My homemade coilgun doesn't work...

Status
Not open for further replies.
X

xenoxion

New Member
Following the instructions **broken link removed** and here, I tried to make my own coilgun. I'm using this nice plastic tube that I got from my school's science lab as a barrel (it's around 1/2" in diameter and ~1 foot long), and I've got this unmarked copper wire that I'm using to wrap around it. I don't know the wire guage of the copper wire, but it appears to be around .04" in diameter, and it appears to be suitable for wrapping. I wrapped the wire in between two washers about 3/4" apart, but my wrapping job wasn't that good. My first two full wraps were nice (going back and forth once), my second two were very crappy, I added some electrical tape after the fourth wrap to hopefully get it going well again, and the last two wraps were OK. I added some metal screws to the tube as testing projectiles, charged up the capacitor and attached the positive lead to the rear end of my coilgun and the negative lead to the front, but nothing happened. I fiddle aroung with it for a little wire, and aside from the wires coming together and making a loud "snap" noise nothing happened. After they crossed, I had to charge the cap up again, but this time a spare piece of wire fell across the terminals of one of the doides and a transistor, shorting out the circuit, so now I have to buy another camera. Anyway, what's wrong with my coilgun? Is it the fact that my middle wraps were kind of crappy? Was my wire too big/small? Do you have to connect the capacitor in any specific way (do I connect the positive or negative lead to the back of my coilgun, or does it even matter)? Help please
 
I think what's a matter is this: You have a couple of coils on ur gun, and the capacitor discharges, and fires all the coils at once, correct? I'd imagine your projectile moves a little bit. What's happening is that once th projectile gets past the first coil, the first coil is still energized, therefore pulling the projectile back towards it. It's kind of a tug o war. Anyway, that's what I got from the website. I didn't read it very carefully because I am TIRED. Need caffeinne :shock: . Anyway, that's my best guess.

To remedy this, you would need a timer, to fire the coils one at a time, so there is no tug of war.
 
The thing is, I'm only using one coil, so there's no timing involved. I think I know what the problem is though.... my wire's way too large, I found some normal 22 guage wire and the one I'm using is about 4x larger in diameter. That, combined with my crappy wrapping job, is probably why it doesn't work. I've got to re-wind the coil with some smaller wire, so does anybody have some advice before I do this and possibly screw up again?
 
if you have a lathe or bench mounted drill, you can put a rod into the lathe or drill, rotate it slowly, and feed the wire onto it...

Tim
 

That might one of the problems but you still will have the tug of war problem even with ONE coil. As long as that one coil remains energized, once the projectile passes through, the coil will try and pull it back (it likely will not be able to but it will slow it down)
 

That's not the problem though, the problem is that the projectile didn't move at all. Also, I'm using a design that has been proven to work (follow the links in my first post), and the cap I'm using is rated 330V, 120uf so I don't think that the coil would stay energized with such a small amount of electricity (from what I've read, higher capacitance is what gives the "pullback" effect).
 
One thing that you might try to make sure that the coil IS generating a magnetic field is to take a compass and put it beside the coil, then fire the coil. You should see the compass needle jump. If it does jump, then I think you've got some kind of problem w/ capacitor or power supply.
 
You could also use a small bar magnet for your test projectile to see if a magnetic field is being generated ...
 
If you're having trouble winding the coils, you could try going to a surplus shop and look for solenoid coils. They vary in dimension and some aren't terribly efficient for C.G. purposes, but it might make a good extermental "control" for your debugging.

You may have tried this already, but also make sure your projectile is ferro-magnetic. Twice in the past, I've tried using projectiles that I thought were magnetic, when they turned out to have non-ferrous cores after I inspected them (zinc).
 
Newb question: what's "ferromagnetic"? Something to do with iron and magnets? I know my projectile (a screw) is magnetic since it sticks to my neodymium rare earth magnet, but I don't know if it's ferromagnetic.

In other news, I went to radioshack and bought some real magnet wire (22, 26, and 30 guage), wrapped a new coil using 5 layers of the 22 guage, and now I think it works. When I connect a 9V battery (I'm currently stuck on a 9V until I buy another disposable camera for the inverter+capacitor) to the leads the screw is propelled a few centimaters forward. I've got another question though: how do I get the enamel coating off the leads of my coil? I used a knife to get a little of it off, but it's not a very clean job, is there a better way? Also, will adding another photoflash cap help or contribute to the "pullback" effect (I'm gonig to use a 120uf 330V, so will adding another identical 120uf 330V help)? How can I inecrease voltage without increasing capacitance? Would, for example, having 4 330V 120uf caps increase voltage to 1320V as well as capacitance, or will only capacitance rise? One more question, how can I construct a DC-DC transformer? I've seen the diagrams and they seem to use some sort of oscillator to produce timed pulses into the transformer, but I don't know why this works, since I thought transformers only work on AC current.
 
I'm not the best physics guy, but here it goes:

Before your gun fires, the projectile will have a number of polar atoms that are randomly oriented in the metal. At this point, it's unmagnetized.

When your coils create the EM pulse in the barrel, the magnetic field will force a certain percentage of those atoms into alignment. A good ferro-magnetic metal like iron ferrite or cobalt will align very easily, and retain that alignment on its own (it becomes magnetized). This lets you get better efficiency. A paramagnetic metal like aluminum or platinum will not be affected, and the coilgun will waste loads energy.

I think once I was told to avoid using pre-magnetized projectiles because of the efficiency problem. If I remember right, his explaination (whoever I heard this from) was that the idea is the make your projectile's atoms go from 0% to ~100% alignment for the best possible efficiency. Strong neodymium magnets are already too close to the 100%, so they are considered "saturated." When the bullet becomes saturated, it can't be magnetized any further, and the coils will have no affect on it.

