreliable and require a very small [[spark gap]](typically 1mm or less) to work correctly in pressurized fuel/air environments.

The gases resulting from the combustion of the fuel/air mixture are released to the barrel via a self-operating valve of some sort, most commonly a [[burst disk]] because of it's simplicity and reliability, although self-venting [[piston valve|piston]]/[[diaphragm valve|diaphragm]] valves have been used. The valve is required to contain the pressure of the mixture pre-ignition, in other words, to prevent the pressurized fuel/air mixture from exiting out the barrel before ignition. Upon ignition of the fuel-air mix, the pressure rises and the valve opens.

===Safety===
A hybrid is one of the more dangerous types of launchers to build, apart from high pressure pneumatics. It is advised to only attempt to build one with pipe that can handle the high pressure environment (300+ [[Pressure gauge|PSI]]), generally SCH 40 steel or better. SCH 80 PVC has been used, but is not safe due to recurring fatiguing problems that have been observed in PVC hybrids and multiple failures even at low mixes. As with any launcher, the entire chamber is only rated to the spec of the lowest-rated part, so care must be taken when constructing the chamber of a hybrid. [[Remotely_activated_valve |Remote ignition]] is a must if PVC is used as a construction material, and is strongly advised for the initial testing of any hybrid. Although it was originally thought that mixes higher than 4x posed an unacceptable risk of [[DDT]] (deflagration to detonation transition), further calculations have revealed that the increased temperature of higher mixes barely counters the decreased burn rate caused by higher pre-ignition pressures, and that even a 20x mix will only burn a few m/s faster than a 1x mix. If DDT of all or most of the fuel load did occur, it would produce an extremely violent shock and pressure spike, which would cause any PVC chamber to rupture, and damage steel or copper components which were not highly overbuilt. The standard for hybrid construction is currently SCH 40 [[Steel Pipe|steel pipe]] and fittings, which have been tested in 2" sizes at mixes of up to 20x, repeatedly without failure. Theoretical burst pressure of SCH 40 2" steel pipe is >4kpsi (ignoring threaded sections and end effects), and there is no recorded incidence of ruptures occurring in SCH 40 steel hybrid chambers. Copper tube barrels have burst and/or bulged due to what is thought to be localized DDT.

SpudFiles Wiki:Community Portal

2008-07-23T15:05:53Z

DYI: /* '''ABS''' */

== '''ABS''' ==

'''Pros :'''

1) Chemical resistance, so can stand up to the average weekender going crazy experimenting with every different thing that can be found in an aerosol can.

2) Light weight, even the weakest of us has no reason to heft and bear these devices.

3) Low cost, it can be obtained almost anywhere, in the correct
dimensions.

4) High impact resistance. Pressurised ABS chambers can be dropped with no ill effects, hit with a hammer without damage, and used with faster burning fuel/oxidiser combinations than PVC.

5) Favourable failure characteristics; except at low temperatures, ABS will not shatter on failure like PVC, and will instead simply rip open, or tear in half in some cases if things like gauges or meters have been tapped through its walls.

'''Cons:'''

1) Rarely pressure rated. Pressure rated ABS is very difficult to acquire, and likely more expensive than just using steel pipe. However, solid wall SCH 40 DWV ABS makes an excellent material for barrels of pneumatics (it can repeatedly survive short spikes of several hundred psi) and combustion chambers for advanced propane combustions as well as oxygen enriched combustions. Cellular core ABS, while rare, should be avoided at all costs.

2) It's still plastic. Threaded joints with metal are dicey, and tapped threads will always weaken the pipe, by a factor of 4 or more. Use in high powered hybrids (this effect has been observed with 20x oxy/propane and higher mixes), where the combustion products are denser and have more heat capacity, can literally flash boil the pipe if it is used as a barrel, causing extreme deformation and usually destruction of even heavily reinforced designs. Bottom line - thick plastic is no substitute for metal in a hybrid, even if it has the same pressure capacity.

3) Decomposition products are nasty! If you have ever taken a whiff after firing it a few times, you will get a burning in your nose. This caustic gas is not good for you! Burning ABS produces a type of cyanide gas which is incredibly deadly (obviously).

== '''PVC''' ==

'''Pros:'''

1 )Inexpensive, the pipe is almost free. Fittings are where the money is dropped, but well worth it

2) Multitude of dimensions to chose from. Pretty much any configuration of pipe fitting can be found somewhere in PVC, but get out your checkbook! 6" sch 80 will run you right around $40 for a 10' piece.

3) Pressure rated variety is easier to find than the ABS equivalent. What you see is what you get. The rated pressure on the side of the pipe is already conservative, so you don't need to incorporate safety factors, unless you want to. Fittings are always stronger than bulk pipe, as long as the glue joints are made and allowed to cure properly and are Schedule 40.

'''Cons:'''

1) Limited Chemical Resistance. Aldehydes and ketones are out, as these readily dissolve the polymer, as in a glue joint, just read the label on the can: Acetone, THF, MEK. Some fuels should be totally avoided such as carb cleaner and insect repellant as they decompose ABS.

2) More brittle than ABS, but by not using oxygen and just burning fuel and air....should never be a problem.

