SpudFiles

Hello everyone, and thank you for even taking the time to click on my thread...
Now, before I get into my questions I feel as though I have to give a bit of history as to what this involves. This past summer my buddies and myself got it into our heads to begin urban climbing everything and anything within an hour drive of my home town. Now for the most part we had great success with the entire venture, mostly due to the fact that we had the handy object of a grappling hook on hand. Now the only issue we ever ran into was getting enough momentium built to launch the hook up onto some of the higher buildings and thus extend the joy of the climb. It wasn't until the night before we all began to head our seperate ways to college, that I came up with the idea of using a spud canon to launch the hook to all those hard to reach spots and truely have some of the more awesome climbs. But because of the time in which this idea popped into my head we didn't have the time to develop and test this idea, so it never quite came to fruitation. Now that Ive remembered the idea, I was wondering if i could get some help with schematics on creating such a canon that would launch both a potato and a grapple hook (which i believe would have to be scewering the potato) a decent height and hopefully be both quite efficent and close to silent [noise isn't that big of a deal, but if we can do little noise that would be great]. Another thing I would like to know is what would be the best propellant for this sort of assualt climbing canon (which if all things go well is going to be mounted to a targeting platform of sorts. Anyway, thanks again for your time...
The Supreme Lord in the Way of the Spork

Well, I won't ask <i>why</i> you want to shoot a grappling hook onto a building, but anyway;

How heavy is this hook, and the line?
What is the diameter of this hook?
How high do you want to shoot it, max?

You want it adjustable-power. For such, you want a pnematic.
I would recomend using a sprinkler valve, moded if you wish, and a relitivly small chamber. (for noise reasons)

As to launching a projectile such as a grappling hook, I would recomend something other than a potato as a sabot. I can't really give you much, as I don't know much about your projectile.

use a supah valve!

i would probably just fabricate a new grappling hook to meet the requirements, but i have a habit of making thigns harder than they have to be, and i like building just about anything myself anyways. if you did make it yourself, you could make it out of a lighter metal like aluminum (if you could find some strong enough). maybe if your really creative you could make the barbs spring loaded so that they fold into a nice cylinder to fit farther down the barrel and then expand out upon exiting the muzzle...but that might be a little too complicated. i agree that it should definitely be a pneumatic. check out this site for ideas:

http://www.qsl.net/wb6zqz/tblperf.html

well that should actually be pretyt easy to make...
just get the smalled diameter pipe that your grappling hook will fit into, and use that as your barrel...
fabricate a cone-shaped piece of something (plactic, PVC, sheet metal, w/e you've got on hand) and attach it firmly to the end of the grappling hook...
tada, you have a shooto-grappling-hook!

Use a crossbow to shoot the hook, way easier/cheeper-can get them from finger hut. I got a 100 pound one for $79.00, it's a recurve and bad to the bone for a 100 pound 1. easy on the wallet, by the time you figure out a cannon/configure one to your needs, you will probly have more then what i paid for my crossbow. Plus it's easy to carry.

that cros bow idea sound nice, but the gun would be better just for the supprise factor for your friends plus more self satisfying,

Ham radio types use spudguns to "launch" antenna rigs -- an application very similar to yours. Here's a link to some designs that could be easily modified:

http://www.antennalaunchers.com/antlaunching.html

I would just like to comment on the title of this topic, what is the practical use of a potato cannon?

Well they are PRACTICALly the funnest things known to man.

As for your cannon, use a wooden salvo with a neoprene ring at the bottom and a reel on the outside of the barrel like the antenna launchers, rather than a potato.

I agree with jakal. you could extend the grappling hook with some pipe and and a tenis ball to the end for a 2.5in barreland take a bow fishing reel and wrap the rope around that and fire away.

THe crossbow idea is nice cause it's silent.However...If you replace the bow by a string connected to a sh...load of rubber bands it will be more powerfull.I've made a gun this way utilising pulleys and about 40 rubber bands.The advantage is you can add more bands if you want to and increase the power without having to pul back the entire bunch at the same time.If it where a bow(takes up more space too) you would always be pulling back the full force of the bow.If you're interested PM me

On my bow, every 1/2" you pull it back, add 5 lbs. (starting at standerd pull of 13 1/2"), it's a recurve, compounds bows are different.