Amateur coil gun approach sound barrier
pulslaser, Thu Mar 02 2006, 09:19PMhi,
I now finish my second induktion coil gun. It uses 8 stages including injector. Each stage has a 40µF 2.5kV capacitor which is discharged through the coil by a trigger spark gap. The spark gap is by triggered by another gap which is triggered by the passing projectil. The projectile, a short piece (2.5 cm) of alu tube has reached a velocity of 270 m/s . So I hope to reach the magic 330 m/s by optimization during next days. More infos will follow at weekend when I will have enough time to do some work
Re: Amateur coil gun approach sound barrier
Simon, Fri Mar 03 2006, 12:01AM
What's the mass of the projectile?
How does the triggering work? Is it optical? Inductive?
(That's serious amateur work, by the way.)
Simon, Fri Mar 03 2006, 12:01AM
What's the mass of the projectile?
How does the triggering work? Is it optical? Inductive?
(That's serious amateur work, by the way.)
Re: Amateur coil gun approach sound barrier
..., Fri Mar 03 2006, 12:27AM
looks nice!
looking at the first post he is using a mechanical trigger...
..., Fri Mar 03 2006, 12:27AM
looks nice!
looking at the first post he is using a mechanical trigger...
Re: Amateur coil gun approach sound barrier
Liam, Fri Mar 03 2006, 06:36AM
Pardon my ignorance (I've never built a coilgun). I understand this is a tremendous amount of power, but isn't the spark gap AWFUL in terms of power loss? I mean, it has to have one of the worst efficiencies of any switch. Could you not find a large enough SCR?
Liam, Fri Mar 03 2006, 06:36AM
Pardon my ignorance (I've never built a coilgun). I understand this is a tremendous amount of power, but isn't the spark gap AWFUL in terms of power loss? I mean, it has to have one of the worst efficiencies of any switch. Could you not find a large enough SCR?
Re: Amateur coil gun approach sound barrier
Desmogod, Fri Mar 03 2006, 08:08AM
Liam, I think the problem with finding a puck to transfer that amount of energy is going to be cost.
i.e. it'll be huge.
Desmogod, Fri Mar 03 2006, 08:08AM
Liam, I think the problem with finding a puck to transfer that amount of energy is going to be cost.
i.e. it'll be huge.
Re: Amateur coil gun approach sound barrier
Plasmaniac, Fri Mar 03 2006, 01:12PM
I've blown an 10kA peak SCR with one similar cap @ just a little over 1kV. In my single stage induction coilgun, I use a mechanical triggered sparkgap, so the losses are a little lower, but it is too slow for multistage designs.
Pulslaser: Do you get higher efficiencys with pieces of aluminum tube than with solid aluminium?
Plasmaniac, Fri Mar 03 2006, 01:12PM
I've blown an 10kA peak SCR with one similar cap @ just a little over 1kV. In my single stage induction coilgun, I use a mechanical triggered sparkgap, so the losses are a little lower, but it is too slow for multistage designs.
Pulslaser: Do you get higher efficiencys with pieces of aluminum tube than with solid aluminium?
Re: Amateur coil gun approach sound barrier
pulslaser, Fri Mar 03 2006, 06:56PM
Simon: triggering is done by a spark gap across the barrel just behind each coil. This gap fires when the conduction projectil passes and discharge the red 6 kV capacitors over the trigger pin of the main switch gaps which in turn discharge the main capacitors through the coils
Liam: it would be very expensive to buy 8 high power thyristors, and there are not as robust than spark gaps which are easily homemade and in case of failure repaired. The losses at high voltages of 2.5 kV are not as serious as in low voltage applications.
Plasmaniac: I found solid projectil much slower (100 m/s) mayby because of higher weight or because in this case the projectil works like a piston and has to suck the air behind into the barrel and press it out infront.
I just made some shots on a 1cm strong piece of wood. It makes a very nice sharp entrance whole
pulslaser, Fri Mar 03 2006, 06:56PM
Simon: triggering is done by a spark gap across the barrel just behind each coil. This gap fires when the conduction projectil passes and discharge the red 6 kV capacitors over the trigger pin of the main switch gaps which in turn discharge the main capacitors through the coils
Liam: it would be very expensive to buy 8 high power thyristors, and there are not as robust than spark gaps which are easily homemade and in case of failure repaired. The losses at high voltages of 2.5 kV are not as serious as in low voltage applications.
Plasmaniac: I found solid projectil much slower (100 m/s) mayby because of higher weight or because in this case the projectil works like a piston and has to suck the air behind into the barrel and press it out infront.
I just made some shots on a 1cm strong piece of wood. It makes a very nice sharp entrance whole
Re: Amateur coil gun approach sound barrier
rupidust, Fri Mar 03 2006, 08:09PM
Nice setup. Is this 125 Joules per stage? That sounds like a reasonable energy level for puck SCRs. The pulse discharge is obviously shorter than most CGs. SCR need to be increadibly large but just need to cover the large current value. What is the current anyhow, coil resistance? An R-puk SCR will cover the voltage and current spec at 2500v to 4000v and surge current starting at 20,000A.
There are not big, but their price will choke you. Acquirement by distributor is out of the question, but might get lucky on ebay or a surplus source. Noise issue of triggered sparks is only reason I opt not for spark gap.
rupidust, Fri Mar 03 2006, 08:09PM
Nice setup. Is this 125 Joules per stage? That sounds like a reasonable energy level for puck SCRs. The pulse discharge is obviously shorter than most CGs. SCR need to be increadibly large but just need to cover the large current value. What is the current anyhow, coil resistance? An R-puk SCR will cover the voltage and current spec at 2500v to 4000v and surge current starting at 20,000A.
There are not big, but their price will choke you. Acquirement by distributor is out of the question, but might get lucky on ebay or a surplus source. Noise issue of triggered sparks is only reason I opt not for spark gap.
Re: Amateur coil gun approach sound barrier
Tipp, Sat Mar 04 2006, 04:24PM
Thats incredable! Very sweet! I'm quite impressed, to say the least.
Best wishes in your efforts to reach 330
Tipp, Sat Mar 04 2006, 04:24PM
Thats incredable! Very sweet! I'm quite impressed, to say the least.
Best wishes in your efforts to reach 330
Re: Amateur coil gun approach sound barrier
pulslaser, Sun Mar 05 2006, 07:50PM
Hi,
after some hours of working with the coil gun I have to admit that the sound barrier is still intact. Mostly I reached some 300 m/s. I think one or two more stages would fix the probleem, but it's not possible with the existing device. Anyway it was a great fun building the device.
To rapidust, I didn't measure current, but according to a pspice simulation it should be around 2..3 kA, the resistance of the coils is negible, 10 to 30 windings of 1mm CuL wire. With the the main spar gaps enclosed in plexiglastubes they don't make much noise. More noise is produced by the recoil forces on the coils. The very tight windings are repelled about 1mm on the barrel after some 50 shots. And of course most noise is made by the impact of the projectil in the target.
More information is found again on my webpage http://www.rapp-instruments.de (sorry in german language)
pulslaser, Sun Mar 05 2006, 07:50PM
Hi,
after some hours of working with the coil gun I have to admit that the sound barrier is still intact. Mostly I reached some 300 m/s. I think one or two more stages would fix the probleem, but it's not possible with the existing device. Anyway it was a great fun building the device.
To rapidust, I didn't measure current, but according to a pspice simulation it should be around 2..3 kA, the resistance of the coils is negible, 10 to 30 windings of 1mm CuL wire. With the the main spar gaps enclosed in plexiglastubes they don't make much noise. More noise is produced by the recoil forces on the coils. The very tight windings are repelled about 1mm on the barrel after some 50 shots. And of course most noise is made by the impact of the projectil in the target.
More information is found again on my webpage http://www.rapp-instruments.de (sorry in german language)
Re: Amateur coil gun approach sound barrier
Steve Conner, Sun Mar 05 2006, 08:53PM
Wow, 300m/s is still a very impressive result, even if "der Schallmauer ist noch nicht geknackt"
I know just enough German to be amazed at the stuff pulslaser is doing, and if you don't know any, it's probably worth struggling with a machine translator.
I think spark gaps are still the best switch for this device though. The traces I saw on the website showed that the coil current was a high frequency oscillation, whose di/dt would probably be too high for a puck SCR. If you lowered the frequency to make more efficient use of the SCR, then I think the induction wouldn't work so well.
Steve Conner, Sun Mar 05 2006, 08:53PM
Wow, 300m/s is still a very impressive result, even if "der Schallmauer ist noch nicht geknackt"
I know just enough German to be amazed at the stuff pulslaser is doing, and if you don't know any, it's probably worth struggling with a machine translator.I think spark gaps are still the best switch for this device though. The traces I saw on the website showed that the coil current was a high frequency oscillation, whose di/dt would probably be too high for a puck SCR. If you lowered the frequency to make more efficient use of the SCR, then I think the induction wouldn't work so well.
Re: Amateur coil gun approach sound barrier
Madgyver, Sun Mar 05 2006, 09:49PM
Holy cow, you said you were working on it earlier, but I didn't think to see something so soon. I am looking forward to see it for real.
Very nice. Are the caps from the "MIR" Shop in Schillerstrasse? I have seen some of these types there.
Besides, I am worried that you start to get into speeds were legal problems could occure. Any thoughts so far?
