Coilgun EM-3 ("Electric bow") / Electromagnetic Projectile Accelerators / Forums

Forums

4hv.org :: Forums :: Electromagnetic Projectile Accelerators

« Previous topic | Next topic »

Coilgun EM-3 ("Electric bow")

previous 1 2 3 next

Move Thread

LAN_403

DerAlbi

Wed Jan 06 2016, 02:14PM

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

Yes yes and you answer is just fine

I think we both now know what the other mean

Still i dont know where a better place of discussion would be

One thing that really interests me is: since you are from russia, what about the legal status? Could you really just sell it?

_Eugen_

Wed Jan 06 2016, 03:35PM

Registered Member #57984 Joined: Thu Nov 19 2015, 09:44AM
Location:
Posts: 58

It is interesting question about russian law.
At first, we have strict definitions in our laws about what can be called "weapon". And coilguns are out of those definitions (as they don't use muscle force or chemical reaction to accelerate projectile).
Secondly (if a coilgun would still be recognized as weapon), we have limitations on energy of projectile - 3 or 7.5 J are reference points. All what is lower is considered as "constructive analogues to weapon" and is not subject to law restrictions. But I created my EM-3 with >9J and I'm still free, so p.1 is probably in force :).
At last, we have old saying which sounds like following: "the severity of law in Russia is compensated by its complete nonfulfillment" :)
Seriously, I think there will definitely be problems if someone try to sell a big lot of coilguns (not one sample to his neighbour). But as I mentioned I don't consider these problems yet. And I don't think Russia is the land where the coilguns will begin to be produced. Asia is more probable.

Karmaslap

Wed Jan 06 2016, 06:01PM

Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65

Eugen speaking of a good exterior design- if you are going for a crossbow type look then a lot of people would probably be excited for a coilgun shaped like Chewbacca's bowcaster from Star Wars
picture of someone's model:
<http://s54.photobucket.com/user/wuherdb/ media/bowcaster_1_7.jpg.html>
I assume people all over the world have seen Star Wars and this would be the most "sci-fi" weapon available. Just a thought for marketing if you ever do want to sell it. \
(Still can't get links to send anywhere)

DerAlbi

Wed Jan 06 2016, 09:26PM

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

And I don't think Russia is the land where the coilguns will begin to be produced. Asia is more probable.

Hopefully Germany!!

In germany it all comes down to "has a coilgun a barrel or not".

@Karmaslap: there is no way a reasonable coilgun will fit into such formfactor. You can do it, but its output power will never ever be satisfactory for the price. As said before... even a small gun has components that must be included and dont scale with the output power linear. There is a price offset..
Small output powers are only interesting if your projectiel is fast and light weight. Coilguns can not offer this combination.

Edit:

One may build a coilgun with >100 m/s and 100 J in projectile, but it worths nothing without stabilization.

Hmmh. Interesting topic of discussion too btw. A coilgun is an extremely clean accelerator. there is no sidwards force or anything asymmetric applied to the porjectile as its pulled, not pushed from behind its center of gravity and there is no chance for asymmetrical force release since the projectile is not guided by the barrel. The initial momentum to induce instability is basically not there. However the air reistance and turbulence might do weird stuff. But on the other hand: a 100J, 100m/s projectile is fat and heavy. It does not get pushed around easily. I do actually have hope that this would yield an effective range of at least 50m. (500ms time of flight) You think thats a pure religious hope?

Karmaslap

Thu Jan 07 2016, 01:23AM

Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65

Derabi, he'd be pretty close to that shape just by simply adding arms to the front. He even has a scope on already. The volume inside the picture I oinked would be much, much too small, of course, but if you smoother around the small pieces into one larger section it would be close to what he has now dependinf on scale.

Depends on if it has a barrel or not? That is... The stupidest thing. You have to love how untechnical the law is. That's why you were looking at teflon and other soft materials?
I don't know what a large coilgun here in the US would qualify as. It's leas dangerous than a compound bow and rhise don't require registration.
Will reply to second half of you post on your own thread.

