The astute observer of Friday's post will have noticed that while the magnetic forces in the loops are nicely contained (the hoop stress on the tubing walls is relatively minor) the forces on the collector plates are enormous and no features are depicted which control or contain those forces.
So yes: in real life, some big clamps of some sort will be required to keep the collector plates from flying apart on the first shot, turning our pretty transformer into something more closely resembling The Flying Spaghetti Monster.
I can think of at least two ways to accomplish this: C-shaped clamps disposed around the perimeter of the collector plates, located between tube insertions; and also, insulated bolts passed through holes in roughly the same location. Given that the output voltage will rise sharply (to a value dependent on the charge remaining in the capacitors and the energy still stored in the pulse transformer) when the armature leaves the rails, it would be prudent to insulate the bolts and plates to the charge voltage of the cap bank despite that the output side should never see more than 1/7 of the charge voltage, not considering ringing voltage reversal.
Free wheeling diodes capable of absorbing the high currents of voltage reversal with fast recovery times are available in industrial "hockey puck" packages, but their cost is high for an underfunded independent lab. I would not consider building a transformer like this unless I had some confidence of obtaining same first or soon after. One thing seems certain: we won't be purchasing them new.
~~~~~~~~
PS: pictures accompanying my posts keep disappearing from older posts (despite that Google + Blogger claim there is no retention limit). I can't find some of the original images on my local computers now. Many of the images I uploaded to accompany those posts were uploaded away from home, and weren't saved on the phone, camera, or computer they were made with. So the older posts which discuss things like the fast micro-Marx generator probably aren't going to get their pictures restored. I mention this since I'm about to post about progress I've made this week on same, and I'd like to refer to those old posts with links, but thousands of words will have to suffice in place of illustrative images.
Showing posts with label railguns. Show all posts
Showing posts with label railguns. Show all posts
Monday, June 11, 2012
Friday, June 8, 2012
a new coaxial high current pulse transformer for pulsed power
(I say "new" in that I have yet to find anything in the scientific literature describing this exact geometry. I recognize someone may have done it and I just haven't seen the evidence / paper / photograph yet.)
This is a (rather poor, hastily made) 3D model of a high current, coaxial pulse transformer design I am fiddling with. Its purpose is to match the relatively high source impedance of a high voltage pulse capacitor bank to the relatively low load impedance of an electromagnetic launcher - AKA railgun. Coaxial geometries -- which is to say, with the current path of the one winding located inside the current path of the other winding -- can achieve coupling efficiencies over 90%.
This device is loosely based on a design by Pappas, et. al.1 but has been reconfigured from a solenoidal coil to a toroidal coil so as to contain the magnetic field within the device.
If I limited myself to using materials I already have on hand (so as to reduce costs) as a starting point, I derive maximum current ratings of about 65,000 amps on the input side and about 250,000 amps on the output side, for pulses of 4mS or shorter (Onderdonk). I am still working on the mutual inductances and what-not, but I seriously doubt I will be able to realize currents that high from my complete system. When I get done slogging through the math, or at least trying to understand the math since I am still a relative math cripple, it may prove impossible to have a transformer with sufficient current loop area to retain the magnetic field adequately and the correct transformation ratio, in which case I will probably scrap the idea of using a transformer entirely. A solenoidal transformer with fewer loops will create too much EMP. That doesn't negate the value of this idea for others of course.
Some leakage is inevitable, especially given the asymmetry necessary to make this design work and the small number of current loops I can manage given the amount of cable I have, but a toroidal configuration will nevertheless contain a large percentage of the generated field whereas a solenoidal design has considerable external field effects, which can be problematic with instrumentation, as noted by Beach2.
The secondary consists of a single electrical turn, divided into seven loops disposed radially around the device's axis of revolution. The seven loops - shown as silver in the model - are fabricated from metal tubing, each end of which is inserted into one of the two circular current collector plates. One plate is connected to the center conductor of the coaxial output and the other plate is connected to the shield of the coaxial output. The two plates and the coaxial outputs are separated by plastic insulation. The collector plate + insulator stack is provided with eight holes and 16 connectors to fasten the tubing to the plates.
The primary consists of a single piece of 15kV 2AWG "jumper" cable, pulled through the loops of the secondary and connected at to the shield output collector plate at one end. The other end is provided to the driving pulser through a coaxial shield connected to the inner conductor output plate. Thus, the secondary and primary form an auto-transformer electrically.
An additional annular brace may be added to the equator of the loop array. This provides additional mechanical bracing to prevent discourage physical stretching of the loops. Note that the brace may be made of metal welded to the loops at the same point on each, since all loops are shorted together. this is probably stronger and lighter -- and certainly cheaper and easier to implement - than any equivalent arrangement of insulating materials.
All conducting paths have been sized with sufficient cross-sectional area to remain far below (50%) of the fusing current (Onderdonk Fusing Current formula) for copper. This will result in significant heating of the device. Increasing material mass would be impractical for the given project because large portions of the material are already on hand, which define many design constraints. I currently have half copper parts for the output current collector, and I have the 27 feet of #2 HV cable required.
Assembly of most of the joints is non-trivial. If copper is used, most of the joints will have to be heat-shrink permanent connections.
The heat of silver brazing would be detrimental to the conductivity of the copper. Alternatively, the same machine could be built using machined and welded aluminum parts. This would be cheaper, however all of the dimensions would have to be increased. Nevertheless, a unit made from aluminum would weigh (and cost) much less than the equivalent ampacity and fusing-current-limit in copper.
For a high inductance transformer such as this to be used between a railgun and a capacitor-discharge current source, large "free-wheeling" diodes would need to be placed across each capacitor, or the capacitor bank, to absorb the residual back EMF from the transformer. Depending on where during the discharge pulse the armature departs the rails, opening the secondary circuit, the back-EMF from the primary could be quite large. Pulse caps do not like voltage reversal. These diodes would add significantly to the cost of using such a pulse transformer.
This work was supported by a grant from The Joss Research Institute, Laurel MD.
1."High Current Coaxial Pulse Transformer for Railgun Applications", J.A. Pappas, M. D. Driga, W. F. Weldon, Proceedings of the Fifth IEEE Pulsed Power Conference, 1985 [link]
2. "Design and Construction of a One Meter Electromagnetic Railgun", F.C. Beach, Naval Postgraduate School Monterey CA, 1996
This is a (rather poor, hastily made) 3D model of a high current, coaxial pulse transformer design I am fiddling with. Its purpose is to match the relatively high source impedance of a high voltage pulse capacitor bank to the relatively low load impedance of an electromagnetic launcher - AKA railgun. Coaxial geometries -- which is to say, with the current path of the one winding located inside the current path of the other winding -- can achieve coupling efficiencies over 90%.
This device is loosely based on a design by Pappas, et. al.1 but has been reconfigured from a solenoidal coil to a toroidal coil so as to contain the magnetic field within the device.
If I limited myself to using materials I already have on hand (so as to reduce costs) as a starting point, I derive maximum current ratings of about 65,000 amps on the input side and about 250,000 amps on the output side, for pulses of 4mS or shorter (Onderdonk). I am still working on the mutual inductances and what-not, but I seriously doubt I will be able to realize currents that high from my complete system. When I get done slogging through the math, or at least trying to understand the math since I am still a relative math cripple, it may prove impossible to have a transformer with sufficient current loop area to retain the magnetic field adequately and the correct transformation ratio, in which case I will probably scrap the idea of using a transformer entirely. A solenoidal transformer with fewer loops will create too much EMP. That doesn't negate the value of this idea for others of course.
