Catching Projectiles (50J+)
DerAlbi, Sun Apr 19 2015, 02:50PMHi 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"
Re: Catching Projectiles (50J+)
Dr. Slack, Sun Apr 19 2015, 04:13PM
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.
Dr. Slack, Sun Apr 19 2015, 04:13PM
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.
Re: Catching Projectiles (50J+)
DerAlbi, Sun Apr 19 2015, 04:54PM
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.
DerAlbi, Sun Apr 19 2015, 04:54PM
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.
Re: Catching Projectiles (50J+)
Bored Chemist, Sun Apr 19 2015, 05:15PM
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.
Bored Chemist, Sun Apr 19 2015, 05:15PM
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.
Re: Catching Projectiles (50J+)
dexter, Sun Apr 19 2015, 06:14PM
i use a cardboard box filled with bubblewrap
is quite easy to stop and recover the projectile
dexter, Sun Apr 19 2015, 06:14PM
i use a cardboard box filled with bubblewrap
is quite easy to stop and recover the projectile
Re: Catching Projectiles (50J+)
DerAlbi, Sun Apr 19 2015, 06:31PM
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.
DerAlbi, Sun Apr 19 2015, 06:31PM
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.
Re: Catching Projectiles (50J+)
BigBad, Sun Apr 19 2015, 08:50PM
What's the projectile made of?
The traditional answer for stopping ballistic objects is sandbags.
BigBad, Sun Apr 19 2015, 08:50PM
What's the projectile made of?
The traditional answer for stopping ballistic objects is sandbags.
Re: Catching Projectiles (50J+)
DerAlbi, Sun Apr 19 2015, 10:10PM
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?
DerAlbi, Sun Apr 19 2015, 10:10PM
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?
Re: Catching Projectiles (50J+)
Ash Small, Sun Apr 19 2015, 11:49PM
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
Ash Small, Sun Apr 19 2015, 11:49PM
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
Re: Catching Projectiles (50J+)
DerAlbi, Mon Apr 20 2015, 12:10AM
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.
DerAlbi, Mon Apr 20 2015, 12:10AM
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.
Re: Catching Projectiles (50J+)
Dave Marshall, Mon Apr 20 2015, 05:52PM
Imagine a plastic shoe box, with a hole a few inches in diameter cut in one end. Something like this, but with a tight fitting top.
Place a thin sheet of something that's easily penetrated but tends to return to it's original shape, perhaps like polyurethane foam, over the opening, then fill the box about 75% of the way with airsoft pellets, and put on the lid. Fire through the foam in to the box of pellets. The foam should prevent most of the pellets from escaping, especially when the sheet is new, and should definitely ensure that any that do escape simply drop out in to a tray below the box, rather than flying off.
A very similar method is used for stopping bullets without causing expansion or other deformation. You'll have to replace the foam every so often, but the sheet should be able to be quite cheap, and you ought to be able to get a number of shots from each sheet. Retrieving the projectiles is as simple as taking the top off and rooting around in the box.
Dave Marshall, Mon Apr 20 2015, 05:52PM
Imagine a plastic shoe box, with a hole a few inches in diameter cut in one end. Something like this, but with a tight fitting top.
Place a thin sheet of something that's easily penetrated but tends to return to it's original shape, perhaps like polyurethane foam, over the opening, then fill the box about 75% of the way with airsoft pellets, and put on the lid. Fire through the foam in to the box of pellets. The foam should prevent most of the pellets from escaping, especially when the sheet is new, and should definitely ensure that any that do escape simply drop out in to a tray below the box, rather than flying off.
A very similar method is used for stopping bullets without causing expansion or other deformation. You'll have to replace the foam every so often, but the sheet should be able to be quite cheap, and you ought to be able to get a number of shots from each sheet. Retrieving the projectiles is as simple as taking the top off and rooting around in the box.
Re: Catching Projectiles (50J+)
Dr. Slack, Mon Apr 20 2015, 08:05PM
So I got in the bath this evening, thinking about your problem (hmmm, probably TMI!) I liked Dave's shoebox idea, perhaps full of sand rather than airsoft, perhaps a corrugated cardboard window rather than foam. But it's still messy, still gets damaged and has to have bits replaced, and needs a rummage around every shot.
So, back up, and rethink. You don't really want to catch the projectile, so much as stop it.
Think Newton's cradle. As the first ball comes in, it stops dead, giving up all its energy (less a tiny bit) to the next ball of the same mass, which carries on at much the same speed. Now you have to stop the next ball, so the problem has just shifted, and the projectile would probably get deformed, stopping dead in a fraction of a mm.
