Science Project Question

Shroom Man 777 · Post by **Shroom Man 777** » 2005-09-08 10:58am

I (along with a bunch of friends) need to mass a project at September 20, anyway, I was wondering, how possible is it to construct a homemade cannon. Not a pussy air pressure one, but one that uses explosive force to propell projectiles and stuff. How hard would it be? I mean, I'm just talking about a home-made musket here. Would it be as simple as getting a pipe, some gunpowder or something, and a projectile? I know it could very well get dangerous and Bad Things could happen, that's why I'm asking you guys.

Suggestions for other (less dangerously stupid?) projects will be welcomed, though I still favor the manly appeal of the cannon. Or the homemade musket.

Jalinth · Post by **Jalinth** » 2005-09-08 11:25am

Shroom Man 777 wrote:I (along with a bunch of friends) need to mass a project at September 20, anyway, I was wondering, how possible is it to construct a homemade cannon. Not a pussy air pressure one, but one that uses explosive force to propell projectiles and stuff. How hard would it be? I mean, I'm just talking about a home-made musket here. Would it be as simple as getting a pipe, some gunpowder or something, and a projectile? I know it could very well get dangerous and Bad Things could happen, that's why I'm asking you guys.

Given how paranoid things are these days, I would strongly suggest another choice. You are essentially bringing a weapon to school - which could leave you in a shitload of trouble.

As to other suggestions, what school grade is this for? A "good" project for Grade 8 is quite different than a Grade 12 physics class (or even worse, Honours 12).

Shroom Man 777 · Post by **Shroom Man 777** » 2005-09-08 11:30am

Eh, I'm 16 years old. And am in the Philippines. So, A.) this means that things are not paranoid on this side of the Pacific and B.), I'm in my last year of highschool.

SCRawl · Post by **SCRawl** » 2005-09-08 12:34pm

I like to borrow from one of my favourite writers, William Gibson, for this advice: when you're technical, go crude. When you're crude, go technical.

In other words, a more crude launching device would better highlight your technical prowess. I suggest a trebuchet, though I don't know if you can put one together from scratch in the next 12 days.

Sir Sirius · Post by **Sir Sirius** » 2005-09-08 01:19pm

In theory it's easy, the problem is that the diffrence between a homemade cannon and a homemade fragmentation granade is far too small for comfort. My uncle blew two of his fingers off as kid trying to fire one he had built.

GrandMasterTerwynn · Post by **GrandMasterTerwynn** » 2005-09-08 03:55pm

Shroom Man 777 wrote:I (along with a bunch of friends) need to mass a project at September 20, anyway, I was wondering, how possible is it to construct a homemade cannon. Not a pussy air pressure one, but one that uses explosive force to propell projectiles and stuff. How hard would it be? I mean, I'm just talking about a home-made musket here. Would it be as simple as getting a pipe, some gunpowder or something, and a projectile? I know it could very well get dangerous and Bad Things could happen, that's why I'm asking you guys.

Suggestions for other (less dangerously stupid?) projects will be welcomed, though I still favor the manly appeal of the cannon. Or the homemade musket.

As has been said, it's trivially easy to gather up a pipe, some gunpowder, and a projectile. The problem is, that it is a fucking stupid idea. But, here are the steps you will need to keep in mind.

A) You need a breech block to be welded onto one end of your pipe. You will need to calculate the amount of explosive force generated by your gunpowder charge, and you will have to make sure that it doesn't exceed the pressure rating of the pipe you're planning to use. It would also be helpful if the blast pressure didn't exceed the strength of your welds. Otherwise you have a pipe-bomb, rather than a cannon. This is important as your projectile needs to have a reasonably snug fit in your barrel.

B) Your would-be pipe-bomb needs to be mounted in something secure that won't permit the barrel to break free due to recoil. This might be obvious, but no, you and your friends would not suffice as a mount. Especially since you'll want to be seperated from this monstrosity by a lot of space.

