• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Coil Gun Update

Status
Not open for further replies.

daviddoria

New Member
I put 12V to a 23000uF cap.... how long should this take to fully charge? Also, i let it charge for like 10 seconds, and it fires a 1 inch nail about 3 feet.... that isn't nearly what i expected with this huge cap.....

http://www.bandtank.com/~calculusap/cg1.jpg
http://www.bandtank.com/~calculusap/cg2.jpg
http://www.bandtank.com/~calculusap/cg3.jpg
http://www.bandtank.com/~calculusap/cg4.jpg
http://www.bandtank.com/~calculusap/cg5.jpg
http://www.bandtank.com/~calculusap/cg6.jpg

whats wrong/ how do i fully charge the cap?

david
 

fazer

New Member
coil gun

so you built a coil gun and ended up being a pea shooter huh!
well there is onley one suggestion that i coild make and that is to run the uotput from the cap thru a radio transformer and see if that works as i have had some luck with this in other cap discharge applications
 

Scubasteve

New Member
hi David,

You gotta read up on this stuff, there are many sources all over the internet.

The capacitor's charging will depend on resistance from your supply and its current capability. The RC time constant determines the rate of charge (t=RC) and it usually takes ~5 of these to charge the capacitor fully. You will know it is charged by the voltage across the capacitor, it will ramp up until it matches the source.

To generate a large electromagnetic field, you need a large current. You are doing this by discharging the capacitor into the coil. Your 12V might be okay for your wire guage.. but it might not be idea. You need to remember, the more voltage across the coil, the more current that is being forced through the coil, it is basic Ohm's law.

You should worry about your capacitors ability to discharge quickly. You are looking for a sharp response through a coil, not anything linear. Magnetic coupling should also be a concern in this design. The closer the object to the coil, the better.

All coilguns work in stages, not just one single coil. The object is loaded and fired out a long tube. As the object is passing through the tube, sensors(usually optical) detect the object and produce an adjustable delay to fire the next coil. With a lot of tweeking, you can get a pretty good velocity.

I think Fazer was along the right track with suggesting a transformer, which would step up the voltage to a level which the coil would want a lot of current, but the transformer might not be able to supply this. I've heard of people using 'photoflash' capacitors which are able to discharge very fast.

If you need any help, don't hesitate to ask more, I've always been interested in these..

Goodluck!,

Steve
 

daviddoria

New Member
NEW DESIGN

1. hook up an AC/DC rectifier to a wall outlet

2. hook up 2x 200v 450uF caps in series (2 because thats all i have :))

3. put the coil in parallel with the caps along with a momentary switch to turn the coil on and off.

sound reasonable?

will it short the circuit? or are the caps acting as a load?

david
 

Scubasteve

New Member
DANGER!

Do not attempt this! If you discharge this into yourself, you have a good chance at dying... This is no joke, this stuff is lethal!

Steve
 

Scubasteve

New Member
If you do try this, please proceed with extreme caution..

Do not use any sort of switch other then a lower voltage one intended to drive a trigger that will discharge the capacitors. This is the safest way to do this, stay back!

I just don't want anyone getting hurt over something so silly,

Steve
 

daviddoria

New Member
how do i design a switch that triggers the big switch? just like a relay/transistor type of thing?

thanks for your concern
david
 

Scubasteve

New Member
Hey there, just switch it without being anywhere near it..

I've seen fancy setups with mechanical actuators with some ball contacts, but I don't think this is necessary. Just proceed with caution and make sure your wires are heavy duty and that you are well isolated. In the end, you'll end up with over 170Volts DC and a good amount of current to back it up..

http://www.oz.net/~coilgun/sitemap.htm

check this out
 

daviddoria

New Member
i've been very cautious... this thing is insane lol

i'll have some pictures up this weekend, but i'm officially renaming this from the "coil gun" to the "coil cannon". hehe

i used capacitors from computer power supplies, however, when i used 2x 470uF (200V) vs. 4x 470uF (200v) i could not tell a difference... why would this be?

do they make switches that dont break when you do stuff like this? i've broken 3, then once i ran out of those i just touched the wires together from a few feet away, but i only get about 4 shots out of 14 AWG stranded before it breaks and i have to put in a new one :)

this has been a great learning experience!

david
 

Scubasteve

New Member
Hehe, sounds like fun! I'm just glad that you're still alive and never forget the dangers with working with that stuff..

The reasoning for this is because either the voltage isn't high enough to enduce your current into the load (Ohms Law!!!), or your caps aren't capable of supplying current fast enough.. Use heavy wire, it will work a ton better

Steve
 

Take_UR_PIC

New Member
CoilGun Update

Your basic problem is that from what I read, you have gone about the problem in completely the WRONG way!!