So, some other material than iron for the first target. How about a lump of tread from a dead auto tyre? Tough, cheap, lossy. As the rubber would absorb some energy, deforming and recoiling, if it had the same mass as the projectile, then the projectile would continue forward, albeit at a lower speed. Increasing the mass of the rubber target above that of the projectile would compensate, and at some mass ratio, related to the coefficient of restitution, the projectile could again drop at zero speed after hitting the rubber target. Arrive at the ratio by sums, or perhaps easier, experiment. If in doubt, err on the low side, so the projectile moves forwards rather than recoils. We now have a lump of auto rubber recoiling at some speed, but, we can repeat the trick, and back it with another, larger piece, which collision will remove more of its energy. You can continue this stack until the recoil speeds are manageable. I suggest hanging all the bits of rubber from strings, as pendulums, rather like a Newton's Cradle, with spaces. The spaces are so that each collision takes place independently.
See this diagram. Three stages of increasing weight rubber are shown. The projectile comes in from the left, stops dead after hitting the first piece of rubber, and drops into a towel (not shown).
Now, an important question. Is auto rubber hard enough to survive a reasonable number of shots, soft enough to avoid damaging the projectile, and lossy enough to absorb the energy in a reasonable number of stages? I think that could be an interesting experiment to do.
While on the subject of dead tyres, consider an alternative (no diagram this time). Take a whole tyre, and punch a small hole in the tread. Fire the projectile tangentially to pass through the hole. It will now skid, bounce, tumble round and round the inside of the tyre, after contacting the inside obliquely, gradually losing energy as it comes to rest.
Dr. Slack, Mon Apr 20 2015, 08:05PM
So I got in the bath this evening, thinking about your problem (hmmm, probably TMI!) I liked Dave's shoebox idea, perhaps full of sand rather than airsoft, perhaps a corrugated cardboard window rather than foam. But it's still messy, still gets damaged and has to have bits replaced, and needs a rummage around every shot.
So, back up, and rethink. You don't really want to catch the projectile, so much as stop it.
Think Newton's cradle. As the first ball comes in, it stops dead, giving up all its energy (less a tiny bit) to the next ball of the same mass, which carries on at much the same speed. Now you have to stop the next ball, so the problem has just shifted, and the projectile would probably get deformed, stopping dead in a fraction of a mm.
So, some other material than iron for the first target. How about a lump of tread from a dead auto tyre? Tough, cheap, lossy. As the rubber would absorb some energy, deforming and recoiling, if it had the same mass as the projectile, then the projectile would continue forward, albeit at a lower speed. Increasing the mass of the rubber target above that of the projectile would compensate, and at some mass ratio, related to the coefficient of restitution, the projectile could again drop at zero speed after hitting the rubber target. Arrive at the ratio by sums, or perhaps easier, experiment. If in doubt, err on the low side, so the projectile moves forwards rather than recoils. We now have a lump of auto rubber recoiling at some speed, but, we can repeat the trick, and back it with another, larger piece, which collision will remove more of its energy. You can continue this stack until the recoil speeds are manageable. I suggest hanging all the bits of rubber from strings, as pendulums, rather like a Newton's Cradle, with spaces. The spaces are so that each collision takes place independently.
See this diagram. Three stages of increasing weight rubber are shown. The projectile comes in from the left, stops dead after hitting the first piece of rubber, and drops into a towel (not shown).
Now, an important question. Is auto rubber hard enough to survive a reasonable number of shots, soft enough to avoid damaging the projectile, and lossy enough to absorb the energy in a reasonable number of stages? I think that could be an interesting experiment to do.
While on the subject of dead tyres, consider an alternative (no diagram this time). Take a whole tyre, and punch a small hole in the tread. Fire the projectile tangentially to pass through the hole. It will now skid, bounce, tumble round and round the inside of the tyre, after contacting the inside obliquely, gradually losing energy as it comes to rest.
Re: Catching Projectiles (50J+)
DerAlbi, Mon Apr 20 2015, 09:22PM
The idea with the tire is interesting.. but i think the friction will make the rubber melt over time and just make the projectile dirty. the proectile has 90° edges.. so its prety sharp when it slides along.
The other thing you discribe (with the picture) is kind of whats going on in a laminated material too. Every layer increases the moved (buldged out) mass and compression absorbs energy. I think tire-rubber is quite hard and will tend to reflect instead of dampen the energy - Its not meant to absorb energy.. that would be bad for the car. You are right that i want to stop the projectile rather than just catching it.
You diagram shows exactly the needed setup, but the implementation is more compact if made of laminated material..
In the end my current setup is allready something like this: ive got the cups screwed on a wood that bends, the inner cup is flexible and can move and is dampened by foam and i just add more stages before that where the projectile impacts. and the frontend is what must endure the most abuse.
