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mini hybrid win!

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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Unread postAuthor: JDP12 » Mon Sep 06, 2010 3:04 pm

Very cool JSR, congrats on getting it working! are you worried about that plastic electrical connector failing or cracking though?
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Unread postAuthor: jakethebeast » Mon Sep 06, 2010 3:12 pm

just remember to hit it with smooth korner like table, then it wouldnt weaken the chamber much
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Unread postAuthor: MrCrowley » Mon Sep 06, 2010 3:34 pm

Wow, this is unlike anything you've built before; it actually works and you used PVC :D

Just kidding, I actually really like it. A 6x mix is pretty impressive too, I thought you'd have fueling trouble at anything about 2x or 3x really. What would performance be like with a longer barrel? But I 'spose the barrel is scaled to the cannons miniture size.
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Unread postAuthor: ilovefire » Mon Sep 06, 2010 6:21 pm

congratulations JSR on a working mini hybrid,
sorry a bit of topic but do you think someone could maybe help me with my mini hybrid it is all finished i just need help with fueling and burst disk stuff thanks
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Unread postAuthor: jackssmirkingrevenge » Mon Sep 06, 2010 11:22 pm

JDP12 wrote:are you worried about that plastic electrical connector failing or cracking though?


It took a 6x mix without the disk bursting several times and doesn't look any worse for wear, I think it can take the strain. I've used similar connectors in HPA applications (such as my rattlesnake V3) and never had a failure of the threaded section.

Wow, this is unlike anything you've built before; it actually works and you used PVC :D


By jingo!

çunt :roll: :D

What would performance be like with a longer barrel? But I 'spose the barrel is scaled to the cannons miniature size.


Really, the barrel is oversized for the pistol-type project this was destined for, so upping the mix is the way to go.

In that regard, I might be able to bend the electrode a little further towards the schrader in order to reduce the spark cap and get better ignition at higher mixes.

ilovefire wrote:do you think someone could maybe help me with my mini hybrid it is all finished i just need help with fueling and burst disk stuff


It would help us help you if you could post some specific questions... looking good by the way!
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Unread postAuthor: ilovefire » Tue Sep 07, 2010 12:44 am

jackssmirkingrevenge wrote:
ilovefire wrote:do you think someone could maybe help me with my mini hybrid it is all finished i just need help with fueling and burst disk stuff


It would help us help you if you could post some specific questions... looking good by the way!


thanks, i found out that i was trying to use to much butane but then i redid my math and i got it to fire quite consistently at a 3x mix but then i screwed up the spark gap trying to make it smaller but now im re epoxying it with about a .5 - 1mm gap so hopefully higher mixtures will come.
and just a suggestion, you could use a metal schrader cap with a seal in it then drill a hole in the middle, and a drilled out schrader valve instead of that plastic fitting you got there. pretty much what i used! :)
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 07, 2010 1:25 am

ilovefire wrote:you could use a metal schrader cap with a seal in it then drill a hole in the middle, and a drilled out schrader valve instead of that plastic fitting you got there. pretty much what i used! :)


That's good for smaller "pengun" calibres but it wouldn't have given me enough flow for a hybrid...

Speaking of which, I was thinking of going really miniature and making a hypervelocity 1mm hybrid :D
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Unread postAuthor: ilovefire » Tue Sep 07, 2010 1:37 am

jackssmirkingrevenge wrote:
ilovefire wrote:you could use a metal schrader cap with a seal in it then drill a hole in the middle, and a drilled out schrader valve instead of that plastic fitting you got there. pretty much what i used! :)


That's good for smaller "pengun" calibres but it wouldn't have given me enough flow for a hybrid...


iv got a 5mm ID barrel on mine and maybe a 4mm hole in the end cap so there isnt to much restriction! or is there?

jackssmirkingrevenge wrote:Speaking of which, I was thinking of going really miniature and making a hypervelocity 1mm hybrid :D


i did think of that this morning but then i thought how would you get a burst disk to work at that size? and if you have a larger bust disk and a smaller barrel whats stopping it from just getting stuck in the barrel?
but im sure your a bit smarter than me and have already thought of all that :lol:
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 07, 2010 1:44 am

ilovefire wrote:iv got a 5mm ID barrel on mine and maybe a 4mm hole in the end cap so there isnt to much restriction! or is there?


