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23 stage no-capacitor full auto coilgun Answered

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*********I have updated my design since posting this topic. The video is the more current design than what is written below.**********


   I came to the conclusion that using capacitors to provide the power for a coil gun is a stupid idea. A bold statement I know. The reason is that they are big and heavy, take time to charge, and need charging circuits. Also, the sharp rise in current that comes from capacitors is bad unless you are making an induction style coilgun, because the induced currents will hurt efficiency.
   If coil guns are ever going to be a practical hand held weapon it will need to be lighter, simpler / less delicate, and more powerful than what you will find on the internet if you look up coil guns. A rate of fire that is competitive with conventional guns will also be needed if a coil gun will be used for anything other than target shooting or maybe hobby hunting. So I designed a coilgun to meet these requirements. Visit my website for a full explanation of the design: http://www.ourbadscience.com/#!em-guns/cwjy
    I realized that a coilgun would not be a practical infantry weapon until batteries are more advanced anyway, so that just adds to the list of why capacitors are out. It will be powered directly off of the batteries, and have many coil stages. This allows a very high rate of fire. To get that rate of fire with capacitors you would need several capacitor banks charging at offset times, so after each bank fires another is just finished charging. That would be terribly bulky.
   The lower voltage from the batteries will give comparatively slow current rise in the coils which normally would make the coil timing weird. I plan to use an unconventional coil timing though. All the coils will be activated at once, and the coils behind the projectile will be shut off as it passes them. This will have several advantages:
-The coils will only be powering up for a split second at the beginning. Most coils will already be at full power when the projectile gets to them (that is not the case in most coil guns).
-Induced current will not be any issue.
-Since the coils will all act as one coil, the projectile will be drawn toward the center of all the coils that are on. Timing of the shut off of the coils will not need to be perfect.
   This will be a pre-tuned passively timed system. I want to use a small adjustable electronic timer for the switch-off timing. This will require some work in the initial adjustment of the timing, but even actively switched coil guns (with optical sensors or something) require that. the advantage of a passive system over an active system is cost and simplicity, and you can pack the coils tighter on the barrel if you are not putting a sensor between each stage. That matters with 23 stages!

As I said check out my website to see more details and pictures for this and other projects: http://www.ourbadscience.com/#!em-guns/cwjy

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Trapper1738 (author)2016-05-15

im thinking of simple way to actually switch the coils on...

nearly all coilgun ammo is mildly conductive, so have a wires in the barrel that would touch the ammo, completing the circuit, which would flip a momentary switch. that switch would then activate the next set of coils.

i dont know a ton about these things, but i have been working on some designs for a handheld coilgun.

my design uses 3-5 small super capacitors. all charge at the same time, they then can discharge indivivually.

however it limits shooting to either a 3-5 round burst every 3-5 seconds or firing roughly every 1 second.

another design idea for faster firing is to fire a second round without recharging, it would have to be almost right behind the first, but its an idea.

tbh this multicoil design you have would be hard to make a handgun with it. simply because the barrel would need to be fairly long.

i think another way to help with the fact that their is a lot of wieght it to create a bulpup degin instead of a rifle.

another cool design theory would be a shotgun. either firing out of multiple barrrles or actually firing several rounds togeather.

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woerldedit (author)Trapper17382017-04-24

There is a video on the Codys Lab channel on youtube where he made a coil gun with the projectile completing the circuits. Unfortunately the current is so high that there is a lot of sparks. That slows down the projectile and destroys it along with the contacts in the gun.

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Qcks (author)2015-05-15

Mmmm.....
Coilguns.... ehh... there's allot here...
First, Capacitors are not the enemy. They have better characteristics then batteries, especially when talking about a coilgun. They have lower inherent internal resistance. That means it takes them less time to produce current on demand. Further, their charge times are an order of magnitude faster. If the capacitors can be hot swapped, they actually work better then a battery, since they charge faster, and can then be somewhat disposable.

After that, Coilguns have inherent drawbacks.
You did mention that this isn't going to be an infantry weapon, but it's worth mentioning that a coilgun shows up on radar. The EM field that it generates causes a radar hit, which, depending on field strength, might never work in a combat situation.

Moving on from that distraction, magnetic fields inherently have issues as the sole means of moving stuff. The more force needed to grab something, the longer it takes to let go. This is known as Magnetic Reluctance. Turning off a portion of the magnet to functionally shorten the magnetic field does work, but it doesn't eliminate the issue. The higher the magnetic field strength the greater the reluctance. This is part of the calculation of reluctance, so it can only be minimized, not eliminated. IF it doesn't decelerate the bullet, the energy in the magnetic field still goes somewhere. This would most likely be expressed as heat throughout the electromagnet, but it will also produce inductive spikes in the circuitry.
The final thing, which is small-ish, is magnetic susceptibility. The ammo has to be magnetically susceptible. Now, partially because of Reluctance, you have two choices. Pre-magnetized ammunition or non magnetized ammo. Magnetic ammunition is going to be permanent magnets. Non-magnetized ammunition is going to be things like bits of iron, cobalt, and nickel. Non magnetized ammo will actually be a problem, since it will inherently retain some amount of magnetic character. This is called Remenance, and would be viewed as an inherent loss. The cost of permanent magnets though make this a bit hard to deal with though.

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AlexanderK23 (author)Qcks2015-08-26

Could use something like this w/ existing design:

4.5mm(.17 BB) neonydium magnets. Could auto align them if needed w/ small bar magnets in the chamber, and would need to integrate a stripping mechanism into your magazine or receiver.

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Jaycub (author)Qcks2015-05-30

Thank you for your thoughts!

I have to strongly disagree about capacitors. If you are using capacitors, you will need to have some other power supply (normally a battery) charging them. Unless you want a 1-shot-and-done coilgun capacitors will add much more bulk/weight and cost/complexity. The only advantage I see of capacitors is their power density, which really is not even helpful for a coilgun using the coil timing system I am using (I will put in a video I have on YouTube that help describe it, I have updated the design a little since I put up this forum topic). They have much lower energy densities than batteries, and the charging circuitry adds a huge penalty for overall efficiency and rate of fire. If you had like 10 capacitor banks charging at staggered times you could get a good rate of fire but that would not be a hand held device.

https://www.youtube.com/watch?v=jKPoqZshDw4

The radio signal it gives off would be an issue yes, you could block it though. Any electrical device will do that to some degree. An aluminum body/shell over the whole device could absorb almost all of the radio signal. To prevent inductive losses from the coils to the metal shell the coils should be enclosed in a nonconductive material that is ferromagnetic, like iron powder mixed with epoxy (this also concentrates the magnetic field and improves the efficiency of the coilgun). These steps would add weight though. Coilguns just end up being heavy. I keep going more and more towards thinking their only use will be in large fixed position accelerators. To be used for launching things into orbit mainly.

As long as you keep the center of the magnetic field ahead of the projectile it will be accelerated forward until you get to a limit cause by friction and other resistive forces. One thing that could be done with the current in the current in coils behind the projectile is to dump it through a coil ahead of the projectile. The normal solution is to dump the waste current through a diode and resistor (and the same thing with the back emf). That is definitely a place to lose efficiency yes. If the magnetic field behind the projectile is too strong, you could lengthen the magnetic field (add more in front), time the coils to start shutting off earlier, or just use longer projectiles.

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mohammed.halawany (author)2015-07-26

1-what is your final kinetic muzzle energy and energy efficincy ,or projctiule speed?

2-have not you thought in using high voltage capacitors wit

IGBT high voltage high current switches using the same technique?

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Jaycub (author)mohammed.halawany2015-07-29

1-I have not completed this yet because of time and other things I have to do so I don't have that answer.

2-Hogh voltage capacitors are not appropriate for this design because of many reasons that I laid out in the article above:

Capacitors are big and heavy, take time to charge, and need charging circuits.
Also, the sharp rise in current that comes from HV capacitors is harmful because the induced currents
will hurt efficiency, both heating the projectile and repelling it back away from the coil (opposite of the intended magnetic force) while also reducing current in the coil.

In a coilgun designed like in the video above there is no need for the coil to instantly reach full power, it has a moment to build current. The magnetic field is meant to roll forward smoothly staying just ahead for the ferromagnetic projectile.

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mohammed.halawany (author)2015-07-26

have you though in spercapacitors instead of batteries for high power density?