3) Cellular core PVC is common at many hardware/home improvement stores. Make sure you buy SCH 40 pipe with a pressure rating printed on the pipe. If the pipe is not specifically marked with a certain PSI rating (ie, 330 PSI, depending on diameter), IT IS NOT PRESSURE RATED!!

[[''Source taken from www.spudtech.com'']]

THIS IS UNACCEPTABLE!!
http://www.spudfiles.com/spud_wiki/index.php?title=Special:Deadendpages
Look at the number of dead end pages! Not Cool!

Muzzle velocity

2008-06-06T00:29:44Z

DYI:

'''Muzzle velocity''' is the velocity of the projectile immediately after leaving the barrel, and other than a few hypothetical situations, is the fastest the projectile will ever go. Muzzle velocity is typically measured by a chronograph, a device that measures the time it takes the projectile to travel between 2 sensors, although less accurate results can be gathered from a [[ballistic pendulum]] or the quite inaccurate [[hang time]] test.

==Muzzle energy==

This is muzzle velocity's companion, and can be calculated as following:
(1/2)(Mass)(Velocity2), where mass is in kilograms, velocity is in meters/sec, and output is in Joules.
For instance, a 100g (0.1Kg) potato going 150 meters/sec (a large [[combustion launcher|combustion]] spud gun is capable of this) would have a muzzle energy of:
(1/2)*(0.1Kg)*(150m/s)2=1125 J.

1.5 joules is approximately 1 foot pounds, the traditional imperial (US) unit of energy for firearms.

It should be noted that in the case of saboted projectiles being simulated with the [[GGDT]], the actual muzzle energy is equal to GGDT muzzle energy * projectile mass/projectile mass+sabot mass.

The following is a table of miscellaneous, rim, and centerfire ammunition muzzle energies, for comparison.
<table cell-border=2 cell-padding=1 align=center><tr><td> '''Projectile''' </td><td align=right> '''Energy, J''' </td></tr>
<tr><td>typical paintball</td><td align=right>17</td></tr>
<tr><td>0.22 rimfire</td><td align=right>180</td></tr>
<tr><td>2" Spud at 300FPS (moderate sized combustion spud gun)</td><td align=right>~400</td></tr>
<tr><td>0.45 colt</td><td align=right>675</td></tr>
<tr><td>410 slug</td><td align=right>1000</td></tr>
<tr><td>2" Spud at 490FPS (large sized combustion spud gun)</td><td align=right>~1100</td></tr>
<tr><td>2" Spud at 600FPS (moderate sized pneumatic spud gun)</td><td align=right>~1600</td></tr>
<tr><td>0.223 (M-16)</td><td align=right>1900</td></tr>
<tr><td>0.60 (M-14, M-60)</td><td align=right>3640</td></tr>
<tr><td>30-06</td><td align=right>4500</td></tr>
<tr><td>100g slug at 1300FPS (moderate sized 10x hybrid spud gun) </td><td align=right>~7600</td></tr>
</table>

[[category:Concepts]]

Barrel

2008-06-02T01:47:08Z

DYI:

The '''barrel''' is the pipe used to launch the projectile, and is, along with the [[chamber]], the only component found in all launchers. The diameter determines what projectiles will fit in the launcher, and the length affects how much energy is transferred to the projectile.

Modifications and improvements to the basic barrel include [[sleeving]], [[rifled barrel|rifling]], [[hop-up]]s and flatline barrels.

There are many diameters of barrels popular in spudding, below are some that fit certain ammo:

* 4.5mm brakeline - fits bbs, good for [[BBMGs]]
* 6mm brakeline - fits [[airsoft bb]]s, a commonly used ammo in BBMGs.
* 3/4" CPVC, 3/4" sch 80 PVC (looser fit), or 3/4" sch 120 PVC - fits .68" [[paintball]]s
* 1/2" sch 40 PVC (.602" id) - fits "AA" batteries, marbles.
* 1/2" sdr 21 PVC (.685" id) - fits .68 caliber paintballs.
* 3/4" sch 40 PVC (.804" id) - fits 12g [[CO2 cartridge]]s, C batteries.
* 1" sch 40 PVC (1.029" id) - size [[C cell|"C" batteries]], smaller sized [[bouncy balls]].
* 1.25" sch 40 PVC (1.360" id) - Fits size [[D cell|"D" batteries]], [[film canister]]s
* 1.5" sch 40 PVC (1.590" id) - a common size, good trade-off between power and [[potato]] usage. [http://www.spudtech.com/components.asp Available rifled from the [[SGTC]]]
* 1.5" sdr 21 PVC (1.700" id) - fits [[golf ball]]s. Traditionally [[sleeving|sleeved]] within SCH-80 PVC.
* 1.5" sdr 26 PVC (1.734" id)- fits golfballs, but it is thinner than sdr 21, so the golfballs fit a little looser. Traditionally sleeved within 2" SCH-80 PVC.
* 2" sch 40 PVC (2.047" id) - fits caulk tubes and (large) potatoes.
* 2" sch 80 PVC (1.913" id) - fits 1.5" nominal pipe well, making it ideal for [[sleeving]] Also used as a golf ball barrel by itself, with the golf ball held in place by a rag patch, or other wadding. Also fits normal light bulbs! [http://advancedspuds.com/concreteballs.htm (Details)].
* 2.5" sch 40 PVC (2.445" id) - fits [[tennis ball]]s well.
* 3" sch 80 PVC (2.864" id) - fits many drink bottles well.
* 3" sch 40 PVC (3.042" id) - fits normal [[steel can|cans]], empty propane torch tanks, certian wine bottles, and gatorade bottles.
* 4" sch 80 steel (3.826" id) - fits softballs PERFECTLY. Kind of heavy though, at over 15 pounds/foot.
* 4" sch 40 PVC (3.998" id) - fits 29 oz. cans

