ETAv2.1 High Velocity Launcher

[inonickname]

I asked for a quote on 6mm id 8mm OD seamless stainless pipe from a UK supplier and still haven't heard back from them

B and Q sell that but in alluminium, not sure if it helps.

Nope, aluminum is both far too soft and weak even when sleeved in 1" OD hardened steel. If it doesn't swell and stretch, it will melt and warp. I'm probably going to get it from online metals, 6.22 mm ID 9.5 OD stainless steel. Then sleeve that.

[DYI]

@rp181: An impact flash is caused by released kinetic energy heating very fine fragments of the target/projectile to incandescence, combustion of those same particles (in the case of aluminum, at least), and visible spectrum EMR emitted directly from the energy release. At least, that's my understanding of it.

@ino: Good call on the aluminum. Any softer metals and alloys tend to fare very poorly in ETC/ETG chambers. I sent you a PM regarding the design on Photobucket.

[inonickname]

DYI, here's a PDF of the drawings.

I've ordered extra long drills to bore the barrel with, so it will still be 6mm even though customs has nicked my bb's... custom projectiles all the way it seems.

The insulator may need redesigning. The plastic will take a massive beating, but I can't see a 10mm rod being pushed through an 8mm hole too easily.

[rp181]

Keep in mind PTFE easily crushes, count on that being replaced frequently, so It may be better to go with dimensions that you can buy stock.

[DYI]

As I never got to build my own ETCG, I can't be certain of what will happen to this one. You'll obviously need a new insulator for every shot, as my experience with the ETG indicates, but whether or not the "endplug" and electrode will be reusable is anyone's guess.

When the propellant is initiated, the electrode will be forced back, spraying some of the insulator forward into the chamber and extruding some of it through the hole in the endplug. There are two possible causes of failure for the steel parts. First, the electrode may slam into the interior of the "endplug" hard enough to severely deform both of them. Second, and less likely, flows of hot, high pressure gas might erode the electrode and/or the "endplug".

The electrode will be single use regardless of material, but unless you're planning on an extremely high voltage ignition, it could pay to replace it with a tougher plastic, such as ABS or nylon.

[Lockednloaded]

sorry you aren't getting that many comments here, its an extraordinary launcher with amazing power. I just think it goes way over the heads of many users,me included

[Gun Freak]

Couldn't have said it better than LnL.
Although I have no idea how the propellent is water (possibly H2O is a product of some sorcerers majick reaction in that little chamber of yours), I still think it is awsome work and an awsome... errmmm... well, I guess it's a gun... Shame it won't be fired again. The title is misleading I'd make an 800 psi pengun but have no way to get 800 psi readily availible to me.

[inonickname]

Yes..the propellant is water. Take "propellant" to mean "working fluid". When you pass a multi kilojoule arc through a small amount of water, it's going to make a lot of very hot gas, very quickly.

I've ordered a delrin rod for the insulator, along with a set of extra long 6mm drills to bore the barrel from a piece of solid stock. (The barrel will be bored from both ends in on or two parts, assembled, then lapped). I don't think I'll redesign the elctrode/insulator. It should survive several low energy shots, but I can't see any way I can submit plastic to a 9km/s 10kj detonation and get multiple uses..

[lozz08]

hey ironnickname, I ordered a pack of 3000 0.25g bbs from ebay, here;
http://shop.ebay.com.au/?_from=R40&_trk ... Categories

sorry I dont know how to hyperlink.

This next bit is important.

There is a legal loophole where you are allowed to import bbs labelled as slingshot ammo. When you purchase from ebay write in the comments to seller section: "please label as slingshot ammo as they are not to be used in any sort of gun."

If for some reason this fails you, or you want some crazy penetration and damaging power, steel bbs can be had legally from an Australian seller here:
http://www.outdoorswarehouse.com.au/pro ... s-6mm.html

[Fnord]

DYI,

If you get a chance in the future, could you do some tests with a .177 bore? I had an ETG nearly finished, designed for BBs at 1.5 - 2KJ, but I never had the chance to test it above 300J.
I also didn't have a proper barrel. Brakeline doesn't have the tight tolerance required for high efficiency. I was also using plain air as a propellant so the problem was likely amplified by the higher temperature.