P.S. I thought railgun was too loud for your neighbours, would a super sonic boom be such a big difference?
Madgyver, Sun Mar 05 2006, 09:49PM
Holy cow, you said you were working on it earlier, but I didn't think to see something so soon. I am looking forward to see it for real.
Very nice. Are the caps from the "MIR" Shop in Schillerstrasse? I have seen some of these types there.
Besides, I am worried that you start to get into speeds were legal problems could occure. Any thoughts so far?
P.S. I thought railgun was too loud for your neighbours, would a super sonic boom be such a big difference?
Re: Amateur coil gun approach sound barrier
pulslaser, Mon Mar 06 2006, 07:45PM
Hi Madgyver,
you're welcome. The machine is at my home in munic Sendling Liesel Beckmann Str. 2. That's in the south of munic, near the Luise Kieselbach Platz at the "Mittlerer Ring". You can reach it by U-Bahn U6 to Partnach Platz or S-Bahn S7 to Mittelsendling.
It didn't bought the capacitors from "Mir", I got them from some old ruby lasers. Because I had a lot of them I even offered some to "Mir" for selling but the weren't interessed.
I didn't though about legality until now. I think the law isn't well defined in these cases.
To my sadness I didn't reach speed velocity, so there no super sonic boom, but of course the is some noise, but not to compare with explosion from 10kJ capacitor discharge happening in plasma driven railgun
pulslaser, Mon Mar 06 2006, 07:45PM
Hi Madgyver,
you're welcome. The machine is at my home in munic Sendling Liesel Beckmann Str. 2. That's in the south of munic, near the Luise Kieselbach Platz at the "Mittlerer Ring". You can reach it by U-Bahn U6 to Partnach Platz or S-Bahn S7 to Mittelsendling.
It didn't bought the capacitors from "Mir", I got them from some old ruby lasers. Because I had a lot of them I even offered some to "Mir" for selling but the weren't interessed.
I didn't though about legality until now. I think the law isn't well defined in these cases.
To my sadness I didn't reach speed velocity, so there no super sonic boom, but of course the is some noise, but not to compare with explosion from 10kJ capacitor discharge happening in plasma driven railgun
Re: Amateur coil gun approach sound barrier
Quantum Singularity, Wed Mar 08 2006, 01:58AM
Congrats pulslaser, even though you might not have broke the sound barrier it is still very fast. Your coilgun is more like what I want to build. Spark gaps are what I am more familiar with (several tesla coils, exploading wire, can crusher, disk launcher, etc...) and it appears that in your configuration the spark gap switches seem to be good enough. I was thinking about building a traditional coil gun with steel projectile but it seems the induction type is more like what I have been experimenting with my disk launcher and is simpler in terms of timing and pulse length.
And tell me if I am correct - I am not an expert but when I was working on my disk launcher a few years ago I came to the conclusion that for this type of launcher you would want maximum coupling between coil & projectile and the greatest rate of change of the magnetic flux lines passing through the projectile? I guess what I am getting at is unlike the railgun discussion where you dont want such a quick pulse (using lower voltage caps all stacked in parallel) this type of launcher would fair better with higher voltage and less capacitance. With the practical limit being when too fast of a pulse causing inertia and air resistence to degrade performance. Does this sound correct?
I am still going to build a monster single stage but I might also work on a smaller multistage gun.
Quantum Singularity, Wed Mar 08 2006, 01:58AM
Congrats pulslaser, even though you might not have broke the sound barrier it is still very fast. Your coilgun is more like what I want to build. Spark gaps are what I am more familiar with (several tesla coils, exploading wire, can crusher, disk launcher, etc...) and it appears that in your configuration the spark gap switches seem to be good enough. I was thinking about building a traditional coil gun with steel projectile but it seems the induction type is more like what I have been experimenting with my disk launcher and is simpler in terms of timing and pulse length.
And tell me if I am correct - I am not an expert but when I was working on my disk launcher a few years ago I came to the conclusion that for this type of launcher you would want maximum coupling between coil & projectile and the greatest rate of change of the magnetic flux lines passing through the projectile? I guess what I am getting at is unlike the railgun discussion where you dont want such a quick pulse (using lower voltage caps all stacked in parallel) this type of launcher would fair better with higher voltage and less capacitance. With the practical limit being when too fast of a pulse causing inertia and air resistence to degrade performance. Does this sound correct?
I am still going to build a monster single stage but I might also work on a smaller multistage gun.