Inside diameter (id) data from www.harvel.com
[[Category:Components]]

Safety

2008-06-02T01:38:45Z

DYI: /* Launcher safety */

Spudguns can be very dangerous if built or used improperly. However, if they are respected, they can be great fun.

==Launcher safety==
*As a very basic summary- DON'T BE AN IDIOT WITH THESE THINGS!!!!!
*Use good, safe [[cannon construction|construction methods]] and materials.
*Follow the rules of basic gun safety: never point the cannon at anything you don't want to destroy, and treat it as if it's loaded at all times. Never look down the [[barrel]].
*Always make sure you are firing in a safe direction that is free of people, pets, livestock, cars, houses and other property. Use a solid backstop or make sure you have a clear landing area.
*Don't look into the [[chamber]] of a [[combustion cannon]] that has failed to fire. Fresh air can make a rich gas mixture lean enough to ignite.
*Don't use [[PVC]] cannons in cold weather. Sub-freezing temperatures makes PVC brittle and increases the chances of catastrophic failure.
*Don't use a cannon that is cracked or heavily scratched, or has been dropped on a hard surface. Joints may be weakened and the pressure ratings on damaged parts cannot be trusted.
*Don't use excessive [[pressure]] in a [[pneumatic cannon]]. PVC pipe is not rated for pressurized air because of the shrapnel risk, so use in a pneumatic gun is considered to be outside pipe specifications in the first place. Never exceed the pressure rating of the lowest rated part.
*Don't use overly powerful [[fuel]]s in a combustion cannon. Solid fuels and very reactive gases such as [[hydrogen]] or [[acetylene]] are not suitable for use in any but a very few specially designed spudguns. Don't use oxygen to enrich the mix in a PVC cannon unless you're either: a) very far away OR b) not too fond of your appendages.
*Use hearing protection when firing loud combustion and [[hybrid cannon]]s, especially in an enclosed space. Use eye protection if there is a chance of splinters or other debris from the projectile hitting the target, or if you're using a launcher made of PVC, because of the ever-present shrapnel hazard from this material.

==Don't shoot living things==
A typical spudgun is capable of launching a [[potato]] weighing 50-150 grams a couple hundred yards with the muzzle energy of a powerful handgun. Longer distances are easily achieved with rocks, PVC darts, [[golf ball]]s, and other aerodynamic projectiles.

This energy, even when carried by a projectile as fragile as the humble tuber, is easily capable of killing someone, or at least breaking bones or putting out eyes. As to property damage, most launchers can put a vegetable through a piece of 1/2" plywood, and many can put it through 3/4" - which is very significant considering the construction of most residential buildings.

The same applies to short/and or small-bore launchers too.

Despite their great potential to do harm, it is not looked upon well if you (attempt) to use your launcher as a hunting instrument. They are often hard to aim, leading to a low probability of a clean (humane) kill - plus; it is illegal to do so.

Some people don't take the extreme danger of a projectile fired from a potato cannon seriously enough. There are frequent news articles about people injured by potato guns firing projectiles other than vegetables, or people being accidentally shot while handling the gun.

Accidental discharges are the most likely cause of injury however some individuals lack the mental capacity to keep their guns pointed away from others at all times. When a potato gun is pointed at a human being the dangers are extreme. Do not under any circumstances let the barrel of a potato gun point towards another human, even if the gun is not loaded.

The bottom line is: don't aim a spudgun at anyone, at any time, even if you think it's not loaded.

==Ammo Safety==
Some advise against shooting bolts, coke cans full of concrete, and other hard objects out of your gun; saying things along the lines of:
"Anything that is much harder than a spud can cause grievous bodily harm if shot at another person, or any animal for that matter."
...in actuality, even a tater will cause "grievous bodily harm" if shot at another living being. The danger lies in an increased chance of ricochet when using sturdy [[ammo]] - use common sense, and don't fire non-shattering ammo at close targets.

Some caution should be taken with shooting loose sub-munitions, specifically gravel or stones, with a [[sabot]] behind them - there is a significant probability of them jamming up, and the barrel being overstressed when the sabot tries to keep moving through the blockage, leading to a failure. Always wrap your lose projectiles in something - paper towels, old socks, and plastic bags are all acceptable.

Shooting water or other heavy objects from a cannon can overstress barrel fittings from the excessive recoil created. A sound grip must also be used when holding such a cannon as it can easily be blown out of one's hands.

