Newbie Project : Coilgun ?

[axl123]

Hello everybody ! I'm starting my first real project in electronic : coil-gun. And I have something to ask. Some of them are ridiculous but I'm just a Vietnamese 11 Grader so I haven't learned anything about circuits or something yet, just got some experiences exploring some basic circuits.

First is what I've achieved :
- I am now using :
A Fuji-color Flash Charger Circuit + 3 ( 150uF - 400V) Cap + 1 Photo-flash Cap
Paper barrel + 3 layers of 2cm long coil.
- The result :
A tiny ferromagnetic screw (very tiny, about 2mm in diameter) went 35cm. Bigger screw just stuck at the center of the coil.

SO:
1. What do you suggest to improve it according to these ?
+ I prefer using battery
+ I want it to be as simple as possible ( I Can't handle complex circuit schematics really )
+ I want it to be as powerful as possible

2. I want to add more battery to improve power and charging time so what's the maximum battery setup ( serial, parallel ? ) If it is needed to get caps of higher rate then it's ok I can get them.

3. And is there any formula to calculate the Output Voltage (to Caps bank) from the Input Voltage (Of batteries ) applied to the flash-charger circuits ?
That's all for now. Thank you all for reading
P/s : sorry my bad english.

 

[Sceadwian]

Well you're in 11th grade, but the math is actually pretty hard core for coil guns, and worse the equipment you need to analyze what's going on with your circuit so you can tune it isn't cheap. It's not like you just hook up components of value A using wire B in configuration C. The circuits for coil guns may seem rudimentary simple, a single state coil gun is nothing more than a charged capacitor discharged through a coil, but the size and shape of the coil and it's load are hyper critical in determining it's results.

Try this, you have a stable setup, it's not high power but it'll give you an idea of what's going on. Skip the screws for a load and use wire cut the different lengths. For an impulse type coil gun there are two factors, the magnetic state of the load and the electrical impression of the magnetic state on the load, and it changes over time, multi state coil guns require very precise timing, single pulse coil guns rely exclusively on the inducing coils inductance value, it's shape and the load itself. You could using what you have right now simply by using the right length of trimmed wire and a proper coil tuned to that length dramatically increase your outputted power.

 

[axl123]

You could using what you have right now simply by using the right length of trimmed wire and a proper coil tuned to that length dramatically increase your outputted power.

So that means I now have to make different coil ? How different ?

Sorry but English's not my native one so I prefer it if you make your idea simpler to understand those magnetic things are pretty complicated. 11 grade in Vietnam's just like 8 grader in US. We may have learned more complicated things than you do but most of us don't understand the basics, we just have to memorize formulas and texts so that we pass tests and get a job That's why 11 here just like 8 there.

 

[cr0sh]

I once built a "coil gun" with little power, but it worked. It was mainly meant as a demonstration device for a larger project (which I never got around to building).

What I did was take some wire (telephone hookup wire, 14-16 ga, I think), and wrapped six coils onto a length of rigid plastic tubing (about half the diameter of a plastic soda straw, but with thicker walls so it didn't bend); each coil had about 50 turns of wire. I connected one end of each coil together (common), and the other ends I ran to brass tacks on a board. I hooked the common end to the negative terminal of a 12 volt wall-wart (1-2 amp). The positive end of the wall-wart I ran to another wire with a bare end. I cut a small finishing nail such that it would fit inside the tube. With it in place, then rapidly sliding the bare wire across the brass tacks, a simple linear motor "coil gun" was demonstrated. It didn't work too bad, actually. I think I did this sometime in 1994 or so.

Anyhow, what I had planned on doing was beefing up the coils (I had a ton of this wire - still do, actually), maybe 2-300 turns (or possibly buying a few pre-wound solenoid cores) - and wrapping them on a larger piece of tubing, perhaps some small diameter PVC pipe. In between each coil segment, I was going to mount a phototransistor/LED device to detect the passing of the projectile, and activate the coil ahead of the projectile for a set period of time; each one tuned to the reduction in time due to the increasing speed of the projective (likely to be a logarithmic pattern, I think). Another possibility would be to only keep the coil on for as long as the projectile is blocking the sensor, so that the coil turns off once the projectile passes the sensor, but before it has reached the center of the coil. It would've taken simple a large transistor and/or MOSFET, plus the sensor and a few other passives - actually a real simple circuit.