C) In the spirit of being seperated from your would-be pipe-bomb, you'll need some sort of long-burning fuse . . . or better still . . . an electrical ignition system exactly like that used to fire off model rockets. Those come with a fuse, a firing box, and most importantly, a really long length of wire.

In short, you will need a good welder, and some good maths to pull this off. You can't willy-nilly dump black powder into your contraption, light the fuse, and hope for the best. That will get you killed. As rank-amateurs, even carefully following the guidelines posted here could get you killed.

tharkûn · Post by **tharkûn** » 2005-09-08 10:14pm

Traditional musket design was guided by centuries worth of empirical data. Certain designs were known to exploded because a lot of poor bastards died when they exploded in the past. This is why gunsmithing was a highly lucrative career and far more challenging than most other smithing.

A few things:

1. First forget about a musket, you want a nice simple fuse ignited cannon if you are really going to do this. Dicking around with the matchlocks, flintlocks, or percussion caps of a musket is NOT healthy.

2. When doing your calculations include a very healthy safety margin. Anything you do yourself will NOT be as strong as value quoted by anyone. Your welds will be weaker than textbook, your charge will be less precise than that in the textbooks, and your projectile will fit worse than textbook.

3. Keep it small and your projectile light.

It is a dumb idea, the trebuchet is a FAR better choice, but if you decide to do this idioacy remember KISS and inflate your margin of safety whenever practical.

Shroom Man 777 · Post by **Shroom Man 777** » 2005-09-09 01:41am

Yeah, I knew there was going to be a (big) risk of getting my fingers blown off, or getting myself perforated with shrapnel. But my dad's got a flak jacket and of course, we could have a long fuse of some kind that would allow us time to run like hell after lighting it.

Crap.

How about rockets? Or a trebuchet/catapult? Or an air-pressure cannon?

Dooey Jo · Post by **Dooey Jo** » 2005-09-09 09:22am

Rockets are a much better idea. For one thing, it's easier; although the theory of the workings of a rocket is way more complicated than that of a cannon, getting the appropriate materials and getting it to work in practise is easier (in fact, you can build rockets out of paper and clay). A rocket will also do very well with lower-grade black powder, and lower-grade equals less fingers blown off! One thing to keep in mind if you're going with that though: You will need to drill a hole, at least halfway through the fuel core in order to increase the area of the burning surface. If you don't, your would-be rocket will just stand there burning like a roman candle turned up-side down (and if you have a payload, that is not a good thing).

I have only managed to get two rockets flying with the inferior design, and both times I used a very fast burning fuel.

So yeah, if you want to do something cool involving sound, smoke and fire, I'd say you should go with rockets. If it's not advanced enough, make a guidance system for your rockets

Post by **Beowulf** » 2005-09-09 06:27pm

However, with today's society, the fact that your rocket uses gunpowder might still cause your project to be frowned upon.

I'd recommend the Trebuchet. No smoke, or fire, but it'll propel things rather impressively, depending on the object.

Zero · Post by **Zero** » 2005-09-09 06:28pm

I always was a fan of the catapult, myself.

tumbletom · Post by **tumbletom** » 2005-09-09 09:04pm

Rockets are a good way to go...I made a rocket out of cardboard and balsa wood once for class (though i didnt make my own fuel--i used one of those model rocket engines)

Also trebuchets are freakn awesome if you have time to build one..... ( of course it depends on how big you wanna make it)

And they have a really cool name

Enigma · Post by **Enigma** » 2005-09-09 09:50pm

I want to make a small trebuchet but I can't find any decent designs over the net. Anyone know how to make a trebuchet?

I've built a catapult about 15 years ago and I still have it but I want to make a trebuchet.

Luke Starkiller · Post by **Luke Starkiller** » 2005-09-09 10:28pm

Enigma wrote:I want to make a small trebuchet but I can't find any decent designs over the net. Anyone know how to make a trebuchet?

I've built a catapult about 15 years ago and I still have it but I want to make a trebuchet.

Put (very) simply you need:

2 A-Frames
1 Solid Base
1 Axle
1 Counter-weighted Throwing Arm

JointStrikeFighter · Post by **JointStrikeFighter** » 2005-09-13 12:02am

On MythBusters they where able to make a cannon with a bore of around 70mm out of a huge arse tree trunk about a metre in diameter. The trunk was strengthened by fitting still hot iron rings around the outside and allowing them to cool before drilling the hole. It worked pretty well; fired a stone ball several hundred metres IIRC. Of course, they then packed it full of high explosives and sealed the end with predictable results.

If you want to go for a rocket Shroom perhaps buying a bunch of model rocket motors and rigging them up to something would be cool. I can see it now;

'Multi-Stage Rocket Crashes into Crowd Killing Many'

Braedley · Post by **Braedley** » 2005-09-13 10:16am

Something easy that still goes boom would be a potato cannon. There are so many designs on the web that I won't even bother listing any. On the plus side, you can actually do an experiment with it (test different hair-sprays and the sort to see the effect on distance).

General Trelane (Retired) · Post by **General Trelane (Retired)** » 2005-09-13 02:09pm

I'd second the potato cannon--you can make it simply, and if you keep it at a reasonable size, the danger risk is minimized. Size the barrel for a typical potato.

I've used ABS plastic waste pipe and a rotary flint. Insert the potato (trim it to fit snug but not tight), spray starting ether into the breech (experiment to get the right air-fuel mixture), screw on the breech cover (which contains the flint), aim, and spin the igniter.

Loads of fun! Can easily get 50 yards or more, and the velocity is low enough that you can see it fly.

lPeregrine · Post by **lPeregrine** » 2005-09-13 06:18pm

Luke Starkiller wrote:
Enigma wrote:I want to make a small trebuchet but I can't find any decent designs over the net. Anyone know how to make a trebuchet?

I've built a catapult about 15 years ago and I still have it but I want to make a trebuchet.
Put (very) simply you need:

2 A-Frames
1 Solid Base
1 Axle
1 Counter-weighted Throwing Arm

Don't forget the sling, it'll give you much more impressive distance.

And add one more vote for the trebuchet, they're a ton of fun to make. I built a small one (~3' arm) in about 2 days, with just a saw and a nailgun. There's plenty of plans online, and it's pretty hard to screw up. I did mine without any calculations at all, and it was just a matter of slight adjustments to the sling to get it working.

SCRawl · Post by **SCRawl** » 2005-09-13 09:04pm

Another bonus to building a trebuchet as opposed to a catapult: you're less likely to break your teeth. Imagine setting a catapult off at the wrong time, with your face in the way. Ouch.

SCRawl · Post by **SCRawl** » 2005-09-14 01:46pm

Braedley wrote:Something easy that still goes boom would be a potato cannon. There are so many designs on the web that I won't even bother listing any. On the plus side, you can actually do an experiment with it (test different hair-sprays and the sort to see the effect on distance).

If you want to look up the potato (or "spud") gun, try here.

Shroom Man 777 · Post by **Shroom Man 777** » 2005-09-18 06:33am

We've built one. HUZZAH! Thanks loads, guys! I'll post the report here when I'm finished writing it.

BTW, I've named it the Objective Interin Ranged Thermo-Kinetic Projectile Delivery System.

Exonerate · Post by **Exonerate** » 2005-09-18 02:27pm

lPeregrine wrote: And add one more vote for the trebuchet, they're a ton of fun to make. I built a small one (~3' arm) in about 2 days, with just a saw and a nailgun. There's plenty of plans online, and it's pretty hard to screw up. I did mine without any calculations at all, and it was just a matter of slight adjustments to the sling to get it working.

Add wheels to the bottom of the trebuchet, it'll launch it's projectiles a longer distance.

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