HPI_Savage_RC

Not sure if this is allowed, since the last time I posted this thread on an R/C forum, it turned into a huge argument, complete with deluded over-zealous safety fanatics, lots of unnecessary legal debating, and maybe a handful of people who actually posted cannons of their own. I'll try anyway...

Anyone here into potato cannons? I've been building them for quite a few years, and they are extremely entertaining. This is my current potato launcher, which I built back in February 2008. It's quite a bit more sophisticated than your average cannon. The fuel is Propylene gas, which is metered using a volumetric metering system to create a stoichiometric mixture with the air inside the chamber. There's an internal fan to mix the fuel and air, vent the combustion products, and turn the gas flow from a laminar into a turbulent flow, which increases the burn rate of the fuel. It has 2 spark gaps inside the chamber, powered by an electronic BBQ igniter. It's breech loaded through aluminum lever clamp fittings. The chamber was designed such that all of the fittings mount inside the main chamber pipe, which creates a streamlined appearance, and blah blah blah...

Enough about me. If you have a potato gun, or have ever built one in your life, post your stories and/or pictures here.





And yes, I'm aware that I suck at photography.

tommygun32

[X(][X(][X(]...ME WANTS!!!!!

Can you show a picture of your breech??

redfisher1974

i had one,not as nice as that one

magnus213

My buddies and I put one of these together back in the day. Perfect stoichiometric ratio achieved by the guess-and-check hair spray method, laminar flow turned into turbulent flow by sometimes spraying my hand when it got in the way of the chamber. Those were some fun afternoons.

rcslsafut

nice ! very nice!!!
i havent seen one quite that thought through
the only ones i have seen are pretty primative
either pump type or ether type.

ImpalaPolicePack

here is mine
cost 30$ cnd to make
i use hair spray as fuel with a bbq igniter

when shooting in the air it takes about 15-20 sec before it touch the ground
and when shooting during the night it makes a 2 feet orange flame at the tip of the barrel

i would not want to be in the path of a potato comming at about 90mph !


hpi savage rc : is your barrel metal or pvc/abs ?

Mr. Mugen

Oh yeah....spud guns. We made every size and shape when we were younger. We made bazooka style and rifle style for long arms and pistols for close attacks. We played capture the flag in a huge farm field which always lead to the hospital. Not once did we get off easy with these. One kid had his eye blown inward from a crabapple out of a pistol type cannon....one had his hearing reduced from a spud to the ear from about 200 yards away. We liked the dangerous games a lot.....

cuzican

I've always had a spud gun or two laying around. Just your basic spud guns though...never anything like the pictures above. I've always used Right Guard aerosol deoderant as a propellant. It seems to be as good or better than anything else I've used.

madmax22

I have build one, going to do another over the winter. I also made a couple mini ones.

HPI_Savage_RC

Yeah, sure. One is the breech open, the other is loading a pre-cut potato slug. These ones are frozen; I'm going to try to shoot one through a VCR tomorrow.





Cool story dude, you truly are the master of subtle sarcasm.

ABS

You shot someone in the head with a cannon capable of firing 200+ yards, and the only injury he sustained was some hearing damage? Wow. I don't fire at living targets, especially people. A shot to the head from my cannon would likely be fatal.

Mr. Mugen

Yes we shot at each other with spud guns. KIDS DO STUPID THINGS I did not shoot anyone point blank nor did anyone else. Read it again and take your time.....kids will do stupid things. Turns out the kid with hearing loss is now a Dr. and the kid who shot him is now a lawyer! Go figure! I thought he would be a vise president...lol.

Kevin

Foxy

Vid please. I love it.

HPI_Savage_RC

I had a few videos on YouTube, but they deleted the audio due to copyright issues, and so they're pretty lame. I'll get some new ones up eventually.

I wasn't surprised that you shot at each other, since I agree, most kids do stupid things. I was simply amazed that one of you took a potato to the head and suffered nothing more than hearing damage.

Mr. Mugen

All I remember from that day was seeing him standing there and next thing he was doing a mid air cartwheel and screaming. That tater hit him pretty hard. Game over. That was the last time we played. There was no hiding the spud chunks and juices from that one.

Dirty_Vinylpusher

Just when I thought I understood the guidelines of what's allowed and not on this website....


We're not allowed to talk about politics, religion or anything else that's not suitable for minors.
But discussing how to build a (potentially lethal) weapon is ok?



[&:]


Either way - HPI, that is an awesome cannon.

monsterbombs

[sm=lol.gif]

we need visual validation

hands without shadows

Its only a weapon if the operator chooses to use it as a weapon.

redfisher1974

Just come up with that off the top of your head? Or do you have some old vcr's to get rid of

Dirty_Vinylpusher

Just like re..... *ahem* you-know-what, then?

SAVAGEJIM

Very ice looking 'tater shooter. You shotter looks like it is very well thought out and planned.

For the ABS piping material, at what PSI can that take safely before it becomes dangerous? I have not looked at the specs on that material yet. I presume it must be comparable to iron if it is used for plumbing purposes.

HPI_Savage_RC

Anything can be a potentially lethal weapon. I could just as easily stab you to death with the fork I was just holding, beat your head in with the aluminum pot I just used to cook my dinner, or sever your carotid artery with the hacksaw laying on the table across the room. All would likely be much more effective than a cannon that fires vegetables for entertainment purposes.

