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Catching Projectiles (50J+)

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DerAlbi

Sun Apr 19 2015, 02:50PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Hi guys...
as i am progressing with my machine... i run into problems catching the projectile.
My setup right now is a layered setup of clay and aramid fiber sheets.. everything made hot, so the clay grips into the fiber...
This is the backside of the thing... allready repaired multiple times.

This massive thing sits in 3 stacked big plastic cups.. the innermost cup is allowed to slide and pushes against foam.. this is kind of an additional energy-absorber (this actually works fine)

After a shot the projectile penetrates nearly the whole clay-aramid-laminat. Its worse then you hit a spot which was hit before.

When the projectile is removed, you see the initial layer of clay (which absorbs the projectile and avoids refelction) and then all the damaged layers of aramid...

This is now not practical anymore to repair... it just sucks. its to weak.

Obviously what i want is...

a safe system which does not reflect the projectile under any condition
doesnt damage the projectile since they are hand made
absorbs the energy easily
easily repaired after multiple shots

I think the laminat of some elastic material and aramid is still the way to go. Its just the clay thats not good enough anymore. It gets displaced to easy and doesnt grip the fibers too well... So i am looking for alternatives.

Maybe using hot glue
This could work.. if hot enough it should grip the fibers good enough.. its flexible when cold and could withstand the impact without beeing displaced. Different layers of energy absorbtion/compressibility could be done by adding flakes of foam into the hot glue. Problem: the hot clue could be not "chewy" enough so it will damage on impact and damaged spots arent safe anymore. Unlike the clay, hotglue is not self-healing when deformed. -> damage needs to be avoided completely.
A toplayer of clay will allways be present of course... it really prevents projectile reflection very well.

Maybe using different stuff like hotglue, that are more flexible..
..but what? Silicone?

If you got ideas..... and or comments on what seem most likely to work... "shoot"

Dr. Slack

Sun Apr 19 2015, 04:13PM

Registered Member #72 Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659

I tend to use a *long* PVC tube, filled with stacked discs punched from corrugated cardboard. There is no chance of reflection once the projectile has bored through 500mm or more of cardboard. Increase the length until it doesn't reach the end. Retrive the projectile by pushing the discs out from one end with a broom.

DerAlbi

Sun Apr 19 2015, 04:54PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Hmmh... thats too much work to get the projectile back... currently i just get it out with my fingers or a pair of plyers. thats kind of important to me.. since not every shot works and i want many shots in a short time when i optimize my design. i actually dont like it even now... getting the projectile out, cleaning it from the clay and inserting it again... it takes my head off the actual problem.

Bored Chemist

Sun Apr 19 2015, 05:15PM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

A trough of water is the traditional answer, but you need to be able to point the projectile down quite steeply or it will bounce off the surface.
Of course, you could fire the shot into the side of a big bag full of water. Just make sure it's far enough away that the electrics don't get wet.

dexter

Sun Apr 19 2015, 06:14PM

Registered Member #42796 Joined: Mon Jan 13 2014, 06:34PM
Location:
Posts: 195

i use a cardboard box filled with bubblewrap
is quite easy to stop and recover the projectile

DerAlbi

Sun Apr 19 2015, 06:31PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

I would like to focus on lamination method.. water and stuff.. thats not practical for multiple shots a minute.. i dont want to walk around the room.. its bad enough that i need to stand up from my chair at all

...and please.. bubble wrap..

How much Joule does your projectile have.. i am penetrating 1cm of plywood with ease.. anything made from cardboard is way to unsafe

I just added wood behind the clay.. to prevent the clay to bludge out.. however that wood disintegrated rather quick..
I think its important to catch the projectile in a increasing amount of mass. I found the wood ok.. the projectile only stuck half way in and the wood distributed the force..
Has anyone any experience in the durability of substances what would be suitable for lamination? Anything that could deform, is easy to repair, easy to work with... anything that does not get hard enough to damage the iron projectile... aaand it must not be too elastic so that the projectile doesnt reflect. However elastic deformation is prefered over the continous need to repair the target.

BigBad

Sun Apr 19 2015, 08:50PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

What's the projectile made of?

The traditional answer for stopping ballistic objects is sandbags.

DerAlbi

Sun Apr 19 2015, 10:10PM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

LOL

So easy, so tempting

Projectile is made from pure iron... the only thing is that i would need a durable sand-sack.... hmmmmmh. Best one so far!
Anyone knows a good material? normal cloth will go kaputt.

The projectile has no sharp tip, butsince its a perfect zylinder, the edges apear to be sharp.
The untreated kevlar will simply push away over time....
Maybe sand is a good backbone.. to protect the projectile tip i will maybe go with hotglue laminat. Sand will deform, but not much, so the hotglue should hold for a while... and the hiot glue will not damage the projectile. put some clay on top, and the projectile is guaranteed to stick...

did i miss something? any improvements?

Ash Small

Sun Apr 19 2015, 11:49PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I've given this a bit of thought, around ten seconds. Dr Slack's tube appeals to me, rather than sandbags or water, and the clay seems to work, to a point.....

Fill a tube with clay, the tube stops the clay moving 'outwards'....not completely, but more so than your previous setup.

You'll still need to dig the projectile out of the clay, but as it can't displace the clay sideways as much, it won't penetrate as far.

You'll still need to re-pack the clay after each shot, but it won't penetrate as far.

Personally, I'd use a length of 2" ID scaffold tube, stuffed with clay.

Just my 2 cent's worth

DerAlbi

Mon Apr 20 2015, 12:10AM

Registered Member #2906 Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 727

Yeah.. the problem is that currently i have close to zero work retrieving the projectile. if that increased by ten-fold... its not attractive anymore.
When i try t optimize my firmare or other stuff i do not want to be distracted by the tests, i want to program, shoot, evaluate, program, shoot, evaluate.. and so on... as you see: no digging in the list

And debugging Coilgun-Firmware is one of the most shitty problems i came across.. since there is no slow or stepwise shot its awfull to debug. there is actually no debugging.. its eithere working or not^^ that takes a lot of concentration.

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