Thats why sand is maybe the best frontend. its easy to repair, has quite some mass and spreads energy hapily. The challenge is to package it..
Lets say the sand would be the second hanging thing in your grapics.. the first would still be clay to catch the projectile and the third one is the moving cup damped by foam... i just wouldnt go with rubber...
As you said, there is a impeact velocity where the projectile tends to reflect (lower speeds) and were it moves through, loosing energy. I need to cover every aspect...
DerAlbi, Mon Apr 20 2015, 09:22PM
The idea with the tire is interesting.. but i think the friction will make the rubber melt over time and just make the projectile dirty. the proectile has 90° edges.. so its prety sharp when it slides along.
The other thing you discribe (with the picture) is kind of whats going on in a laminated material too. Every layer increases the moved (buldged out) mass and compression absorbs energy. I think tire-rubber is quite hard and will tend to reflect instead of dampen the energy - Its not meant to absorb energy.. that would be bad for the car. You are right that i want to stop the projectile rather than just catching it.
You diagram shows exactly the needed setup, but the implementation is more compact if made of laminated material..
In the end my current setup is allready something like this: ive got the cups screwed on a wood that bends, the inner cup is flexible and can move and is dampened by foam and i just add more stages before that where the projectile impacts. and the frontend is what must endure the most abuse.
Thats why sand is maybe the best frontend. its easy to repair, has quite some mass and spreads energy hapily. The challenge is to package it..
Lets say the sand would be the second hanging thing in your grapics.. the first would still be clay to catch the projectile and the third one is the moving cup damped by foam... i just wouldnt go with rubber...
As you said, there is a impeact velocity where the projectile tends to reflect (lower speeds) and were it moves through, loosing energy. I need to cover every aspect...
Re: Catching Projectiles (50J+)
BigBad, Mon Apr 20 2015, 09:44PM
It turns out that when it impacts the projectile stops and whatever it impacts starts moving; bit like Newton's cradle.
So (if the projectile doesn't penetrate like a needle) you want as much mass thickness of material as there is mass per unit length of the projectile.
BigBad, Mon Apr 20 2015, 09:44PM
It turns out that when it impacts the projectile stops and whatever it impacts starts moving; bit like Newton's cradle.
So (if the projectile doesn't penetrate like a needle) you want as much mass thickness of material as there is mass per unit length of the projectile.
Re: Catching Projectiles (50J+)
Bored Chemist, Tue Apr 21 2015, 08:49PM
re Rubber: boing!
You may find this helpful.
which refers to this.
Bored Chemist, Tue Apr 21 2015, 08:49PM
re Rubber: boing!
You may find this helpful.
which refers to this.
Re: Catching Projectiles (50J+)
ConKbot of Doom, Thu Apr 23 2015, 07:15AM
what about a water brake, with water flowing though a pipe?
Water is pumped in from the left, and the projectile enters from the right, enters the pipe, partially filled with water, where it gets slowed to a stop. The water flowing, is contained by the fitting on the end and drains back to your reservoir, and the initial splash is contained too. Maybe saw the reducing tee in half, only glue the bottom half on, and clamp the top on, so when the projectile washes its way back to the entrance, you take the cover off and grab it out. Or use a bigger drain line, and just pluck your projectile from the reservoir.
ConKbot of Doom, Thu Apr 23 2015, 07:15AM
what about a water brake, with water flowing though a pipe?
Water is pumped in from the left, and the projectile enters from the right, enters the pipe, partially filled with water, where it gets slowed to a stop. The water flowing, is contained by the fitting on the end and drains back to your reservoir, and the initial splash is contained too. Maybe saw the reducing tee in half, only glue the bottom half on, and clamp the top on, so when the projectile washes its way back to the entrance, you take the cover off and grab it out. Or use a bigger drain line, and just pluck your projectile from the reservoir.
Re: Catching Projectiles (50J+)
Dr. Slack, Thu Apr 23 2015, 08:18AM
Water brake, brilliant.
My concern is that water is low viscocity and high modulus. The first means that you'd be tempted to use a pipe barely larger in diameter than the projectile to get it to stop in a reasonable distance, the second means that if you did, your pipe would feel barrel-exploding type forces, and you'd need a very strong pipe.
Use close-fit pipe, and add bubbles to the water from a fish-tank pump or some other means, to make the water much less 'hard', like the way novice divers can dive into a pool of bubbles so they don't get really hurt when they mess up the triple somersault.
Or, instead of the long pipe, construct it from a series of Tees connected together, so there's a pressure relief channel every few inches.
Dr. Slack, Thu Apr 23 2015, 08:18AM
Water brake, brilliant.