I think that generally how it goes, but don't quote me that. :wink: Anyway, now that the coilgun is working I guess you're already on the right track.
 
xenoxion said:
One more question, how can I construct a DC-DC transformer?
Click to expand...

Bassically, transformers need AC to do anything. However, you can use a simple osscilator, such as a 555, to convert the DC to AC. This output is then fed into the transformer, and rectified at the output of the transfo, so it is back to DC again. Make any sense? (I wonder if it would just be easier to use a voltage regulator instead...)

xenoxion said:
...use some sort of oscillator to produce timed pulses into the transformer, but I don't know why this works, since I thought transformers only work on AC current.
Click to expand...

The timed pulses could be expressed as a rise in voltage, then a drop, the a rise again, and so on. This is AC: high then low then high etc. A common misconseption is that AC has to go from +v to -v in a sinusoidal fasion.

Tim
 
A sample of my similar and slightly larger 45 J and other coilguns.
**broken link removed**

1. The distance between projectile's outer diameter and coil's inner diameter should be small as possible without causing excessive friction. 2mm - 4 mm diameter difference is common. Since you have a 1/2 inch diameter tube, you need a very wide projectile to fit. I suggest using a smaller inner diameter tube with a thin wall because you are discharging only 6.5 Joules of power. J = .5 * F * V^2

2. Increase your power to at least 25 Joules by connecting 4 of the small caps in parallel, (+) to (+) and (-) to (-). Configuring capacitors in parallel increase the capacitance and preserves the voltage. Configuring capacitors in series increases the overall voltage and lowers the capacitance. Use a steel round less than 8mm in diameter and 30mm in length. Make the coil the same 30mm in length with 8 to 10 layers of 22 gauge stranded (tinned copper) wire. Coil assembly may be found at my site.
https://www.anothercoilgunsite.com/nf-projects.htm

3. No need to connect these small 350v @ 120uF capacitors in series to obtain higher voltages. The very low < 25 Joules energy levels these produce is not going to cause noticable suck back forces on the projectile. This is because the discharge time is extreamly fast for such a small Farad rating.

4. Varnish, varnish the enamal coating from the enamal coated wire. To varnish, use a source of flame. A cig lighter suffices. I usually use my more than sufficient all purpose, always present teeth. My coils operate without a barrel; hence, I use insulated wire.

5. Stick with the camera charging until you build a foundation for both coilguns and intermidiate level of electronics. Where most beginner and spur of the moment coilers fail is in the electronics. Coilguns are an extension of electronics. It is the kinetic implementation of learned theories concerning diodes, transistors, ICs and microprocessors. Its a glorified pumped-up series LC discharge circuit where the complexity spans from a wire and a switch upto optics, microcontrollers, and energy recovery.


https://www.anothercoilgunsite.com
 
Thanks guys! I just got a camera to use it with, and I tested it, the only problem is my projectile only goes about a foot (measuring distance from coil to where the projectile lands, including the barrel).

donniedj: The gun that I just made has a 1/4" hard plastic tube as the barrel, but that didn't seem to help.
Make the coil the same 30mm in length with 8 to 10 turns of 22 gauge stranded (tinned copper) wire. Coil assembly may be found at my site.
Click to expand...
Did you mean 8-10 turns or layers? I used only 5 layers since I saw that on another site somewhere, but I think that's part of my problem. Also, can I just light the tip of my magnet wire on fire to get rid of the enamel?

Thanks again!

EDIT: one more thing I just forgot, when my coilgun is fired, the caps seem to discharge over my switch, causing a small shower of sparks and a rather loud "bang" noise (not as loud as when the cap normally discharges, but still pretty loud). Is this normal, and if it's not, how do I fix it?
 
A few more questions...

1. I want to be able to shoot a screw that's about an inch long. How long should my coil be and how many layers should I do using 22 guage magnet wire? Right now the coil's about 7/8 of an inch long and 5 layers, and the screw barely goes a foot.

2. Is the shower of sparks + bang noise in my previous post normal, and if not how do I fix it?

3. Is there any way I can connect multiple camera units to create a larger power supply? I've got a few more capacitors that I'd like to add in parallel, but the only problem is it would take a long time to charge. Can I, for example, wire two camera circuits in parallel (I'm pretty sure the cameras go to 300VDC instead of AC, but can someone clear this up for mer?), then use that dual power supply to charge 5 330V 120uf caps?

4. As I said before, I've got 5 330V 120uf caps. If I connect them in parallel, can I also add a 330V 80uf cap to those, or will it screw something up?
 

1. Increase that 5 layer coil to 10 layers. Go ahead and try 11 and 12 layers thereafter.

2. The shower of sparks is normal whenever you perform a slow manual
mechanical contact switch. Micro particals of metal will contact each
other first before the majority of the metal joins in. This very small area
rapidly heats and cause high resistance, which in turn causes heat and so
on. This is true even for low power battery discharges. The higher the
source energy of course the hight the BANG BANG spectacle.

3. Parallel charging: You connect power sources like any other output
by means of ORING. That means to attach a Diode to the output of each
power supply, then connect all the Diode outputs together. Anode to (+)
pin. This forms a higher current output withough the individual supplies
influencing one another.

4. At this low level in the game, the smaller 80uF paralleled with the (5)
120uF will not make any difference. If you do not OR the (5) caps to the
(1) cap, the caps will continually discharge into each other to creat an
average voltage. It is better to use (6) 120uF caps. The coil only sees a
TOTAL capacitance during discharge, so (1) 1000uF or (1000) 1 uF caps
is theoretically the same.
 
I've always wondered about those loud discharges. It seems like a waste of good energy. Maybe there are some special fast-acting switches that can eliminate the specticle?
 
Status
Not open for further replies.
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…