[[category:Concepts]]

Ball valve

2008-03-21T02:14:31Z

DYI:

[[Image:Ball_valve.jpg|frame|A typical PVC ball valve]]
'''Ball valves''' open with a 90* twist of lever, similar to the operation of a [[butterfly valve]]. They are about the cheapest valve you can get, but also (typically) yield the worst performance, due to the slow [[opening time]].
The flow of a ball valve, however, is quite good due to its straight-through nature. This will tend to even out the situation in cannons with very long barrels and/or heavy projectiles (and thus long barrel dwell times).

Opening time can be shortened by:
* Using a spring or a pneumatic ram to actuate the valve
* Applying dish soap or other lubricant to the moving part. Oil or oil based lubricants should ''not'' be used, because they can damage the seals. Lubricating the ball valve will decrease friction and will result in a faster opening time.

However, there is more performance to be gained by using a faster valve, such as a [[butterfly valve]], [[piston valve|piston]] or [[diaphragm valve]], or a [[burst disk]].

It is possible to achieve extremely low opening times with ball valves through somewhat unconventional methods. Unfortunately, to open in the time necessary to make it a practical valve, a rather large amount of energy must be applied - so much, in fact, that in the lone test this was actually tried, the kinetic energy of the handle completely demolished the valve, and the ram was never recovered. This only serves to prove that you really are better off with a faster valve.

[[category:valves]]

FAQ

2008-03-21T02:01:27Z

DYI: /* Combustion vs. Pneumatic */

==Introduction==
This page aims to answer some of the common '''"Which is better?"''' questions seen on the forums in a simple manner.

Normally, there is no simple resolution to the question, because if there were, you wouldn't need to ask it. For example, if we '''knew''' pneumatics were best, then you wouldn't see any combustions.

It's not as simple and clear cut as people asking the question might think. However, this page will hopefully give you the information you need to make the decision for ''yourself'', depending on what is most important to you in your launcher.

==Combustion vs. Pneumatic==

''"Which is better, Combustion or Pneumatic?"''

This is probably the most common question that gets asked on the forums, and the big problem with it is that it is unanswerable. Without knowing what a person wants from a spudgun, nobody can put one type ahead of another.

However, most experienced spudgunners will agree on this short list ''if muzzle velocity or muzzle kinetic energy is the only criteria used for ranking the guns'':

* [[Combustion Cannon|Combustion]]
* [[Pneumatic cannon|Pneumatic]]
* [[Hybrid Cannon|Hybrid]]

Where down is increasing "power" but also increasing difficulty to use, build and cost.

Below are the main advantages and disadvantages in easy lists to help you decide on your own:

'''Combustion cannons'''

Advantages:
* Usually cheaper and easier to build.
* Less sensitive to minor leaks (such as around a threaded cleanout plug).
* Usually quicker to refuel and reload.
* More portable. Just needs a can of some flammable vapour.
* Can be made bigger, but still kept practical.
* Easier to later upgrade.

Disadvantages:
* Less power, with a upper limit to what is practically possible (with all safe fuels).
* Less controlled (Maintaining consistency and altering power)
* Often inconsistent and unreliable (Advanced Combustion launchers can overcome this, but often cost more to construct).
* Potentially noisier. This can be remedied to some extent by having a good [[Chamber to barrel ratio|Chamber to Barrel Ratio]].
* Very large chambers are more prone to [[DDT|DDT]], although this is only likely to occur in chambers that are very long, on the order of 10m or more, depending on a whole host of other variables. The diameter of a tube is directly related to its DDT runup distance, i.e. the wider the tube, the less likely detonations are

'''Pneumatic cannons'''

Advantages:
* Normally more powerful, with less of a "ceiling" to power (The particle speed of the gas does limit power to some extent).
* More controllable and consistent, as power can be varied with pressure.
* Easier to simulate, with reasonable accuracy, in a modeling program such as [[GGDT]].

Disadvantages:
* Takes longer to fill, unless you have a decent [[compressor]] or [[Gas bottle|bottled gas]] (Especially true with large chambers).
* More expensive, particularly if you include the cost of a compressor or regulated CO2.
* Less portable.
* More complicated to construct and much less forgiving of construction problems (such as weak or leaking joints and fittings).
* Leaks are a greater problem since the gun needs to maintain pressure for the entire time between filling and firing. (And, leaking can cause a valve to open prematurely.)
----

As a final note, a large majority of the launchers that Spudfiles (and other similar spudgun forum) users build are pneumatic cannons, but amongst people who don't take it up as a hobby, combustion cannons are more common.

==Working on==

* [[PVC vs. ABS]]

==To come soon==
* Metal vs. Plastic
* Boys vs. Girls (I'm kidding about this one)

Hybrid cannon

2008-03-11T19:08:23Z

DYI:

[[Image:hybrid.jpg|right|thumb|300px| A very well built hybrid, although it is not safe for handheld operation due to its use of a PVC chamber]]
A '''hybrid''' is a type of spudgun that combines principles of the [[combustion cannon|combustion]] and [[pneumatic cannon|pneumatic]] spudgun. It uses a pressurized mixture of fuel and air to get more power out of a given chamber volume than a normal combustion or pneumatic gun could.
The hybrid is capable of higher velocities than a combustion or pneumatic spudgun; projectiles fired by a hybrid have broken the sound barrier. This is possible because of the higher pressure and temperature gases generated by a hybrid combustion.