My concern is that water is low viscocity and high modulus. The first means that you'd be tempted to use a pipe barely larger in diameter than the projectile to get it to stop in a reasonable distance, the second means that if you did, your pipe would feel barrel-exploding type forces, and you'd need a very strong pipe.
Use close-fit pipe, and add bubbles to the water from a fish-tank pump or some other means, to make the water much less 'hard', like the way novice divers can dive into a pool of bubbles so they don't get really hurt when they mess up the triple somersault.
Or, instead of the long pipe, construct it from a series of Tees connected together, so there's a pressure relief channel every few inches.
Re: Catching Projectiles (50J+)
DerAlbi, Thu Apr 23 2015, 06:00PM
I feel a bit like this would be overkill But hey, its definitively something to keep in mind, if some day i need some test-steup for continous shooting! this concept is quite interesting.
What bothers me is the water flow rate. Or the water at all: you cant avoid asmetric waterflow or projectile entry. you kind of mess up your tube with that... right`? hmmmh. Solutions? Also in a thin tube the pressure must go somewhere. this would either result in a high water reservoir or in extrem stress for valves and/or pumps.
A thicker tube would avoid that rpoblems but the water-flow would be insane. or one uses something thicker like honey
Please note that any discussion about that would be (for now) pure theory. Its at the current state not practical to have such advanced setup.
DerAlbi, Thu Apr 23 2015, 06:00PM
I feel a bit like this would be overkill
But hey, its definitively something to keep in mind, if some day i need some test-steup for continous shooting! this concept is quite interesting.What bothers me is the water flow rate. Or the water at all: you cant avoid asmetric waterflow or projectile entry. you kind of mess up your tube with that... right`? hmmmh. Solutions? Also in a thin tube the pressure must go somewhere. this would either result in a high water reservoir or in extrem stress for valves and/or pumps.
A thicker tube would avoid that rpoblems but the water-flow would be insane. or one uses something thicker like honey
Please note that any discussion about that would be (for now) pure theory. Its at the current state not practical to have such advanced setup.
Re: Catching Projectiles (50J+)
Ash Small, Thu Apr 23 2015, 07:29PM
"UHMWPE fibers are used in armor, in particular, personal armor and on occasion as vehicle armor, cut-resistant gloves, bow strings, climbing equipment, fishing line, spear lines for spearguns, high-performance sails, suspension lines on sport parachutes and paragliders, rigging in yachting, kites, and kites lines for kites sports. Spectra is also used as a high-end wakeboard line.
For personal armor, the fibers are, in general, aligned and bonded into sheets, which are then layered at various angles to give the resulting composite material strength in all directions.[11][12] Recently developed additions to the US Military's Interceptor body armor, designed to offer arm and leg protection, are said to utilize a form of Spectra or Dyneema fabric.[13] Dyneema provides puncture resistance to protective clothing in the sport of fencing"
Some form of 'ballistic pendulum' padded with Dyneema might do the trick
Ash Small, Thu Apr 23 2015, 07:29PM
"UHMWPE fibers are used in armor, in particular, personal armor and on occasion as vehicle armor, cut-resistant gloves, bow strings, climbing equipment, fishing line, spear lines for spearguns, high-performance sails, suspension lines on sport parachutes and paragliders, rigging in yachting, kites, and kites lines for kites sports. Spectra is also used as a high-end wakeboard line.
For personal armor, the fibers are, in general, aligned and bonded into sheets, which are then layered at various angles to give the resulting composite material strength in all directions.[11][12] Recently developed additions to the US Military's Interceptor body armor, designed to offer arm and leg protection, are said to utilize a form of Spectra or Dyneema fabric.[13] Dyneema provides puncture resistance to protective clothing in the sport of fencing"
Some form of 'ballistic pendulum' padded with Dyneema might do the trick
Re: Catching Projectiles (50J+)
BigBad, Thu Apr 23 2015, 11:35PM
Just wrap some sandbags in multiple plastic bags and forget about it.
BigBad, Thu Apr 23 2015, 11:35PM
Just wrap some sandbags in multiple plastic bags and forget about it.
Re: Catching Projectiles (50J+)
Ash Small, Fri Apr 24 2015, 02:15AM
Yes, BB, I agree, but Dyneema isn't a lot more expensive than polythene, it won't need replacing as often which, I think, is Der Albi's point. Sand is also excellent to put behind whatever takes the impact. The 'ballistic pendulum' bit just seems to make sense to me, as it allows more energy to be absorbed without deforming the projectile, but maybe it's not required.