You could power the whole thing off of large capacity batteries, or if you wanted more "oomph", a small capacitor array for each coil and a charging circuit of some sort. It likely wouldn't have been that powerful, but it would've been a fun project. I ended up moving on to other things, and the demonstrator was eventually dismantled.

 

[Sceadwian]

Bigger coils do not necessarily mean a better coil gun, too high of an inductance can prevent it from discharging fast enough and it'll hold the load, the load can be changed but again you're adding total energy not necessarily velocity with a bigger load. Once you get past a certain point you have to do multistage coil guns which are basically opto interrupters that trigger the following via SCR's as the load passes each coil. I've never built one so I don't know any of the practicalities of it, you can try this website though.
Barry's Coilgun Designs

 

[BrownOut]

Hi Axl123, I admire your willingness to experiment and learn. Please be very careful. The output voltage from the flash unit can easily exceed the maximum voltage of your capacitors, turning them into tiny bombs. This is very dangerous. I would advise you get rid of the flash unit and just use a low voltage setup. I'll bet you can get as good or better results using low voltage. Whatever you decide, make sure you never, never, never exceed the rated voltage of your capacitors.

 

[Sceadwian]

How did you determine that Brownout? He didn't list any specs for the flash charger, if this is the flash charger from a disposable camera then there should be no way to overvoltage the caps as long as you only supply it with a 1.2-1.5 volt power source, do NOT apply a higher voltage than 1.5 volts to the flash charger or what you say is true they could explode, batteries in parallel will only increase the total number of charging pulses you'll get not the rate. You'd have to design a completely new charger circuit to increase the charge rate without worrying about exploding the caps or the damaging flash charger.

I've dead shorted an 80u photoflash cap charged to 300 volts and the bang was loud enough to scare the crap out of me, 3 more 150u's and you really are in dangerous pulse power territory, if you manage to actually overvoltage one of these caps so it dead shorts it'll go off like a firecracker as that electricity that normally causes a loud pop when it vaporizes the air will cause a decent boom as it vaporizes all the electrolyte in the cap. When I was kid of a friend of mine showed what happened when you applied 24-36 volts to 6-12 volt electrolytics, they pop good and sometimes they go off like little rockets, I would not want to see the results of a high voltage electrolytic being overvoltaged.


I'm sorry Brownout but you will not necesarily get better results from a low voltage setup in general, but it depends heavily on the coil, and the load and mode of operation of the coilgun. In order to get the same power you need bigger coils and bigger capacitors for the same energy, but as I stated previously bigger coils are not better because the capacitance, resistance the inductance will cause a ringing effect and the pulse will take much longer to discharge through the coil. You want high voltage carefully timed and applied spiked through a coil with as low a resistance and inductance as you can that will get the load past the coil before it starts a holding effect. As far as mode of operation you can also use non-ferrous load, commonly aluminum is used where the current pulse through the coil sets up magnetic pulse which generates an opposing current and magnetic field in the load itself. Ferrous based rail guns are attraction based, it is hyper critical that the magnetic pulse is 0 when the load reaches the coil or the ringing that occurs will cause the coil to pull the load back. There really is a lot of math and details involved in a good coilgun, also a lot of trial and error.

 

[BrownOut]

Different flash chargers have different voltages, and it's not something that's easily measurable. Thats how I determine it. I"m pretty sure that I didn't say you necessarily get better results from low voltages. You've failed to read my post properly. I said I BET he can get results as good or better. I stand by that, after all, he's only getting 35cm as things stand. And if you read cr0sh's post, he got better results with a 12 volt system, at least that's how I read his post.

I repeat, high voltage can be dangerous. Please be careful, and consider a low voltage solution.

 

[axl123]

Nah I knew that already I'm thinking about adding more battery in series and parallel to improve charge time ( and also get bigger caps). I'm aware of those overvoltage things so I'm just gonna apply a voltage clock before connecting the capacitors. Thanks anyway.

About discharging time, I'm thinking of adding some kind of detectors so it ain't a worry now. Small coil generates lower electromagnetic force in fact. I guess I'll go with bigger coil and a good solution about discharging and the suckback prob.

Btw, I want my coil gun to be lethal and penetrate skin, skull =)) I'ma do it !

 

[BrownOut]

Also keep in mind that if you charge 150uf to 400v, you have 24J of energy, enough to cause death if accidently discharged through your body. Oh, but you already know everything. So throw caution to the wind, noob. I'll be looking for you during the Darwin Awards

 

[axl123]

Also keep in mind that if you charge 150uf to 400v, you have 24J of energy, enough to cause death if accidently discharged through your body. Oh, but you already know everything. So throw caution to the wind, noob. I'll be looking for you during the Darwin Awards

I'm not English native so I didn't know what that mean :| Was that just a funny line or making fun of me ? I really don't know (for really real). Btw I didn't say I knew ev'rything

 

[DerStrom8]

Here's a good site for building a simple coil gun:

How to build Mini efficient coil launcher from disposable camera flash (circuit diagram)

The instructions are fairly simple and straightforward, and the coil gun works really well. I hope this helps!
Der Strom

 

[Sceadwian]

axl, you're never going to get a railgun that powerful using a single stage, even if you know what you're doing it's not easy to get that much power out of them, not without serious time spent on the details.

Different flash chargers have different voltages, and it's not something that's easily measurable.

Brownout, are you feeling okay? I have a meter within reach that can monitor a flash cap charging up to near 1000 volts, and it cost 5 dollars.

After Axl's last comment though I'm not going to suggest they don't anything as it's proving to be something that they'll obviously not have the attention span to follow through with.

A comment such as

Btw, I want my coil gun to be lethal and penetrate skin, skull =)) I'ma do it !

shows your lack of actual interest in developing a coil gun and shows starkly your intersest in simply causing destruction or making something 'neat' both of which aren't good reasons do do anything.

 

[BrownOut]

Brownout, are you feeling okay?

I feel fine, but you never sound too healthy to me.

I have a meter within reach that can monitor a flash cap charging up to near 1000 volts, and it cost 5 dollars.

I'll remember to stay far, far away from your lab if you're working on HV projects with a $5 meter.

 

[Sceadwian]

Brownout, really? So you're going to actually stand by a statement that says there is no way to reliably measure voltage of 300-500 volts using a standard meter? Forget the 5 dollar one (I know for fact that it's not legally certified in the US) I have a Craftsman meter that's 20 bucks that I know has legal certification, that one goes up to 1000 volts a well, and came with certified leads.

High voltage is dangerous territory, it is not however some obscure realm where the unintiate shouldn't go, you should just approach with severe caution. Axl has shown that he is not doing that, he intent is on results not saftey,

 

[BrownOut]

Once again, you've failed to properly read my posts. I never said this:

So you're going to actually stand by a statement that says there is no way to reliably measure voltage of 300-500 volts using a standard meter?

Maybe some remedial reading program would be helpful. Or maybe just try getting a life.

 

[Sceadwian]

Different flash chargers have different voltages, and it's not something that's easily measurable.

How did I misread that? ANY generic multimeter can safely measure the DC value the cap is charged to, _NO_ disposable flash camera unit on this planet will use more voltage than 1000 volts, 300-500 is typical, if you'd care to disagree with that show me a unit that does. Otherwise you're just being as cantankerous as usual.

 

[BrownOut]

Easily measurabe? Is not the same as

So you're going to actually stand by a statement that says there is no way to reliably measure voltage of 300-500 volts using a standard meter?

People who post here should have the IQ to know the difference. And BTW, not ANY DMM measures to 1000V. You have no idea what the OP is working with, and so you don't know if he can measure it or not. Further, DMM's aren't perfect at measuring charging capicators. And, the OP mentioned in the VERY FIRST POST that he was interested in INCREASING the power of his charge circuit using more batteries. I know you feel comfortable with an 11th grader knowing how to increase power safely, and I hope you don't have one at home. As for me, if I see someone who looks like he's about to drive off a cliff, I suggest he don't do it, or suggest a safer place to drive. Just because it didn't take me a whole page of posts to know this kid might be over his head was no reason for you to chime in with your condescending remarks.

 

[axl123]

Long time... I was just kidding I used 2 batts in serial, same 400V Caps and nothing happened. I hope you guys stop arguing and help me more Or if you guys help any better, safer project to help me study physics and electrics then suggest me Something lethal i guess =))

 

[vlad777]

Check out this coilgun:

YouTube - Portable 1.25kJ Coilgun