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Magnet coil help (turns, gauge, for coilgun)

supak111

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Apr 29, 2012
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No I have not, seems complicated. Also I need to figure out the diameter of the barrel first. It will depend on material of the barrel. Want to wind the coil as close to the barrel if not wind it onto the barrel so there isn't any space in between the two.

But lets say: 1/2" center hole, coil width 1", coil diameter?? 14g wire diameter: .0675"
 

CDRIVE

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I didn't imply I was going to calculate it for you? It was a rhetorical question because it's not an insignificant issue.

Here's another rhetorical question: Did you calculate the weight of 120ft of 14AWG solid copper wire?

Chris
 

supak111

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I'm saying I wouldn't be able to calculate the diameter of the coil, hopefully someone here can with the info I provided.

1.5lbs 14g @ 120ft
 

BobK

Jan 5, 2010
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wire diameter 0.0675 in. means you will get 14.7 (call it 15) turns per inch. At 1/2 in diameter, that is 23.5 ft for a single layer 1 inch long. Each layer would be 0.135 in larger than the previous one, so 4 layers will just about use up your 120 ft of wire.

Question, why are you starting with the length of the wire? That seems backwards to me.

Bo
 

supak111

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Ok thanks.

Its just the roles of magnet wire I have at the moment, where should I start? I don't mind buying different wire if 14g isn't what I need.
 

BobK

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Whoops, my previsous calculation was off a bit. Four layers would use up on 120 inches of wire, not feet! It will take 19 layers and the outer diameter of the coil will be 3 inches.

You should start with the desired muzzle velocity. Then you can calculate the forces needed to to accelerate your projectile to that velocity. Then you should figure out how much force a given coil can impart. I don't think you are going to be able to calculate these, or find tables anywhere, so you are going to have to experiment. You are going to need equipment that will blow your budget before you even get started.

And, by the way, for this coil, the inducance is 3mH. This is means it will take about 10ms for the current to ramp up to 125A when supplied with 40V. Sort of makes 2000 shots per second a little difficult, doesn't it? Oh, I know, your 2000 shots per second is only on the bigger ship mounted gun. But the bigger gun will have much bigger coils with much more inductance. I think you are talking about many kilovolts to be able to turn these coils on and off in 1/2 msec. And now the insulation begins to be a problem. Do you see where this is going?

Bob
 

supak111

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Weight of the 14g 120ft wire is writen on the spools I have.. Well I was told by you guys that my batteries will probably not go to 125a anyways, haven't yet found the short circuit rating for them. Lets say that they only put out 50a at 40v and the coil is 3mH as you said, how did you figure out the time it takes to reach 50a? Found a calc before cant find it now. Also if I have many of these coils each one even if it doesn't reach it's max AMP will still speed up the projectile some degree correct? Just wanna know if more and more coils will keep on speeding up the projectile?
 
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CocaCola

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Also if I have many of these coils each one even if it doesn't reach it's max AMP will still speed up the projectile some degree correct?

Nope, they could just as easily retard the speed if not properly designed and timed...
 

supak111

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Lets assume my timing will be ideal with opto switches, would adding more & more of the same coils keep accelerating the projectile then? Im assuming It would
 

CocaCola

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Lets assume my timing will be ideal with opto switches, would adding more & more of the same coils keep accelerating the projectile then? Im assuming It would

Yeah in a perfect world (fantasy land) if everything worked perfect theoretically more coils would increase speed if designed to do so...

But, as I keep trying to point out we live in the real world where there are many, many factors and and laws of physics you have to account for...
 

supak111

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Yeah in a perfect world (fantasy land) if everything worked perfect theoretically more coils would increase speed if designed to do so...

But, as I keep trying to point out we live in the real world where there are many, many factors and and laws of physics you have to account for...

So are you saying by me adding more coils with perfect opto-switch timing I wouldn't gain more speed? Why?

Don't worry about super long barrel length required for many stages or weight of many 1.5lbs coils. Just assume I'm building a proof of concept prototype. Just explain why wouldn't more coils keep accelerating the projectile?

