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Or anyone intrested in electrothermal launchers.
As i said i really appreciate that you have interest in my ETG. It is very ghetto, reason i didnt posted about it before but now that the god of ETG's showed interest in my humble gadget here it is.
Edit: Video link added--> https://vimeo.com/132975809
With the exception of the capacitor bank, it was made from what i had, the tools i had at the time was a drill and some burins, it was made before i had access to machining facilities. One electrode is made of stainless steel and it fits over the plasma cartridge it is held in position by the momentum of a thick steel plate, the other electrode is a 5 mm brass bar with a hole in the center to hold an aluminium bridgewire (.8mm thick), the plasma cartridge is made of nylon, considering i found it offers acceptable performance compared to other polymers also it leaves almost no residue after ablation and doesn't quench the discharge so easily but its difficult to work especially with dull tools, the walls of the cartridge are 4 mm thick and the capillary channel is 5mm diameter 14mm long, the barrel is an aluminium tube 6.12mm ID 30cm long, which i cannibalized from a "cheap" airsoft gun, the barrel is inserted and glued with cyanocrylate to the stainless electrode which is protected by a nylon cap to avoid damage of the glue joint by the shock made by the impact with the steel plate.
Here is a photo of it,
In analogy to yours the propellant consists of an aluminium water mixture, a very fine aluminium powder (20-70 um particle) suspended in water (40/57.5 by weight) with 2.5% carboxymethyl cellulose as gelling agent, i tried pyrotechnic magnalium but it reacts with water alone too quickly. For this particular launcher-power source set, i found the ideal amount of propellant to be approximately 85 mg/KJ.
The capacitor bank consist of 80 450V 680uf electrolitic capacitors, i bought them new relatively cheap ($170) as they are chinese knock off rubycon and nippon-chemicon, the weight variation is almost 50%!, yet they have worked fine so far i m pretty sure i had done more than 200 shots some of them involving inductive loads, the capacitors are connected in parallel series and conform 4 banks which are in parallel, each 800v 3400uf, for a total energy of 4Kj this enables me to have some control of the energy in increments of 25%, all successful shots leaved 370-450V on the capacitor banks.
And now the ugliest of the ugly my glorious Cap bank (this photo only shows three banks the other was in construction)
Considering how much energy remained in the capacitors i compared the deepness of the bulge made in 16 gauge stainless steel sheet by the impact to the one made by a pellet gun with a measured 22J, i estimate the efficiency to be 15-20%, i estimate velocities of 1500-2000 m/s with .2g BB, every time i tried to launch something heavier than .7g at energies higher than 1.5KJ (effective delivered electrical energy) the glue of the barrel broke or the plasma cartridge exploded.
Here is a capture i took thorough a shade 6 glass while firing the shoot that made the crater of my profile picture, it was 800V 4KJ potential energy 2.2KJ delivered .2g airsoft BB, 350mg propellant. as can be seen there is a really big leak, the cause was a bad union between the breech and the barrel (it was glued ) and it eroded and ruined a good length of the barrel also the muzzle blast is really big and the standoff distance was like 20 cm so it engulfed the target and can't be seen.
I tried to color correct the green hue but still it looks really bad so sorry for it, also here you can see the square steel plate that provides inertial confinement to the electrode
Here is the result of that shoot
Here a shoot i did towards putty to compare with yours
Capture of the plasma cartridge shooting to the atmosphere without barrel at 1KJ, the plasma plume measured approximately 70cm, it is really freaking bright this was thorough a 14 shade glass
The most recent photo has a bit more than two years, now i have machining tools so expect something better in the near future also i'm going to buy another 4KJ of the same capacitors soon , i got noticed that they are available again at the same price. I'm not sure if someone has done it but i got curious to see what happens if such thing hit an higher biological entity so i used an old chicken leg, the smell after that was.. if someone is curious to see what happened i can send you the link of the photo.
I hope you have found my post interesting it is great to see the god of ETG's curious about my achievements!.
Last edited by equusvenustas on Wed Jul 08, 2015 5:16 pm, edited 1 time in total.
Good god it's glorious.
Congratulations on joining the big leagues with DYI and Larda (or is that the minor leagues considering projectile dimensions? ).
Some more details and video would be nice but I realize your current situation. Can't wait to see what you build next.