DerAlbi

Thu Jan 07 2016, 01:36PM

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

I am pretty sure i am stuck with a rail-like system inside the gun itself. i have to see how i can make it mechanically relieable. Its a limitation that really sucks.. but where would be the fun if there wasnt a problem ^-^
The major problem is right now that the peliminary evaluation said that the coils itself are considered to be a "barrel". This is pretty much BS, but yeah.. thats what i am fighting against.
The legal definition of a barrel is:
1) it must be of a strong enough material (haha, everythign is storn enough, if not it would be kind of stupid)
2) It must be tubular. However noone can really tell me which shape is recognized as tubular. If there is a slot along the tube.. is it still a tube? Yes, but mathmatically no. So how big must the slot be? Or 2 slots? or...
3) Its length must be twice the cliber
4) It must play an active part in guiding the projectile. <- thats what the coils do NOT. The projectile follows the magnetic pull force and that alone is the guidance. The magnetic field however is hot "a strong enough material".

So if inside the coil is a rail-like system, i should be fine. But... well.. you know. -.-

_Eugen_

Thu Jan 07 2016, 04:00PM

Registered Member #57984 Joined: Thu Nov 19 2015, 09:44AM
Location:
Posts: 58

Eugen speaking of a good exterior design- if you are going for a crossbow type look then a lot of people would probably be excited for a coilgun shaped like Chewbacca's bowcaster from Star Wars
picture of someone's model:
<http://s54.photobucket.com/user/wuherdb/ media/bowcaster_1_7.jpg.html>
I assume people all over the world have seen Star Wars and this would be the most "sci-fi" weapon available. Just a thought for marketing if you ever do want to sell it. \

Well, I prefer classic design with wooden parts. Also don't like transparent cases (a lot of gaussers are fond of it for some reason). Although I like Star Wars !! :)

there is no sidwards force or anything asymmetric applied to the porjectile as its pulled, not pushed from behind its center of gravity and there is no chance for asymmetrical force release since the projectile is not guided by the barrel. The initial momentum to induce instability is basically not there.

Misconception here. The field is stronger close to the coils' winding, so projectile is sliding along inner wall of barrel. It produces strong instability during acceleration already, because the wall cannot be as smooth as in firearms with their massive barrels.

I do actually have hope that this would yield an effective range of at least 50m. (500ms time of flight) You think thats a pure religious hope?

Alas, I'm sure You are wrong. In my experiments (and other I have seen) I had my unfinned projectiles unstable on 1 m with 30 m/s speed. So with 100 m/s it will be only about 3 m ...

hen918

Thu Jan 07 2016, 06:00PM

Registered Member #11591 Joined: Wed Mar 20 2013, 08:20PM
Location: UK
Posts: 556

Could you not have a multi-stage coil-gun with coils shorter than twice the inner diameter connected together with, say 3 2mm rods, lengthways around the circumference of the non-existent barrel? Would this be non-barrel enough?

DerAlbi

Thu Jan 07 2016, 10:13PM

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

Yeah hen.. the problem is that the whole construction is then still the barrel if they just define it to be one. There is no doubt that its nowhere near the technical truth.. but as someone else said it allready in this forum: when it comes to weapons, there is no chance for rational arguments

Misconception here. The field is stronger close to the coils' winding, so projectile is sliding along inner wall of barrel. It produces strong instability during acceleration already

The misconception is yours.

(or not?)
It depends on how bad the coilgun is. every coilgun that suffers from suckback will have an inherent instability - no agument there.
However if you do it right and you have really only a forward pulling force then the "magnetic center" is in front of the projectile this means the projectile centers it self as long as its not allready extremely missaligned. This beeing said in my design only the first half of the projectile is magnetically active. I am very far away from ever experiencing suckback.

Which reminds me.. I made a video about that.....
Here you see a top-down view when a projectile accelerates. The setup is backlit so the 1000FPS-camera shot shows a bright ring where the air-gap is.
As you can see there is no tendendcy that the projectile will stick to the walls. On the contrary: if you watch closely you see that a slight asymetry is corrected by it self because the tip is pulled towards the middle. And this is only positioned by hand.. imagine if you have a low tolerance rail inside the coil.. which lateral forces will be left? nothing to talk about. but it all depends on how controlled your setup is.