Some leakage is inevitable, especially given the asymmetry necessary to make this design work and the small number of current loops I can manage given the amount of cable I have, but a toroidal configuration will nevertheless contain a large percentage of the generated field whereas a solenoidal design has considerable external field effects, which can be problematic with instrumentation, as noted by Beach2.
The secondary consists of a single electrical turn, divided into seven loops disposed radially around the device's axis of revolution. The seven loops - shown as silver in the model - are fabricated from metal tubing, each end of which is inserted into one of the two circular current collector plates. One plate is connected to the center conductor of the coaxial output and the other plate is connected to the shield of the coaxial output. The two plates and the coaxial outputs are separated by plastic insulation. The collector plate + insulator stack is provided with eight holes and 16 connectors to fasten the tubing to the plates.
The primary consists of a single piece of 15kV 2AWG "jumper" cable, pulled through the loops of the secondary and connected at to the shield output collector plate at one end. The other end is provided to the driving pulser through a coaxial shield connected to the inner conductor output plate. Thus, the secondary and primary form an auto-transformer electrically.
An additional annular brace may be added to the equator of the loop array. This provides additional mechanical bracing to prevent discourage physical stretching of the loops. Note that the brace may be made of metal welded to the loops at the same point on each, since all loops are shorted together. this is probably stronger and lighter -- and certainly cheaper and easier to implement - than any equivalent arrangement of insulating materials.
All conducting paths have been sized with sufficient cross-sectional area to remain far below (50%) of the fusing current (Onderdonk Fusing Current formula) for copper. This will result in significant heating of the device. Increasing material mass would be impractical for the given project because large portions of the material are already on hand, which define many design constraints. I currently have half copper parts for the output current collector, and I have the 27 feet of #2 HV cable required.
Assembly of most of the joints is non-trivial. If copper is used, most of the joints will have to be heat-shrink permanent connections.
The heat of silver brazing would be detrimental to the conductivity of the copper. Alternatively, the same machine could be built using machined and welded aluminum parts. This would be cheaper, however all of the dimensions would have to be increased. Nevertheless, a unit made from aluminum would weigh (and cost) much less than the equivalent ampacity and fusing-current-limit in copper.
For a high inductance transformer such as this to be used between a railgun and a capacitor-discharge current source, large "free-wheeling" diodes would need to be placed across each capacitor, or the capacitor bank, to absorb the residual back EMF from the transformer. Depending on where during the discharge pulse the armature departs the rails, opening the secondary circuit, the back-EMF from the primary could be quite large. Pulse caps do not like voltage reversal. These diodes would add significantly to the cost of using such a pulse transformer.
This work was supported by a grant from The Joss Research Institute, Laurel MD.
1."High Current Coaxial Pulse Transformer for Railgun Applications", J.A. Pappas, M. D. Driga, W. F. Weldon, Proceedings of the Fifth IEEE Pulsed Power Conference, 1985 [link]
2. "Design and Construction of a One Meter Electromagnetic Railgun", F.C. Beach, Naval Postgraduate School Monterey CA, 1996
Monday, March 26, 2012
tooling progress (mill)
A great many projects are waiting for the mill to return to service. I have news about that.
The new phase converter arrived a while back. I've had it mostly-wired up for a week. I've been
er, not well, and also busy as f__k, and so I didn't really think my purchases through. So I still
don't have every thing I need to make it all go. I do have all but one thing, however, and it will
arrive tomorrow afternoon. That one thing is a 3-phase, 4-pole twist-lock connector that I
didin't happen to have on hand. Everything else is in place. When it arrives it will be a matter
of 20 minutes to be online.
Herewith an aside on the futility of saving good quality useful parts for a rainy day:
I have a boat-load of twist-lock connectors of all sorts - recessed inlets and panel mount outlets,
cord connectors, conventional outlets, and more, all for various voltages, currents, phases, et-
bloody-ceteras. And every time I have need such a thing in the past ten years, I have gone through
that collection, and literally nine times out of ten (probably more like 99 in a 100) I have come up
empty handed. The percentages do not make the space taken up (not to mention the capital
value) of them just sitting around here. So I am going to sell every twist-lock and similar power
connector I have (which is a lot, I assure you) on eBay and make a whole bunch of money to re-pay
my recently-raped hobby fund a little, even if I blow them out the door at bargain basement prices
as I intend to do.
I also ran out of money, through some serious miscommunication and well, never mind that.
That's being corrected.
So, by the next time I can find or make some free time in between self-schooling and work, I will
be able to make some parts for the Mad Scientists Light Switch, the triggered spark gap switch,
and so forth and so on.
The new phase converter arrived a while back. I've had it mostly-wired up for a week. I've been
er, not well, and also busy as f__k, and so I didn't really think my purchases through. So I still
don't have every thing I need to make it all go. I do have all but one thing, however, and it will
arrive tomorrow afternoon. That one thing is a 3-phase, 4-pole twist-lock connector that I
didin't happen to have on hand. Everything else is in place. When it arrives it will be a matter
of 20 minutes to be online.
Herewith an aside on the futility of saving good quality useful parts for a rainy day:
I have a boat-load of twist-lock connectors of all sorts - recessed inlets and panel mount outlets,
cord connectors, conventional outlets, and more, all for various voltages, currents, phases, et-
bloody-ceteras. And every time I have need such a thing in the past ten years, I have gone through
that collection, and literally nine times out of ten (probably more like 99 in a 100) I have come up
empty handed. The percentages do not make the space taken up (not to mention the capital
value) of them just sitting around here. So I am going to sell every twist-lock and similar power
connector I have (which is a lot, I assure you) on eBay and make a whole bunch of money to re-pay
my recently-raped hobby fund a little, even if I blow them out the door at bargain basement prices
as I intend to do.
I also ran out of money, through some serious miscommunication and well, never mind that.
That's being corrected.
So, by the next time I can find or make some free time in between self-schooling and work, I will
be able to make some parts for the Mad Scientists Light Switch, the triggered spark gap switch,
and so forth and so on.
Monday, February 21, 2011
playing with arc-flash for fun and profit
I worked on the big pulser (for the railgun) over the weekend.
Lately, job #1 has been to figure out a way to connect the capacitors to the "hot" collector plate. The means had to be inexpensive, reasonably low effort, and capable of handling the full 60,000 amps from each capacitor.
The arrangement I am trying first is to clamp four soft copper straps to the capacitor's bolt terminal with a nut, and clamp the opposite ends under the bolt rings of the old ignitron housings. The rest of the housing won't carry current. Some nice low-rise clamping rings would be better, but I don't feel a pressing need to make six of them (with eight holes each, ugh) right this minute.
I made the straps and installed them yesterday. This involved cutting out forty-eight 1" x 4" x .030" straps from copper sheet (with sheet metal sheers), removing all the corners and sharp edges on the belt sander, and punching forty-eight half-inch holes near one end of each strap.
After that, I felt an urge to know the leakage rate of the capacitors. I decided to perform a "megger" (a high voltage insulation tester) test on all six caps. Now meggers, by their nature, typically put a fair mount of voltage across the unknown. My instrument, an old Genrad unit, puts out anywhere from 100V to 500V DC.
Then, before I could start with the measurements, I had to figure out how I would safely discharge the cap bank after it had been charged by the megger.
Step the first was to wind half a dozen turns in my test leads onto some big ferrites. That should, in theory, keep the hash from the arc out of the detector circuitry of the megger. I would disconnect it by hand before shorting the bank if I trusted my gloves, but I don't. Anybody out there have a set of lineman's (Class 2 or 3) gloves in test-passing condition that they don't want?