For a start, you need MUCH thicker wire to allow the current to flow thus building up a magnetic field in the coil more rapidly. Something like 10 AWG or even heavier is required.

The NEXT stage is to add ANOTHER coil on the end of it, and sense when the projectile is just about to leave the initial STARTING coil, and enter the ACCELERATING coil. It is not unknown for military coil guns to have up to 64 stages!!

Basically the system works like this;

You have an initial HIGH current STARTER coil, then subsequently smaller and THINNER coils as you progress down the "barrel". Bear in mind the whole THIN thing means that the coils get EXPONENTIALLY shorter, but FATTER as you go down the barrel, this makes the whole thing horn shaped. The BIG problem is switching each of these stages at

A) The right time

B) Fast enough

Try an eight stage gun, you'll be surprised at the results. I built on many years ago and put a hole in the garage door. Needless to say, my parents were NOT very happy!

IMHO you'd have far more fun, and results with a RAIL GUN. The Swiss have on of these that can fire a projectile at over 27Km/S!!!
 

Nostrafus

New Member
Well since I seem to be the one here with the longest interest and study of linear accelerators (Gauss style) I'll interject my opinion.

Well for one, you need a large power source, what's yours ?

I know you said 12v, but can you give further details, are you using a transformer, or just the 12v through the coils.

Because standard gauss experimentation uses around 400v DC. (AC doesn't work as well, don't know why)

Also you need a way to time your coils, using either photosensors, or magnets, improper timing will drop a coils distance by several yards.

Also consider dropping the size of your round, since there isn't a powerful enough source to create a decent man portable weapon you need a small round, I'd say get a box of copperhead .21 cal copper bb's.

This alone should increase your distance.

Then there's the matter of your wire size, and construction, if you run your wires backward, or your coils aren't tight enough, or you have a bad patch of wire, or your wire is too thick, you'll get a slower round with less distance.

Also your barrel will affect the round, if your using metal switch to plastic, the round is your core for the electromagnet, not the barrel, and make sure it's as thin as possible, and also as tight on the round without restricting movement, it should be about 1mm larger in diameter than the round, and be no more than 1/8th inch thick.

Also consider experimenting with a transformer style barrel.

Instead of using one coil, use two.

Here's how you build.

Get 32 or less gauge wire and wrap it around your inner barrel, then when it is complete, measure your barrel, and get another barrel just large enough to fit over the first, then use a slightly larger gauge wire (no more than 2 sizes larger)

Send the current down both, this will create a much larger magnetic force since the two seem to act on each other swapping current and magnetism, I haven't figured out why yet since it doesn't work like a permenant magnet does when it passes inside a coil, because if it did, it would create an infinite loop of electricity that would defy physics and eventually explode. (make sure you have a good enough resistor before it goes back to the power supply as this type is unstable and can easily spike enough to blow your power, I'd also suggest 2 fuses in series)

Also consider a heatsink for your power supply, and if your barrel can get small enough, get a few circular heat sinks to cool off your coils.
 

Nostrafus

New Member
Yes I know, most of my info seems to go against popular belief, especially the fine coils bit, but when studying them I found that if the coils are made too large the electromagnet moves to fast, and doesn't catch the round as well, it's like having a guy on rollerskates trying to hold onto a car that's doing 60, but with a fine wire, it has a longer distance to travel, thus, is slower, and catches the round better so with the rollerskate analogy again the guy's just trying to keep a hold of a car doing 30 instead.

Just my opinion.

Also the finer the wire, the more powerful an electromagnet is, that I do know is fact, straight from an encyclopedia.
 

snoopy

New Member
first of all thinner wire gives you more amp turns( less thicknes lets you put of more layers fatter wire the circumference is to large to do any good) also you need caps out of cameras because they discharge very quickly. ive been useing just plain ol' magnet wire and about 7 flash caps... using only one charge board. with a 250v trigger people i have seen using multible coils seems they dont know the meanning of K.I.S.S (keep it simple stupid) also listen to all warnings the caps start to add up quick ( listen to that cap bank charge)
 

hellraiser06

New Member
Your capacitor has too much capacitance; it won't be able to discharge fast enough for a decent coil gun. A transformer would be really good! if you step up the voltage to about ~1000VDC, it would be really good for a coil gun. Also, with my experience in coil gun designing, I have found that the more wraps of wire (must be magnet wire) you have, the more powerful the coil gun.

Hellraiser06


P.S. someone said on the first page that all coilguns are multi-stage... That is wrong! There are lots of single-stage coilguns out there and they are very good for a fist coilgun.
 
Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top