A hybrid launcher consists of seven basic elements:

*High pressure combustion chamber
*Pressure-triggered main valve (usually a [[burst disk]], see below)
*[[Barrel]]
*Fuel system (usually [[fuel meter|metered propane]])
*Air injection valve (usually schrader or quick connect)
*High-voltage [[Ignition source]]
*One or more [[pressure gauge]]s

==Operation theory==
A hybrid is first injected with a measured amount of fuel - much more than would be used in a regular combustion. However, without adequate oxygen, the mixture would be far too rich to ignite, so the chamber is then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a [[stoichiometric]] fuel/air ratio in the chamber.

A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, [[pressure gauge]]s and fuel [[fuel meter|meters]] are used for this.

The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered [[ignition source]] such as a [[stungun]], flyback, or other high-voltage source; grill igniters frequently won't jump a spark gap in pressurized fuel/air environments.

The gases resulting from the combustion of the fuel/air mixture are released to the barrel via a self-operating valve of some sort, most commonly a [[burst disk]] because of it's simplicity and reliability, although self-venting [[piston valve|piston]]/[[diaphragm valve|diaphragm]] valves have been used. The valve is required to contain the pressure of the mixture pre-ignition, in other words, to prevent the pressurized fuel/air mixture from exiting out the barrel before ignition. Upon ignition of the fuel-air mix, the pressure rises and the valve opens.

===Safety===
A hybrid is one of the more dangerous types of launchers to build, apart from high pressure pneumatics. It is advised to only attempt to build one with pipe that can handle the high pressure environment (300+ [[Pressure gauge|PSI]]), generally SCH 40 steel or better. SCH 80 PVC has been used, but is not safe due to recurring fatiguing problems that have been observed in PVC hybrids and multiple failures even at low mixes. As with any launcher, the entire chamber is only rated to the spec of the lowest-rated part, so care must be taken when constructing the chamber of a hybrid. [[Remotely_activated_valve |Remote ignition]] is a must if PVC is used as a construction material, and is strongly advised for the initial testing of any hybrid. Although it was originally thought that mixes higher than 4x posed an unacceptable risk of DDT (deflagration to detonation transition), further calculations have revealed that the increased temperature of higher mixes barely counters the decreased burn rate cause by higher pre-ignition pressures, and that even a 20x mix will only burn a few m/s faster than a 1x mix. If DDT did occur, it would produce an extremely violent shock and pressure spike, which would cause any PVC chamber to shrapnel, and damage most steel or iron chambers beyond repair. The standard for hybrid construction is currently SCH 40 steel pipe and fittings, which have been tested in 2" sizes at mixes of up to 11x, repeatedly without failure. Theoretical burst pressure of SCH 40 2" steel pipe is >2kpsi, and no catastrophic failure has ever been achieved, accidentally or by design, in a hybrid made from safe materials.

Triggered burst disk

2008-02-16T01:34:14Z

DYI:

[[Image:Triggered_burstdisk.PNG|frame|The firing cycle of a triggered burst disk]]
A triggered [[burst disk]] system consists of two burst disks mounted between the chamber and barrel of a [[pneumatic cannon]], with a trigger chamber in between and a trigger valve that either dumps said chamber to the atmosphere, or connects it to the main chamber.

The burst disks must be dimensioned to break somewhere between half and full chamber pressure. The trigger chamber is filled to half the chamber pressure, and then the chamber is filled to full pressure. When the trigger valve is opened, one of the disks is subjected to the full chamber pressure and ruptures, in turn overloading and rupturing the second burst disk.

The design has the advantages of quick opening and full flow of a burst disk, and with the reliability and repeatability of normal [[pilot valve]]s. It has the other disadvantages of a burst disk system, as well as higher consumption of burst disks.

Implementations of this idea may be found here: [http://www.spudfiles.com/forums/triggered-burst-disk-by-pilgrimman-t12809.html] and here[http://www.spudfiles.com/forums/sctbdcv1-5-450psi-50mm-steel-cannon-updated-with-new-vid-t12103.html].

[[category:valves]]

Pneumatic cannon

2008-02-16T01:24:57Z

DYI:

[[image:pneumatic ballvalve cannon.jpg|right|thumb|300px|Pneumatic ball valve cannon]]
A '''pneumatic cannon''' is a cannon powered by pressurized gas, usually air or CO2. They are generally simpler to build than [[combustion cannon]]s, and using typical compressor pressures of 120 psig or so and a decent valve, they will outperform most combustion launchers of the same size.

==Basic Elements==

Pneumatic launchers consist of five basic elements:

*Compressed gas storage reservoir ([[chamber]] for short)
*Filling valve (bicycle [[Schrader valve]]s, [[quick disconnect]]s, etc.)
*Firing valve ([[ball valve]]s, [[sprinkler valve]]s, [[piston valve]]s, bolt-style valves(see piston valves) [[quick-exhaust valve]]s, and [[burst disk]]s are the most common)
*[[Barrel]]
*[[Pressure gauge]] (for safety & repeatable launches)

==Operation & Theory==

In order to fire, the operator loads a projectile into the barrel, fills the chamber with a compressed gas (see [[Pneumatic air sources]] for common filling methods), and activates the main valve thus dumping the air in the chamber to the barrel.