I did read up earlier on elastic and non-elastic collisions, after Bored Chemist's post (which I did enjoy reading). I'm not sure if Dr Slack's 'Newton's balls' thing works with rubber, as, against intuition, it won't be an 'elastic collision'. I did say I'm not sure about this point
Ash Small, Fri Apr 24 2015, 02:15AM
BigBad wrote ...
Just wrap some sandbags in multiple plastic bags and forget about it.
Just wrap some sandbags in multiple plastic bags and forget about it.
Yes, BB, I agree, but Dyneema isn't a lot more expensive than polythene, it won't need replacing as often which, I think, is Der Albi's point. Sand is also excellent to put behind whatever takes the impact. The 'ballistic pendulum' bit just seems to make sense to me, as it allows more energy to be absorbed without deforming the projectile, but maybe it's not required.
I did read up earlier on elastic and non-elastic collisions, after Bored Chemist's post (which I did enjoy reading). I'm not sure if Dr Slack's 'Newton's balls' thing works with rubber, as, against intuition, it won't be an 'elastic collision'. I did say I'm not sure about this point
Re: Catching Projectiles (50J+)
ConKbot of Doom, Fri Apr 24 2015, 03:32AM
Oh yes, definitely not close fitting pipe, at least if you want to make it out of plastic. Perhaps injecting the water tangentially, at a steep angle, so that you get swirling going on inside the pipe, which will mix air in, as desired, and if the pipe isnt too long, you could even get the center to stay filled with air. Ideally that would try to self-center the projectile, but with a blunt end, I'd expect it to 'dig' in, and yaw the round more. Maybe add some shallow tapers to try and guide the slug where it needs to go, and if you can make it from PVC and survive the impacts, just replacing the pipe on occasion isnt the end of the world.
Or if a specific weight of oil can get frothed up and hold that for a bit as you pump that, you could use that instead of water.
Check out different firmness of clay too, they vary from soft, hand formable stuff, to really firm stuff thats meant to be sculpted with tools. Maybe a firmer clay would deform less, meaning more energy could transfer into a foam or sand damper? If the container you mount it in is stout enough, and the projectile doesnt fully embed itself, you could pull the projectile out, and touch up the surface of the clay with a hammer pretty quickly.
ConKbot of Doom, Fri Apr 24 2015, 03:32AM
Oh yes, definitely not close fitting pipe, at least if you want to make it out of plastic. Perhaps injecting the water tangentially, at a steep angle, so that you get swirling going on inside the pipe, which will mix air in, as desired, and if the pipe isnt too long, you could even get the center to stay filled with air. Ideally that would try to self-center the projectile, but with a blunt end, I'd expect it to 'dig' in, and yaw the round more. Maybe add some shallow tapers to try and guide the slug where it needs to go, and if you can make it from PVC and survive the impacts, just replacing the pipe on occasion isnt the end of the world.
Or if a specific weight of oil can get frothed up and hold that for a bit as you pump that, you could use that instead of water.
Check out different firmness of clay too, they vary from soft, hand formable stuff, to really firm stuff thats meant to be sculpted with tools. Maybe a firmer clay would deform less, meaning more energy could transfer into a foam or sand damper? If the container you mount it in is stout enough, and the projectile doesnt fully embed itself, you could pull the projectile out, and touch up the surface of the clay with a hammer pretty quickly.
Re: Catching Projectiles (50J+)
Bored Chemist, Sat Apr 25 2015, 11:58AM
We may have finally found a use for porridge.
Bored Chemist, Sat Apr 25 2015, 11:58AM
We may have finally found a use for porridge.
Re: Catching Projectiles (50J+)
Dr. Slack, Sun Apr 26 2015, 09:07AM
This damned water brake has been nagging at my mind. I think I have the answer.
You have a long trough of water, with a magic window that consists of a 'water-diode' at the end, that lets objects in, but doesn't let water out. Fire the projectile through the window, reach in and fish it out of the trough where it's stopped.
I have a simple design for this water diode, but I'll hold back on the details for the moment. Hint, it's not a passive device.
Dr. Slack, Sun Apr 26 2015, 09:07AM
This damned water brake has been nagging at my mind. I think I have the answer.
You have a long trough of water, with a magic window that consists of a 'water-diode' at the end, that lets objects in, but doesn't let water out. Fire the projectile through the window, reach in and fish it out of the trough where it's stopped.
I have a simple design for this water diode, but I'll hold back on the details for the moment. Hint, it's not a passive device.
Re: Catching Projectiles (50J+)
Ash Small, Sun Apr 26 2015, 09:23AM
Surely, if it's not a 'passive device', a better analogy would be 'water transistor'?
Ash Small, Sun Apr 26 2015, 09:23AM
Dr. Slack wrote ...
.Hint, it's not a passive device.
.Hint, it's not a passive device.
