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Another first pneumatic spud gun...

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Another first pneumatic spud gun...

Unread postAuthor: mtaylor » Tue Apr 10, 2007 11:31 pm

This is MY first pneumatic spud gun. I have made several combustion guns before, but I grew tired of the hassle of the right mixtures of propellant/air and having to keep it so darn clean... Actually, my combustion guns were cool: I made my own sparking device by inserting threaded rod in towards the center of the combustion chamber from opposite sides, so the spark would start the combustion process from the absolute center of the chamber. The thing kind of freaked me out with how loud it was, so I created a "laser activator." I created a circuit that would drive an electronic barbeque ignitor only AFTER a laser pointer was shined onto a receiver. This allowed me to be as far away as possible, as long as I had a line of sight to the receiver.

Digression... I now created my first pneumatic spud gun. One that will never shoot spuds. I have two barrels, one for the small Nerf vortex and golf balls and one for shooting ping pong balls. The ping pong balls are best when filled with something. For instance, cut a small 'v' into the ping pong ball, and fill with water, or paint... Then, most importantly, dry the outside of the ball, push back the 'v' into the ball and take a knife blade dipped in hot candle wax, and seal the ping pong ball. This allows for a water tight seal, so the contents don't leak out and get all over. The compression chamber is two lengths of 2" and the barrels are 2" and 1.5". Modified Rain Bird valve.

I tested it today with 40psi and the Nerf Vortex. I shot it straight up and I almost lost sight of it. Then, I shot it "near" level toward an apartment style mail box that was 30 yards away. I thought that the ball would lose about a foot of altitude between the box and where I was crouched, but as I fired it, the ball sailed right over the box at an incredible speed. At near level flight, it reached 90 yards out. I had to hoof it into the tall weeds behind my apartment complex to go retrieve my ball!

Later, when my wife wanted me to go take out the trash, I took one of my water filled ping pong balls out and the gun pressurized to 50psi, then I fired it at the dumpster, where it created an awesome mist as it vaporized onto the face of the dumpster. I went over to it and threw the trash in and found quite a dent from the ball. Ha, this gun is cool.

Did I mention that I am an electrical engineering student, head of robotics club and I plan on mounting this thing on top of a robot "tank?" The tank will turret, be wireless and have wireless video mounted to a pan/tilt above the barrel. I just need to find the time...
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Unread postAuthor: hi » Tue Apr 10, 2007 11:39 pm

thats cool. i would suggest shotening the hose though, it would accuate the valve faster. you did a really good job with the primer. (you did use primer didnt you?) how far can it shoot a tater?
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Unread postAuthor: TwitchTheAussie » Tue Apr 10, 2007 11:42 pm

I envy your intelligence. Thats a mad yet simple cannon, I love it. What size is your tank gonna be and could you put up the circuit diagram for the remote ignition?
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spudgunning is like sex, once you've tasted, you can't wait til next time.
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Unread postAuthor: mtaylor » Tue Apr 10, 2007 11:46 pm

you did a really good job with the primer. (you did use primer didnt you?)


By primer, do you mean paint?

i would suggest shotening the hose though

I was planning on making it shorter once I got the turret portion of the robot completed. The hand-held valve will be compressed using a pull-type solenoid.

how far can it shoot a tater?


Sadly, it will never smell the stink of tater. I had enough of that when I was shooting combustion guns. I imagine that one of my water filled ping pong balls will go quite far with even higher pressures... I do however have a goal of besting my previous record of 275 yards with a little combustion gun. I have the impression that pneumatics shoot further, do to higher internal pressures.
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Unread postAuthor: mtaylor » Tue Apr 10, 2007 11:53 pm

and could you put up the circuit diagram for the remote ignition?


I had a feeling that someone would ask for a schematic for the laser-ignition... I will draw one up and attach it to this topic.

What size is your tank gonna be

It will have a base that is slightly shorter than the length of the gun. I will have to create a frame for it first (out of Lexan, plexi, aluminum). Then find motors (possibly from http://www.robotcombat.com) and lastly interface my already existing electronic hardware (http://www.tayloredengineering.com/avr_products.html) and write software for it. The really insanely cool part, is that it will be controlled wirelessly using a PlayStation 2 controller, with its two joysticks and 14 buttons!
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Unread postAuthor: hi » Tue Apr 10, 2007 11:53 pm

yes, pneumatics are more powerful if you make it right. as for the primer... you should have used it, too late now. it makes the solvent weld (solvent weld is another word for glueing pvc together)

http://www.burntlatke.com/weld.html

that might help a little, use it next time. because you didnt use primer, you probably shouldnt go past about 100 psi or so, something might pop off.
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Unread postAuthor: TwitchTheAussie » Wed Apr 11, 2007 12:00 am

mtaylor wrote:The really insanely cool part, is that it will be controlled wirelessly using a PlayStation 2 controller, with its two joysticks and 14 buttons!