The expansion of the compressed gas propels the projectile down the barrel. The barrel length determines the amount of energy transferred to the projectile and ultimately the velocity of the projectile.

Higher performance launchers use techniques such as:
* Faster valve opening times - see [[sprinkler valve modification]]
* Higher flow valves to maximize the airflow through the valve
* Using higher gas pressures.
* Even better, all of the above!

Less common, but also effective in increasing power, some people will also use a gas with a higher speed of sound and particle speed (e.g. helium).

==Related Links==

Downloading the [[GGDT]] (Gas Gun Design Tool) is highly recommended to those interested in pneumatic launchers.

Acetylene

2008-02-05T03:12:42Z

DYI:

'''Acetylene''' (chemical formula C2H2) is a flammable gas used for welding and cutting. Its low DDT runup distance, high flame front speed, and extreme reactivity generally make it a poor spudgun fuel. The molecule contains an unstable and energetic Carbon - Carbon triple bond that is easily broken.

Acetylene is a very reactive gas, with a flammability limit of 2.5 to 82% in air. It can decompose spontaneously with no air present if the pressure of the gas exceeds 15 psi. It is more prone to [[detonation]] than any other gas. Acetylene also has an extremely low ignition energy, and even the static charges developed in plastic pipes could theoretically ignite it.

In addition to these dangers, the gas doesn't even contain as much energy per volume as [[propane]], it's gross calorific value is 56000 kJ/m2 as opposed to propane's 101000 kJ/m2. The destructive power comes from the extremely rapid release of energy, which creates very high pressure spikes. Acetylene can create slightly higher pressure levels than propane, but the fact that propane can be used practically in hybrids, while acetylene cannot, means that this slight pressure advantage isn't really much of an advantage at all.

[[category:Fuels]]

SpudFiles Wiki:Community Portal

2008-02-01T15:18:50Z

DYI: /* '''PVC''' */

== '''ABS''' ==

'''Pros :'''

1) Chemical resistance, so can stand up to the average weekender going crazy experimenting with every different thing that can be found in an aerosol can.

2) Light weight, even the weakest of us has no reason to heft and bear these devices.

3) Low cost, it can be obtained almost anywhere, in the correct
dimensions.

4) High impact resistance. Pressurised ABS chambers can be dropped with no ill effects, hit with a hammer without damage, and used with faster burning fuel/oxidiser combinations than PVC.

5) Favourable failure characteristics; except at low temperatures, ABS will not shatter on failure like PVC, and will instead simply rip open, or tear in half in some cases if things like gauges or meters have been tapped through its walls.

'''Cons:'''

1) Rarely pressure rated. Pressure rated ABS is very difficult to acquire, and likely more expensive than just using steel pipe. However, solid wall SCH 40 DWV ABS makes an excellent material for barrels of pneumatics (it can repeatedly survive short spikes of several times its burst pressure) and combustion chambers for advanced propane combustions as well as oxygen enriched combustions. Cellular core ABS, while rare, should be avoided at all costs.

2) It's still plastic. Threaded joints with metal are dicey, and tapped threads will always weaken the pipe, by a factor of 4 or more.

3) Decomposition products are nasty! If you have ever taken a whiff after firing it a few times, you will get a burning in your nose. This caustic gas is not good for you! Burning ABS produces a type of cyanide gas which is incredibly deadly (obviously).

== '''PVC''' ==

'''Pros:'''

1 )Inexpensive, the pipe is almost free. Fittings are where the money is dropped, but well worth it

2) Multitude of dimensions to chose from. Pretty much any configuration of pipe fitting can be found somewhere in PVC, but get out your checkbook! 6" sch 80 will run you right around $40 for a 10' piece.

3) Pressure rated variety is easier to find than the ABS equivalent. What you see is what you get. The rated pressure on the side of the pipe is already conservative, so you don't need to incorporate safety factors, unless you want to. Fittings are always stronger than bulk pipe, as long as the glue joints are made and allowed to cure properly and are Schedule 40.

'''Cons:'''

1) Limited Chemical Resistance. Aldehydes and ketones are out, as these readily dissolve the polymer, as in a glue joint, just read the label on the can: Acetone, THF, MEK. Some fuels should be totally avoided such as carb cleaner and insect repellant as they decompose ABS.

2) More brittle than ABS, but by not using oxygen and just burning fuel and air....should never be a problem.

3) Cellular core PVC is common at many hardware/home improvement stores. Make sure you buy SCH 40 pipe with a pressure rating printed on the pipe. If the pipe is not specifically marked with a certain PSI rating (ie, 330 PSI, depending on diameter), IT IS NOT PRESSURE RATED!!

[[''Source taken from www.spudtech.com'']]

THIS IS UNACCEPTABLE!!
http://www.spudfiles.com/spud_wiki/index.php?title=Special:Deadendpages
Look at the number of dead end pages! Not Cool!

SpudFiles Wiki:Community Portal

2008-02-01T15:17:24Z

DYI: /* '''ABS''' */

== '''ABS''' ==

'''Pros :'''

1) Chemical resistance, so can stand up to the average weekender going crazy experimenting with every different thing that can be found in an aerosol can.