Step two was to don rubber gloves, leather gloves, face shield, and ear muffs.
I got my measurement on the low range (100 V) and decided to take measurements at all the other ranges too. I discharged the caps after each measurement. I used a "chicken stick" (insulating shorting stick with copper bar at one end) and an extra little bit of brass lying on the top of the collector plate to strike the arcs to, so the collector plate wouldn't get too badly torn up.
At 100 volts, the 'pop' was impressive, but one does not need hearing protection. A modern firecracker is louder. At 200 volts, I decided the hearing protection was a good idea after all. At 400 volts, I worried what the neighbors might be thinking.
Note that these are 10,000 volt caps. So I was playing with 4% of the total energy this cap bank can store. I won't lie: when this machine lets go with a full charge, I don't want to be in the same room with it. Fortunately I won't have to. I have a nice concrete block wall separating my workshop from the rest of the garage. With that and the remote control panel I'm building, we ought to be golden.
In reality, we don't want this (a short circuit discharge) to happen at any voltage. Without any significant inductance or resistance for a load, the very high currents and high voltage reversal caused by high frequency ringing (since the "load" inductance is so small) stress the dielectric in the caps rather badly. It is to be avoided. These caps don't grow on trees. Ordinarily, when the caps need to be discharged (either to remove residual charge at the end of a shot, or due to an aborted shot) the caps are drained more slowly (and safely) by a large bank of power resistors connected to the cap bank through a pair of high voltage relays.
This is also why I'm testing insulation and clearances to the cabinet and the like. I do not want an uncontrolled arc happening out in the open. Aside from the obvious undesirability and damage, it will also be EXTREMELY LOUD. We're talking broken-windows-loud. Under normal operating conditions, I expect most of the energy to be absorbed or muffled in various ways. In fact, I am going to rather a lot of effort to ensure that happens.
Figuratively speaking, I have in the past had the local villagers light torches, take up pitch-forks, and storm my castle because I frightened them. News media, emergency services, and attorneys were involved. So, let's just say I am not comfortable allowing extremely loud noises to escape from my property these days.
Oh, and I hope to have the shop's old rolling door finally ripped out and replaced with a wall before the first gun firings take place. That should cut down on the blast noise a LOT.
After doing the above, I decided I really need to do a proof test on each individual capacitor, and that means disassembling everything I assembled over the weekend. Well, to be honest, I had other reasons for doing that too. I need to do a proof test on the collector stack, and THAT has to be done with the capacitors disconnected (but with the stack still mounted on the caps) for what I hope is an obvious reason.
Photos to come later.
PS: I often forget what I've described and what I have not. It occurs to me that I have not described the capacitor bank high current connections, which I've been referring to above as "the collector stack" so I'll do that now. The capacitors I have are very early pulse caps using 1960s technology. They are set up for relatively low inductance connections, although improvements have been made in pulse cap design since these were made. The capacitor connections are made between the case and a single 1/2-13 brass bolt located in the center of a round, convoluted, hard rubber insulator. The return connections to the case are made to four brass blocks soldered to the corners of the case. Threaded holes are provided in said blocks to accept 3/8 brass studs.
To minimize stray inductance, the six capacitors are bussed together with aluminum plates separated by a thin layer of strong insulating material. The ground/return plate sits directly on the capacitors' ground return blocks. It has six holes about 4" across to provide clearance for the high voltage connections. A 1/2" thick plate (could be different material, and thinner) of phenolic-linen laminate goes on top of that. It also has big holes to clear the high voltage connections. The "hot" or output plate has big holes too, but they are surrounded by rings of eight 1/4-20 threaded holes so that "something" can be connected there. Originally that "something" was an ignitron on top of each capacitor, which sat inside of a coaxial housing which connected to those rings of holes.
I am still using those housings and the original connections for my new connections, only because they are handy and they eliminate - for now - the need to make a whole bunch of new parts.
Lately, job #1 has been to figure out a way to connect the capacitors to the "hot" collector plate. The means had to be inexpensive, reasonably low effort, and capable of handling the full 60,000 amps from each capacitor.
The arrangement I am trying first is to clamp four soft copper straps to the capacitor's bolt terminal with a nut, and clamp the opposite ends under the bolt rings of the old ignitron housings. The rest of the housing won't carry current. Some nice low-rise clamping rings would be better, but I don't feel a pressing need to make six of them (with eight holes each, ugh) right this minute.
I made the straps and installed them yesterday. This involved cutting out forty-eight 1" x 4" x .030" straps from copper sheet (with sheet metal sheers), removing all the corners and sharp edges on the belt sander, and punching forty-eight half-inch holes near one end of each strap.
After that, I felt an urge to know the leakage rate of the capacitors. I decided to perform a "megger" (a high voltage insulation tester) test on all six caps. Now meggers, by their nature, typically put a fair mount of voltage across the unknown. My instrument, an old Genrad unit, puts out anywhere from 100V to 500V DC.
Then, before I could start with the measurements, I had to figure out how I would safely discharge the cap bank after it had been charged by the megger.
Step the first was to wind half a dozen turns in my test leads onto some big ferrites. That should, in theory, keep the hash from the arc out of the detector circuitry of the megger. I would disconnect it by hand before shorting the bank if I trusted my gloves, but I don't. Anybody out there have a set of lineman's (Class 2 or 3) gloves in test-passing condition that they don't want?
Step two was to don rubber gloves, leather gloves, face shield, and ear muffs.
I got my measurement on the low range (100 V) and decided to take measurements at all the other ranges too. I discharged the caps after each measurement. I used a "chicken stick" (insulating shorting stick with copper bar at one end) and an extra little bit of brass lying on the top of the collector plate to strike the arcs to, so the collector plate wouldn't get too badly torn up.
At 100 volts, the 'pop' was impressive, but one does not need hearing protection. A modern firecracker is louder. At 200 volts, I decided the hearing protection was a good idea after all. At 400 volts, I worried what the neighbors might be thinking.
Note that these are 10,000 volt caps. So I was playing with 4% of the total energy this cap bank can store. I won't lie: when this machine lets go with a full charge, I don't want to be in the same room with it. Fortunately I won't have to. I have a nice concrete block wall separating my workshop from the rest of the garage. With that and the remote control panel I'm building, we ought to be golden.
In reality, we don't want this (a short circuit discharge) to happen at any voltage. Without any significant inductance or resistance for a load, the very high currents and high voltage reversal caused by high frequency ringing (since the "load" inductance is so small) stress the dielectric in the caps rather badly. It is to be avoided. These caps don't grow on trees. Ordinarily, when the caps need to be discharged (either to remove residual charge at the end of a shot, or due to an aborted shot) the caps are drained more slowly (and safely) by a large bank of power resistors connected to the cap bank through a pair of high voltage relays.
This is also why I'm testing insulation and clearances to the cabinet and the like. I do not want an uncontrolled arc happening out in the open. Aside from the obvious undesirability and damage, it will also be EXTREMELY LOUD. We're talking broken-windows-loud. Under normal operating conditions, I expect most of the energy to be absorbed or muffled in various ways. In fact, I am going to rather a lot of effort to ensure that happens.
Figuratively speaking, I have in the past had the local villagers light torches, take up pitch-forks, and storm my castle because I frightened them. News media, emergency services, and attorneys were involved. So, let's just say I am not comfortable allowing extremely loud noises to escape from my property these days.
Oh, and I hope to have the shop's old rolling door finally ripped out and replaced with a wall before the first gun firings take place. That should cut down on the blast noise a LOT.
After doing the above, I decided I really need to do a proof test on each individual capacitor, and that means disassembling everything I assembled over the weekend. Well, to be honest, I had other reasons for doing that too. I need to do a proof test on the collector stack, and THAT has to be done with the capacitors disconnected (but with the stack still mounted on the caps) for what I hope is an obvious reason.
Photos to come later.
PS: I often forget what I've described and what I have not. It occurs to me that I have not described the capacitor bank high current connections, which I've been referring to above as "the collector stack" so I'll do that now. The capacitors I have are very early pulse caps using 1960s technology. They are set up for relatively low inductance connections, although improvements have been made in pulse cap design since these were made. The capacitor connections are made between the case and a single 1/2-13 brass bolt located in the center of a round, convoluted, hard rubber insulator. The return connections to the case are made to four brass blocks soldered to the corners of the case. Threaded holes are provided in said blocks to accept 3/8 brass studs.
To minimize stray inductance, the six capacitors are bussed together with aluminum plates separated by a thin layer of strong insulating material. The ground/return plate sits directly on the capacitors' ground return blocks. It has six holes about 4" across to provide clearance for the high voltage connections. A 1/2" thick plate (could be different material, and thinner) of phenolic-linen laminate goes on top of that. It also has big holes to clear the high voltage connections. The "hot" or output plate has big holes too, but they are surrounded by rings of eight 1/4-20 threaded holes so that "something" can be connected there. Originally that "something" was an ignitron on top of each capacitor, which sat inside of a coaxial housing which connected to those rings of holes.
I am still using those housings and the original connections for my new connections, only because they are handy and they eliminate - for now - the need to make a whole bunch of new parts.
Friday, February 18, 2011
Don't Put Your Tongue On That Capacitor, You Don't Know Where It's Been!
Lately, because the lack of a mill has back-burnered the final bits and pieces for my Mad Scientist Light Switch, I've been working on the railgun project instead. From the very beginning, one of my philosophies for this project was that I was going to everything right. Because time after time, I had seen other amateur railguns which were almost right in most respects, but wherein the builder got one or two crucial details wrong, and it hurt them. The details really do matter, especially when you're trying to take something which works better at large scales and scale it down.
I've been thinking a lot about safety. It's one of those details that a lot of a amateur mad scientists don't think about much. Honestly, it astonishes me that only a small handful of amateurs have killed themselves working with Tesla coils or big pulse caps. And I think I've had just about all the second chances with high voltage and lasers and explosives that the fates are likely to grant me. I'm going to try to avoid unplanned excitement for a while.
Government labs are different. They care about safety, and they spend a lot of money on it. PhDs don't grow on trees. But sometimes even smart people miss a possibility and something bad happens. I shall describe one such incident in hopes that we'll all learn from it.
This is entirely from memory, because I can't find the paper in which it is described. I do have a dead-trees copy somewhere in a box in the basement. Therefore, if I find that or (an online) copy, I'll correct any errors I make and point to a copy you can read.
Back in the 1950s, the biggest homopolar generator in history (so far) had recently been completed at Australia National University. And it wasn't long before this 500 MJ monster was connected to a new railgun. Now railguns want a lot of current, and they have a fair amount of voltage drop across the muzzle- several kilovolts in the plasma armature devices that were in vogue back then. That's a problem if you're using an HPG for your power supply, since they are great at putting out a lot of current into a dead short, but they aren't good at developing much voltage. So, back then, the standard method was to do pulse compression, much as we do today for high powered pulsed-power projects. They would discharge the HPG into an inductive transmission line which had the railgun connected to the other end. Then they'd use a series of short circuiting or opening switches to compress the magnetic field of the line, causing the voltage to soar during the pulse.
The devices used had to be very fast, and had to handle millions of amperes. They included special fuses, exotic circuit breakers, and mechanical switches driven by high explosives.
During preparations for one shot, a heavy equipment cart with metal wheels was rolled over a hydraulic hose which provided high pressure oil to the bearings of the HPG. No apparent damage was caused, and nobody thought anything of it until later. That was because there was no pressure on the hose. But the hose HAD been damaged, and a tiny leak had been created.
All was made ready in the run room, personnel left, and the heavy steel door between the gun room and the control room was closed and locked.
Various power supplies were charged, trigger generators armed, and then the HPG was spun up to speed, which included pressurizing the bearings. The high pressure oil leaked out of the supply hose in a very fine mist. Unknown to the operators, and not visible on the remote cameras, oil vapor was now filling the gun room.
When the shot was fired, the various plasma clouds and sparks promptly ignited the vapor in the room, causing a significant explosion which blew the heavy steel blast door from its hinges, injuring the technician seated nearest it.
The point being: ask yourself a LOT of questions that begin, "what would happen if..." before you ever apply power to anything.
Now I've just completed a 1,000 PSI gas injector system which will pre-accelerate the armature before it reaches the rails. This simple "system" consists of:
• a storage plenum (2" Sch.80 steel pipe + fittings)
• an electrically operated valve with high CV*, or flow capability
• a gauge and utility valves for filling and emptying the plenum without opening the main valve
• coupling plumbing and hardware to fit railgun breach-block
Here's a pic:
Later, after commissioning tests, it will be desirable to place a DeLaval nozzle between main valve and gun breach, to increase gas speed within the gun.
One of the "gotchas" I discovered recently was in the breachblock assembly, which gives me a way of connecting things to the back end of the gun, such as a high pressure injector system. The breach closure must be designed so it can be easily removed for cleaning, inspection, disassembly, and re-loading.
The breachblock assembly must contain 1,000 PSI of gas pressure. Further, the plug which closes it is 2" in diameter, so now we're seeing 3,140 pounds of force on the breach-plug. Don't worry, I designed it to take that and then some. It's massive. But that was only the forces within the two-part system of breach-plate and breach plug-plate.
Then I looked at the interface -- and more significantly, the gas seal -- between the breach plate and the rest of the gun. What if my original seal design -- with two seals, one being a "backup" -- would fail at the inner seal? The additional exposed area inside the outer seal raises the force on the breach plate to about 20,000 pounds-force. I'm not sure I want to load the bolts that much. So I eliminated the outer seal! Now if the single remaining seal fails, all that happens is that gas at design pressure leaks out undramatically. I don't expect that inner seal to fail, but no one ever expects the Spanish Inquisition!
The big pulser-without-a-name had been designed with interlocks originally, but they were all defeated, broken, or missing by the time it came to me. I will of course be repairing / replacing them. I need to sit down at some point and work through the entire sequence / time-line of a shot preparation, firing, and safing. Eventually, I'll probably even have a check list and some rotating beacons, because those things not only improve safety, they're just good fun for any red-blooded geek.
"Arming test lights on, one through four?"
"Arming test lights on, one through four!"
Ya know, all this work would be a lot easier if I had a team and a budget. Sure wish I'd gone to school.
_________________________________________
* (CV = valve coefficient, which equates to flow restriction through the valve. In COTS valves, it is usually driven by the valve's smallest opening, typically the valve seat)
I've been thinking a lot about safety. It's one of those details that a lot of a amateur mad scientists don't think about much. Honestly, it astonishes me that only a small handful of amateurs have killed themselves working with Tesla coils or big pulse caps. And I think I've had just about all the second chances with high voltage and lasers and explosives that the fates are likely to grant me. I'm going to try to avoid unplanned excitement for a while.
Government labs are different. They care about safety, and they spend a lot of money on it. PhDs don't grow on trees. But sometimes even smart people miss a possibility and something bad happens. I shall describe one such incident in hopes that we'll all learn from it.
This is entirely from memory, because I can't find the paper in which it is described. I do have a dead-trees copy somewhere in a box in the basement. Therefore, if I find that or (an online) copy, I'll correct any errors I make and point to a copy you can read.
Back in the 1950s, the biggest homopolar generator in history (so far) had recently been completed at Australia National University. And it wasn't long before this 500 MJ monster was connected to a new railgun. Now railguns want a lot of current, and they have a fair amount of voltage drop across the muzzle- several kilovolts in the plasma armature devices that were in vogue back then. That's a problem if you're using an HPG for your power supply, since they are great at putting out a lot of current into a dead short, but they aren't good at developing much voltage. So, back then, the standard method was to do pulse compression, much as we do today for high powered pulsed-power projects. They would discharge the HPG into an inductive transmission line which had the railgun connected to the other end. Then they'd use a series of short circuiting or opening switches to compress the magnetic field of the line, causing the voltage to soar during the pulse.
The devices used had to be very fast, and had to handle millions of amperes. They included special fuses, exotic circuit breakers, and mechanical switches driven by high explosives.
During preparations for one shot, a heavy equipment cart with metal wheels was rolled over a hydraulic hose which provided high pressure oil to the bearings of the HPG. No apparent damage was caused, and nobody thought anything of it until later. That was because there was no pressure on the hose. But the hose HAD been damaged, and a tiny leak had been created.
All was made ready in the run room, personnel left, and the heavy steel door between the gun room and the control room was closed and locked.
Various power supplies were charged, trigger generators armed, and then the HPG was spun up to speed, which included pressurizing the bearings. The high pressure oil leaked out of the supply hose in a very fine mist. Unknown to the operators, and not visible on the remote cameras, oil vapor was now filling the gun room.
When the shot was fired, the various plasma clouds and sparks promptly ignited the vapor in the room, causing a significant explosion which blew the heavy steel blast door from its hinges, injuring the technician seated nearest it.
The point being: ask yourself a LOT of questions that begin, "what would happen if..." before you ever apply power to anything.
Now I've just completed a 1,000 PSI gas injector system which will pre-accelerate the armature before it reaches the rails. This simple "system" consists of:
• a storage plenum (2" Sch.80 steel pipe + fittings)
• an electrically operated valve with high CV*, or flow capability
• a gauge and utility valves for filling and emptying the plenum without opening the main valve
• coupling plumbing and hardware to fit railgun breach-block
Here's a pic:
Later, after commissioning tests, it will be desirable to place a DeLaval nozzle between main valve and gun breach, to increase gas speed within the gun.
One of the "gotchas" I discovered recently was in the breachblock assembly, which gives me a way of connecting things to the back end of the gun, such as a high pressure injector system. The breach closure must be designed so it can be easily removed for cleaning, inspection, disassembly, and re-loading.
The breachblock assembly must contain 1,000 PSI of gas pressure. Further, the plug which closes it is 2" in diameter, so now we're seeing 3,140 pounds of force on the breach-plug. Don't worry, I designed it to take that and then some. It's massive. But that was only the forces within the two-part system of breach-plate and breach plug-plate.
Then I looked at the interface -- and more significantly, the gas seal -- between the breach plate and the rest of the gun. What if my original seal design -- with two seals, one being a "backup" -- would fail at the inner seal? The additional exposed area inside the outer seal raises the force on the breach plate to about 20,000 pounds-force. I'm not sure I want to load the bolts that much. So I eliminated the outer seal! Now if the single remaining seal fails, all that happens is that gas at design pressure leaks out undramatically. I don't expect that inner seal to fail, but no one ever expects the Spanish Inquisition!
The big pulser-without-a-name had been designed with interlocks originally, but they were all defeated, broken, or missing by the time it came to me. I will of course be repairing / replacing them. I need to sit down at some point and work through the entire sequence / time-line of a shot preparation, firing, and safing. Eventually, I'll probably even have a check list and some rotating beacons, because those things not only improve safety, they're just good fun for any red-blooded geek.
"Arming test lights on, one through four?"
"Arming test lights on, one through four!"
Ya know, all this work would be a lot easier if I had a team and a budget. Sure wish I'd gone to school.
_________________________________________
* (CV = valve coefficient, which equates to flow restriction through the valve. In COTS valves, it is usually driven by the valve's smallest opening, typically the valve seat)
Monday, January 31, 2011
The Beast With No Name
Around 1995 or so, I received a call from a good friend, asking me if I might be interested in a very large and very heavy high voltage capacitor bank -- capacitors specifically intended for pulse discharge duty -- with its own charging and switching circuitry; in short a complete, turn-key pulsed discharge machine. I immediately said, "yes" and then wondered where I was going to put it since I was living in an apartment at the time.
The thing was immense, weighing just a bit shy of 2,000 pounds. It consisted of two 28" wide rack panel cabinets mounted on a steel skid with four groaning casters. The shorter of the two contained the high voltage power supply, ancillary power supplies for things like control voltages, and a bit of relay control "logic" to interact with operator input and interlocks while enforcing safety rules.
The larger of the two cabinets contained the pulse capacitors (six), a parallel plate current collector stack (nice low inductance design), six ignitrons (one on each cap) in coaxial housings, as well as a bunch of other hulking heavy duty high voltage equipment to trigger the ignitrons, including a nice glass hydrogen thyratron.
This thing was designed in the 1960s and built in the 1970s. It was moderately cutting edge stuff for its time. The company wanted to investigate industrial applications for pulsed power including well frac'ing, and magnetic metal forming. Fortunately, all of the designer's personal notes and sketches, as well as notes from later techs who worked on the machine to rehabilitate it in the early 1990s, were saved and given to me when I got the thing. That has been incredibly valuable.
What happened is that the company's focus had moved on and narrowed - they had made interesting strides in metrology. They were being purchased by another company already famous in the business. They needed to clean house, and SOMEHOW, that two thousand pound white elephant had to go. If I could move it, I could have it. It sat for a bit while I figured out where in the hell I was going to put it, and how. The owner of the company was awfully patient with me.
Well, I had a sort of professor emeritus status with the entity which at that time was right in the middle of morphing from The Dream Park Corporation (bankrupt) into The Diabolic Company. Said organization had just moved into an IMMENSE building which had previously held a K-Mart. I asked, and I was basically told, "any place that won't interfere with the haunted house operation, knock yourself out".
The short version is: I stashed it there.
I got some friends to help me move it.
And we dropped it. But that's a story not terribly relevant here and now.
The astonishing thing was, we didn't do it any harm - er, probably. There was a little sheet metal damage, but it had slid down and landed with a jolt, we didn't really drop it off the dock. The only thing affected was the ignitrons. You see, ignitrons are finicky beasts. They have their advantages (they can switch HUGE charge transfers) but one of their idiosyncrasies is that once they have been used in crowbar or capacitor discharge duty, it is crucial that they not be moved or jarred. When ignitrons ares used in those high-wear modes, the structure which supports the ignitor electrode over the pool of mercury becomes very fragile. And shifting or sloshing of that pool of mercury is likely to damage the ignitor, rending the tube inoperative. True story.
The way we were rolling that thing around the lab and bumping it over doorways to get to the dock, all six of those tubes were toast before we ever got around to dropping it off the dock. Of course, I didn't find that out until later. About the same time in fact that I found out replacement ignitrons cost $1,500. Each.
Not having a spare nine grand burning a hole in my pocket, I decided to use another means of switching. I got rid of the ignitrons to a friend who was collecting mercury anyway. Don't ask. One less hazardous materials disposal pickup (we have an awesome trash department) for me to deal with.
Meanwhile, I needed a way to move this beat around without a Class IV forklift. While I still had the shop and lab space at DiaboliCo's haunted house building, I took to rebuilding it. I removed the power supply and its cabinet, disassembled the ignitron housings, and plate stack, removed the cabinet, and eventually unstacked the six pulse caps. They weigh about 150 pounds each. I'm guessing. It I ever weighed them, I've lost it, though I ought to have the shipping weight in my folder. Anyway. Then I split the big steel skid the whole thing had been mounted on, with a torch. I added more steel, and two new casters, and I had two skids. Then everything was reassembled onto those. Mind you, with a few rare exceptions when I was in a hurry and people were around to help, I was doing most of this alone, all Leedskalnin-style, with levers, blocks, ropes, pulleys and the convenient architectures of the building.
After that, the machine followed me around, all 2,000 pounds of it, through two moves, and has been sitting in my workshop alongside my collection of other Large Heavy Objects, waiting for me to figure out which way to go with it. In the mean time, I've been learning about high speed and high current switching devices. Since I acquire the thing, I've learned a GREAT DEAL.
I've been given one type of switch - which I've yet to fire, tho I am inching closer - and I've designed and built another type - which I've also yet to fire. I'm inching closer to that event too.
Stupid mill.
While the mill has been down I've been working on the parts of the long-stalled railgun project. The parts that don't require the mill, that is. That would including the pulser, or as the previous owner called it, "The Banger" (as far as I am concerned, it still doesn't have the great name it should, yet). From what he told me of their insane escapades, I bet every one of them needed hearing aids. Exploding wires are louder than gun shots, kids.
The first thing I did was excavate the machine itself from a mound of boxes. The new effort provoked a quick round of shop-cleaning this weekend. The second thing I did was remove all of the ancillary parts that were necessary for triggering the ignitrons, about 50 pounds of transformer, capacitors, rectifier, and blah-blah oh yes and a nice thyratron.
I ought to describe how the thing worked before I got my grubby mitts on it and tore half its guts out. It'll be illustrative of how things often go in the pulsed power world. Say you've got a whacking huge amount of energy you want to apply to load with a whacking huge switch. Trouble is, whacking huge switches by their very nature, tend to require a whacking huge something to activate them. Might be a huge pulse of electricity. Or perhaps some compressed air. Explosives are often used. Not kidding. So you come up with this pretty substantial trigger pulse to trigger your whacking huge switch. That pretty substantial trigger energy has to be switched by a substantial switch. The substantial switch needs at least an adequate switch, and so on, finally ending at the big red, jolly, candy-like button on your control panel.
So, this is how this particular machine was originally designed to work:
1. The operator sets the voltage at which they want the machine to fire on a dial (a Simpson relay meter).
2. The operator places the work in the fixture, which is already connected to the machine's output bus.
3. The operator presses the 'Start' button, and I would presume, gets the hell away from there.
4. The machine charges, slowly I assume, and when the meter needle reaches the aforementioned setpoint, the machine discharges in the following sequence:
5. because the Simpson meter contacts aren't good for any current at all, when they make contact, they are used to control another, ordinary industrial control relay.
6. that relay's contacts apply a voltage to a control grid in a pentode
7. the pentode turns on and dumps the charge of a small high voltage capacitor through the primary of a pulse transformer
8. the secondary of the pulse transformer delivers a small high voltage pulse to the
9. hydrogen thyratron located in the capacitor cabinet, which turns on and connects one side of six beefy high voltage capacitors to ground, dumping their charge through the ignitor electrodes of six ignitrons. Inside each ignitron, 100 joules of energy vaporizes a small amount of the mercury in the pool into the vacuum of the tube. The mercury vapor connects the anode and the cathode, turning on the ignitron tube until there is no more current to keep the vapor hot. Functionally, it behaves a lot like an SCR.
Seems a bit complicated, don't it? But that's the way it is. I'm going to try to do this with more sophisticated (and more importantly, obtainable) components, but there is still (and will always be) a long series of steps between you and the big drama. That's another good point worth raising - isolation. You don't want any kind of freak fault to allow the main store energy to get out into places it doesn't belong, such as remote control pendants. That would be bad.
Oh yeah, it came with a crude remote control pendant. I'm already working on a more sexy remote control, uh, "pendant". Well, panel anyway. Okay really, it's more of a box. With a panel that mounts inside the box. Like a miniature rack, sort of. Only with storage inside the lid. I'll try not to let it get any bigger. Also, it's long term project, and won't be done before the pulser-with-no-name is in operation.
Speaking of names, I could use one. It's an idiosyncrasy of mine - I like to name things. If you've got any clever ideas, leave me a comment or something.
The thing was immense, weighing just a bit shy of 2,000 pounds. It consisted of two 28" wide rack panel cabinets mounted on a steel skid with four groaning casters. The shorter of the two contained the high voltage power supply, ancillary power supplies for things like control voltages, and a bit of relay control "logic" to interact with operator input and interlocks while enforcing safety rules.
The larger of the two cabinets contained the pulse capacitors (six), a parallel plate current collector stack (nice low inductance design), six ignitrons (one on each cap) in coaxial housings, as well as a bunch of other hulking heavy duty high voltage equipment to trigger the ignitrons, including a nice glass hydrogen thyratron.
This thing was designed in the 1960s and built in the 1970s. It was moderately cutting edge stuff for its time. The company wanted to investigate industrial applications for pulsed power including well frac'ing, and magnetic metal forming. Fortunately, all of the designer's personal notes and sketches, as well as notes from later techs who worked on the machine to rehabilitate it in the early 1990s, were saved and given to me when I got the thing. That has been incredibly valuable.
What happened is that the company's focus had moved on and narrowed - they had made interesting strides in metrology. They were being purchased by another company already famous in the business. They needed to clean house, and SOMEHOW, that two thousand pound white elephant had to go. If I could move it, I could have it. It sat for a bit while I figured out where in the hell I was going to put it, and how. The owner of the company was awfully patient with me.
Well, I had a sort of professor emeritus status with the entity which at that time was right in the middle of morphing from The Dream Park Corporation (bankrupt) into The Diabolic Company. Said organization had just moved into an IMMENSE building which had previously held a K-Mart. I asked, and I was basically told, "any place that won't interfere with the haunted house operation, knock yourself out".
The short version is: I stashed it there.
I got some friends to help me move it.
And we dropped it. But that's a story not terribly relevant here and now.
The astonishing thing was, we didn't do it any harm - er, probably. There was a little sheet metal damage, but it had slid down and landed with a jolt, we didn't really drop it off the dock. The only thing affected was the ignitrons. You see, ignitrons are finicky beasts. They have their advantages (they can switch HUGE charge transfers) but one of their idiosyncrasies is that once they have been used in crowbar or capacitor discharge duty, it is crucial that they not be moved or jarred. When ignitrons ares used in those high-wear modes, the structure which supports the ignitor electrode over the pool of mercury becomes very fragile. And shifting or sloshing of that pool of mercury is likely to damage the ignitor, rending the tube inoperative. True story.
The way we were rolling that thing around the lab and bumping it over doorways to get to the dock, all six of those tubes were toast before we ever got around to dropping it off the dock. Of course, I didn't find that out until later. About the same time in fact that I found out replacement ignitrons cost $1,500. Each.
Not having a spare nine grand burning a hole in my pocket, I decided to use another means of switching. I got rid of the ignitrons to a friend who was collecting mercury anyway. Don't ask. One less hazardous materials disposal pickup (we have an awesome trash department) for me to deal with.
Meanwhile, I needed a way to move this beat around without a Class IV forklift. While I still had the shop and lab space at DiaboliCo's haunted house building, I took to rebuilding it. I removed the power supply and its cabinet, disassembled the ignitron housings, and plate stack, removed the cabinet, and eventually unstacked the six pulse caps. They weigh about 150 pounds each. I'm guessing. It I ever weighed them, I've lost it, though I ought to have the shipping weight in my folder. Anyway. Then I split the big steel skid the whole thing had been mounted on, with a torch. I added more steel, and two new casters, and I had two skids. Then everything was reassembled onto those. Mind you, with a few rare exceptions when I was in a hurry and people were around to help, I was doing most of this alone, all Leedskalnin-style, with levers, blocks, ropes, pulleys and the convenient architectures of the building.
After that, the machine followed me around, all 2,000 pounds of it, through two moves, and has been sitting in my workshop alongside my collection of other Large Heavy Objects, waiting for me to figure out which way to go with it. In the mean time, I've been learning about high speed and high current switching devices. Since I acquire the thing, I've learned a GREAT DEAL.
I've been given one type of switch - which I've yet to fire, tho I am inching closer - and I've designed and built another type - which I've also yet to fire. I'm inching closer to that event too.
Stupid mill.
While the mill has been down I've been working on the parts of the long-stalled railgun project. The parts that don't require the mill, that is. That would including the pulser, or as the previous owner called it, "The Banger" (as far as I am concerned, it still doesn't have the great name it should, yet). From what he told me of their insane escapades, I bet every one of them needed hearing aids. Exploding wires are louder than gun shots, kids.
The first thing I did was excavate the machine itself from a mound of boxes. The new effort provoked a quick round of shop-cleaning this weekend. The second thing I did was remove all of the ancillary parts that were necessary for triggering the ignitrons, about 50 pounds of transformer, capacitors, rectifier, and blah-blah oh yes and a nice thyratron.
I ought to describe how the thing worked before I got my grubby mitts on it and tore half its guts out. It'll be illustrative of how things often go in the pulsed power world. Say you've got a whacking huge amount of energy you want to apply to load with a whacking huge switch. Trouble is, whacking huge switches by their very nature, tend to require a whacking huge something to activate them. Might be a huge pulse of electricity. Or perhaps some compressed air. Explosives are often used. Not kidding. So you come up with this pretty substantial trigger pulse to trigger your whacking huge switch. That pretty substantial trigger energy has to be switched by a substantial switch. The substantial switch needs at least an adequate switch, and so on, finally ending at the big red, jolly, candy-like button on your control panel.
So, this is how this particular machine was originally designed to work:
1. The operator sets the voltage at which they want the machine to fire on a dial (a Simpson relay meter).
2. The operator places the work in the fixture, which is already connected to the machine's output bus.
3. The operator presses the 'Start' button, and I would presume, gets the hell away from there.
4. The machine charges, slowly I assume, and when the meter needle reaches the aforementioned setpoint, the machine discharges in the following sequence:
5. because the Simpson meter contacts aren't good for any current at all, when they make contact, they are used to control another, ordinary industrial control relay.
6. that relay's contacts apply a voltage to a control grid in a pentode
7. the pentode turns on and dumps the charge of a small high voltage capacitor through the primary of a pulse transformer
8. the secondary of the pulse transformer delivers a small high voltage pulse to the
9. hydrogen thyratron located in the capacitor cabinet, which turns on and connects one side of six beefy high voltage capacitors to ground, dumping their charge through the ignitor electrodes of six ignitrons. Inside each ignitron, 100 joules of energy vaporizes a small amount of the mercury in the pool into the vacuum of the tube. The mercury vapor connects the anode and the cathode, turning on the ignitron tube until there is no more current to keep the vapor hot. Functionally, it behaves a lot like an SCR.
Seems a bit complicated, don't it? But that's the way it is. I'm going to try to do this with more sophisticated (and more importantly, obtainable) components, but there is still (and will always be) a long series of steps between you and the big drama. That's another good point worth raising - isolation. You don't want any kind of freak fault to allow the main store energy to get out into places it doesn't belong, such as remote control pendants. That would be bad.
Oh yeah, it came with a crude remote control pendant. I'm already working on a more sexy remote control, uh, "pendant". Well, panel anyway. Okay really, it's more of a box. With a panel that mounts inside the box. Like a miniature rack, sort of. Only with storage inside the lid. I'll try not to let it get any bigger. Also, it's long term project, and won't be done before the pulser-with-no-name is in operation.
Speaking of names, I could use one. It's an idiosyncrasy of mine - I like to name things. If you've got any clever ideas, leave me a comment or something.
Friday, January 28, 2011
Action This Day
I ordered the remaining parts for the railgun pre-accelerator today. There are a few supporting parts for it which I still don't have. These include:
• the CO2 tank itself - which I'll "buy" from my local industrial gas supplier - about $100 I'm guessing
• a regulator capable of taking CO2 tank pressure and delivering anything from 100 PSI to 1,000 PSI. Of these three items, this will be the most challenging to find at a price I can afford.
• a bit of metal tubing and a few inexpensive (small size) tubing fittings
I think that's it. And what the hey, if I can't get the railgun to work, it'll be a short step to making the most dangerous compressed gas gun in amateur hands. (let's not and claim we did)
No movement on the mill. I'm trying to be patient, but already I'm wondering whether I ought to replace the motor - a heinous thought. But the mill going down is why I started working on the railgun program again. I need something to keep me off the streets and out of the doldrums.
The Mad Scientist Light Switch is on hold because of the mill. I could have it had it done by the end of January if not for the mill problem, I was that close to being done.
The test rig for the fast distortion-triggered, pseudospark mode, spark gap switch (say that three times fast) is on hold because of the mill and some materials not yet purchased. I still haven't figured out a good way to connect the switch to one of the caps in the pulser without pulling the cap out.
The avalanche transistor trigger for the VIG is also on hold due to spending money on other things. Can't do it all at once. Anyone got a cheap source for the Zetex ZTX415 avalanche transistor? $25 seems a bit steep for a single tiny rock. Anyone? Anyone? Bueller? Oh right, I keep forgetting that nobody reads this bloody thing.
Hey! I think I hear an echo.
Lessee, what other programs are "open"? The Tesla coil of course. Haven't touched it because it is at a stage where it needs far too much attention and money. I can't even look at it again until some of these other shorter-term projects are completed. THEN I can (hopefully) knock that thing out and then (hopefully) sell it. It will, at least, be unique in at least one way.
The fast mini-Marx is on hold for lack of money to spend on it. Have to finish some of these other projects first. Cash flow is tight and I'm already spending more money on hobby project than my wife would prefer.
Not much else to talk about today. Until next time...
• the CO2 tank itself - which I'll "buy" from my local industrial gas supplier - about $100 I'm guessing
• a regulator capable of taking CO2 tank pressure and delivering anything from 100 PSI to 1,000 PSI. Of these three items, this will be the most challenging to find at a price I can afford.
• a bit of metal tubing and a few inexpensive (small size) tubing fittings
I think that's it. And what the hey, if I can't get the railgun to work, it'll be a short step to making the most dangerous compressed gas gun in amateur hands. (let's not and claim we did)
No movement on the mill. I'm trying to be patient, but already I'm wondering whether I ought to replace the motor - a heinous thought. But the mill going down is why I started working on the railgun program again. I need something to keep me off the streets and out of the doldrums.
The Mad Scientist Light Switch is on hold because of the mill. I could have it had it done by the end of January if not for the mill problem, I was that close to being done.
The test rig for the fast distortion-triggered, pseudospark mode, spark gap switch (say that three times fast) is on hold because of the mill and some materials not yet purchased. I still haven't figured out a good way to connect the switch to one of the caps in the pulser without pulling the cap out.
The avalanche transistor trigger for the VIG is also on hold due to spending money on other things. Can't do it all at once. Anyone got a cheap source for the Zetex ZTX415 avalanche transistor? $25 seems a bit steep for a single tiny rock. Anyone? Anyone? Bueller? Oh right, I keep forgetting that nobody reads this bloody thing.
Hey! I think I hear an echo.
Lessee, what other programs are "open"? The Tesla coil of course. Haven't touched it because it is at a stage where it needs far too much attention and money. I can't even look at it again until some of these other shorter-term projects are completed. THEN I can (hopefully) knock that thing out and then (hopefully) sell it. It will, at least, be unique in at least one way.
The fast mini-Marx is on hold for lack of money to spend on it. Have to finish some of these other projects first. Cash flow is tight and I'm already spending more money on hobby project than my wife would prefer.
Not much else to talk about today. Until next time...
Wednesday, January 26, 2011
onward, mischief soldiers...
The mill is still down. The Variable Frequency Drive (VFD) -- which synthesized clean(ish) 3-phase power from the 240V 1-phase power available in my shop -- has died. It seems likely I brought about its death. I bricked the motherboard with an incautious press of a button in Eurotherm's software, enabling me to write user data over the firmware memory space. I'd like to ask my readers a question:
WHO THE FUCK DESIGNS SOMETHING THAT ALLOWS THE USER, THROUGH SOFTWARE, TO ACCIDENTALLY AND IRREVOCABLY DESTROY THE DEVICE?
Seriously, if you helped design the Eurotherm 605 series of inverter drives, I'd like to hear from you. Just send me your street address, where you work now, your daily habits, and a photograph, and one of my... associates will be in touch.
Where was I?
Goddamned mill is down. See? Now I'm swearing. I'm swearing mad. That's why we're called "mad scientists", at least part of the time. I've got a search going on eBay and am checking a few drives a day. Something will turn up. I'll try to be patient with this, because I prefer to use an inverter drive and not a DIY (nor commercial) "phase converter". But I'll go that rout if I lose my patience. We'll see.
Since I scored the firing valve for the railgun pre-accelerator, I have been busily figuring out the plumbing necessary to connect it to the breach block of the gun, the plenum chamber, and the gas supply. All of this must safely work at 1,000 PSI. I did a lot of homework, read a lot of ANSI and ASME standards, and the corresponding pipe schedule tables, and determined that Sch. 80 seamless steel (not iron) pipe will give me a safety factor of two in working pressures(burst limits are far higher). In reality, I have a safety factor to failure of at least 4X for some components, and 6X - 8X on others.
Yasee, I frequently work with high pressure gas flowing through tiny metal tubes. That doesn't worry me much, because the amount of energy stored by compressed gas depends on both the actual mass and the pressure. The bigger the enclosed volume, the more mass. It goes up fast, and so does the potential danger. The stored energy in compressed gas is incredible.
It may be difficult to get the pre-accelerator valve to fire reliably at low pressures but to be honest, that may not be necessary. I have a hard time imagining any live (electrical) shot that won't have huge friction between the rails. A lot of contact force is required between the armature and the rails to have any hope of getting that armature the length of the gun without being vaporized. The maximum contact force will be determined by what can be pushed down the barrel by 1,000 PSI or less. That was an arbitrary number, but about the biggest I'm willing to try to work with using hardware of my own construction. The breach block assembly is going to be, um, "interesting" to design. If it doesn't leak on the first version, I'll have a heart attack.
For a while there, it looks like I'd lost my CAD files for the railgun project, but thankfully I was mistaken. Found the backup too.
So I'll be looking at that breach block assembly soon.
I also need to revisit how the bus connections are made to the gun rails, and I need to think about how to keep this beast quiet - a muzzle blast suppressor at worst or a complete containment tank for the entire range at worst. Ugh. I'd really rather not. But I've no desire to have the local constabulary knocking on my door (okay, okay, this is the new millennium so busting down my door). Even though I'm fairly certain I'm not breaking any laws (though it's so hard to be sure these days) it is better not to frighten the horses.
WHO THE FUCK DESIGNS SOMETHING THAT ALLOWS THE USER, THROUGH SOFTWARE, TO ACCIDENTALLY AND IRREVOCABLY DESTROY THE DEVICE?
Seriously, if you helped design the Eurotherm 605 series of inverter drives, I'd like to hear from you. Just send me your street address, where you work now, your daily habits, and a photograph, and one of my... associates will be in touch.
Where was I?
Goddamned mill is down. See? Now I'm swearing. I'm swearing mad. That's why we're called "mad scientists", at least part of the time. I've got a search going on eBay and am checking a few drives a day. Something will turn up. I'll try to be patient with this, because I prefer to use an inverter drive and not a DIY (nor commercial) "phase converter". But I'll go that rout if I lose my patience. We'll see.
Since I scored the firing valve for the railgun pre-accelerator, I have been busily figuring out the plumbing necessary to connect it to the breach block of the gun, the plenum chamber, and the gas supply. All of this must safely work at 1,000 PSI. I did a lot of homework, read a lot of ANSI and ASME standards, and the corresponding pipe schedule tables, and determined that Sch. 80 seamless steel (not iron) pipe will give me a safety factor of two in working pressures(burst limits are far higher). In reality, I have a safety factor to failure of at least 4X for some components, and 6X - 8X on others.
Yasee, I frequently work with high pressure gas flowing through tiny metal tubes. That doesn't worry me much, because the amount of energy stored by compressed gas depends on both the actual mass and the pressure. The bigger the enclosed volume, the more mass. It goes up fast, and so does the potential danger. The stored energy in compressed gas is incredible.
It may be difficult to get the pre-accelerator valve to fire reliably at low pressures but to be honest, that may not be necessary. I have a hard time imagining any live (electrical) shot that won't have huge friction between the rails. A lot of contact force is required between the armature and the rails to have any hope of getting that armature the length of the gun without being vaporized. The maximum contact force will be determined by what can be pushed down the barrel by 1,000 PSI or less. That was an arbitrary number, but about the biggest I'm willing to try to work with using hardware of my own construction. The breach block assembly is going to be, um, "interesting" to design. If it doesn't leak on the first version, I'll have a heart attack.
For a while there, it looks like I'd lost my CAD files for the railgun project, but thankfully I was mistaken. Found the backup too.
So I'll be looking at that breach block assembly soon.
I also need to revisit how the bus connections are made to the gun rails, and I need to think about how to keep this beast quiet - a muzzle blast suppressor at worst or a complete containment tank for the entire range at worst. Ugh. I'd really rather not. But I've no desire to have the local constabulary knocking on my door (okay, okay, this is the new millennium so busting down my door). Even though I'm fairly certain I'm not breaking any laws (though it's so hard to be sure these days) it is better not to frighten the horses.
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