As someone else said, it's only a weapon if you use it as one.

Also, nobody has said anything about how to build one.

None yet, but this should tide you over for now.

[youtube]http://www.youtube.com/watch?v=j2aLLGWOrcA[/youtube]

If the moderators object to the above video, I will remove the link.

Between myself and the friend who supplied the stuff in the above video, we have enough broken electronics to fill a small shed to the brim. They all meet their demise eventually.

I used Barlow's cylindrical vessel burst pressure formula, and got somewhere around 400PSI for the chamber. According to my maths, stoichiometric propylene combustion in air can produce a maximum of ~130PSI in the chamber if the starting pressure was equivalent to atmospheric. Because the projectile moves down the barrel as the fuel combusts and effectively increases the volume of the pressure vessel, the maximum chamber pressure is probably quite a bit lower than that. So the safety factor is estimated to be ~4.

SAVAGEJIM

That is good to know. And Yes, you are so correct that the chamber must bear the most pressure loading because by the function of PV equation, it is very clear that the spud at the muzzle will exert so much less pressure than the spud in the chamber and the gas is immediately put behind it. (I know you know this, I am just stating this for the untrained who happen on this thread). Guns work on this very same principle: the chamber is made of thicker and/or stronger material than the barrel because the chamber pressure is the absolute greatest until the bullet is further down the barrel.

I remember older black powder cannons being build tapered as shown in this link:
http://en.wikipedia.org/wiki/File:Bu..._1888-1913.jpg

Well, these cannons might have begun to use more advanced propellants than black powder, maybe even some of the earlier forms of cordite.
The point of this pic is to show that you are right, the chamber, which must bear the most pressure loads, is thicker, but as you progress down the barrel to the muzzle, the barrel becomes thinner walled because not as much pressure load is put on this part of the gun.


For anyone who intends to try to make such a spud shooting device, or even a pumpkin cannon (much larger scale), please do you homework and dont just jump into this venture without knowing for sure what pressures your device will be exposed to and what your materials can take. If you do not, you can make something that will explode on you, and that is very deadly.

If you have the time and want to learn, the Barlow pressure calculation can be shown in this link. (This is just the first step, there are so many more things to consider. Note that the OP has gauges, valves, a neat and cleanly designed and made trigger system, and I bet he also has a safety waste gate system built in to protect from over pressurizing.)
http://www.engineeringtoolbox.com/barlow-d_1003.html

Please ALWAYS consider a larger safety factor, even if you do not need it. It is always better to be safe than sorry, and having a heavy device with really beefy material that will never rupture is way better than a very light device that could kill you by exploding on you.

I am not trying to give anyone design plans for such a thing, just point people to the right direction and stress to them to calculate, calculate, and calculate again before attempting to try to make the actual thing. Safety and responsibility are always essential. Just like a propeller RC plane can become a deadly projectile with a slicing and dicing whirlwind Ginsu knives in front of it, responsibility and care must be practiced.

Dirty_Vinylpusher

Well if you wanna nitpick......

There was mention of trying to shoot a frozen potato through a VCR....
Something capable of doing that is definitely classed as potentially lethal weapon.

An AK-47 being used as a baseball bat is every bit as much a weapon as one that's being pointed straight at someone.




The pictures and information in this thread are enough to replicate said object.



Either way - that comment wasn't directed at you, nor was it an attempt at getting this thread removed.
Foxy has already posted here wanting more pics of it so obviously it's ok.
I don't have a problem with it, I just find it odd considering some of the threads that get removed or locked, and others that are allowed to stay open.

HPI_Savage_RC

Good post SAVAGEJIM, I completely agree that people should have a good knowledge of the materials and physics they are working with before trying to build something like this.

Yeah, but I can also hammer a nail through the back of someone's skull and into their cerebrum, killing them instantly. Does that mean that a thread about building a wooden deck using a hammer and nails should be deleted?

It's all about how you use it. Nobody has said anything about using the cannon as a weapon.

You might be able to build something that looks like it, but if you are sufficiently intelligent to do all of the wiring and electronics mounting (which are hidden), and have sufficient knowledge of gas chemistry to properly operate the fuel meter, then you are more than capable of building a MUCH more effective 'weapon' should your desire be to kill people.

SAVAGEJIM

I do not disagree that a spud shooter can be lethal, aside from one that is poorly designed and made and can explode and kill the user, if someone were down range and were hit by a frozen hunk of potato, yes, it can be lethal.

But I do disagree about the example of an Kalashnikov being used as a baseball bat. The Kalashnikov was designed from paper and made at the factory for one purpose, to kill others, it is purposefully designed as a weapon.

The spud shooter in this case is not designed as a weapon nor is it ever intended to be used against a person, or even an animal (I bet it would be a very poor hunting implement to begin with). It is designed entirely as an entertainment piece and was also a mental exercise. Yes, it can be deadly if shot at someone, but to classify this as a weapon when it was never designed or intended to be used as such, I do not agree. I bet if you did try to use it as a weapon, you would much rather have a better chance of hitting the broad side of a barn than anything smaller. Plus I am sure the effective range of this shooter would probably greatly diminish and the ability to even hit and hurt someone at range would greatly go down.

There are so many things that can be lethal. Our RCs are no different. A 10-12lbf nitro MT truck jumping in the air and hitting someone in the head can be just as deadly as a spud shooter. And just like my example above, an RC airplane can become a deadly ballistic missile.