2) Light weight, even the weakest of us has no reason to heft and bear these devices.

3) Low cost, it can be obtained almost anywhere, in the correct
dimensions.

4) High impact resistance. Pressurised ABS chambers can be dropped with no ill effects, hit with a hammer without damage, and used with faster burning fuel/oxidiser combinations than PVC.

5) Favourable failure characteristics; except at low temperatures, ABS will not shatter on failure like PVC, and will instead simply rip open, or tear in half in some cases if things like gauges or meters have been tapped through its walls.

'''Cons:'''

1) Rarely pressure rated. Pressure rated ABS is very difficult to acquire, and likely more expensive than just using steel pipe. However, solid wall SCH 40 DWV ABS makes an excellent material for barrels of pneumatics (it can repeatedly survive short spikes of several times its burst pressure) and combustion chambers for advanced propane combustions as well as oxygen enriched combustions. Cellular core ABS, while rare, should be avoided at all costs.

2) It's still plastic. Threaded joints with metal are dicey, and tapped threads will always weaken the pipe, by a factor of 4 or more.

3) Decomposition products are nasty! If you have ever taken a whiff after firing it a few times, you will get a burning in your nose. This caustic gas is not good for you! Burning ABS produces a type of cyanide gas which is incredibly deadly (obviously).

== '''PVC''' ==

'''Pros:'''

1 )Inexpensive, the pipe is almost free. Fittings are where the money is dropped, but well worth it

2) Multitude of dimensions to chose from. Pretty much any configuration of pipe fitting can be found somewhere in PVC, but get out your checkbook! 6" sch 80 will run you right around $40 for a 10' piece.

3) Pressure Rated. What you see is what you get. The rated pressure on the side of the pipe is already conservative, so you don't need to incorporate safety factors, unless you want to. Fittings are always stronger than bulk pipe, as long as the glue joints are made and allowed to cure properly and are Schedule 40.

'''Cons:'''

1) Limited Chemical Resistance. Aldehydes and ketones are out, as these readily dissolve the polymer, as in a glue joint, just read the label on the can: Acetone, THF, MEK. Some fuels should be totally avoided such as carb cleaner and insect repellant as they decompose ABS.

2) More brittle than ABS, but by not using oxygen and just burning fuel and air....should never be a problem.

3) Cellular core PVC is common at many hardware/home improvement stores. Make sure you buy SCH 40 pipe with a pressure rating printed on the pipe. If the pipe is not specifically marked with a certain PSI rating (ie, 330 PSI, depending on diameter), IT IS NOT PRESSURE RATED!!

[[''Source taken from www.spudtech.com'']]

THIS IS UNACCEPTABLE!!
http://www.spudfiles.com/spud_wiki/index.php?title=Special:Deadendpages
Look at the number of dead end pages! Not Cool!

Pneumatic cannon

2008-02-01T03:44:07Z

DYI:

[[image:pneumatic ballvalve cannon.jpg|right|thumb|300px|Pneumatic ball valve cannon]]
A '''pneumatic cannon''' is a cannon powered by pressurized gas, usually air or CO2. They are generally far simpler than [[combustion cannon]]s, but using typical compressor pressures of 120 psig or so, they can be outperformed by a well built combustion launcher of the same size.

Pneumatic launchers consist of five basic elements:

*Compressed gas storage reservoir ([[chamber]] for short)
*Filling valve (bicycle [[Schrader valve]]s, [[quick disconnect]]s, etc.)
*Firing valve ([[ball valve]]s, [[sprinkler valve]]s, [[piston valve]]s, bolt-style valves(see piston valves) [[quick-exhaust valve]]s, and [[burst disk]]s are the most common)
*[[Barrel]]
*[[Pressure gauge]] (for safety & repeatable launches)

In order to fire, the operator loads a projectile into the barrel, fills the chamber with a compressed gas (air [[compressor]]s, hand pumps, [[Pressure regulator|regulated]] bottled gas, and 12 gram [[CO2 cartridge]]s are common filling methods), and activates the main valve thus dumping the air in the chamber to the barrel.

The expansion of the compressed gas propels the projectile down the barrel. The barrel length determines the amount of energy transferred to the projectile and ultimately the velocity of the projectile.

High performance launchers use techniques such as [[sprinkler valve modification|modifying valves]] for faster opening times, using homemade valves, maximizing the amount of airflow through the valve, and, more importantly, using higher pressures and gases with a higher particle speed, like helium.

The [[GGDT]] (gas gun design tool) is highly recommended to those interested in pneumatic launchers.

Hybrid cannon

2008-02-01T03:38:59Z

DYI: /* Safety */

[[Image:hybrid.jpg|right|thumb|300px| A very well constructed hybrid cannon]]
A '''hybrid''' is a type of spudgun that combines principles of the [[combustion cannon|combustion]] and [[pneumatic cannon|pneumatic]] spudgun. It uses a pressurized mixture of fuel and air to get more power out of a given chamber volume than a normal combustion or pneumatic gun could.
The hybrid is capable of higher velocities than a combustion or pneumatic spudgun; projectiles fired by a hybrid have broken the sound barrier. This is possible because of the higher pressure and temperature gases generated by a hybrid combustion.