More than you think... the diameter is 20% less, but a 5mm barrel has a cross section of 0.1964cm<sup>2</sup>, while a 4mm port has an area of 0.1257cm<sup>2</sup>, meaning a 36% flow reduction which obviously has a significant effect on performance.

i did think of that this morning but then i thought how would you get a burst disk to work at that size? and if you have a larger bust disk and a smaller barrel whats stopping it from just getting stuck in the barrel?


I was thinking I would use a silicone seal as in my non-burst disk cartridges, I have one seal that will hold a 1mm BB at 800 psi...
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Unread postAuthor: ilovefire » Tue Sep 07, 2010 1:50 am

jackssmirkingrevenge wrote:More than you think... the diameter is 20% less, but a 5mm barrel has a cross section of 0.1964cm<sup>2</sup>, while a 4mm port has an area of 0.1257cm<sup>2</sup>, meaning a 36% flow reduction which obviously has a significant effect on performance.


im not really sure what you just did but i understand that i need to go see if i can make that hole a bit wider then :?

jackssmirkingrevenge wrote:I was thinking I would use a silicone seal as in my non-burst disk cartridges, I have one seal that will hold a 1mm BB at 800 psi...


well that makes sense :lol:
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 07, 2010 1:58 am

ilovefire wrote:im not really sure what you just did but i understand that i need to go see if i can make that hole a bit wider then :?


I think one of the most basic things for a spudder to comprehend is the relationship between diameter and area.

For example, for the same pressure, a launcher with a 2 inch barrel has 4 times the power potential of a launcher with a 1 inch barrel, even though it sounds like it should only be double.

Similarly, if you go from say a 10 inch diameter chamber to a 5 inch diameter chamber of the same length, chamber capacity is not 50% but 25%.

This is why for example as you reduce in calibre it's so important to up the pressure in order to keep performance up.
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Unread postAuthor: ilovefire » Tue Sep 07, 2010 2:14 am

jackssmirkingrevenge wrote:
ilovefire wrote:im not really sure what you just did but i understand that i need to go see if i can make that hole a bit wider then :?


I think one of the most basic things for a spudder to comprehend is the relationship between diameter and area.

For example, for the same pressure, a launcher with a 2 inch barrel has 4 times the power potential of a launcher with a 1 inch barrel, even though it sounds like it should only be double.

Similarly, if you go from say a 10 inch diameter chamber to a 5 inch diameter chamber of the same length, chamber capacity is not 50% but 25%.

This is why for example as you reduce in calibre it's so important to up the pressure in order to keep performance up.


oh right that dose make sense now you tell me, thanks for explaining it
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 07, 2010 11:01 am

A but of judicious hammering later, managed to shorten the spark gap, it's now happily igniting at 8x, with that a 0.22 almost made it through the 0.6mm steel plate :)

Some videos at 8x, then I'll try upping a few x...

edit: the videos I promised:

Firing at a soup tin at 8x filmed at 420fps, now do you understand why I don't hold it ;)

[youtube]http://www.youtube.com/watch?v=zHBxANGz-FI[/youtube]

0.6mm steel target shot at 8x filmed at 420 fps, just barely didn't penetrate:

[youtube]http://www.youtube.com/watch?v=Pmu0Xo0GfOw[/youtube]

Deliberately filmed in poor lighting at 1000 fps to show the ignition flash:

[youtube]http://www.youtube.com/watch?v=kQYZN7K80Ho[/youtube]
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Unread postAuthor: JDP12 » Tue Sep 07, 2010 11:47 am

That's sweet! Are you content with the performance now at 8x?
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Unread postAuthor: jackssmirkingrevenge » Tue Sep 07, 2010 11:48 am

Let's see if it objects to ignition at 9x ;)

edit! woohoo! first click piezo ignition at 9x (6.3mL butane/propane, chamber pressure 135 psi) and it's probably only a few fps from penetrating the steel. Lovely splash from the lead fragments though, I also put in the "before" and "after" 0.22 pellets. With a steel projectile I have no doubt it would have penetrated.

No more time for testing this afternoon, but I'll definitely keep adding x to push the limit of what piezo ignition can achieve...
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