Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: Spudgun! And what a spudgun...

  1. #1
    Join Date
    Mar 2006
    Posts
    2,478

    Default Spudgun! And what a spudgun...

    http://www.makezine.com/blog/archive...tc_megala.html

    Last time I saw something like that it was manned by six guys in jumpsuits in a James Bond movie.

  2. #2
    Join Date
    Feb 2005
    Location
    Florida
    Posts
    802

    Default

    Would you like your chips, mashed or smashed

    Or I should say.. Coke or Pepsi?
    Or that brew that you hate
    Last edited by marconi; 04-05-2007 at 15:03.
    "My signature has been taken, so Insert another here"
    http://repairfaq.ece.drexel.edu/sam/laserfaq.htm
    *^_^* aka PhiloUHF

  3. #3
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,489,132

    Smile

    I've always loved potato guns. (I own two of them.) This is the page that first got me started with the things.

    That site lead me to this one, where I leared about the joys of making sparkler bombs. (No, they don't really explode like a bomb... "Sparkler Flare" would be a better name.)

    Eventually I ended up at a web page titled "Stuff the warning label said not do to". (The site has since been taken down, but you might find it in an archive somewhere.) On that page, among other crazy ideas like butane lighter grenades and match-head rockets, were detailed plans for a MACH-1-plus capable potato gun. He called it the BFPG-9000.

    It used compressed air and had a 20 ft long barrel. And the geek actually had the math to back up his claims of mach-1 muzzle velocity. (As if the sonic boom, which was clearly heard on the video he had and sounded just like the sharp crack of a rifle, wasn't proof enough that the thing was shooting spuds in excess of the speed of sound!)

    The best thing was that the firing pressure was well within the range of what you could buy on the open market. I think it was like 150 PSI or something. So it wasn't really exotic at all. (Schedule 40 PCV, a large reservoir for the air, and a big-ass dump valve.)

    I never had the balls to build it though.

    Adam

    PS: If you're curious what a tiny 1 inch exploding mortar shell can do to a bread loaf pan, have a look at this old video in the gallery. (Just click on the black movie icon to load the video.) Sure wish they still sold those things!

  4. #4
    Join Date
    Feb 2005
    Location
    Florida
    Posts
    802

    Default

    Yeah Adam , I remember seeing that Mach-1 about a year or two ago.

    Man.. that thing was tuff..

    I also thought about building it.
    Altho, Id have to take it to the transmitter property to fire it off.
    My neighbors may not like it as much as I .
    "My signature has been taken, so Insert another here"
    http://repairfaq.ece.drexel.edu/sam/laserfaq.htm
    *^_^* aka PhiloUHF

  5. #5
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,489,132

    Smile

    I fired one of mine in my backyard several years ago... I was trying to knock a soda can off the top of my neighbors privacy fence. Instead, the shot went a tad low, and the potato pierced the dog-eared fence board! Left a 2" diameter hole right through the damn thing!

    Potato guns can be scarry! Once I shot a golf ball out of one. I aimed it nearly vertical (within 5 degrees or so). The ball was in the air so long (longer than 30 seconds) that we thought we had lost it. Then we heard a tremendous "Thunk", followed by the unmistakable sound of a golf ball bouncing on concrete. It had traveled laterally about 200 yards, bounced off a neighbors flat patio roof 3 doors down, and then bounced onto his concrete patio several times before coming to rest in his backyard!

    I have no doubt that you could kill a man with a hairspray-powered potato gun and a golf ball at up to 50 yards if you managed a head-shot.

    Oh, and from my experiments, a hairspray explosion in a 4 inch combustion chamber of just about any reasonable length will only generate a maximum pressure of around 40 PSI, even with a 5 ft long, 1.5 inch barrel. So while the explosion itself is reasonably safe, what comes out of the barrel end might not be.

    I normally use the aerosol product "Static Guard" as my fuel, because it's not as sticky or smelly as hair spray, and I get more consistent firings. I've got one gun with close to 400 cycles on it, and it's still in great shape. (No signs of stretching, charring, or cracking.)

    Adam

  6. #6
    Join Date
    Mar 2006
    Posts
    2,478

    Default

    Little did I know! Awesome posts. Best I ever did was tiny, and even that stunned me. It was match heads. Red ones. And two bolts and a nut. I put the bits of match-head between two bolts in a cavity formed in a nut, and dropped it outside off a high doorway in a back garden between two rows of houses. Nice garden, tree, low walls, quiet respectable place, so I was nervous about breaking the silence. I held my head way back, arm outstretched and dropped it. Clunk. I felt that foolish going down 11 steps to pick it up that the sense of danger seemed stupid. Anyway, I had another go, not expecting anything, but repeating the care I'd used before just in case. There a bang. An almighty bang too, it rang and made me wonder if doors and windows would be opened followed by shouting. But there was silence. Weird silence, there should have been a falling bolt by then, somewhere. Then it fell through the tree with an astonishing TCHRACK!! like a potion-filled Gaul ripping through a phalanx of Romans, and chunked down into the hard mud, half standing. The other one was gone I know not where.

    The upshot (I love bad puns) is that if a 6 inch bolt 1 CM or so thick can be slammed out of a 'muzzle' just a few millimetres long, and be thrown so high by about ten match heads that the bolt took more than 2 minutes to return to earth, I have to wonder whether those red match heads are among the highest explosives known. I don't understand explosives and ballistics, but that's because I never explored further. If a few match heads can do that much, then it seemed like I'd get so far out of my depth, so easily, that I never tried anything else.