Surely, if it's not a 'passive device', a better analogy would be 'water transistor'?
Re: Catching Projectiles (50J+)
DerAlbi, Sun Apr 26 2015, 01:41PM
Ive got news: a total FAILURE I went ahead and tried to stop the projectile..
The setup is made of essentially 5 buffer zones..
1) clay to avoid relfection
2) hard foam covered with 6 layers of kevlar laminated with hotglue*
3) the hard foarm is pushed against soft, but allready compressed foam
4) 3. presses against a heavy cup thich has wax at the bottom with all sorts of metals i found in it. (just to add weight). The cup is then suspended again with foam.
5) the whole thing is of course screwed to wood which also flexes..
*The Kevlar laminated with hotglue made initially a really good impression. The glue penetrated the fibers (after heatreating and massaging each layer in) and on the contrary to clay it avoids the fibers from getting pushed away. The main failure of pure clay was that the projectile slipped through holes in the kevlar.. which now seemed to be avoided. Six layers were allready stiff and hard as hell and this made me put it directly on hard foam since it didnt be spuposed to bend much anyway.
I was completely wrong in my self gut-feeling. Projectile kinetics is really not intuitive anymore.
Here the shot:
After the shot the projectile stopped in the backside-protection-clay. This was initially placed to give the push to the foam an increasingly growing compression force.
After removing the projectile one could get a good impression on the impact site:
Where in closeup you can see how the projectile just went through the kevlar like... well like a projectile that goes through way insufficient material
The laminat looked like this initially
..and of course there is a exit wound
DerAlbi, Sun Apr 26 2015, 01:41PM
Ive got news: a total FAILURE
I went ahead and tried to stop the projectile.. The setup is made of essentially 5 buffer zones..
1) clay to avoid relfection
2) hard foam covered with 6 layers of kevlar laminated with hotglue*
3) the hard foarm is pushed against soft, but allready compressed foam
4) 3. presses against a heavy cup thich has wax at the bottom with all sorts of metals i found in it. (just to add weight). The cup is then suspended again with foam.
5) the whole thing is of course screwed to wood which also flexes..
*The Kevlar laminated with hotglue made initially a really good impression. The glue penetrated the fibers (after heatreating and massaging each layer in) and on the contrary to clay it avoids the fibers from getting pushed away. The main failure of pure clay was that the projectile slipped through holes in the kevlar.. which now seemed to be avoided. Six layers were allready stiff and hard as hell and this made me put it directly on hard foam since it didnt be spuposed to bend much anyway.
I was completely wrong in my self gut-feeling. Projectile kinetics is really not intuitive anymore.
Here the shot:
After the shot the projectile stopped in the backside-protection-clay. This was initially placed to give the push to the foam an increasingly growing compression force.
After removing the projectile one could get a good impression on the impact site:
Where in closeup you can see how the projectile just went through the kevlar like... well like a projectile that goes through way insufficient material
The laminat looked like this initially
..and of course there is a exit wound
Re: Catching Projectiles (50J+)
hen918, Sun Apr 26 2015, 02:06PM
Well done! your work on improving efficiency is certainly getting you useful projectile energies. Kevlar penetrating, next it'll go through tank armour!
hen918, Sun Apr 26 2015, 02:06PM
Well done! your work on improving efficiency is certainly getting you useful projectile energies. Kevlar penetrating, next it'll go through tank armour!
Re: Catching Projectiles (50J+)
DerAlbi, Sun Apr 26 2015, 02:26PM
video discribtion states its an unoptimized shot that was just 20% for the sake of power.
What i now just really realized is that the fibers actually were not cut but couldnt sustain the stress.
I try another spot with 1.0 .. 1.5cm of a hotglue-blobb covered with 2 layers of kevlar.
What is really annoying right now is that the hotglue actually kind of welds onto the projectile which is only to be cleaned up by acetone. I hope solid hotglue can absorb a bit of energy an distribute it without breaking to bad. I know its a long-shot but.. i just want to play with the failes concept before discarding it... i just want to learn more about this...
Edit: i tried the blobb of hotglue: its actually quite effective to stop the projectile. it penetrates around 1cm deep. (the blob was covered with 1 layer of kevlar and there was 1 layer in betweeen - just for fun.) The projectile fused again to the hotglue
All this penetration.. its quite destructive to the target. I kind of want to avoid this..
it needs to stop way slower without sinking to deep into anything. hmmmmmmmmmmmmmmmh
Daaaamned. Really the watter-thingy? puuh. so much work.
i would need a 2cm(or 1inch) tube make sure the i can actually aim at it. that would need quite a flow rate and thus it self will throw the water quite far. Turbulent flow would reduce that issue.