Here is another video that i made for my argument why the coil itself is not a barrel thats actually guiding the projectile.
if that was true then they should explain to me how the projectile finds its way even with such bad missalignment. The position is clearly corrected without a sourrounding coil... therefore the coil is not a guide in any way. Well.. at least thats what i say... who cares -.-

Hope you enjoy the video, like share and subscribe!

just kidding

Karmaslap

Thu Jan 07 2016, 10:38PM

Registered Member #58215 Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 65

I was planning to post this in Deralbi's thread, but I'll do it here.

I do actually have hope that this would yield an effective range of at least 50m. (500ms time of flight) You think thats a pure religious hope?

Alas, I'm sure You are wrong. In my experiments (and other I have seen) I had my unfinned projectiles unstable on 1 m with 30 m/s speed. So with 100 m/s it will be only about 3 m ...

A cylinder moving through a fluid is an absolutely horrible projectile from an aerodynamics perspective.
<

>
look at page 10 of this paper. It is a cylinder moving through water, but it will do the same things in air (there are some youtube videos of cylinders coming out of the barrel and moving to funny angles as well, if you find slow-mo videos)

The person who directed me to this paper mentioned that flat, flip, and see-saw are the most relevant for air, but look how straight the "Straight" one is! (it isn't). Plus, any could happen. You can't predict where the projectile will go.
A cylinder is clearly the best choice of a projectile- really, anything that takes advantage of the most possible area is. There is a little bit of projectile design for coilgun information available online, mostly recommending adding fins, rounded nose, or even gluing plastic parts (Deralbi you might like doing that- the projectile has a plastic nose? lawmakers aren't afraid of plastic) onto the nose or tail to make it more "bullet" shaped. Spinning the projectile seems to be the easiest way to stabilize it, but even then a rounded nose and something done to the back to make the projectile more aerodynamic is needed. I think that most people haven't put effort into this because not many have needed more than a steel cylinder. The field strength is higher on the outside of the air gap as well, so more material in the middle doesn't help (I still need a greater understanding of how saturation, projectile material, and projectile geometry impact the resultant kinetic energy, but conceptually adding more weight to the projectile in the area of lowest field doesn't help as much?)
I'll mess around in MS paint and post a picture of what I'm thinking a decent projectile design might be.

It is clear that a cylinder will be no good unless we figure out a way to spin the projectile. How fast to spin it? I'm thinking maybe even 20 RPS will help greatly?

The misconception is yours.

Actually, he's right. If you define the direction you would expect the projectile to travel through the coil in as the Z axis, and the other the R axis, then The magnetic field is greater the closer you get to the walls of the coil- the strength of the Z axis field depends on R. The strength of the field in the R direction also depends on R- there is a magnetic field in both directions, of course, though in the R direction it is very small comparatively. In a long enough coil and at high enough forces, a projectile which did not enter in the exact center would find itself drifting toward the coil inner wall.

Deralbi- very interesting videos!! I like seeing things like that. I think here that for your number 4 any lawyer opposing you would say that it is clear that the coil is guiding the projectile (via the magnetic field), and the second video shows quite clearly that it plays an active part in guiding the projectile.
However, the coil is not a strong enough material
The coil is NOT twice the length of the projectile! most coilguns are single-stage with the length of the coil equal to the length of the projectile. So, no single stage coilgun could have a barrel be the coil. (but they might say the tube most people use is. You just so happen to use teflon which is not strong.

And I don't think they can define the coil and the magnetic field together as being both strong enough and tubular? You could make square coils and a square projectile and it would still shoot.

Edit: The first video looks like a bullet is coming at you and shooting the screen like from a James Bond film. That's bound to scare someone and the first thing they will think of is "it's a bullet from a gun" The second video is much better at showing that it is a science experiment.

previous 1 2 3 next

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob