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Foreshadowing for the summer...

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Foreshadowing for the summer...

Unread postAuthor: Killjoy » Tue Jul 06, 2010 1:53 am

[youtube]http://www.youtube.com/watch?v=-ov-175Z5n8[/youtube]

And after several failed (shorted out) ignition systems, I modified an existing ignition system idea and created mine which does not use a high voltage arc but is very reliable and simple to use.

Image
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I'll let you guys figure out how it works, shouldn't be hard to guess. I'll go into more detail in the coming weeks as my project finishes materializing.
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Unread postAuthor: inonickname » Tue Jul 06, 2010 3:00 am

An FAE?

At a guess I'd say your using the airflow to agitate fine charcoal dust to make a fuel-air explosive. That's just judging by the manifold at the back and the black stains on that copper.. You may just be loading it with BP for all we know :P
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Unread postAuthor: POLAND_SPUD » Tue Jul 06, 2010 3:11 am

a glowplug ?
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Unread postAuthor: Hotwired » Tue Jul 06, 2010 2:54 pm

Metal wire/wool and a pyro substance.

Second guess would be fine wire wool that gets burned and blasted all over the tube.
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Unread postAuthor: Killjoy » Wed Jul 07, 2010 1:23 am

Hotwired nailed it.
I take a little bundle of steel wool, swirl it around in some ultra fine BP, and then clamp it in. 12 volts is all it takes, and it never fails.
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Unread postAuthor: inonickname » Wed Jul 07, 2010 1:34 am

Alright...Why the air compressor?
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Unread postAuthor: SpudBlaster15 » Wed Jul 07, 2010 3:20 am

inonickname wrote:Alright...Why the air compressor?


It looks like my dream is coming true... FEAR is coming out of storage. :D

Nice work on the igniter Killjoy, and I hope you stick around and post more often. Your posts were always some of my favourite to read back in the day.

Can't wait to see what you're working on this time around.
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Unread postAuthor: inonickname » Wed Jul 07, 2010 6:28 am

SpudBlaster15 wrote:
inonickname wrote:Alright...Why the air compressor?


It looks like my dream is coming true... FEAR is coming out of storage. :D

Nice work on the igniter Killjoy, and I hope you stick around and post more often. Your posts were always some of my favourite to read back in the day.

Can't wait to see what you're working on this time around.


Oh I recognize it now you say that...The chamber did seem disordinately large for such a small powder charge.
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Unread postAuthor: psycix » Wed Jul 07, 2010 2:56 pm

I think....
The powder charge is just the ignition for a hybrid mix.
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Unread postAuthor: Killjoy » Thu Jul 08, 2010 3:58 am

I do apologize for my absence. School was rather hectic this year and along with a rough break up with the girlfriend I've been kept preoccupied for the past couple months.

But what better way to mend a broken heart then by flat out f*cking sh*t up with a giant cannon. FEAR is back and I have a month of free time to demolish all junk I have accumulated.

The video is from spring break. It was the first test with the barrel using a new sliding breech mechanism of mine. Basically it slides and retracts to allow removal so projectile can be placed, then the segment is put back and extended to connect everything.

Sadly, I ignored my gut and my calculations and assumed the internal flow guider made from 10 gauge steel could withstand 1000+psi for a few milli-seconds. Boy was I wrong and now I have a few things else to fix.

Pristine Breech Mechanism
Image
The sliver pipe attached to the union can slide forward to fill the gap between burst disk and barrel. The rubber thing with handles was the attachment for a 4" "thumper" barrel.

The U bend was parallel to the end of the chamber before firing. Note the bent connecting bolts.
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Engineering Failure
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My summer toy.
Image

And yes the BP charge is used to ignite the 10x fuel mix.
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Unread postAuthor: Hotwired » Thu Jul 08, 2010 4:23 am

Isn't that the same problem we've (or maybe it was just me) put forward as cause of failure in large PVC over-under cannons before?

Where the elbows making the 180* turn were too weak they were cracking if too free to flex in response to the mass of gas being dumped during firing e.g. no barrel or an unclamped barrel.

It looks like you have the elbows only support being themselves if the connector to the barrel is just a sliding not locking connection so the recoil forces from the gas will be transmitted to the rest of the cannon through that 180* bend and er... trying to unbend it.


Shame about the connection, good luck with the repairs and strengthening.
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Unread postAuthor: Killjoy » Thu Jul 08, 2010 4:53 am

Yeah the thought crossed my mind that I should support the elbows so as to prevent this kind of damage due to the resultant forces due to the pressure, but I was impatient and figured one test couldn't do much damage. Yet another one of my "you're a dumb*ss" moments.

Repairs should be quick none the less. Some new bolts, a little sledge work bending everything back, and some support welding and I should be set to go.
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