DerAlbi, Sun Apr 26 2015, 02:26PM
video discribtion states its an unoptimized shot
that was just 20% for the sake of power.What i now just really realized is that the fibers actually were not cut but couldnt sustain the stress.
I try another spot with 1.0 .. 1.5cm of a hotglue-blobb covered with 2 layers of kevlar.
What is really annoying right now is that the hotglue actually kind of welds onto the projectile which is only to be cleaned up by acetone. I hope solid hotglue can absorb a bit of energy an distribute it without breaking to bad. I know its a long-shot but.. i just want to play with the failes concept before discarding it... i just want to learn more about this...
Edit: i tried the blobb of hotglue: its actually quite effective to stop the projectile. it penetrates around 1cm deep. (the blob was covered with 1 layer of kevlar and there was 1 layer in betweeen - just for fun.) The projectile fused again to the hotglue
All this penetration.. its quite destructive to the target. I kind of want to avoid this..
it needs to stop way slower without sinking to deep into anything. hmmmmmmmmmmmmmmmh
Daaaamned. Really the watter-thingy? puuh. so much work.
i would need a 2cm(or 1inch) tube make sure the i can actually aim at it. that would need quite a flow rate and thus it self will throw the water quite far. Turbulent flow would reduce that issue.
Re: Catching Projectiles (50J+)
Andy, Sun Apr 26 2015, 08:34PM
What about different layers of thin cermic and kelver, kelver by it self is type of like carbon firbre in F1 cars, its designed to disingrate, burning up the energy, unlike body armour with cermic, to spread the energy, but keep the structure inteak.
Andy, Sun Apr 26 2015, 08:34PM
What about different layers of thin cermic and kelver, kelver by it self is type of like carbon firbre in F1 cars, its designed to disingrate, burning up the energy, unlike body armour with cermic, to spread the energy, but keep the structure inteak.
Re: Catching Projectiles (50J+)
Kizmo, Sun Apr 26 2015, 09:19PM
Stack of newspaper backed off with steel plate worked fine with my high power ETG experiment.
Kizmo, Sun Apr 26 2015, 09:19PM
Stack of newspaper backed off with steel plate worked fine with my high power ETG experiment.
Re: Catching Projectiles (50J+)
DerAlbi, Sun Apr 26 2015, 10:06PM
What energies did you have?
DerAlbi, Sun Apr 26 2015, 10:06PM
What energies did you have?
Re: Catching Projectiles (50J+)
DerAlbi, Fri May 01 2015, 03:58AM
Just as an update: i am currently implementing "ConKbot of Doom"s i decided to give it a try. I might actually work. I have now a 60cm long tube with d=2.5cm.
What i noticed so far is that the water does not wash out the projectile from the tube which kind of sucks. but i dont want to decrease the tube diameter further and water pressure (in sensable amounts) doesnt help either.
hmmmh.
DerAlbi, Fri May 01 2015, 03:58AM
Just as an update: i am currently implementing "ConKbot of Doom"s i decided to give it a try. I might actually work. I have now a 60cm long tube with d=2.5cm.
What i noticed so far is that the water does not wash out the projectile from the tube which kind of sucks. but i dont want to decrease the tube diameter further and water pressure (in sensable amounts) doesnt help either.
hmmmh.
Re: Catching Projectiles (50J+)
Dr. Slack, Fri May 01 2015, 05:47AM
I see as you're trying out wet methods, you might be interested in the details of the magic water window to use as the projectile entry point to the water brake. I've have a quick look at Mr Doom's picture, the water is sort of discouraged from exitting by the right hand fitting, and by having only a partially filled main tube, so no real pressure drop across the entry point.
This method borrows from the technology of jet entrainment pumps, of which the laboratory water-jet filter pump is probably the best known. These pumps tend to use a single high pressure jet, but there is also a configuration that uses multiple jets arranged in an annulus, for pumping things that may contain solids. Descriptions of these pumps tend to emphasize the venturi, which is essential for efficiency. However as this pump needs to generate very little head, and zero flow, that can be sacrificed for simplicity. The solid in this case is the projectile that has to pass through the middle of the pump.
This is an illustration of the latter type. Two of the several jets arranged in a ring around the entry pipe are shown. A hydraulic jump exists in the left hand end of the tube tube, where the fluid in the jets slows to a stop and the pressure increases. It is this pressure increase that holds back the pressure in the tank or pipe.
Doing a momentum balance at the jump, it can be shown that the product of the total jet area times its pressure must exceed the window area times its pressure head. As the for this application the jet area could easily be 10% of the window area, and the window needs hold back only 10mbar (10cm head), very little pressure is needed at the jets. For initial experiments, a flow from the tap would be sufficient, though a recirculating pump would be less wasteful for continuous operation. A central heating pump or pond fountain pump would provide more than enough pressure.
