My new air cannon

J

jwpaine

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Joined
Mar 10, 2007
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My new air cannon I built this weekend:
http://www.youtube.com/watch?v=Ah5LNBifOWo

Boy is this a hoot!

Next thing I need to do is solve the equation given vertical hang time with known gravity to find the initial velocity. I wonder how I will go about factoring in air resistance when finding the initial velocity given hang time - that will require some serious differential equations... I'll have to look into that.

Cheers - John
 
Hmmm...if you were my son, I'd send you to a far away private school :lol:
 
Denis said:
Hmmm...if you were my son, I'd send you to a far away private school :lol:
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Hah! Well, I've gotten to where I am today because my parents have allowed me to do stuff like this. A few summers ago I had my 8 foot garage-door spring powered trebuchet in the front lawn......had a bit of an accident once and it threw an apple through our window :D

I'm in college, BTW, majoring in Engineering Physics.

Cheers!
 
Sweet! :wink:

But now my eleven-year-old wants to build one! :shock:

Eliz.
 
Re:

stapel said:
Sweet! :wink:

But now my eleven-year-old wants to build one! :shock:

Eliz.
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Small ones can be even more fun, especially for kids of that age - you two could make a small one that shoots foam balls - a small air chamber and barelel - at most it might scare the cats. For a small one, the sprinkler valve is $10 + another $10 or so for the parts.

I don't recommend making combustions ones - too dangerous, especially with PVC. I once made a large cannon out of PVC, using combustible propane / air mixture - I would set it off with a spark from an oil burner ignition transformer (10kv spark) from a safe distance. I remember shooting a D-Cell battery past the tree line, over the lake at my camp...well over a quarter mile.

Small ones are fun too - as long as they are pointed in a safe direction.

I am so excited because I am now done with Calc II - just got back from taking my final! :D :D
Cheers - John
 
JW. You are MIT bound. You are an anomaly, but in a good way.:):)
 
That's cool JW. Except we can't see your face too well. You look like the Unabomber. :):)
 
galactus said:
That's cool JW. Except we can't see your face too well. You look like the Unabomber. :):)
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Yeah, I know, but it's only to be safe. 60 lbs of air doesn't seem like a lot, but a failure would have enough energy behind it to send fragments of plastic into your body...I don't want my face to be unprotected. PVC pipe can withstand fairly high pressures, but when it fails, it shatters - those pieces can't be picked up by x-ray :) If one of the pieces going into the valve were to fail, it would have enough velocity to break bone. Safety must be urged when doing these types of projects. I'll put in 80+ PSI, but I'm not going to be looking at it when it goes off.

Have a good summer, ya'll - I'll post more videos here over the summer when I am down to my camp. I have a few projects lined up to keep me sane until school starts up again :D
 
John,

That was really good! I am specially impressed that you are so safety conscious. If I were you, I would throw a folded blanket over my cannon, that will catch stray fragments in case of an accident.

As for air drag - start with "kv" (or \(\displaystyle k\frac{dx}{dt}\).)

Tht LaTex is acting like super-script again!!
 
Majoring in Engineering Physics?. That's cool, JW. Sounds like a heady and interesting field. Then, get your degree in theoretical physics?. :):):) Bosonic string theory
 
John,

Nice piece of engineering/fabrication! I'm impressed. We used to make chemical (lighter fluid) cannons from steel soda pop cans (about 6 cans, taped end to end). A slightly used tennis ball was just about the perfect fit (and not too deadly -- though you still wouldn't want to be on the receiving end). Oranges work, too. :D Lighter fluid (just a couple of drops) was squirted into the back of the cannon through a small hole. Spin the cylinder to spread the fluid, allow to vaporize. Grasp the cannon firmly with both hands, tucking it under one arm. Someone else applies a match to fuel port. I leave the rest to your imagination. (PS Steel shrapnel is easily detectable with X-rays. Fortunately we avoided need for such.)

I must confess, we didn't do a rigorous analysis of the design, since we were lacking information on loads resulting from a chemical explosion. We just started with very small amounts of "propellant" and derived the optimal amount empirically. (Being considerably older now, and perhaps slightly(?) wiser, I cannot recommend this approach to the public at large.)

Your point about the dangers of compressed gases is spot on. I recommend you calculate hoop stresses of all components. Also calculate longitudinal/tension loads for end cap and joint failures. A factor of safety of 4.0 is a minimum for pressure vessels. A factor of safety of 10.0 is used on items involved in human safety. Securing your cannon prior to pressurizing/firing might also be a good idea (perhaps by laying a sand bag on it). Just some thoughts from a fellow enthusiast... :D

The engineering physics sounds rather useful. Could you please design a good fusion reactor. :D The world is in bad need of one. (They're hoping the one being built in southern France will get them above the break even point.) It will be a pleasant change when we can leave hydrocarbon fuels behind -- and also not have to worry about nuclear waste that lasts for tens of thousands of years.

Enjoy your summer!

Bill
 
Pretty neat, JW. You know what?.....you ought to try building a trebachet. I don't know if that is spelled correctly. You know what that is?. A catapult type contraption. Throw pianos, cows, etc. :D
 
galactus said:
Pretty neat, JW. You know what?.....you ought to try building a trebachet. I don't know if that is spelled correctly. You know what that is?. A catapult type contraption. Throw pianos, cows, etc. :D
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Done and done :p

Built a few, actually - and there is quite a bit of math involved. Mine were not big enough to throw cows, though :D Here is a video of me about 3 years ago with one of my Trebuchet made out of 2x4s and powered by 250lbs of garage door springs: http://youtube.com/watch?v=ATSQAuxcHU8

Here is a pic:
n563050705_748570_6858.jpg


As my Youtube description says:
This is my little trebuchet that I made a few years back. Traditional counterweight acceleration due to gravity is too low, so I decided to put on some heavy garage door springs.... I think this is around 250 lbs of pull at full extension (that is a **** load of energy) When adjusted correctly, I remember throwing apples almost a foot ball field. In this video, as far as I can remember it is actually being powered by heavy black rubber bands... I unforchiently don't have a video of when I added the springs. See how fast the end of that arm is going? Now think how fast the end of the sling is going, and that is the initial velocity when the pin slips out... that is one fast apple.
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Trebuchets are a lot more fun than air cannons. I should build another one sometime. I guess this is what I do for fun, living on a small island with nothing else to do :D

Cheers!
 
Touche, JW. Now, next is an Aludium Q36 Explosive Space Modulator. :D
 
galactus said:
Touche, JW. Now, next is an Aludium Q36 Explosive Space Modulator. :D
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You can't give me an easier project? I don't even have an engineering degree yet.... jeesh! :D

Have a good summer -
John
 
That was a joke of course. Apparently, you're too young to remember the space man from Bugs Bunny. That was his device to destroy the Earth because it obstructed his view of Venus. :D
 
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