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Forums
4hv.org :: Forums :: Electromagnetic Projectile Accelerators
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Coilgun EM-3 ("Electric bow")

Author Post
_Eugen_
Mon Dec 28 2015, 07:45PM Print View
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Hi.
Here is my multistage coilgun EM-3.



I called it "Electric bow" as it fires arrow-shaped projectiles.



Arrows are accelerated by optically-triggered SCR switches:



Data table with characteristics per each stage and for the whole device:



The construction is rather complicated to describe it in one post. Much more details, photos and videos are here: http://coilgun.ucoz.com/index/em_3_quot_electric_bow_quot/0-4

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DerAlbi
Mon Dec 28 2015, 08:38PM
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Interesting concept. I like the light trap solution!
Its a bit big for 10J ouput energy but that comes with the efficiency - which is suprisingly high for your arrangement to be honest

Maybe you could add a video of a longer distance shot.. you projectiles should be very stable! It would also be interesting how consistent your output energy is. (Measure multiple shots)

mkF means MikroFarad = "µF"
mcHn for MicroHenry = "µH"
Russians...

Big flaw: Your circuit diagram is missing diodes in parallel to your capacitors to avoid reverse polarity. Since you use electrolytics you will destroy them in a very short time!

Anyway... nice to see something finished Kind of. The Diodes are really worrying.
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_Eugen_
Tue Dec 29 2015, 07:40AM
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Big flaw: Your circuit diagram is missing diodes in parallel to your capacitors to avoid reverse polarity. Since you use electrolytics you will destroy them in a very short time!


That is only simplified animation, not diagram. Reverse diodes are of course installed (P600J).
As for long distance shots - going to do this. Accuracy testing shows that approximately 50 m may be reached with my bow target.
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DerAlbi
Tue Dec 29 2015, 12:48PM
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I am relaxed then
Did you get this gouping by aiming with your hand or did you put it in a vice?
Either way i find this quite good for 1sec flight time. I had bigger problems in my design with inconsistencies due to projectile premagnetisation and sensor noise. But thats caused by my tendency to overcomplicate things
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_Eugen_
Wed Dec 30 2015, 06:17PM
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The accelerator was fixed (not in vice, just with some heavy objects like books etc :) Alas, the ditance in test was only 10 m, so the accuracy is quite poor - probably because of flexibility of the arrows. Anyway, there is a lot to improve.
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Karmaslap
Tue Jan 05 2016, 08:43AM
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Wanting to reply to this actually is what got me to finally make an account and not just lurk.
If you can get the timing down for it-
You should add an additional piece of iron/steel at the other end of the crosbow. It does not have to be the same weight as the nose to imbalance flight, (same diameter, but shorter to take advantage of flux?) but doing this will essentially double the number of stages your gun has. Not to mention, when the rear end of the projectile comes through, your projectile is already sped up so you don't get the horrible inefficiency of the first stage for it. I think it is dedinitely worth looking into.

For stability, you should add flexible fins that wrap around the rear of the shaft(trim the plastic before second piece of iron if you do add another piece and put fins there. Once dart leaves the barrel, the fins will pop out and help stabilize it.
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_Eugen_
Tue Jan 05 2016, 12:18PM
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You should add an additional piece of iron/steel at the other end of the crosbow. It does not have to be the same weight as the nose to imbalance flight, (same diameter, but shorter to take advantage of flux?) but doing this will essentially double the number of stages your gun has. Not to mention, when the rear end of the projectile comes through, your projectile is already sped up so you don't get the horrible inefficiency of the first stage for it. I think it is dedinitely worth looking into.

I thought about such constructions. But calculation shows that any heavy object on rear end of the arrow will definitely disbalance it (even a short one). Another thing is that my coilgun is SCR-driven and has single cap battery per stage, so the stage can work only once.
For stability, you should add flexible fins that wrap around the rear of the shaft(trim the plastic before second piece of iron if you do add another piece and put fins there. Once dart leaves the barrel, the fins will pop out and help stabilize it.

Can't imagine this. To unwrap after the shot and sustain airflow the fins must have high rigidity, but such fins will damage inner surface of the barrel and it will fastly loose its transparency, and also they must make high friction during acceleration (if I understand your idea).

Nontheless, I must say that you rise important question. In fact I think the projectile's construction is the only problem which interferes commercialy avaliable coilguns to be produced. Neither low speed nor efficiency.
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DerAlbi
Tue Jan 05 2016, 11:07PM
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In fact I think the projectile's construction is the only problem which interferes commercialy avaliable coilguns to be produced. Neither low speed nor efficiency.
Bold statement.
Let me explain why i think otherwise:
1) If you buy a gun you want raw kinetic energy. You want to feel the primitve manly powers, kickback and you want to have reasonable accuracy and precission for competetive behavior. Normal guns provide those features. Even crossbows. But coilguns? Everything below 20..30J is basically no fun to shoot. You say "yes it is" but think about customers who are not allready biased by the great self-made technology... And dont just think about Youtube videos where you shoot glass or anything that shatters easily. People will be disapointed as soon as they shoot anything that does not have an inherent spectacular effect when beeing hit. Even 100m/s is quite disapointing over a short distance because you notice the lag between shot and impact. Its no match to a supersonic bullet.
2) To provide usefull projectile energy you have to provide even more electrical energy. Thats directly related to efficiency. Every electrically stored joule will add weight (1g.. 2g) This adds up to quite a heavy machine adding the copper coils and batterys and a reasonable (>500W) cap-charger. No one wants a gun that fires once every 10sec. It is frustrating to use. No fun. The waiting time is basically the same as when microsoft office starts up. You allways want it to "just work allready!!!!"
3) To be on the marked you need customers which will decide to use a coilgun over any alternative. The price point of an electronic gun will allways be high in contrast to its output power. You need to convice. Noone who can buy a regular gun (eg in USA) will decide for a coilgun or will recommend it further. A normal handgun is way cheaper and has 5..20x the kinetic energy and supersonic and easy-to-buy projectiles. just think about with who/what you are competing. A commercial design can not only rely on a niche market. The prototype costs for the casing and everything alone demands a quite high number of guns to be sold just to compensate for your development costs. And you need to sell it at a way higher price than you can build it to live.
4) to reach alternative customers outside of the USA (which have more restrictive gun laws, thus nicer police and less gun related deaths) you need to be inside the legal system and you need to be able to sell your guns without the need to registration or licencing - a coilgun is not worth such effort. It basically needs to be free and 18+ but must be forbidden to carry it in public and that has implications on how to build your gun to go around legal definitions. There is quite a lot engineering involved in that alone.
5) You need a community that can play with the gun.. you need firmware to customize your gun, the acceleration profile (create more kickback stimulation, or a smoother acceleration profile or what not.. you also need security features.. what happes if you drop the gun? What happes when it rains? What happens when somebody puts a wrong projectile in... you are responsible for every engineering fault - and no offence - i like your design, its a nice idea, well built, but not the best show-off if you want to convince professionals about your engineering skills.
6) It must be reliable. It must work out of the box for thousands of shots. Even when dirty. Just think about your Light-traps alone... what if they get blocked by dust or someone uses graphite dust to lubricate the barrel. You need propper heat management for rapid fire, a solid reloading mechanism and a solution when it finally still jams.
7) Design for Manufacturing. DFM does need special considerations. If you want a reliable production process you have to take special precautions to make assembly as efficient and easy as possible. every complicated solution is basically no solution. Just rethink your build-process... was there anything that was not as easy to assemble as you wished it was? How to change it without compromising weight, volume or output power?

I could go on but as a conclusion: you need to rethink your statement from a customers view. A view of someone who is not allready biased by the technology. If you neglect thats a coilgun what is left over a crossbow? Higher price? Less performance? Heavier? Yes, maybe higher fireing rate. But everythin else? The energy density of any coilgun is just pathetic.

I am playing with the same idea... even with my design i am currently humble about the future of such endeavour.
However i provide security, high output power (~120J), low weight (5.5kg) and a usefull formfactor (85cm long rifle). But high price (1.5k€).

I dont think with a more inefficient design you will be able to be get even close to this (even you might not need to get close to this). There is quite a lot of bulky stuff you need in any coilgun of any size. So a bigger gun is acutally better because the longer acceleration path provides more room for electronics. you can not build a smaller and proportional weaker and proportional cheaper coilgun. The formfactor just will not give you the volume for everything. (Battery, battery/cap-charger and stuff)

Projectile design: you must basically rely on having no design at all. The best is to use a world wide available standard projectile format. Anything else will leave any customer dependend on your continous production. Would you spend money on a product where you are dependend on a maybe soon failed start-up company? Never ever.

I hope i gave you an insight in what i am thinking about.... how would you do it? Do you think what i say is overcomplicated salesman-talk or do you think that basically anything on the market will make a nice bussiness? I honestly dont think so. But i wish it was true...
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Karmaslap
Wed Jan 06 2016, 12:29AM
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_Eugen_ wrote ...

I thought about such constructions. But calculation shows that any heavy object on rear end of the arrow will definitely disbalance it (even a short one). Another thing is that my coilgun is SCR-driven and has single cap battery per stage, so the stage can work only once.

Can't imagine this. To unwrap after the shot and sustain airflow the fins must have high rigidity, but such fins will damage inner surface of the barrel and it will fastly loose its transparency, and also they must make high friction during acceleration (if I understand your idea).

Nontheless, I must say that you rise important question. In fact I think the projectile's construction is the only problem which interferes commercialy avaliable coilguns to be produced. Neither low speed nor efficiency.

Is projectile balance not more important than simply the presence of another heavy object in the rear? so a little lighter on the front, and add more onto the back? You wouldn't need to add more SCRs to the design, but it would introduce more capacitors and more complexity. It's just the thought I had, seems you have looked into it.

They really wouldn't. Even adding a simple streamer to the rear of a long projectile will stabilize it if it is moving fast enough- the fins could be fairly flimsy plastic (think the plasticy paper?) , with not much force pushing them to the outside of the barrel and they would still unfurl once they left. Even this small force would eventually scratch the barrel, I suppose, but it would take a lot of shots. Again, just an idea if the dart is tumbling in flight.
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_Eugen_
Wed Jan 06 2016, 12:33PM
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to DerAlbi: I think you do really have tendency to overcomplicate things :)
I just wanted to say that stabilization of projectile is the problem with little attention payed for (relatively to speed, power, efficiency etc). One may build a coilgun with >100 m/s and 100 J in projectile, but it worths nothing without stabilization. As for your list of statements:
1), 2) - it is up to the customer, I think. Many crossbows have <100 m/s and loading time is more than 10 sec - nevertheless they are spead goods. Moreover, I do suppose that some coilgun models avaliable in Internet could be commercilally attractive provided they had stabilized shots (and nicer design) (although I don't pretend on it with my EM-3 - I just put it into a suitable case, although 90% gaussers in Internet don't even think about it).
3) - I suggest it is unfair to compete coilguns with conventional firearms. Their opponents might have been pneumatics, bows and crossbows.
4) - 7) The problems you are writing about are true but they concern future times, when the coilguns (if created) will be produced by hundreds and thousands. We decidedly cannot foresee all troubles especially about reliability - they can be revealed only in mass production and exploitation. But some questions can (and must ) be anticipated now. For example we can forbid for user to apply graphite dust by manuals :)
As for law limitations - that is not our business, I think. Although you are right that coilguns are in "law vacuum" now, but I rely that these problems will be solved essentially. I see my own challenge to produce a sample with "interesting" characteristics (including as good design as it is possible for hobbyst) - all other tasks are not my deal. I absolutely agree with you that even in our test models we must try to ensure water-proof and electrically safe design.
Projectile design: you must basically rely on having no design at all. The best is to use a world wide available standard projectile format. Anything else will leave any customer dependend on your continous production. Would you spend money on a product where you are dependend on a maybe soon failed start-up company? Never ever.

I didn't meet "world wide available standard projectile format" for coilguns - may be some examples? The only thing I can imagine is standard steel balls (sold for crossbows and slingshots) - I have projected some systems for such a projectile, but my latest calculations show that it will be dispersed very strongly because of the gap between the barrel and projectile, which is inherent to coilguns.
Sorry for my short answers, but I think this detailed discussion is somehow out of place in this thread :).
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DerAlbi
Wed Jan 06 2016, 02:14PM
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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?
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_Eugen_
Wed Jan 06 2016, 03:35PM
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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.
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Karmaslap
Wed Jan 06 2016, 06:01PM
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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)
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DerAlbi
Wed Jan 06 2016, 09:26PM
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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?
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Karmaslap
Thu Jan 07 2016, 01:23AM
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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.
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DerAlbi
Thu Jan 07 2016, 01:36PM
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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. -.-
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_Eugen_
Thu Jan 07 2016, 04:00PM
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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 ...


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hen918
Thu Jan 07 2016, 06:00PM
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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?
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DerAlbi
Thu Jan 07 2016, 10:13PM
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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
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Karmaslap
Thu Jan 07 2016, 10:38PM
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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.
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DerAlbi
Thu Jan 07 2016, 11:15PM
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 517
Hmmh. I am still not sure. Most people have only experience with bad designed coilguns where projectile instability occurs because they suffer from suckback so they actually rely on the barrel to guide the projectile at the end. As you can see in my videos the projectile tip is actually round (if not, then now i told you so ). I will not panic before i test this... also water is a bit different to air since it applys much more presure and turbulance.. but that only shortens the distance for visible effects.
Not that you might not be right, however i will keep in mind that the experience is based on bad designs. As long as no one has built a big gun yet, we cant verify.
Spinning the projectile is complicated. It puts enormeous stess to the guiding-system inside the coils. It might just cause more trouble than its solving. For now i just hope that the fundamental difference between pushing and pulling is on my side.


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.
The magnetic field is NOT the coil. If the guidance is done by magnetic field, then the coils not not active in the guidance only because its the source of the field. And even if they tell me that, then i just say: the coil issnt the source, but the current flow is. The first video only shows that the "missconception" is currently not mine If there was a strong force towards a wall of the coil the air gap would have closed and wouldnt stay symetrically.
The second video shows how the projectile touches the coil, yes. But how did it go into the coil without mechanical guidance? If the coil as physical body would be responsible, then this would not have worked. The position got corrected by the magnetic field alone, then it was sucked in further (and yes in that case instable). So is the coil a barrel?

And dont mix up projectile length with projectile diameter (caliber).

The first video looks like a bullet is coming at you
Who cares. the coil stayed magnetized.. the projectile could never leave the coil
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Karmaslap
Thu Jan 07 2016, 11:40PM
Registered Member #58215
Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 62
The flight characteristics are independent of the coilgun's design so long as they both spit the projectile out lengthwise. It's definitely not the best design. Look at shotgun slugs for high speeds- they are tapered in the front, and have grooves on them in the back so that they spin themselves. If a cylinder was fine, they wouldn't go through that much trouble.
(A cylinder is NOT a good shape, I just had trouble finding online where to direct you to to see that... because everyone knows it is a bad shape and so nobody even plays with it in air anymore)
If you just want your range to be 50m... who knows. I did see the rounded tip in the first video, but wasn't sure if that was just a weird perspective. Your guidance system is based on the detection of eddy currents and not photogates? Have you calculated energy losses to eddy currents in the projectile?

Spinning it before it shoots is difficult. putting grooves on it so it spins itself might be easier.

You can tell me that, but any opposing lawyer would not listen I think. The current flows through the coil, they generate the field that stabilizes the projectile.. so the coil is necessary. It isn't a typical barrel at all, but they might say that your teflon is a barrel?

woops, I mixed them. thanks.
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DerAlbi
Fri Jan 08 2016, 02:22AM
Registered Member #2906
Joined: Sun Jun 06 2010, 02:20AM
Location: Dresden, Germany
Posts: 517
The flight characteristics are independent of the coilgun's design so long as they both spit the projectile out lengthwise.
Nohohohooooo! Thats what i try to say for about 2 posts now Bad designed coilguns that have any suckback effect going on accelerate the projectile lateraly instable! A bad coilgun therefore will spit out the projectile with more parasitic lateral momentum than a proper designed CG. This is important.
If you are far away from suckback, then you accelerate allways to the center of the coil. As soon as the projectile is perfectly in the middle of the col the projectile position is lateral unstable if the current hasnt allready stopped. so... Lengthwise is not euqal to Lengthwise.

Your guidance system is based on the detection of eddy currents and not photogates? Have you calculated energy losses to eddy currents in the projectile?
Thats a question for my own thread, but the short answer is that its way more complicated than that^^ The eddy current loss is not as important as the fact that there is one at all. And its not a guidance.. its a detection.

putting grooves on it so it spins itself might be easier.
No way. In a conventional gun, thats no problem. The additional friction is just holding back the gas that most likely will just build up more pressure in the mean time - this might even be beneficial. In a coilgun that friction is directly contributing to bad efficiency. You can not afford it in any way. If you want to spin it, spin it before the shot.
And...... "taofledermaus" on youtube is a nice channel to watch. but he is focussed on supersonic bullet design. but one thing i learned: even a smooth-bore-shotgun can shoot quite precise.

the current flows through the coil, they generate the field that stabilizes the projectile.. so the coil is necessary.
If you talk about whats necessary then everything is the barrel Its also wouldnt work without the capacitors. that cant be the fact they nail me with.
but they might say that your teflon is a barrel?
Depends on what they define as "tubular". I guess thats another definition they just invent when its needed. I will try my best to make the inner design rail-like. Thats all i can currently do.

And sry Eugen, i know we are hijacking your thread It just went that way...
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Karmaslap
Fri Jan 08 2016, 06:34AM
Registered Member #58215
Joined: Wed Dec 30 2015, 11:27AM
Location: Boise, Idaho
Posts: 62
Moving to your thread to reply, haha
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