A hybrid launcher consists of seven basic elements:

*High pressure combustion chamber
*Pressure-triggered main valve (usually a [[burst disk]], see below)
*[[Barrel]]
*Fuel system (usually [[fuel meter|metered propane]])
*Air injection valve (usually schrader or quick connect)
*High-voltage [[Ignition source]]
*One or more [[pressure gauge]]s

==Operation theory==
A hybrid is first injected with a measured amount of fuel - much more than would be used in a regular combustion. However, without adequate oxygen, the mixture would be far too rich to ignite, so the chamber is then with pressurized air. The amount of air depends on how much fuel was added, and is calculated to achieve a [[stoichiometric]] fuel/air ratio in the chamber.

A hybrid using twice as much fuel and air as a comparable combustion gun is said to be using a 2X mix. Higher mixtures can be used and will produce even higher pressures. The fuel and air needs to be measured and matched carefully to ensure reliable operation, [[pressure gauge]]s and fuel [[fuel meter|meters]] are used for this.

The ignition of a hybrid gun is more difficult than a normal combustion, as the length of a spark is roughly inversely proportional to the density of the gas. This necessitates the use of high-powered [[ignition source]] such as a [[stungun]], flyback, or other high-voltage source; grill igniters frequently won't jump a spark gap in pressurized fuel/air environments.

The gases resulting from the combustion of the fuel/air mixture are released to the barrel via a self-operating valve of some sort, most commonly a [[burst disk]] because of it's simplicity and reliability, although self-venting [[piston valve|piston]]/[[diaphragm valve|diaphragm]] valves have been used. The valve is required to contain the pressure of the mixture pre-ignition, in other words, to prevent the pressurized fuel/air mixture from exiting out the barrel before ignition. Upon ignition of the fuel-air mix, the pressure rises and the valve opens.

===Safety===
A hybrid is one of the more dangerous types of launchers to build, apart from high pressure pneumatics. It is advised to only attempt to build one with pipe that can handle the high pressure environment (300+ [[Pressure gauge|PSI]]), generally SCH 40 steel or better. SCH 80 PVC has been used, but is not advised due to recurring fatiguing problems that have been observed in PVC hybrids. As with any launcher, the entire chamber is only rated to the spec of the lowest-rated part, so care must be taken when constructing the chamber of a hybrid. [[Remotely_activated_valve |Remote ignition]] is a must if PVC is used as a construction material, and is strongly advised for the initial testing of any hybrid. Although it was originally thought that mixes higher than 4x posed an unacceptable risk of DDT (deflagration to detonation transition), further calculations have revealed that the increased temperature of higher mixes barely counters the decreased burn rate cause by higher pre-ignition pressures, and that even a 20x mix will only burn a few m/s faster than a 1x mix. If DDT did occur, it would produce an extremely violent shock and pressure spike, which would cause any PVC chamber to shrapnel, and damage most steel or iron chambers beyond repair. The standard for hybrid construction is currently SCH 40 steel pipe and fittings, which have been tested in 2" sizes at mixes of up to 11x, repeatedly without failure. Theoretical burst pressure of SCH 40 2" steel pipe is >2kpsi, and no catastrophic failure has ever been achieved, accidentally or by design, in a hybrid made from safe materials.

What is a spudgun?

2008-02-01T03:24:35Z

DYI:

'''Spud guns''', '''potato cannons''', '''produce accelerators''', or '''weapons of mashed destruction''' are all names for recreational launching devices, usually made of common plumbing pipe.

There are two common means to launch projectiles from a spudgun. The [[pneumatic launcher|first]] uses the energy stored in a compressed gas and the [[combustion launcher|second]], more common method, uses the energy released by combusting fuel vapors.
Also, there exists a rare mix of pneumatic and combustion launchers, a [[hybrid launcher|"hybrid"]], that combusts a pressurized fuel-air (or fuel/oxidizer) mixture.

As more advanced concepts continue to be designed and built, the general definition of a spudgun has become a homebuilt launcher that uses expanding gases to propel a projectile, and does not use any compounds which contain their own oxidiser for the actual propulsion.

The object of any of these varieties of spudguns is to propel projectiles in the direction of a designated (safe) target, for recreation and sometimes science experiments.

Common [[catogory:projectile|projectile]]s include: [[potato]]es, (obviously), [[mandarin orange|mandarins]], [[tennis ball]]s, [[golf ball]]s, bb's, airsoft, or marbles.... in fact, pretty much any spare vegetable or commonly available object you can ram down the barrel. This is part of the beauty of spudguns.

Some spudguns are very simple, inexpensive designs, such as the aerosol-spray-powered combustion or ball-valve and bike pump operated pneumatic. Some can get complicated and/or expensive, such as large home-made piston valved pneumatics and propane metered combustion guns. A decent potato gun can be built for as little as $15 or $20 at the local hardware store. Some people have spent thousands.

When proper safety is practiced, spudding is no more dangerous than other common hobbies, such as model airplanes. Though as with any activity that can be dangerous, safety should always be your number one priority. So please, take the time to read our [[safety]] section.

[[category:Concepts]]