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Jaycub (author)mohammed.halawany2015-07-29

Supercapacitors have good power density but poor energy density compared to batteries (the intent of this design is to have a high rate of fire, high ammo capacity, and great efficiency. Then wait for a good power supply later).

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SpaceBison117 (author)2015-05-15

You said something about low voltage of the batteries. Low voltage will mean low current and thus small B field. B=UnI. For a strong field should you not use something that will give you a high current?

For the most part though it seems like a neat idea.

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Jaycub (author)SpaceBison1172015-05-27

Higher current improves the magnetic field strength yes, current is proportional both to voltage and resistance, and is affected by back emf. Higher voltage would allow the current to rise more quickly in the coil (helps is overpower the inductance of the coil and force the charge carriers through) but the actual resistance of the coils is too low for my multimeter to even read (reads zero resistance). The coils will probably flow as much current at 22 volts as the batteries can generate (several hundred amps).

The useable magnetic field strength is not actually unlimited like you suggest. For a "reluctance" coilgun (type of coilgun which attracts a ferromagnetic projectile) there is a point where increasing the magnetic field does not increase the force on the projectile. This is called saturation. An induction coilgun does not have this issue though. My next coilgun after this will probably be an induction coilgun. That is in some ways a more complex system though and that will need higher voltage.

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Jaycub (author)Jaycub2015-05-27

Another reason to be fine with the output of these batteries is that part of my approach here is to accept that the power supplies we have today are not ready for a gun like this. So I will accept the batteries for what they are and try to optimize the other aspects of the design.

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CodyC3 (author)2014-12-30

couldent you make it so you just have a ridiculosly long set of coils so you dont have to do the timer buisness? and also, how can you perfectly time the coin going from one set of coils to the next?

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Jaycub (author)CodyC32014-12-31

If you use one long coil, you can only accelerate the projectile in the first half of the length of the coil. By breaking it up into smaller coils you are not wasting half of your accelerator. The timing would halve to be manually tuned, making an adjustment and then measuring the change in speed, then repeating for each coil. Since I wrote this I have decided to use an optically triggered system (infrared LED and phototransistor between each coil). There are many drawbacks to the optically timed system, including cost, complexity, and the space it takes up on the barrel. The 3ft barrel could hold 23 of the coils I made, but with the optical sensors on there it holds only 19 coils. Another drawback of the optically timed system is that I had to drill holes all down the barrel. The reason I chose to use the optical system instead of the passive timing I originally wanted was to simplify the initial coil timing process, and make the system more reliable when there are changes (like battery voltage or barrel slope in relation to gravity).

Here is a video I made showing some of my progress so far:

https://www.youtube.com/watch?v=d9phwt8f_Gc

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steveastrouk (author)2013-08-31

And you have batteries with zero output resistance do you ?

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Jaycub (author)steveastrouk2013-08-31

No, why are you asking that? I did not say anything about batteries with zero resistance. Lithium polymer batteries would be great, I might settle for NiCd or NiMH.

Or maybe you could have a small generator powered by a turbine, driven by liquid CO2. How do you think that would compare in energy density to a modern battery?

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steveastrouk (author)Jaycub2013-08-31

You make a great play about having the coils on, and then turning them off. What happens to the energy stored in the field ? How do you STOP them quickly ? They have just as much inductance going off, as on.

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Jaycub (author)steveastrouk2013-08-31

Yes there will be some delay in turn off for each coil but it is not a problem. When you open the circuit the current will drop quickly enough... As I mentioned buried somewhere in the main description, the projectile will be drawn to the center of the whole set of "on" coils. So the exact time of each coil shutting off will not be so critical as timing is with more normal coil timing configurations. The last 2 or 3 coils could be shut off ahead of the projectile to simplify it even more. As an added bonus the magnetic field behind the projectile dropping will induce currents in the projectile that will actually contribute to acceleration.

You seem to be hostile toward this idea, is there a reason? Or does it just seem that way only to me?

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Nightmare77 (author)2013-08-23

That is awesome u a genies

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Jaycub (author)Nightmare772013-08-24

u a genies 2!

Thanks though seriously. Have you worked with coilguns?

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Nightmare77 (author)2013-08-23

That is awesome u a genies

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