Dr. Slack, Fri May 01 2015, 05:47AM
I see as you're trying out wet methods, you might be interested in the details of the magic water window to use as the projectile entry point to the water brake. I've have a quick look at Mr Doom's picture, the water is sort of discouraged from exitting by the right hand fitting, and by having only a partially filled main tube, so no real pressure drop across the entry point.
This method borrows from the technology of jet entrainment pumps
, of which the laboratory water-jet filter pump is probably the best known. These pumps tend to use a single high pressure jet, but there is also a configuration that uses multiple jets arranged in an annulus, for pumping things that may contain solids. Descriptions of these pumps tend to emphasize the venturi, which is essential for efficiency. However as this pump needs to generate very little head, and zero flow, that can be sacrificed for simplicity. The solid in this case is the projectile that has to pass through the middle of the pump.This is an illustration of the latter type. Two of the several jets arranged in a ring around the entry pipe are shown. A hydraulic jump exists in the left hand end of the tube tube, where the fluid in the jets slows to a stop and the pressure increases. It is this pressure increase that holds back the pressure in the tank or pipe.
Doing a momentum balance at the jump, it can be shown that the product of the total jet area times its pressure must exceed the window area times its pressure head. As the for this application the jet area could easily be 10% of the window area, and the window needs hold back only 10mbar (10cm head), very little pressure is needed at the jets. For initial experiments, a flow from the tap would be sufficient, though a recirculating pump would be less wasteful for continuous operation. A central heating pump or pond fountain pump would provide more than enough pressure.
Re: Catching Projectiles (50J+)
DerAlbi, Fri May 01 2015, 06:28AM
Hehe, i currently have some success simply by adding foam to the water stream... by the means of an additional tube. The foam-size is so that the foam+projectile blocks the tube, pressure builds up and actually has some surface area to work against. thats soo easy
Thats like flushing the toilet with paper to get a spider down the drain However the success is limited since the foam-pieces sometimes block the pipe too well..
I am currently thinking about a sponge that sits directly at the tube-entry limiting the water flow. the sponge would get hit and pushed along the pipe. if the foam is fixed by a thread it wouldnt fall out, but would relieably push the projectile out again. the question is, if the projectile would destroy the sponge over time or even penetrate it. As i see it since the sponge is 90% water, it should not suffer so much.. but i bet it will... this never follows intuition here -.-
hmmmh.
DerAlbi, Fri May 01 2015, 06:28AM
Hehe, i currently have some success simply by adding foam to the water stream... by the means of an additional tube. The foam-size is so that the foam+projectile blocks the tube, pressure builds up and actually has some surface area to work against. thats soo easy
Thats like flushing the toilet with paper to get a spider down the drain
However the success is limited since the foam-pieces sometimes block the pipe too well..I am currently thinking about a sponge that sits directly at the tube-entry limiting the water flow. the sponge would get hit and pushed along the pipe. if the foam is fixed by a thread it wouldnt fall out, but would relieably push the projectile out again. the question is, if the projectile would destroy the sponge over time or even penetrate it. As i see it since the sponge is 90% water, it should not suffer so much.. but i bet it will... this never follows intuition here -.-
hmmmh.
Re: Catching Projectiles (50J+)
DerAlbi, Sat May 02 2015, 11:59PM
I am back with some progress! but the only thing i can say: the water brake is a failure....
the pipe with d=2.5cm and length=60cm is waaaaaaay too short. Even 3 Joule shoots right through... more joules splash back water even with all my counter-measures. Thats unsafe and impractical. The water pipe is either too thick (but if thinner, hard to aim at) or too short (but if longer too big).
Water is flowing with ~8L/min. clearly does not apply since the gets pushed flows aside. It might be that if the velocity increases the stopping distance still stays nearly the same. Still: i cant say that this is nearly safe enough. Given the size of the apparatus and all the work it needs to keep working...
So far: failure.
DerAlbi, Sat May 02 2015, 11:59PM
I am back with some progress! but the only thing i can say: the water brake is a failure....
the pipe with d=2.5cm and length=60cm is waaaaaaay too short. Even 3 Joule shoots right through... more joules splash back water even with all my counter-measures. Thats unsafe and impractical. The water pipe is either too thick (but if thinner, hard to aim at) or too short (but if longer too big).
Water is flowing with ~8L/min.
clearly does not apply since the gets pushed flows aside. It might be that if the velocity increases the stopping distance still stays nearly the same. Still: i cant say that this is nearly safe enough. Given the size of the apparatus and all the work it needs to keep working...So far: failure.
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