[nukewater]

OK this is for all you engineer problem solvers out there. Here is what i told slapyo last night.
I am trying to make a potato launcher in the style of the old AA guns, pivoting x and y axis. So i figure the y axis would be easy.. the x is my problem.. here is the situation.
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i have 2 disks right... one atop the other.. the bottom.. has wheels... so it wont move.. buthas a pole in the middle

now. i have another disc.. that slides ONTO the pole on the other disc

ok so the top disc has wheels so it can move freely on the bottom disk around the pole

ok.. so say i put a gear.. lying horizontly on the top disk

attatch it by chain to a gear attatched to the pole (which is attatched to the bottom disk)

so when the gear on the top disk is twisted, it would want to spin the bottom disk right

but since the bottom disk is emplanted and wont move.. will the tourque effect rotate the top disk

so the bottom disk would try to spin in a clockwise fashion, but it couldnt so the top disk would spin in counter-clockwise
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that theoretically would promote a twist action, would it not? all you engineers let me know

also anyone into potato launchers can help me out 2.

*Ps.. i wanna be an engi when i gro up.. TFC style with the monkey wrench and the cigar in my mouth *

 

[mkuchere]

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12-02-2003 at 01:02, nukewater wrote:
I am trying to make a potato launcher

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LMAO!!!

 

[rellimpk]

Hey, potato launchers rock!!! I´ve made a few in my day, but nothing THAT complex!

 

[siragan]

Pneumatic are way way way better. I think that the peak power of a hair spray combustion cannon is somewhere around 25psi, and the cannon I made could do 150psi on compressed air.

I knew a guy who made a 300psi spool valve actuated cannon capable of getting a potato *almost* supersonic.

here´s a pic of my cannon:

concerning your whole pivoting issue, I think that conical bearings would be good for the application...

 

[birddog]

i would agree with the conical bearing idea. BTW if you get the cans of butane used to refill lighters, it works MUCH better than hair spray. I could get into some discussions about how to make the darn thing much more powerful but i will save that for another day.

 

[nukewater]

well i contemplated using pneumatics, but the idea of hauling a compressor around seemed burdenfull. i THINK i figured out how to make it spin, i had to ask my physics teacher and even HE didnt know.. noone seems to know so im gonna go on my own judgement saying it will work.. any ideas on how i should build my 2x 40mm barrel AA-style potato launcher? The option is still open to pneumatics if the opportunity arrises itsself

 

[pballer98c]

wow! how complicated. mine is very simple yet effective! i have all the parts for a pneumatic one i can use during paintball... should built it soon. g/l (sorry im not helping at all)

 

[birddog]

Well, Schedule 40 PVC is popular, burst strength of 200 psi. I would recommend deciding on a propellent then how far you want to go, how big you are willing to go, and then the construction will kind of decide itself. Things I learned: the chamber for the gas should be 3 times the volume of the barrel. Barrels over 3 feet in length were pointless. too large of a chamber for gas is not good either - the pressure builds to slowly to get good acceleration. Let me know what you decide, then I can help with the final design. I have built more than a few of these...

 

[siragan]

do the whole thing in machined aluminum and use a giant spool valve.. they´re incredibly strong, consistent, and reliable valves.

Burt pressure is a thing of the past
Use pneumatics (much more powerful- trust me you´ll want the extra power)

throw on a long barrel for good gas expansion
Mount the whole thing on bearings, and possibly use workgears to adjust pitch/yaw/elevation/etc

You can use compressed air or co2 or other types of gas as a propellant. You can pick up a regulator just about anywhere... even put the reg right on the tank you´re using.

Of course you could always make a dinky little pvc ******* cannon and then realize you´ve wasted your time because it has no balls.

spending the extra time and money is well worth it.

 

[birddog]

I will admit that PVC is the cheap way out and it doesn´t have the capability that aluminum does. Keep in mind that not everyone has the time money and knowledge to work with aluminum under pressure and still make it safe! PVC is easy and is a great way to learn about how size and shape affect everthing.
Just curious, what kind of range are you getting with your compressed air? The thing about long barrels is you need more volume of propellant otherwise you will indeed lose range and accuracy. This is easier to figure out with compressed air than with burn compression, but it doesn´t take much trial and error to get it right.
If this is your first cannon, build a "little pvc ******* cannon" to learn the basics. aluminum under 200 psi+ is not something to fool around with if you don´t have a clue what you are doing. and if this were a site with limited access and I knew people wouldn´t kill themselves doing it, I would post the design of a cannon that uses a powder charge. you wanna talk about range! but it took forever to get the design to hold together for repeated use. In short, yes PVC is the cheap way out, but is a great way to learn the basics. Aluminum is a bad choice for sustained pressure, stainless is the way to go. If you have any questions about an idea, ask. We will all try to give an answer based on how you want to approach this.