Each additional coil will still add some X amount of energy to the projectile, as long as that energy amount is more then the friction between each subsequent coil I believe it will keep accelerating. I get that each subsequent coil will add less and less energy as the projectile is flying faster through the opto-switch so at some point it will stop accelerating because of the: friction / projectile residual magnetism / eddy currents... But if that speed is say 2000fps+, or more then say 600J (about 9mm energy), I'm ok with that (FOR NOW).
 

CDRIVE

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I've lived on the coast all my life, so my favorite metaphor would be ."This thread is like shoveling **** against the tide"!

Chris
 

(*steve*)

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Supack111, just so you know... We normally close threads related to weapons very quickly.

The fact that I (or any of the other moderators) have not closed this is some indication of what we think.
 

supak111

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I understand, there is no energy there so no need to close the thread.

PS and Im not using HV caps so really nothing dangerous here.
 

supak111

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I just want to try my design and see how it compares say to these:

http://hackedgadgets.com/2007/01/27/top-5-coil-guns/

My design is really totally different then what everyone is doing. Who knows it may turnout to be worse then even those low efficiency guns people already built. I don't mind if the design totally fails guys, at least then I'll know its not better then what everyone else is doing.

Can I ask you guys this: If you were building one and need it to eventually to pulse at 2000Hz, what would you use for power switching? As I am using an opto-switch I want a nice ON and OFF square wave. Whats most efficient/require least heatsink for this? I feel like iGBTs now are way too much as they can handle 600v+ and I will never do more then maybe 60v.
 

CocaCola

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So are you saying by me adding more coils with perfect opto-switch timing I wouldn't gain more speed? Why?

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I keep trying to point out we live in the real world where there are many, many factors and and laws of physics you have to account for...

Seriously do you think your elementary ideas are anything revolutionary or new to coil gun design? Do you really believe that you are the first one to come up with them and no other person has been down that road?

There are glaring problems and issues in your design (and most every coil gun design) that are blatantly clear to many of us here... I can only imagine the smack down that you would receive if you came across someone who had actually devoted 'pro' level study and experimentation to coil guns... It's novel but not a realistic replacement for traditional weaponry... Rail guns on the other hand show some promise but there are so many obstacles still with them that it's going to take a long while (and billions of dollars) before they could be made into an reliable alternative and then probably only on the large scale, not a sidearm...

It's a fun 'toy' play with, explore and learn something, take caution as it can be dangerous but at the end of the day you will likely see the light and reality will hit back...

Your first clue might be from simply watching a few Youtube videos, why is it that these people test their coil guns in their office or living room with cardboard box bullet traps? My electric and green gas airsoft guns that shoot 6mm plastic pellets will shred cardboard at the distances they are shooting... And on that note my dad is on a 'pro' slingshot kick right now, and I'll be damned those slingshots make every home build coil gun I have seen look like a childs dart gun...
 

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CocaCola

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Can I ask you guys this: If you were building one and need it to eventually to pulse at 2000Hz, what would you use for power switching?

Go back and read Bob's post a few post back, I know you glossed over it and ignored it like every other factual and physics issue brought up, but please read it again and try to understand what he is saying...

If I was doing it I would explore CGI Effects...
 

supak111

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But non of the people that have built them have used:

- more then 2kJ
- have not used say 100 coils, max I've seen is 5.
- have not used my design, and yes my design "maybe" revolutionary in this field believe it or not. I won't know until I at least make a small prototype will I? Like I said I am an inventor by profession and I earn my living by improving peoples inventions or products before or after they go on the market. Problem is that I can't just buy a coilgun off the shelf and then just simply implement my design improvements, but I have to first build one and then add my 2 cent improvement which is why I was asking for help.

I know they are toys now but there are some people out there that have some descent energy in their projectiles. Not gun comparable or anything but if they let the projectile accelerate for a much longer T duration shouldn't there be something to it?
 
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