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Long range spud gun

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Long range spud gun

Unread postAuthor: pat656 » Tue Apr 22, 2008 6:55 pm

I need to make a spud gun with a 2.5 inch barrel, max of 6ft long, remote firing system(stand far away) and need to shoot it as far as possible. What kind of material do i need to use for the gun and propane or aerosol?

Thanks,
Patrick
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Last edited by pat656 on Tue Apr 22, 2008 6:56 pm, edited 1 time in total.

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Unread postAuthor: JDP12 » Tue Apr 22, 2008 6:56 pm

umm... try searching first. why do you need to stand far away? try searching and finding a propane meter, will probably be your best bet..

welcome to forums
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Unread postAuthor: pat656 » Tue Apr 22, 2008 6:58 pm

This is a school project and the teacher does not us to want to stand close to it, but we are allowed to use propane or aerosols
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Unread postAuthor: JDP12 » Tue Apr 22, 2008 7:14 pm

then look on the wiki somewhere, i believe there is an article on remote ignition. i would use a propane meter as well.

as far as length, decide either max barrel length or max chamber length, then calculate out the Chamber:Barrel ratio for the optimal length of the other
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Unread postAuthor: DYI » Tue Apr 22, 2008 7:31 pm

Has no one yet realised that he could build a hybrid? Mine was done for under $150, and if he lives in the U.S. it could be completed in a very short time. Propane has very little advantage over compressed air unless you can burn more of it in a given volume than usual.

And the simplest remote ignition methods involve nothing more complex than running longer wires. He probably doesn't need to go so far as to use RC ignition systems on a school project.
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Last edited by DYI on Tue Apr 22, 2008 7:32 pm, edited 1 time in total.
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Unread postAuthor: JDP12 » Tue Apr 22, 2008 7:32 pm

true he could....
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Unread postAuthor: tmacd995 » Tue Apr 22, 2008 8:23 pm

I would agree with DYI (obviously) that longer wires would make the best school project grade wires. I don't understand the nature of the project, so I can't weigh in on whether or not a hybrid is appropriate. If your parents are paying for the materials, then by all means you should build a hybrid.
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Unread postAuthor: pat656 » Tue Apr 22, 2008 8:30 pm

I am on a budget, so i cannot use metal, but I do have an extensive supply of PVC.
The object is to shoot the spud the farthest, but like i said, the barrel can only be 2.5 inches in diam. and the whole gun can only be 6 ft long (sorry, earlier i didn't say the whole gun 6 ft)
I am really just looking for what kind of fuel and how to construct combustion chamber
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Unread postAuthor: D_Hall » Tue Apr 22, 2008 8:44 pm

Personal opinion? I'd go with compressed air and call it a day.
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Unread postAuthor: DYI » Tue Apr 22, 2008 8:49 pm

Just checking, but you do realise that using metal is cheaper than using PVC, right? By making fittings out of offcuts of steel plate, I made a 1000 psi capable hybrid chamber for $25.

With PVC, your options are very limited. My advice in this case is reinforcement; put the chamber pipe inside a larger pipe (stovepipe is useful here), and stuff fiberglass matting in the space between. Then pour fiberglass resin into the intervening space, and wait for 12 hours. You now have a chamber safe enough to use within a few hundred yards of people and property, that has probably cost you well over $100 worth of resin alone, and still isn't as safe or convenient as the $25 steel chamber.

And with a length limit, you definitely will need to use a hybrid to gain any very clear advantage.
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Unread postAuthor: pizlo » Tue Apr 22, 2008 8:59 pm

What is the budget, and is it adjustable? Adding other chambers side by side wont help, because of chamber barrel ratios.
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Unread postAuthor: THUNDERLORD » Tue Apr 22, 2008 9:04 pm

Looks like your not going to trigger this thing remotely but in case you do,
My thoughts are be careful, because there are many stray signals transmitting that can carry over onto the channel and it could trigger randomly.
EDIT: I wrote remotely but i meant wireless
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Unread postAuthor: starman » Tue Apr 22, 2008 9:27 pm

Sounds like you're shooting tennis balls for the competition. Just a little heads-up...2.5" PVC pipe and parts are a little harder to come by than other standard sizes.

I would go with an advanced combustion, propane powered and metered, fan turbulence induction, basically a typical advanced combustion as described here... http://www.burntlatke.com

Use at least 2 spark gaps and a stun gun ripped out of its case **....extend the trigger switch wires out as far as you need to a remote trigger box or panel and associated trigger switch. Use a 4" chamber with volume of 250 - 300 cu in. with your 6' barrel.

Tennis balls seal very tightly in 2.5" pvc so a burst disk will be somewhat less effective. However, a basic 30-40 psi masking tape burst disk still might offer enough umppf to easily get the winning shot.

Just some ideas for you to chew on....

** If you do tear apart a stun gun, be sure to keep the spark gap intact, distance wise, that's created naturally on the probes. This is actually a safety feature.
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Unread postAuthor: biggsauce » Wed Apr 23, 2008 1:13 am

I'm confused... does it have to be a combustion? If not, why not a piston valved pneumatic? Within a 4" tee a 3" piston would be great for a beginner. Tie a string to a ball valve for remote firing.

For a combustion, an over under design with a 6ft barrel should do just fine.
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