You rock man. Plain and simple you just rock.
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Unread postAuthor: mtaylor » Wed Apr 11, 2007 12:15 am

use it next time. because you didnt use primer, you probably shouldnt go past about 100 psi or so, something might pop off.

If you were wondering if I used a pvc appropriate cement, well then, duh... Of course. I don't want to kill myself. This is only a hobby for me. I have bigger things to fry.
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Unread postAuthor: mtaylor » Wed Apr 11, 2007 12:29 am

This is a follow up for TwitchTheAussie:
Below is a scanned schematic for the laser-activated combustion circuit.
Note:
You have to modify an electronic barbeque ignitor. I got mine from Lowes Hardware store. It came with a AAA battery installed, with a big dumb red button on the top. Two leads came out from the bottom, which should be connected to the sparking mechanism on the gun.
Remove the stupid push button switch and create a way to bypass it and tie it into a relay. A relay is a electrically driven switch. When activated, the ignitor should be sparking. The relay is activated using the rest of the control circuit.

The sensor for the receiver should be shrouded inside a copper pipe, to keep the sunlight off of it. It is sensitive to light, and the major contributing light source should be the laser.
The sensor is a variable resistor that sorts of looks like a really small solar cell. The circuit is calibrated using the variable resistor, which usually has some sort of handy way of setting it.

I got the idea for this circuit when I was about 16. There is a circuit "similar" to it in a book available from Radio Shack. You can ask the store employees "general" questions, if you have any, but they are usually stupid and just want to sell you a cell phone, so don't bother.

Remember, the control circuit is not really attached to the barbeque ignition circuit. It only drives the relay, which drives the barbeque circuit.

Before the gun is loaded, adjust the variable resistor so you hear the relay pop with just enough current running though it. Now, back off the resistor a little, so the relay is just about ready to pop, but hasn't yet. A small increase in light being shined onto the sensor should increase the amount of current flowing though the circuit just enough to give it that final push, switching on the barbeque ignitor and BOOM!
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Unread postAuthor: mtaylor » Wed Apr 11, 2007 12:31 am

By the way, I was able to fit the control circuitry into one of those little Starbucks After Coffee mint tins... So, it shouldn't take up too much space.
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Unread postAuthor: TwitchTheAussie » Wed Apr 11, 2007 1:32 am

Sweet as man thanks for that. Time to draw some hybrid plans.
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Unread postAuthor: spudthug » Wed Apr 11, 2007 5:42 am

ok first of all nice simple gun looks good...by primer he means pvc glue primer...u rsupposed to sand the pipe put pipe cleaner opn then put primer on then glue it...if u dont it is usually not afe past 100 psi...
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4" piston valved cannon-half done..( i spilt my cement...)

Hybrid- 75% done. need to build propane holder and drill/tap sparkplug hole..
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Unread postAuthor: locksmith » Wed Apr 11, 2007 11:12 am

Nice cannon the ammo possibilitys are endless
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Unread postAuthor: judgment_arms » Wed Apr 11, 2007 11:43 am

mtaylor wrote:...I don't want to kill myself...


So, did you realize that you used DWV? Those end caps are DWV and so is your tee. And incase you didn’t know:
DWV + pressure = fragmentation…
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Call me "Judge", it's easier to type.

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Unread postAuthor: mtaylor » Wed Apr 11, 2007 12:11 pm

I checked the cement that I used. It is pressure rated up to the limit of the pipes that I used, which max out at 230psi. The end caps will are also pressure rated. These fittings are for natural gas piping etc. Plus, the T-joints are layed, as they have the pressure rated piping inside the length of it. The bottom line is that the first thing to go would be the pipes, which are rated at 230psi, like I said. Even if the end caps come off, who cares? It'd just be an extra projectile going down range, away from me. I'm not going crazy with it or anything, so as a first gun, shooting Nerf footballs, it is fine.

-Nuff said.
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