Re: Amateur coil gun approach sound barrier
pulslaser, Wed Mar 08 2006, 05:52PM
Hi Tristan,
first of all thank's to youre congrats. The trigger gap is located behind the coil and the projectil triggers when it leaves the coil but trailing parts is still in the coil. I haven't implemented any delay circuit. I cannot measured the effective delay but I think it should be smaller than some microseconds. Of course You come in trouble with very high speeds, so one should place the trigger gap as close as possible behind the coil. I have tried to compensate the increasing speed by making the coils of the last stages shorter in the hope that even with late triggering there is some part of projectil still in the coil. I don't know if this makes any difference.
I think shortest possible pulse should be used, because the region where the magnetic field influence the projectil is very small. Althoug I haven't made any simulation I think field density is highest in/near the coil and degrades quickly with distance from the coil. But I have to admit that I didn't think about a upper limit by air resistance and inertia.
Like You I think that spark gaps are the best choice in this Voltage range, because there cheap and easily homemade. If I would have enough money to spend I would prefer to use ignitron, this kind I used in my railgun. But they are very expensive and seldom sold in ebay, over some years I just got two of them.
Best wished four your next gun
pulslaser, Wed Mar 08 2006, 05:52PM
Hi Tristan,
first of all thank's to youre congrats. The trigger gap is located behind the coil and the projectil triggers when it leaves the coil but trailing parts is still in the coil. I haven't implemented any delay circuit. I cannot measured the effective delay but I think it should be smaller than some microseconds. Of course You come in trouble with very high speeds, so one should place the trigger gap as close as possible behind the coil. I have tried to compensate the increasing speed by making the coils of the last stages shorter in the hope that even with late triggering there is some part of projectil still in the coil. I don't know if this makes any difference.
I think shortest possible pulse should be used, because the region where the magnetic field influence the projectil is very small. Althoug I haven't made any simulation I think field density is highest in/near the coil and degrades quickly with distance from the coil. But I have to admit that I didn't think about a upper limit by air resistance and inertia.
Like You I think that spark gaps are the best choice in this Voltage range, because there cheap and easily homemade. If I would have enough money to spend I would prefer to use ignitron, this kind I used in my railgun. But they are very expensive and seldom sold in ebay, over some years I just got two of them.
Best wished four your next gun
Re: Amateur coil gun approach sound barrier
Quantum Singularity, Wed Mar 08 2006, 06:45PM
Ahh, I C. And for anyone wondering, pulslaser was answering questions I asked him in an email.
Another questions... you say your not sure about the delay in triggering especially with very high speed projectiles. You have it set to trigger as fast as it can by your design. Have you tried testing it by not running all the stages to tell the effect of each stage? Like run just the first stage and record data, then the first two stages, then the first 3 stages... and so on. You could calculate the energy transfer of each stage and determine maybe if the later stages with the faster velocity arent transfering as much energy to the projectile. And if it was found that triggering want fast enough could you put the trigger inside the coil slightly instead of after it? Like space out the last few turns just slightly and put the triggering in the small gap?
Quantum Singularity, Wed Mar 08 2006, 06:45PM
Ahh, I C. And for anyone wondering, pulslaser was answering questions I asked him in an email.
Another questions... you say your not sure about the delay in triggering especially with very high speed projectiles. You have it set to trigger as fast as it can by your design. Have you tried testing it by not running all the stages to tell the effect of each stage? Like run just the first stage and record data, then the first two stages, then the first 3 stages... and so on. You could calculate the energy transfer of each stage and determine maybe if the later stages with the faster velocity arent transfering as much energy to the projectile. And if it was found that triggering want fast enough could you put the trigger inside the coil slightly instead of after it? Like space out the last few turns just slightly and put the triggering in the small gap?
Re: Amateur coil gun approach sound barrier
pulslaser, Wed Mar 15 2006, 11:31PM
I have made this measurements by recording the flash of the spark gaps with a photocell. Measuring the time the projectil needs to reach and trigger the next gap and knowing the distance I can calculate the speed increase by each coil. It's nice to see that the data compare well with the theoretical increase of speed by assuming a constant energie deposition at each stage .
Next I will change my projectil tube from some aluminium alloy to pure aluminium. A friend told me that there may be a possible increase up to 100% because of lower resistance.
sorry, I forgot to upload the images and didn't find possibilty to re edit the post
[Mod edit: double post merged.]
pulslaser, Wed Mar 15 2006, 11:31PM
I have made this measurements by recording the flash of the spark gaps with a photocell. Measuring the time the projectil needs to reach and trigger the next gap and knowing the distance I can calculate the speed increase by each coil. It's nice to see that the data compare well with the theoretical increase of speed by assuming a constant energie deposition at each stage .
Next I will change my projectil tube from some aluminium alloy to pure aluminium. A friend told me that there may be a possible increase up to 100% because of lower resistance.
sorry, I forgot to upload the images and didn't find possibilty to re edit the post
[Mod edit: double post merged.]
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