What exactly is your insulator made from? Since I intended to make a low-maintainance(haha) ETG, I was concerned about the insulator carbonizing and creating unwanted electrical connections. My end goal was to make one from some type of ceramic, reinforced by a metal housing and using some type of epoxy to fill the gaps between(the epoxy would not be exposed to much heat).
How much electrode corrosion have you experienced? Mine were threaded so I could just sand them clean and adjust as necessary, but as I said, 300 J didn't give results I could judge by.

(Yes, I fell for your false advertising trick. People relate to penguns more easily than some crazy electricaldischargedihydrogenmonoxideplasmificationidontunderstandthepicturelinearacceleratinghighfructosecornsyrupdevicetypething. I was originally going to ask this earlier, but lost my post to a browser crash and didn't feel like retyping it.)

[DYI]

Although I have no idea how the propellent [sic] is water...

Better wording would be that the working fluid is water. The propellant is technically a mixture of steam, H₂, O₂, and some H and O, along with whatever might remain of the paper chamber liner.

@Fnord:
.177" bore is unlikely. 4mm may occur at some point, but it's not a high priority at the moment.
What capacitance were you using for your tests? How did it perform at 300J?
My barrel has a poor tolerance as well, but efficiency is still reasonably good.

My insulators are currently ABS. I've also tried Nylon, but never got to do any fair comparison tests - I didn't have proper tools to cut the 2" long engagement on the 1/4"-20 threads, and since ABS was easier to cut its thread quality ended up being much better. The Nylon insulators, which seemed to perform poorly, may have been a casualty of the stress and deformation caused by threading the electrode into poorly-cut internal threads.

The main new design feature of ETAv2.1 over the previous version is the 1" diameter steel insulator casing. Machinable ceramic would likely be preferable over the existing plastic, but the facilities available to me don't allow me to work with it.

ETAv2.1 uses a steel electrode, which is eroded enough that re-facing is required after every shot. The surface boils and is then deposited back as solid globules, ruining the surface. There is, of course, also heavy carbonization. At 2kJ, a reusable insulator could be possible, but it would not be a simple task at all.

Also, the "false advertising" has almost doubled the daily viewership of the thread over the first day of its implementation. Not entirely conclusive, but interesting. I would expect reduced comments on a more technical topic, simply because a low percentage of members have the knowledge to discuss them. Viewership, however, is almost entirely dependent on title (and whether or not the thread happens to be in the recent posts list). I guess that being in the "Mini Showcase", the only correct placement for this thread, is also reducing the number of viewers.

[Gun Freak]

I tend to look at every single thread, even if I dont care what it is about, because every thread posted interests me a bit. Most of the time I dont even look at the title of the thread before I click on it. But this thread interested me a lot so I replied. Very groovy little creation here 8)

[rp181]

Ever think about ceramic?
Take a look at Macor, great stuff.

Oh ya, its expensive...

I read somewhere about multi-stepping the process. Use part of the energy to get everything vaporized, than dump the rest of the energy through the steam.

[inonickname]

hey ironnickname, I ordered a pack of 3000 0.25g bbs from ebay, here;
http://shop.ebay.com.au/?_from=R40&_trk ... Categories

sorry I dont know how to hyperlink.

This next bit is important.

There is a legal loophole where you are allowed to import bbs labelled as slingshot ammo. When you purchase from ebay write in the comments to seller section: "please label as slingshot ammo as they are not to be used in any sort of gun."

If for some reason this fails you, or you want some crazy penetration and damaging power, steel bbs can be had legally from an Australian seller here:
http://www.outdoorswarehouse.com.au/pro ... s-6mm.html

I DID ask him to label them as slingshot ammo. The piece of shit didn't. No way in hell am I going to import something similar again and be taken to court over it. I'll just make my own projectiles.

Steel bb's are a bit pointless for this. The idea is velocity, not energy. A steel projectile will also require greater amounts of propellant and have a greater chance of destroying the chamber.

To give you an idea of the forces involved here, I'm using a 6-8mm ID chamber with a 60mm OD-hardened steel chrome plated bar. This is not actually strong enough, and it will fail eventually. A lot of the survival of the chamber will be to do with it's inertia.

[Crna Legija]

To give you an idea of the forces involved here, I'm using a 6-8mm ID chamber with a 60mm OD-hardened steel chrome plated bar. This is not actually strong enough, and it will fail eventually. A lot of the survival of the chamber will be to do with it's inertia.

holy crap , how much pressure do you expect it to generate