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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: Ragnarok » Wed Oct 27, 2010 11:18 pm

jackssmirkingrevenge wrote:Most epoxies cure faster when at higher temperatures

Pretty much. When I'm sculpting miniatures, for which I use a "putty" like epoxy, I often leave them over the lamp on my desk (which I usually have on when sculpting).
Normally, it takes about 3-4 hours to cure them enough that I can start the next stage (a full cure takes 12-24 hours), but over the lamp, it's usually good for the next stage after an hour.

Strictly, the lamp is a little hotter than the recommended putty cure temperature, but it doesn't seem to do the models any real mischief. But I do bring that up as getting epoxy too hot can be detrimental to the curing process.
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Unread postAuthor: jackssmirkingrevenge » Wed Oct 27, 2010 11:43 pm

Another good point to make which really affects proper curing is that epoxy tends to get more viscous in colder temperatures, and allowing it a few minutes in a bain marie before mixing is extremely helpful and also reduces curing time.
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Unread postAuthor: Ragnarok » Thu Oct 28, 2010 11:02 am

jackssmirkingrevenge wrote:Another good point to make which really affects proper curing is that epoxy tends to get more viscous in colder temperatures

Yeah, that's one to remember with my sculpts if they're over the lamp - don't ever pick them up, wonder "is this cured yet" and poke it to find out. Because what you'll usually find is that "no, it wasn't" and "epoxy gets really soft when it's warm".

The next question is then usually: "Can I fix this before it cures completely?"
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 28, 2010 11:09 am

Presenting the most pathetic hybrid shot on spudfiles :roll: :D

[youtube]http://www.youtube.com/watch?v=xw9M-ozhqbk[/youtube]

Two things of interest, the blow-by starts to move the target before the projectile actually exited the muzzle, and the amount of time the tray gets stuck to the backstop :)

This was at 4x, but with a 2 foot barrel and just 20mL of chamber volume, that's a C:B ratio of around 0.12:1 :roll: so hardly surprising. I'm hoping to take it higher but it will need some mods to allow it to keep the disk in place, watch this space.

edit: took it to 10x, much better :D oh and in spite of the tiny C:B ratio, quite friggin deafening!

[youtube]http://www.youtube.com/watch?v=LgqQXpkgKt8[/youtube]
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Unread postAuthor: Fnord » Thu Oct 28, 2010 12:15 pm

JSR,

20ml at 4x is only 320 joules of avalible energy, plus a bit extra from initial pressure. (if Rag's old figure of 4000 J/liter is correct)


Also, 80 ml of air expanded to 8 times normal volume is 640 ml; even less than your barrel volume.
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Unread postAuthor: Ragnarok » Thu Oct 28, 2010 12:42 pm

Fnord wrote:If Rag's old figure of 4000 J/liter is correct...

It's most true at about 0 degrees C, but it's pretty close for 20 degrees (when it's more like 3720, but 4000 is still about 93% accurate).

Energy from pressure will be about 11 joules, so the total is like ~310J.
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Unread postAuthor: jakethebeast » Thu Oct 28, 2010 12:52 pm

JSR, im scared :D :D
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Unread postAuthor: MrCrowley » Thu Oct 28, 2010 2:42 pm

For a moment I thought you shot your chamber through a target :D

You should do a video in HD when you get a chance. :)
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Unread postAuthor: jackssmirkingrevenge » Thu Oct 28, 2010 10:36 pm

MrCrowley wrote:For a moment I thought you shot your chamber through a target :D


I actually have a few failed hybrid cartridge prototypes that would fit nicely into the barrel :roll: :D

You should do a video in HD when you get a chance.


Expect much more HD/HS videos and chrony results over the weekend, I'm especially curious to see how it compares with my 12 bore HPA coaxial.

I'll probably take it over 10x too, in the meantime check out the damage to the CO<sub>2</sub> capsule ammunition after just 2 shots :D
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 29, 2010 10:57 am

A couple of shots to unwind after a long day's work, I love this thing :)

Here it is at 11x, straight through a biscuit tin lid and the 1/2" ply box behind it, would have gone through both sides were it not for the solid granite backstop.

[youtube]http://www.youtube.com/watch?v=b-hKXiFaIrM[/youtube]

Target is a PC power supply, in both real time and at 420 frames per second, again it doesn't quite communicate how loud it is. My HPA pneumatic 0.75" failed to go through similar metal, hybrids win again :roll:

[youtube]http://www.youtube.com/watch?v=v4GhtiGB9GQ[/youtube]

Here's the power supply after I opened it up, very modern art :) note how dusty it is from years of neglect, which is the "smoke" just visible in the videos after impact.
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0.75&quot; holes in sheet metal make quite an impression, especially to someone raised with pen guns :D
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Unread postAuthor: Technician1002 » Fri Oct 29, 2010 11:33 am

I think one of those shots could be entered in the best shot contest.. Nice job.

Are you holding a better shot for the contest?
:shock:

Two things of interest, the blow-by starts to move the target before the projectile actually exited the muzzle, and the amount of time the tray gets stuck to the backstop Smile


I noticed the same thing on high speed shots. Here is a 3 frame sequence from some HS video. The blast is peeling the label off the bottle before the projectile exits.
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3 frames of HS video before the projectile exited the barrel.
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Frame before the label comes lose.
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Unread postAuthor: jackssmirkingrevenge » Fri Oct 29, 2010 12:31 pm

Technician1002 wrote:Are you holding a better shot for the contest?


To be honest I wasn't planning on entering, since I'm offering one of the prizes, hanging back for new blood and whatnot.

Another shot at 1000 frames per second in the meantime, as if the soup tin wasn't even there :D

[youtube]http://www.youtube.com/watch?v=zyU_pSKa52M[/youtube]

I noticed the same thing on high speed shots. Here is a 3 frame sequence from some HS video. The blast is peeling the label off the bottle before the projectile exits.


You can see the effect in the above video too, the CO<sub>2</sub> capsule is a slightly loose fit in the barrel.
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Unread postAuthor: Technician1002 » Fri Oct 29, 2010 12:36 pm

I entered, then decided to offer a prize since this contest is user funded, offering a prize and entering should not be a problem. If it is a problem, I should either remove my prize or my entry.

I entered early in hopes to set the bar for later entries to raise. It looks like it is happening.

A contest with no prizes is OK, but a contest with no entries is even worse.

I like the soup tin. It needs more light. A full tin is impressive as hydrostatic shock rips the entire back out of the can.
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Unread postAuthor: Ragnarok » Fri Oct 29, 2010 1:14 pm

Hmm... this doesn't actually seem to be indicative of all that much energy. I've shot air rifles at empty CO2 cartridges before, and they usually look like that after just a shot or two.

Would it be possible to get an actual chrony reading?
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Unread postAuthor: spudamine » Fri Oct 29, 2010 1:33 pm

Nice work, I'd be interested in seeing you try this configured as one of your ejecting cartridges, see how much power it loses. It's the same sort of size as the cartridge I'm musing over. You've got to admit having that sort of power semi-auto would be kind of fun although you'd need a monster of a magazine.
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