    Heard about a good one though. Two actually. One was a welder who filled 2 litre pop bottles with oxyacetaline mix for optimum burn, set up, then extinguished by putting the torch into sand. He'd take the bottles to a quarry and ignite them with fueled rag strips. I always thought that could be cool if you wanted to make music with that quarry as a reverb, use the pop bottle as the impulse source for an Acoustic Mirror type response. The other thing was a guy who had some old cast iron wood stove on some site somewhere, on a fire. I never really knew why, maybe for the experiment I'm describing here... He had the thing almost closed. It was cherry red with the heat. HE had a small syringe full of paraffin (kerosene). He ejected the stream across several tens of feet into the cavity of that stove, and it blew the heavy cast iron door off it.

    A third.. nearly forgot this. Hilti gun catridges. A guy I knew was working on a site that used these. (I still have some he gave me, somewhere safe). He fired ball bearings with them at old pots and pans. They'd go through 5mm aluminium easily. He showed me the results of a session one day when I visited. He told me a strange story of one that made a stunning bang, more extreme than any of the others, and the event was compounded by mystery. No ball bearing. No impact, no trace. Eventually with nothing left to contemplate but the epty shell casing, he picked it up and found the ball, somehow displacing the charge and sitting in the space left by it. I used to set off the odd catridge in a jewellry vice, hitting the other end with a small panel beater's iron, when I wanted to releive boredon or tension. A small bit of brass shearing off and doubling back 180 degrees and embedding itself impressively in my thumb put an end to that. I've seen a few electric arcs at close range including a direct 240 100A company head short about two feet from my eyes, but nothing seems to beat the aggression of chemical energy release. The Chinese had sense, they spent most of their time with it making it look cool instead of killing people, so far as I know.

  7. #7
    Join Date
    Mar 2007
    Posts
    11

    Default

    Quote Originally Posted by Buffo View Post
    It used compressed air and had a 20 ft long barrel. And the geek actually had the math to back up his claims of mach-1 muzzle velocity. (As if the sonic boom, which was clearly heard on the video he had and sounded just like the sharp crack of a rifle, wasn't proof enough that the thing was shooting spuds in excess of the speed of sound!)

    The best thing was that the firing pressure was well within the range of what you could buy on the open market. I think it was like 150 PSI or something. So it wasn't really exotic at all. (Schedule 40 PCV, a large reservoir for the air, and a big-ass dump valve.)
    That isnt possible from plain air, it just dosent travel past the speed of sound or near it, it would have to be helium or hydyogen to reach that speed or a hybrid gun that uses compressed air and propane, these have reached mach 1 before.
    thats right im a recovering spuddist

  8. #8
    Join Date
    Jan 2007
    Location
    Florida
    Posts
    4,382

    Default

    Potato guns and lasers--
    they go together

    like

    catsup and mustard


  9. #9
    Join Date
    Jan 2006
    Location
    Charleston, SC
    Posts
    2,147,489,132

    Default

    Quote Originally Posted by aaron_inc View Post
    That isnt possible from plain air, it just dosent travel past the speed of sound or near it.
    Aaron;

    You are incorrect. As little as 60 psi of plain air can reach sonic velocity if vented through a nozzle. (Which can be any narrowing of the pipe diameter, such as a partially open valve.) I've seen it happen here at the chemical plant where I work. This is why all tank vents have to be grounded, and why it's extremely dangerous to vent a pressurized tank that has a flammable mixture of air and solvent vapor. When the mixture passes through the valve body it can go supersonic, which builds up a static charge that can discharge, creating a spark that will cause an explosion. We lost a man to just such an event back in 1997. I was the EMT that responsed to the explosion, and I was a part of the investigation and hazop that followed to determine what happened.

    In a potato gun you have a large diameter reservoir that necks down to a smaller diameter barrel, so you have the same nozzle effect, and the same potential to reach sonic velocities. Granted, that's when there's nothing in front of the nozzle to block the air flow, so the nozzle effect is going to be less efficient in a real potato gun because you'll have a higher pressure on the outlet side of the nozzle. Nonetheless, given a long enough barrel for the object to accelerate in, it *is* possible to use air pressure to shoot an object at sonic velocity.

    In fact, If we're just talking about accelerating the air and not a projectile, I believe you can reach sonic velocity at much lower pressures, though I don't have any real-world experience to back up that claim. A simple google search turns up a few plumbing vent products that talk about air pressure spikes traveling at sonic velocity through empty pipes at around 1/5 the pressure in the incident above, but I can't speak for the accuracy of those sites.

    Adam

    Edit: Just browsed through a few compressible fluid dynamics sites, and discovered that the critical pressure is just 13.1 PSI(G). Also, I should amend my paragraph discussing nozzle efficiency above, since once you reach choked sonic flow through the nozzle, the downstream pressure is irrelevent. But up to that point a resitriction downstream will limit the acceleration of the air through the nozzle.
    Last edited by buffo; 04-06-2007 at 05:24.

  10. #10
    Join Date
    Mar 2006
    Posts
    2,478

    Default

    Quote Originally Posted by Buffo View Post
    ...given a long enough barrel for the object to accelerate in, it *is* possible to use air pressure to shoot an object at sonic velocity.
    Agreed. That's just another form of leverage over time, same as allows the focussing of energy down the loose long line of a whip.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •