Improving my railgun
McFluffin, Tue Mar 28 2006, 06:01AMHello all! Maybe this should be in the projects section, but here goes... I have been assembling parts to build a railgun for the last year or so, and finally shot off a small one on Thursday. However, it didn't work so well, so I am going to try to work on things.
I started off with four 3600uF capacitors that can be charged up to 350V. I used a piece of plastic from an old monitor LCD screen to tie together two pieces of um...copper/aluminum. I didn't have thick enough copper, so I took a piece of alluminum and put a copper jacket around it to improve conductivity and strength of the rails. Charging is done with a half bridge and a variac, which lets me charge it up to around 190V in a fairly short amount of time. I'm not sure how fast I could do it, but I am keeping the variac at 30W during the charging. The large range for it goes up to 1800W, but I had an incident where the fuse exploded(yes, it actually shattered), so I decided that I shouldn't try to charge things up to quickly. Triggering is via an SCR puck. I have three of them clamped in a nice array(common -, but different +s), and a box of 21 more if I need them. This was hte setup that I used to fire my coilgun, so I figured that it was at least worth trying before I started changing things around. I wasn't really sure if the 1 SCR was really sufficient, but it was a fairly small capacitor bank/voltage, so I thought I was fairly safe.
Connections are made between close devices with some fairly thin(maybe a couple of mm) copper. I have several large sheets of it and could probably stack it up if I need to make things heavier duty. Wires are made from some fairly thick cables that come from Toyota Priuses(my dad works for Toyota and they had some sort of recall, so I can get a lot of these. I also managed to get a broken inverter which had 7 IGBT bricks and 3 large 450V capacitors :) among other cool stuff). The wires are maybe .25 inch and are stranded copper. I have used these along with some aluminum buss that came with some of the capacitors to try to further reduce resistance across the capacitors.
I fired the device and nothing really happened. It made a loud pop and the aluminum sort of dissipated. Not real exciting. I then took some copper and connected the 3 SCRs together and wired them up. I also added a voltage doubler and added a second bank of 8 capacitors that are 3300uF @ 430V(Jason might recognize these :)). I am using less than half of my capacitors right now. The system when charged to 350V stores around 2.5kJ of energy. I had seen another amature railgun thread in which someone used steel wool to get bad results, but results nonetheless on their mini railgun, so I decided to try it out. I fired it off and it shot lots of sparks off out the front, but really none to the back, so I was fairly happy that at least things seemed to be moving in the right direction. The steel wool mostly just burned and moved a couple of cm, but not out of the barrel. I could smell burned plastic and the plastic sheet was a little melted. Additionally, the steel wool contact areas gouged the rails. I tried another test with it later, and it did the same thing, so I decided to stop trying to use it.
I then tried several aluminum projectiles. The first projectile was aluminum and didn't work well because it made poor contact. This made a nice flash, but didn't really do much for the railgun concept. These were all fabricated from aluminum foil folded over many times and put into a U shape. When I fired the first one, it moved much further than the steel wool had(no sparks out of the front though), but not out of the barrel. It just wasn't strong enough and tore apart before leaving. I made a third projectile that included a piece of aluminum in the center to try to make it more solid. This time, I blew out an SCR. I am guessing it had to do with not having enogh power to fire them all. I had been warned about this, so I sort of deserve it. I have 12 9600uF caps in a bank that I might use to try to prevent this in the future. I was hoping to make a massive SCR bank out of the box of SCRs, but don't have any plastic to use as an insulator to make the clamp. A fried was suppose to bring some over, but he forgot. I'll try bugging him again.
So, this has led me to several conclusions. The first is that I need to upgrade the SCR firing circuit. The second is that steel wool really shouldn't be used as a projectile as it is too damaging to the device. I tried making a projectile out of carbon, but found it fairly hard to machine. I might also try one of the plasma sabot projeciles using an aluminum backing. Third, I need to work with some augmented rails some more. I didn't really have enough wire to signifigantly augment them. Is there really an advantage of parallel augmented rails? I could try dumping quite a bit of power into a large electromagnet if anyone thought it might be interesting to try(I am afraid too much power into this small device might blow it up from using series augmented with any more power). Finally, I am curious if it would be worth it to run the system at 700 or 800V. I hear the higher the voltage, the better.
I have some pictures, but need to either put a floppy drive on my computer or get a chance to barrow my dads computer. I'll also see if I can get some dimensions. The device is maybe around 8 inches long and 3 inches wide. Perhaps .5 inch thick.
Re: Improving my railgun
mike0t4ever, Tue Mar 28 2006, 06:59PM
just a quick question
does your projectile start at rest in the rails or is it injested at some initial speed? (injection can be very beneficial)
i'm also curious as to your bank connection layout (the scr's in particular) a circuit diagram would be nice (hint hint)
augmentation can help but only if you set it up properly (you also need to know when to power the rails and when to power the augmenting coils, ideally you want to fire the coil before the rails to let the current and magnetic field build up, but not too soon)
permanent magnets can be an alternative to that (especially with a stationary projectile)
interesting work though keep it up (just be safe)
mike0t4ever, Tue Mar 28 2006, 06:59PM
just a quick question
does your projectile start at rest in the rails or is it injested at some initial speed? (injection can be very beneficial)
i'm also curious as to your bank connection layout (the scr's in particular) a circuit diagram would be nice (hint hint)
augmentation can help but only if you set it up properly (you also need to know when to power the rails and when to power the augmenting coils, ideally you want to fire the coil before the rails to let the current and magnetic field build up, but not too soon)
permanent magnets can be an alternative to that (especially with a stationary projectile)
interesting work though keep it up (just be safe)
Re: Improving my railgun
McFluffin, Wed Mar 29 2006, 02:55AM
I drew up a rough schematic that can be found at:
The diodes are 100A surge, 600V rated diodes. There are perhaps 20 on the capacitors, but only 3 across the rails. I have 100 of them, so it would probably be in my best interest to add some more. They are in bunches of three crimped with connectors so that they can be mounted on each capacitor and are mounted on most capacitors. This just seemed a convienent way to mount them and doesn't really have to do with trying to protect individual capacitors as I assume that they should be able to clamp the backlash nearly equally well from anywhere on the capacitor bank. However, I now realise that it is probably much better to put them directly across the rails rather then on the capacitors. Not included in the schematic is also a diode coming out the the voltage doubler. I had some EMF kill the diode in the voltage doubler, so I might add an inductor to try to stop this.
Currently the projectile only rests on the rails. I have some pneumatics equipment, so I might try to inject is pneumaticaly in the future. However, for simple tests its sufficient to just let it start at rest, however inefficient.
As far as safety, I'd definitly like to shield the cap bank in case of failure, but don't have any material to do so. I might go down to my local junkyard and try to pick up some polycarbonate or other clear material. I added a bleeder resistor, which should help in any long term charge effects with the capacitors.
How much do magnets really help? I've heard a lot of debate over this. I have a pile of magnets(some neolydium) that I could try using. One of the main concerns that I have is how I should actually place them. I'd imagine if you don't place them right, you might make things worse.
Thanks for your help!
EDIT: Just fired a piece of alluminum quite successfully. It was launched out and did no damage to the device. Hit a target a few feet off and bounced back two feet or so.
McFluffin, Wed Mar 29 2006, 02:55AM
I drew up a rough schematic that can be found at:
The diodes are 100A surge, 600V rated diodes. There are perhaps 20 on the capacitors, but only 3 across the rails. I have 100 of them, so it would probably be in my best interest to add some more. They are in bunches of three crimped with connectors so that they can be mounted on each capacitor and are mounted on most capacitors. This just seemed a convienent way to mount them and doesn't really have to do with trying to protect individual capacitors as I assume that they should be able to clamp the backlash nearly equally well from anywhere on the capacitor bank. However, I now realise that it is probably much better to put them directly across the rails rather then on the capacitors. Not included in the schematic is also a diode coming out the the voltage doubler. I had some EMF kill the diode in the voltage doubler, so I might add an inductor to try to stop this.
Currently the projectile only rests on the rails. I have some pneumatics equipment, so I might try to inject is pneumaticaly in the future. However, for simple tests its sufficient to just let it start at rest, however inefficient.
As far as safety, I'd definitly like to shield the cap bank in case of failure, but don't have any material to do so. I might go down to my local junkyard and try to pick up some polycarbonate or other clear material. I added a bleeder resistor, which should help in any long term charge effects with the capacitors.
How much do magnets really help? I've heard a lot of debate over this. I have a pile of magnets(some neolydium) that I could try using. One of the main concerns that I have is how I should actually place them. I'd imagine if you don't place them right, you might make things worse.
Thanks for your help!
EDIT: Just fired a piece of alluminum quite successfully. It was launched out and did no damage to the device. Hit a target a few feet off and bounced back two feet or so.
Re: Improving my railgun
dan, Wed Mar 29 2006, 06:28AM
Why are you using SCR's? Just use projectile switching with pnumatic injection. You also don't have to worry about back-emf too much since a rail gun has minimal inductance anyway. Any back-emf that is generated can easily be absorbed by the capacitors.
dan, Wed Mar 29 2006, 06:28AM
Why are you using SCR's? Just use projectile switching with pnumatic injection. You also don't have to worry about back-emf too much since a rail gun has minimal inductance anyway. Any back-emf that is generated can easily be absorbed by the capacitors.
Re: Improving my railgun
McFluffin, Thu Mar 30 2006, 12:23AM
I don't have enough building material currently to make something for pneumatic injection. So, using the SCRs and just letting it sit will have to do for now.
If you think the EMF shouldn't be a problem, why is that diode blowing up? I checked things out after the last fire, and it died again :( I had three together that time. I tried adding an inductor(a shorted transformer that I had, maybe 4 inch cube iron core) and it only charged up to 190V which is like I wasn't using the doubler at all. However, it went fairly slow which meant that I didn't have to manually turn the voltage up. Also, isn't the back EMF in the other direction which would cause reverse charging of the capacitors? I have been warned to avoid that.
McFluffin, Thu Mar 30 2006, 12:23AM
I don't have enough building material currently to make something for pneumatic injection. So, using the SCRs and just letting it sit will have to do for now.
If you think the EMF shouldn't be a problem, why is that diode blowing up? I checked things out after the last fire, and it died again :( I had three together that time. I tried adding an inductor(a shorted transformer that I had, maybe 4 inch cube iron core) and it only charged up to 190V which is like I wasn't using the doubler at all. However, it went fairly slow which meant that I didn't have to manually turn the voltage up. Also, isn't the back EMF in the other direction which would cause reverse charging of the capacitors? I have been warned to avoid that.
Re: Improving my railgun
dan, Thu Mar 30 2006, 01:07AM
Maybe I was wrong.. At the currents that are involved with a rail gun are so great that even the smallest stray inductance causes back-emf. Paralleling diodes wouldn't help that much since semies doesn’t really like to share the current evenly. Maybe you need to get yourself a hockey puck diode rated for 1000A continuous and several 10KA's peak to clamp that nasty back-emf. (not sure if this is over kill) I'm not sure if this clamping diode across the rails would help much since this stray inductance is literally everywhere in the circuit but the diode would be clamping the majority of it. Electrolytics are bad for rail guns since they are generally very slow and they don't like to be reversed charged. However they are fairly rugged and should be able to take this abuse. I have shorted some of my electrolytic capacitor banks at full charge with a screw driver and they where completely undamaged. Their capacitance shifted by less than +/-0.1uf.(not sure about ESL or ESR though but probably not enough to care about.)
Having the projectile at rest also isn't really good either because it is probably going to partially weld it self on to the rails slowing it down. You really need some sort of injection either mechanical or pneumatic. Just don't pull a Sam Barros and let the injector do all the work. With the caps just vaporizing the projectile and making pretty sparks come out the muzzle but not actually contributing a whole lot to muzzle velocity.
dan, Thu Mar 30 2006, 01:07AM
Maybe I was wrong.. At the currents that are involved with a rail gun are so great that even the smallest stray inductance causes back-emf. Paralleling diodes wouldn't help that much since semies doesn’t really like to share the current evenly. Maybe you need to get yourself a hockey puck diode rated for 1000A continuous and several 10KA's peak to clamp that nasty back-emf. (not sure if this is over kill) I'm not sure if this clamping diode across the rails would help much since this stray inductance is literally everywhere in the circuit but the diode would be clamping the majority of it. Electrolytics are bad for rail guns since they are generally very slow and they don't like to be reversed charged. However they are fairly rugged and should be able to take this abuse. I have shorted some of my electrolytic capacitor banks at full charge with a screw driver and they where completely undamaged. Their capacitance shifted by less than +/-0.1uf.(not sure about ESL or ESR though but probably not enough to care about.)
Having the projectile at rest also isn't really good either because it is probably going to partially weld it self on to the rails slowing it down. You really need some sort of injection either mechanical or pneumatic. Just don't pull a Sam Barros and let the injector do all the work. With the caps just vaporizing the projectile and making pretty sparks come out the muzzle but not actually contributing a whole lot to muzzle velocity.
Re: Improving my railgun
pulslaser, Thu Mar 30 2006, 03:54PM
I think you shouldn't put to much work in injection, especially you should not use selfswitching. In this case you will get an arc in front of your projectil, where shurely should not be. In my last railgun I discharged 12 kJ through the projectil in rest and didn't got any arcing or welding but rather high speed (330 m/s). In my former experiments with injection and selfswitching there was always arcing and heavy erosion of the rails and low speed (< 100m/s).
pulslaser, Thu Mar 30 2006, 03:54PM
I think you shouldn't put to much work in injection, especially you should not use selfswitching. In this case you will get an arc in front of your projectil, where shurely should not be. In my last railgun I discharged 12 kJ through the projectil in rest and didn't got any arcing or welding but rather high speed (330 m/s). In my former experiments with injection and selfswitching there was always arcing and heavy erosion of the rails and low speed (< 100m/s).
Re: Improving my railgun
dan, Thu Mar 30 2006, 08:12PM
Wow this is very interesting most amateur rail guns that I have seen not using some sort of injection fail miserably (projectile welds itself to the rails) or don't perform well at all.
It was my understanding that in order to reduce the chance of welding the projectile it had to be injected fast enough. Also in order to reduce the chance of welding the rails and projectile should be perfectly machined to avoid 'high points' which is what causes the majority of the arcing. But that some arcing (and thus rail erosion) was inevitable.
I have noticed that there is very little amateur research with rail guns do to their complex design and precision machining involved so it is interesting to see one work at all. Pulslaser, What kind of switch were you using? At these energy levels Solid State would be very pricey so the only option would be a triggered spark gap or something.
Rail guns seem to be horribly inefficient. This is why there really isn’t any more serious reasearch being done on them anymore. Yes some do get muzzle velocities in the 10km/s range but this is firing a very small tungsten projectile(less than a gram) with several Mj of input energy. So it doesn't surprise me that you only get the projectile out of the muzzle with 1.2kj at only a few hundred volts. I would suggest rearranging your cap bank for more V since this would allow higher discharge currents. I would also get rid of anything solid state.
But the whole name of the game is exparimentation.. Try different things injection vs. stationary, different projectiles, etc. Maybe even using injection and then a few ms later when the projectile is in between the rails trigger the switching device to dump the capacitors charge into the rails.
dan, Thu Mar 30 2006, 08:12PM
Wow this is very interesting most amateur rail guns that I have seen not using some sort of injection fail miserably (projectile welds itself to the rails) or don't perform well at all.
It was my understanding that in order to reduce the chance of welding the projectile it had to be injected fast enough. Also in order to reduce the chance of welding the rails and projectile should be perfectly machined to avoid 'high points' which is what causes the majority of the arcing. But that some arcing (and thus rail erosion) was inevitable.
I have noticed that there is very little amateur research with rail guns do to their complex design and precision machining involved so it is interesting to see one work at all. Pulslaser, What kind of switch were you using? At these energy levels Solid State would be very pricey so the only option would be a triggered spark gap or something.
Rail guns seem to be horribly inefficient. This is why there really isn’t any more serious reasearch being done on them anymore. Yes some do get muzzle velocities in the 10km/s range but this is firing a very small tungsten projectile(less than a gram) with several Mj of input energy. So it doesn't surprise me that you only get the projectile out of the muzzle with 1.2kj at only a few hundred volts. I would suggest rearranging your cap bank for more V since this would allow higher discharge currents. I would also get rid of anything solid state.
But the whole name of the game is exparimentation.. Try different things injection vs. stationary, different projectiles, etc. Maybe even using injection and then a few ms later when the projectile is in between the rails trigger the switching device to dump the capacitors charge into the rails.
Re: Improving my railgun
pulslaser, Thu Mar 30 2006, 10:26PM
I got best results with isolating projectils loaded with copper brushes. The flexible brushes don't need excatly alligned rails with ultraflat surface and at least in my experiments they work without any arcing and even can be used for several shots if they are made from reinforced epoxid. Switching was done with a ignitron tube, for efficient spark gap switching te vltage was too low and I didn't had scr big enough. More images and pictures a found on my pages ( sorry in german)
pulslaser, Thu Mar 30 2006, 10:26PM
I got best results with isolating projectils loaded with copper brushes. The flexible brushes don't need excatly alligned rails with ultraflat surface and at least in my experiments they work without any arcing and even can be used for several shots if they are made from reinforced epoxid. Switching was done with a ignitron tube, for efficient spark gap switching te vltage was too low and I didn't had scr big enough. More images and pictures a found on my pages (
sorry in german)
Re: Improving my railgun
Quantum Singularity, Fri Mar 31 2006, 03:22AM
Ignitron tube... I may have to look into this because if I ever get back into my railgun project I will be using 12kJ cap too. Is an ignitron that can handle that kind of power rare and expensive? And what V levels do you consider a spark gap to be ok? My big 2 caps are 10kV along with a few smaller 10kV caps too. I figure spark gaps are probably fine at these levels?
Quantum Singularity, Fri Mar 31 2006, 03:22AM
Ignitron tube... I may have to look into this because if I ever get back into my railgun project I will be using 12kJ cap too. Is an ignitron that can handle that kind of power rare and expensive? And what V levels do you consider a spark gap to be ok? My big 2 caps are 10kV along with a few smaller 10kV caps too. I figure spark gaps are probably fine at these levels?
Re: Improving my railgun
Dr. Shark, Fri Mar 31 2006, 10:52AM
Ignitrons are very scarce, although you might have more luck on your side of the pond. At 10kV you will be fine with a sparkgap, but I've got the feeling that 12kJ 10kV is not really a good combination. You are probably better of with more energy or less voltage, as ultimately it is the charge transfered though the projectile that speeds it up.
On my railgun (which has been shelfed years ago, OK...) I am using both pneumatic injection and active switching. Common, it is really not so hard to pick up a few beefy SCRs on eBay, especially for a railgun powered off electrolytics.
Dr. Shark, Fri Mar 31 2006, 10:52AM
Ignitrons are very scarce, although you might have more luck on your side of the pond. At 10kV you will be fine with a sparkgap, but I've got the feeling that 12kJ 10kV is not really a good combination. You are probably better of with more energy or less voltage, as ultimately it is the charge transfered though the projectile that speeds it up.
On my railgun (which has been shelfed years ago, OK...) I am using both pneumatic injection and active switching. Common, it is really not so hard to pick up a few beefy SCRs on eBay, especially for a railgun powered off electrolytics.
Re: Improving my railgun
dan, Fri Mar 31 2006, 12:29PM
At 10KV there would need to be some sort of active switching or the rails would have to be far enough apart. The projectile can be injected and then the spark gap can fired just as the projectile is fully inside the rail gun. (Optically triggered) In theory the higher the voltage the better since it allows higher and faster discharge currents and thus a stronger magnetic field is generated. This is what moves the projectile after all. However if you do not have enough energy for a given voltage level the discharge will be over before the projectile moves a few inches down the rails. Or if you have too much energy and not enough voltage the projectile will leave the muzzle before the capacitors have been discharged.
I'm not sure the exact setup the 'pros' use but I would guess it would be similar to what I described above.(injection + active switching) I mean building a several Mega Joule capacitor bank out of low voltage capacitors would be impractical. Also to discharge them fast enough (several 10's of ns) they would really need HV pulse capacitors.
SCR's are slow and will only lengthen the discharge time and probably reducing efficiency. Yes the spark gap will lose a few joules but I'm betting that it will more than make up for that. The basic operation of a rail gun may seem simple but there are literally endless design parameters that have to be taken into account. Just naming a few, pulse length, rail length, capacitor energy storage, charging voltage, injection speed (if applicable), projectile size & type(solid, brushed, plasma), stray inductance, ….
As you may notice most of them are closely related to each other and the design of the rail gun must built around those factors. However all of this said the improvements all depend on your ability to obtain materials and your skill level to design and build it.
dan, Fri Mar 31 2006, 12:29PM
At 10KV there would need to be some sort of active switching or the rails would have to be far enough apart. The projectile can be injected and then the spark gap can fired just as the projectile is fully inside the rail gun. (Optically triggered) In theory the higher the voltage the better since it allows higher and faster discharge currents and thus a stronger magnetic field is generated. This is what moves the projectile after all. However if you do not have enough energy for a given voltage level the discharge will be over before the projectile moves a few inches down the rails. Or if you have too much energy and not enough voltage the projectile will leave the muzzle before the capacitors have been discharged.
I'm not sure the exact setup the 'pros' use but I would guess it would be similar to what I described above.(injection + active switching) I mean building a several Mega Joule capacitor bank out of low voltage capacitors would be impractical. Also to discharge them fast enough (several 10's of ns) they would really need HV pulse capacitors.
SCR's are slow and will only lengthen the discharge time and probably reducing efficiency. Yes the spark gap will lose a few joules but I'm betting that it will more than make up for that. The basic operation of a rail gun may seem simple but there are literally endless design parameters that have to be taken into account. Just naming a few, pulse length, rail length, capacitor energy storage, charging voltage, injection speed (if applicable), projectile size & type(solid, brushed, plasma), stray inductance, ….
As you may notice most of them are closely related to each other and the design of the rail gun must built around those factors. However all of this said the improvements all depend on your ability to obtain materials and your skill level to design and build it.
Re: Improving my railgun
pulslaser, Fri Mar 31 2006, 06:11PM
Hi Dan,
if You want to discharge in ten's of nanoseconds you will not need any rails which are longer than 1 cm. In ten's of nanoseconds, if you assume a relistic speed, I think world best is arround 6000m/s in air, your projektil will be accelerated for 0.3 milimeter. Of course you're right high voltage -> high current -> high force. But high speed is also reached with lower but longer pulse.
And lower currents are much easier to handle. Of course if you have to spend some megajoule with low voltage the capacity becomes very large and the rails have to be very long, but this isn't mostly the problem of amateur builder.
pulslaser, Fri Mar 31 2006, 06:11PM
Hi Dan,
if You want to discharge in ten's of nanoseconds you will not need any rails which are longer than 1 cm. In ten's of nanoseconds, if you assume a relistic speed, I think world best is arround 6000m/s in air, your projektil will be accelerated for 0.3 milimeter. Of course you're right high voltage -> high current -> high force. But high speed is also reached with lower but longer pulse.
And lower currents are much easier to handle. Of course if you have to spend some megajoule with low voltage the capacity becomes very large and the rails have to be very long, but this isn't mostly the problem of amateur builder.
Re: Improving my railgun
McFluffin, Fri Mar 31 2006, 07:22PM
I got a chance to put some images online. Here is the general setup of the power:
You'll notice some tape on a capacitor on the right...the screw mount on it broke. Thats the voltage drouble and I figure as long as it still works, it doesn't really need to be on that good. The blue capacitors are the 350V ones and you can see part of the larger bank to the left. Its connected by two of the orange wires as are most things. The black and red probes go to my DIMM to measure voltage. Finally, the black and red wires coming in is from the power supply to trigger the SCR. The resistor network is in that bit of blue.
This is the last projectile that I used, which worked pretty well:
You can see that it got damaged pretty badly, but the damage doesn't go to deep. I'd like to try to make a brushed projectile to replace it.
Front view of railgun:
Top view after the last shot:
I also had a general question about osciloscope use. I have seen people trace out the voltage versus time on people's scopes for their capacitor discharge. How is this done? Do you need a digital scope to do that? I was thinking it might have something to do with external trigger on it, but don't really know. I have a Tektronix 2213 if that helps anyone(
As far as the triggering issue, I was under the impression that my SCRs were working pretty well. I wouldn't imagine that it would be worth it to try to construct a spark gap design using only 350V or so. In any case, this isn't a mega-joule design, so I'm not going to worry about some of the larger power design issues. I also don't have any (large) 10kV capacitors, so thats not really going to be an issue either.
As you'll see from the pictures, I'm on a steep learning curve for learning how to machine things. I am getting better very quickly, but things aren't as nice as I'd like them to be. I can get materials fairly easily. There is a scap yard near my house where I can get copper for around $4 a pound as well as polycarbonate(not too expensive I've been told, but I've never gotten any there). The only problem is that they close at 4:30 and I don't drive and get out of school at 3:15. So, the only way I can get there is to bug someone for a ride and try to get there quick.
Update:
Here is a picture of it firing!
McFluffin, Fri Mar 31 2006, 07:22PM
I got a chance to put some images online. Here is the general setup of the power:
You'll notice some tape on a capacitor on the right...the screw mount on it broke. Thats the voltage drouble and I figure as long as it still works, it doesn't really need to be on that good. The blue capacitors are the 350V ones and you can see part of the larger bank to the left. Its connected by two of the orange wires as are most things. The black and red probes go to my DIMM to measure voltage. Finally, the black and red wires coming in is from the power supply to trigger the SCR. The resistor network is in that bit of blue.
This is the last projectile that I used, which worked pretty well:
You can see that it got damaged pretty badly, but the damage doesn't go to deep. I'd like to try to make a brushed projectile to replace it.
Front view of railgun:
Top view after the last shot:
I also had a general question about osciloscope use. I have seen people trace out the voltage versus time on people's scopes for their capacitor discharge. How is this done? Do you need a digital scope to do that? I was thinking it might have something to do with external trigger on it, but don't really know. I have a Tektronix 2213 if that helps anyone(
. "Link2")
As far as the triggering issue, I was under the impression that my SCRs were working pretty well. I wouldn't imagine that it would be worth it to try to construct a spark gap design using only 350V or so. In any case, this isn't a mega-joule design, so I'm not going to worry about some of the larger power design issues. I also don't have any (large) 10kV capacitors, so thats not really going to be an issue either.
As you'll see from the pictures, I'm on a steep learning curve for learning how to machine things. I am getting better very quickly, but things aren't as nice as I'd like them to be. I can get materials fairly easily. There is a scap yard near my house where I can get copper for around $4 a pound as well as polycarbonate(not too expensive I've been told, but I've never gotten any there). The only problem is that they close at 4:30 and I don't drive and get out of school at 3:15. So, the only way I can get there is to bug someone for a ride and try to get there quick.
Update:
Here is a picture of it firing!
Print this page