Well, thanks for the compliments!, I consider i m not close from being at the level of Larda or DYI yet, but i can certainly say i am a member of the 1km/s club , i already have some work done in my hybrid i think it will help to fix the projectile size issue
What details you would like me to add?, I have some videos of it shooting but i don't have where to host it, i don't want to use youtube, any recommendations? i have though of using vimeo but i don't know how good is.
Soon i will post a drawing of my new prototype it will be made in a lathe and everyting.
Mainly just build materials and drawings/CAD of the "plasma chamber" as you call it.
Vimeo seems good. I stopped using YouTube recently due to the growing acceptance of HTML5 video (webm) and the ability to host video on my own website without overly complicated non-free solutions like jwplayer/flowplayer/etc.
You could simply upload them on a site like MediaFire for people to download and watch. Or you could send them to me to host.
I don't have any drawings but i could make some as its a very simple launcher, also i don't have CAD but i suppose i could use blender just wait a day or two and i will post the drawings and if i can do it fast enough a render.
Thank you for the offer but i think i will try Vimeo, i don't want to unnecessarily occupy space on your server .
HOT DAMN looks like fun!!!
Your pre- machine tools ETG certainly works better than mine did! The craters have different aspect ratios because you were using heavier BBs, but I'd say this works just as well as my last pure ET gun did (before I introduced the aluminum fuel). I also suspect that the finer grade of aluminum powder is helping the reaction go to completion with the decreased oxidizer proportion as compared to my tests. The longer barrel is certainly helping as well.
This is a pretty ingenious launcher, and works surprisingly well considering the tools and materials used. You've done some good work here, and I'm looking forward to seeing what you can do with machine tools. Also looking forward to a video, and seeing if you can figure out how to measure the muzzle speed without the measuring device getting blinded by the EMP. Me and an electrical engineer I know designed such a device and had it built a few years ago. The PCB was promptly seized at the border on suspicion of being missile electronics
Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.
Re: A post for DYI
What can i say!, i am really happy you are impressed for what i achieved with my limited resources and materials, but i need to say you are my inspiration, you showed me it is possible to accomplish my dream of seeing "meteorites" and cleared some of the path! you had the audacity to embark and pursue the "impossible" in hobbyist terms, you helped me a lot by leaving a trail towards the key, have perseverance search and learn about real research done by scientists!, but still it wasn't easy, i had to do my homework, as you probably has observed even the slightest changes in design, propellant, electric pulse characteristic etcetera, greatly changes the behavior of this devices for the good or the bad, i thought i needed pulse capacitors to reach a respectable efficiency but i managed to have acceptable performance with knock off electrolytics.
Now i added a video link about it, its very bad footage because i never intended to publish this ugly launcher but by seeing the success of it here i recovered some footage i had lost of it.
Yes definitely the finer aluminium powder helps, i tried with little pieces of Al foil but it didn't do anything, also judging by the size and loudness of the muzzle blast i think the barrel is short, i've been searching for a longer one but i haven't found pipe that fits the BBs as good as airsoft barrels, and in my country airsoft is almost unknown. This are just assumptions but if i manage to contain all leaks, extend the barrel to 50cm and use a finer Al powder i think i could increase the power by 20% or more.
For measuring the speed i've been thinking about using a long PVC pipe as vacuum tunnel, pumped down to 2.5X10-2 Torr with a "cheap" vacuum pump used to evacuate refrigeration systems, obviously i will add an appropriate expansion chamber to contain the light of the muzzle blast, i think the projectile will outrun the gases so no worries about aerodynamic drag, then some couple of meters away put the shooting chrony sensor gates at twice the distance to increase its speed range and use two laser pointers as light source beaming thorough small holes on the pipe and using a cylindrical lens to spread the beam.
I almost finish the drawings about my new electrothermal launcher i hope to post them really soon. I cant comprehend how a chronograph PCB can be mistaken as missile electronics, yet a smartphone is much more dangerous and has a legitimate potential to be used as flight computer.
Here is the new design of the ETG i still need to figure out how to use the lathe properly none the less i will try to make it before this month ends
Edit: drawing added
Edit again: Drawing of the design of Quagga
Edit again again: well i finally found about the 2008 problem while searching "electrothermal", i have to ask for apologies for saying your problems were "cool and absurd", im certain those were really hard times for you.
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