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Ramjet BBMG

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Demon » Sun Dec 11, 2011 2:52 pm

Yes, but there's a pressure .0275 bar pressure loss. How can I shoot BB's while both the air intake and barrel muzzle face the sam direction ?

This is getting out of the intuitive bounds and I don't fully understand :?:
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Unread postAuthor: Demon » Sun Dec 11, 2011 2:57 pm

Have you thought about the drag effect on performance, especially considering the thrust will be directed forward?


Yes, would the air intakes be wide open it would slow down the aircraft. So, that's an indirect way for the main engine to propell the BB's out of the barrel.
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Unread postAuthor: wyz2285 » Sun Dec 11, 2011 3:19 pm

How can I shoot BB's while both the air intake and barrel muzzle face the same direction?

:lol: :lol: :lol: :lol:
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 11, 2011 3:23 pm

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Unread postAuthor: Demon » Sun Dec 11, 2011 3:24 pm

wyz2285 ... yes ?    

JSR, then why not use a windmill under the belly instead ?
I said no extra weight :evil: !


Basically, what I'm looking for is a semi-auto rifle with a reasonable ROF, unharmful tracer-like projectiles.

But juggling with all that and low weight can only result in compromises...
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Unread postAuthor: al-xg » Sun Dec 11, 2011 4:00 pm

then why not use a windmill under the belly instead ?

That is basically what you are already doing...


I also think a cut down mini-airsoft gun would be a more efficient solution, there are too many losses in trying to get the energy back through air flow.

I'm guessing this is an electric plane ?


I really can't see this working, 300fps airspeed won't generate enough pressure to propel a BB to anywhere near that velocity.
Airguns are really inefficient.


Timetravel EDIT:

sorry for hijacking but you have to see it:
http://truthfrequencynews.com/?p=21344


That smoke grenade was going very fast in the second video !
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Last edited by al-xg on Sun Dec 11, 2011 4:06 pm, edited 1 time in total.
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Unread postAuthor: POLAND_SPUD » Sun Dec 11, 2011 4:00 pm

sorry for hijacking but you have to see it:
http://truthfrequencynews.com/?p=21344



@demon
JSR, then why not use a windmill under the belly instead
so first you put battery on the plane, motor converts that to motion (you get some energy lost as it isn't 100% efficient), then propeller pushes the plane forward (again energy loss), then you put a small windmill that converts air movement (reltive to the plane) into motion (energy loss), then you use that motion to power a compressor compressing air (energy loss), then you use air to fire bbs (again not 100% effient)

That's wasteful you know.
You'd get more out of a battery if you use it to power the motor that powers the compressor... and that's more or less what an airsoft gun does

you got a battery that powers the motor, that motor compresses air which you use to shoot bbs out of the barrel
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Unread postAuthor: Demon » Sun Dec 11, 2011 4:38 pm

You are right. The only advantage is the non existent extra coils and magnets + steel casing of the brushless motor. Even at that, the extra drag might just void that advantage.

I think I'll simply go with a 3ish RPS slingshot shooting stabilised combos of capacitors and bright directionnal LED. That or I'll cook my own glow stick chemicals, either way it'll be a PITA to arm just before launch. I'll see if I can come up with something simple and efficient.

Edit:

Just tested a 330uf capacitor with a high intensity 5mm LED and the results are interesting. With the current resistor, it holds it's charge for about a second, while being very bright. Projectile cost's about .54$ per shot. Not that bad.
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 11, 2011 5:09 pm

Here's a "quick" sketchup view of what I would have in mind.

The twin booms are principally composed of two 2 or 3 litre soda bottles which are also the air tanks, filled to 150 psi or so.

In a central nacelle there is the valve mechanism, BB chamber, barrel and camera facing forward, and pusher propellor in the rear.
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Unread postAuthor: Demon » Sun Dec 11, 2011 5:24 pm

Here's more what I had in mind (Picture)

A BBMG won't give me what I want on the aircraft. The dreamed system would be a 3RPS tracer round rifle, sort of AH-64 style.
The 330MFD capacitor + High Intensity directionnal LED seems to be the perfect projectile for such launcher.

Now what's left is to design a 300fps 3RPS launcher :scratch:
I hesitate between pneumatic and sling powered. I hear slingshots are more efficient.
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Unread postAuthor: POLAND_SPUD » Sun Dec 11, 2011 5:26 pm

you're saying
me wants OV bronco



my resonse is
ok, but I want a remotelly controlled turret on it
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Unread postAuthor: Demon » Sun Dec 11, 2011 5:34 pm

There already are two turrets on the airplane :)
The live FPV cam in the cockpit and the HD camera on top of the wing section.
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 11, 2011 5:40 pm

Simpsons did it :)

Image

Image
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Unread postAuthor: POLAND_SPUD » Sun Dec 11, 2011 5:53 pm

I was about to post the same pic :-D

now that would be cool but I'd much rather see an RC mounted airsoft gun than see a project that never gets finished because it is too ambitious...

so I am saying -> get a cheapo airsoft gun + glow in the dark bbs
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Unread postAuthor: Demon » Sun Dec 11, 2011 5:58 pm

Meh, yes, maybe, but ...

I want to be all like "IMMA FIRING MAH LAZOR" and glow in the dark bb's will barely be visible.

3RPS/300FPS is a goal impossible to reach with the weight restrictions.

So, ... I think it's rocket time. Barrel-accelerated rocket time.

(I am well aware of the 30 degree rule for setting off model rockets)

EDIT:
More to think of it, I might make an hybrid of both ideas. The Cap+LED round would be accelerated by a small amount of sugar rocket out of the short barrel, and then trace it's bright red light accross the sky.
3RPS would be as easy as 3.1415 since the recharging system would be electrically controlled.
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