coil gun

Coilgun From Wikipedia, the free encyclopedia (Redirected from Coil gun) "Gauss gun" redirects here. For fictional weapons of this type, see electromagnetic  projectile  projectile devices devices (fiction (fiction). ). This article article needs needs additi additional onal citati citations ons for for verific verification ation.. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (April 2008) Coilgun Simplified diagram of a multistage coilgun with three coils, a barrel, and a ferromagnetic  projectile

A coilgun is a type of projectile accelerator that consists of one or more coils used as electromagnets in the configuration of a synchronous linear motor which accelerate a magnetic projectile to high velocity. The name Gauss gun is sometimes used for such devices in reference to Carl Friedrich Gauss, who formulated mathematical descriptions of the magnetic effect used by magnetic accelerators. Coilguns consist of one or more coils arranged along the barrel that are switched in sequence so as to ensure that the projectile is accelerated quickly along the barrel via magnetic forces. Coilguns are distinct from railguns, which pass a large current through the projectile or sabot via sliding contacts. Coilguns and railguns also operate on different  principles. The first operational coilgun was developed and patented by Norwegian  physicist Kristian Birkeland. In 1934 an American inventor developed a machine gun based similar in concept to the coilgun. Except for a photo in a few publications, very little is known about it. [1]Contents [hide] 1 Construction 1.1 Switching 1.2 Resistance 1.3 The magnetic circuit 1.4 Projectile saturation n

1.5 Projectile magnetization and reaction time 2 See also 3 References 4 External links

[edit] Construction A coilgun, as the name implies, consists of a coil of wire, an electromagnet, w ith a ferromagnetic projectile placed at one of its ends. Effectively a coilgun is a solenoid, a current-carrying coil which will draw a ferromagnetic object through its ce nter. A large current is pulsed through the coil of wire and a strong magnetic field forms, pulling the  projectile to the center of the coil. When the projectile nears this point the electromagnet is switched off and the next electromagnet can be switched on, progressively accelerating the projectile down successive stages. In common coilgun designs the "barrel" of the gun is made up of a track that the projectile rides on, with the driver into the magnetic coils around the track. Power is supplied to the electromagnet from some sort of fast discharge storage device, typically a battery or high-capacity high voltage capacitors designed for  fast energy discharge. A diode is used to protect polarity sensitive capacitors (such as electrolytics) from damage due to inverse polarity of the current a fter the discharge. There are two main types or setups of a coilgun: single-stage and multistage. A singlestage coilgun uses one electromagnet to propel a ferromagnetic projectile. A multistage coilgun uses several electromagnets in succession to progressively increase the speed of  the projectile. Many hobbyists use low-cost rudimentary designs to experiment with coilguns, for  example using photoflash capacitors from a disposable d isposable camera, or a capacitor from a standard cathode-ray tube television as the energy source, and a low inductance coil to  propel the projectile forward. A superconducting coilgun called a quench gun could be created by successively quenching a line of adjacent coaxial superconducting coils forming a gun barrel, generating a wave of magnetic field gradient traveling at any desired speed. A traveling superconducting coil might be made to ride this wave like a surfboard. The device would  be a mass driver or linear synchronous motor with the propulsion energy stored directly in the drive coils.[2] [edit] Switching One main obstacle in coilgun design is switching the power through the coils. There are several common solutions — the simplest (and probably least effective) is the spark gap, which releases the stored energy through the coil when the voltage reaches a certain threshold. A better option is to use solid-state switches; these include IGBTs or power  MOSFETs (which can be switched off mid-pulse) and SCRs (which release all stored energy before turning off).[3] A quick-and-dirty method for switching, especially for  those using a flash camera for the main components, is to use the flash tube itself as a switch. By wiring it in series with the coil, it can silently and non-destructively (assuming that the energy in the capacitor cap acitor is kept below the tube's safe operating o perating limits) allow a large amount of current to pass through to the coil. Like any flash tube, ionizing the gas

in the tube with a high voltage triggers it. However, a large amount of the energy will be dissipated as heat and light, and, due to the tube being a spark gap, the tube will stop conducting once the voltage across it drops sufficiently, leaving some charge remaining on the capacitor. A multistage coilgun [edit] Resistance The electrical resistance of the coils and the equivalent series resistance (ESR) of the current source limit the efficiency of a coilgun. [edit] The magnetic circuit Ideally, 100% of the magnetic flux generated by the coil would be delivered to and act on the projectile, but this is often far from the case due to the common air-core-solenoid /  projectile construction of most coilguns. Since an air-cored solenoid is simply an inductor, the majority of the magnetic flux is not coupled into the projectile, instead being stored in the surrounding air. The energy that is stored in this field does not simply disappear from the magne tic circuit once the capacitor  finishes discharging; much of it returns to the capacitor when the circuit's electric current is decreasing. As the coilgun circuit is inherently analogous to an LC oscillator, it does this in the reverse direction ('ringing'), which can seriously damage polarized capacitors such as electrolytic capacitors, which are far cheaper and smaller for a given capacity than other types. The capacitor charging to a negative voltage can be prevented by placing a diode across the capacitor terminals; this diode and the coil must dissipate all of the stored energy as heat. While this is a simple and effective solution, it requires expensive high-power  semiconductors, and a coil which will not overheat. Some designs attempt to recover the energy stored in the magnetic field by using a pair of  diodes. These diodes, instead of being forced to dissipate the remaining energy, recharge the capacitors with the right polarity to be used again for the next discharge cycle. This will also avoid the need to recharge the capacitors from zero, thus significantly reducing charge times. In order to reduce component size, weight, durability requirements, and most importantly, cost, the magnetic circuit must be optimized to deliver more energy to the  projectile per discharge cycle while still using the same en ergy input. This has been addressed to some extent by the use of end iron and back iron, which are pieces of  magnetic material that enclose the coil and help reduce the reluctance of the magnetic circuit. The results of this vary widely, due to the use of materials ranging anywhere from magnetic steel to video tape. The inclusion of an additional piece of magnetic material in

the magnetic circuit also magnifies the problems of flux saturation and other magnetic losses. [edit] Projectile saturation Another significant limitation of the coilgun is the occurrence of ferromagnetic projectile saturation. When the flux in the projectile lies in the linear portion of its material's B(H) curve, the force applied to the core is proportional to the square of coil current (I) - the field (H) is linearly dependent on I, B is linearly dependent on H and force is linearly dependent on the product BI. This relationship continues until the core is saturated; once this happens B will only increase marginally with H (and thus with I), so force gain is linear. Since losses are proportional to I2, increasing current beyond this point eventually decreases efficiency although it may increase the force. This puts an absolute limit on how much a given projectile can be accelerated with a single stage at acceptable efficiency. [edit] Projectile magnetization and reaction time Apart from saturation, the B(H) dependency often c ontains a hysteresis loop and the reaction time of the projectile material may be significant. The hysteresis means that the  projectile becomes permanently magnetized and some energy will be lost as a permanent magnetic field of the projectile. The projectile reaction time, on the other hand, makes the  projectile reluctant to respond to abrupt B changes; the flux will not rise as fast as desired while current is applied and a B tail will occur after the coil field has disappeared. This delay decreases the force, which would be maximized if the H and B were in phase.

Coilguns are a type of electromagnetic launcher which, along with their cousins, railguns, are sometimes called Mass Drivers (especially pertaining to their artillery versions) and Gauss Guns (especially pertaining to their firearm versions). They are more formally known as electromagnetic linear accelerators. Using coilguns as a means of shooting a  payload into orbit is detailed in the Launch Guns article in the Orbital Travel section. The first coilgun was patented in 1900 by Norwegian researcher Kristian Birkeland. However, his attempts to produce a practical weapon proved disappointing, and the concept was abandoned and languished for many decades. Interest in the concept revived in the wake of the Reagan Administration’s SDI program, and NASA began looking into the possibility of using coilguns to launch orbital payloads. The NASA program has designed and built an experimental coilgun that can accelerate a 10 kilogram projectile to 39,600 kph. Today, many hobbyists and private interests build home-made coilguns, and the concept has gathered a great many enthusiastic supporters. Coilguns consist of a series of electromagnetic coils that accelerate a metal projectile to high velocity. They are more mechanically complicated than railguns, but since there is no direct contact between the projectile and the coils they avoid the erosion and arc-over   problems of railguns. Each coil section along the barrel’s length is switched on rapidly in sequence, pulling the  projectile forward, then switched off as the projectile passes so the next coil section can grab it with its magnetic field. Rapidly switching from one coil to the next in sequence can accelerate a projectile to astounding velocities unobtainable by modern gasexpansion weapons. A simplified diagram of coilgun operation. Unlike railguns, coilguns can be made arbitrarily long, allowing for greater potential velocities using gentler accelerations. The main engineering obstacle to this technology is not so much producing enough power or strong enough magnetic fields, but overcoming timing and switching problems. Because the projectile zooms so rapidly through the barrel, the magnetic fields switching on and off have to be precisely timed. Also, the current and voltage needed to produce the fields do themselves take time to build to strength and to fade away, especially in the  bullet-time microseconds the projectile will typically be in the launch ba rrel. This can result in a loss of velocity, both from less-than-optimal field strength as well as slowfading fields behind the projectile tugging on it and slowing it down. Precision timing  programs and compatible hardware are therefore an essential component of any coilgun, and one of the main reasons why they have proven much harder to engineer than their  conceptual cousin, the railgun. Coilguns do pose a number of advantages over railguns, however, and many believe that while railguns will see practical use at first, coilguns will eventually supplant them. Coilguns use less overall power, are quieter, can be scaled down much more easily, and

require far less maintenance (no rails to replace after so many firings) and will therefore  prove cheaper to operate and maintain. Because a coilgun projectile does not actually come in contact with the barrel, there is very little friction and coilgun projectiles can  potentially be accelerated to much greater velocities. And because rail wear is not an issue, coilguns can also be fired much more often and with a much greater rate of fire. However, coilguns use up an enormous amount of current with every shot. Portable but  potent power sources and energy transfer technologies are required in order for them to  be made practical. Emerging devices such as compulsators, flywheel batteries, ultracapacitors, explosive power generators, superconducting batteries, and so on may be the key to making this technology battlefield-ready. Coilguns also have a large amount of recoil, at least equal to that of modern artillery and firearms of comparable size. Ways to counter or lessen this recoil wo uld have to be integrated into the weapon. And because of all the current eaten up by the coils, the weapon will also generate a large amount of heat. Passive and active cooling systems may also become a necessary part of coilgun designs. COILGUN ARTILLERY Tech Level: 13 The first practical application of coilgun technology will most likely be in the form of  artillery, the "Mass Driver" often mentioned in science fiction. Their performance is expected to at least equal the railguns currently being developed by the US Navy for their  DD-X destroyer project, which has a muzzle velocity in excess of Mach 7 and a range of  290 miles. Projectiles would likely be somewhat needle-like cross section and be made as frictionless as practical. They need to be able to slice through the lower atmosphere as efficiently as they can, as air friction will sap over 20% of their muzzle velocity just in the first 16 meters of flight. Explosive warheads would be superfluous, as the projectile is expected to hit its target at over 5000 feet per second, and explosives would only be needed in certain specialized circumstances. The damage done is expected to come  purely from the enormous kinetic energy of the impact from the dense projectile. Coilgun artillery would shoot their projectiles in sub-orbital parabolic arcs which could reach over 80 miles high. During flight, the projectile can pick up navigational data from GPS satellites and adjust its trajectory accordingly with small maneuvering fins on its aft section. Supplying power to the coilgun would be problematic but can be achieved with several different schemes. If used on naval ships, the ship’s engines could supply the large amount of current needed directly. Land-based artillery would need a mobile generator  and compulsator/flywheel arrays built into its chassis, making them potentially huge lumbering vehicles.

Alternately, the power source could be built into a separate vehicle, mainly a truck with a mobile generator complimented with banks of capacitors and compulsators. The coilgun itself would be a separate mobile unit. This could make the system much more mobile, and generator trucks could service multiple coilgun units simultaneously. In areas where railway service is available, coilguns could be mounted and deployed on train cars. A generator could be carried in a separate car, or it could draw power off of the main train engine itself. Because of their enormous potential range of hundreds of miles, a coilgun mounted on a flatbed railcar could still be useful in battlefields far from the rail line. COILGUN SPACE SYSTEMS Tech Level: 13 At tech Level 13, circa 50 years from now, it seems likely space launch systems will  become sophisticated and common enough that the cost of orbital launches falls dramatically. This would allow the lifting of large weapon payloads into orbit that  previously were considered to be too cost prohibitive to be practical. Since coilguns would also be emerging at this time, an orbital coilgun anti-ballistic missile satellite like that originally envisioned during the SDI program seems inevitable. Orbital coilguns have a tremendous advantage over orbital railguns, as they would have no rails to replace on a regular basis, plus would need less overall power in order to deliver the same performance. Such satellites could b e powered by nuclear plants or by solar panels, and could store their energy in banks of long-term flywheel batteries. The flywheels would be aligned in counter-rotating pairs along different axes, both to minimize progressional instability as well as do double duty as gyroscopic stabilizers. These coilgun ABM satellites would acquire targets rising over the atmosphere on suborbital parabolic arcs, and fire at the enemy vehicle is at or near the apex of its flight. This is much more complex than it sounds, as everything in orbit is moving at very high relative speed. Any one ABM satellite would probably only get a handful of chances to target a bogey as it whips by on its orbit, so the coilgun satellite would probably fire large  bursts to ensure it could take down whatever it was aiming at. The recoil from the shots would also act as thrust, meaning the satellite would have to readjust its aim after every burst. However, it can a lso use its gun as a mass driver in the space propulsion sense, and correct its orbit with it while on the other side of the planet. This would be in addition to whatever additional thruster system it may have. The coilgun satellite could also target objects rising into higher orbit-bound trajectories or  other objects in space. Coilguns are sure to be incorporated into armed spaceships when such vehicles become available, and would be employed as both an anti-missile defense as well as a short range offensive weapon to use against non-maneuvering targets such as satellites and stations. COILGUN VEHICLE WEAPONS

Tech Level: 14 Scaling coilguns down small enough to be used in armored fighting vehicles and aircraft would be a daunting but not impossible task. Because barrel lengths would be shorter, more power would have to be applied to the coils to maintain their relatively high muzzle velocities. At this Tech Level, a key technology comes into play that can supply this added power in a compact form: explosive power generators (EPGs). These come in two general forms. In the first, an explosive charge induces large spin in a flywheel or compulsator nea rinstantaneously, which in turn is used to create the power needed for the shot. The second kind uses a specific mix of elements to produce an electron dense, high-energy shockwave whose energy is fed directly into capacitors. In order to keep the weapon system as simplified to use as possible, the explosives for the EPGs would be incorporated into the round itself, eliminating (or at least greatly decreasing) the need for a bulky independent power sources for the weapon. Like in modern weapons, the only thing soldiers would need to power the weapons would be the ammunition. The weapon ignites the charge and uses it to power its coils, while that same impulse is used to impart initial velocity to the projectile as it starts down the barrel. In use as frontline weapons, direct-fire coilgun projectiles would fly much faster than missiles and have much higher potential penetration than modern conventional arms. They would be able to reload and fire at much faster rates as well. Using coilguns as aircraft armament would require some special considerations. Coilgun  projectiles would travel and hit their targets much faster than air-to-air missiles, making them very attractive armaments for aerial combat. What they wou ld lack in maneuverability they would make up for in raw velocity. In order to offset recoil adversely affecting the aircraft, the projectiles would be small and needle-like with minimal inertial kickback per shot. At the velocities they would be travelling, even such small projectiles would still cause massive damage should they hit. MAN-PORTABLE COILGUNS Tech Level: 14 Coilguns would still be large, heavy, and bulky, but it would be possible at this point to reduce their size enough for a single soldier with a specialized harness to carry one into the field. Its main purpose would be to act as a squad support and, coupled with armor piercing rounds, as a direct fire anti-vehicle weapon. As its assumed power supply in the form of EPGs can be made compact enough to at least carry in backpack form, the two main problems of a man-portable unit beco me recoil compensation and heat regulation.

Even scaled-down coilguns would deliver a large kickback per shot. A steady-cam like  body harness for the gun would be needed. These are full-torso, rigid harnesses with a free-swinging articulated arm designed to bear the brunt of the weapon’s weight and recoil. A famous example is the harnesses worn by the heavy gunners in the movie Aliens. Still, these may not be enough, and active recoil compensation systems, such as directing the waste gas from the EPGs and sliding counterweights may be needed to make these workable. Heat regulation may become a serious consideration. While there is no friction produced  by shooting the projectile itself, the constant charging an d discharging of the coils would  produce a lot of waste heat. In order to prevent performance degradation or even extreme damage such as melting, an active cooling system may be needed. Even if the power  system is small enough to be incorporated into the magazines or rounds themselves, a small backpack-sized cooling system may still be required to make the weapon system  practical. VERY RAPID FIRE (VRF) COILGUN Tech Level: 15 This particular weapon comes from the Traveller RPG universe, where it is more  properly known as a VRF Gauss Gun, and does seem to be a natural outgrowth of coilgun capabilities. As was stated previously, engineering the coordinated rapid on-off switching of the accelerator coils is one of the major hurdles facing researchers in making coilguns a feasible weapon system. Eventually, though, this problem is expected to be fully solved and even perfected to the point that the on-off sequencing would take milliseconds at most. The weapon could fire projectiles as fast as they could be fed into the barrel. Combined with a high-speed ammo feed system, a weapon can be designed that would  prove to be an entirely new class of devastating autofire weapon. A VRF Coilgun would have a rate of fire dwarfing even the most prolific modern systems. It would be capable of continuously firing dozens of rounds per second, which when combined with a coilgun’s extremely high penetration and muzzle velocity, creates a very formidable anti-personnel and area denial weapon. Even targets armored against single shots from coilguns may buckle when hit by hundred round bursts. It could devastate even the most heavily armored infantry. But even such a formidable weapon system would have some drawback s. First and foremost would be its power requirements. It would need an extremely potent source to fire so many projectiles so fast. Because needing to evacuate the waste gasses from EPGs would slow the weapon down, an array of advanced flywheel batteries or a more high tech source, such as superconductor batteries, would probably be used instead. The weapon would also generate helacious heat as it fired, both from the electricity in the coils as well as superheated air in the barrel. VRF coilguns, their barrels especially,

would therefore need to be cryogenically cooled. Without a sophisticated active cooling system, its likely the weapon would start melting after only a single burst. Recoil would also be a major problem. Thousands of rounds firing per minute, even if  they are small needle-like projectiles, creates a tremendous amount of force. A VRF Coilgun would have to be heavily anchored and compensated for its recoil just as well as modern artillery pieces twice their size. There’s also the issue of ammo capacity. VRF coilguns would eat ammunition voraciously, so their rounds would probably come in hoppers of a thousand or more. All these considerations would preclude VRF coilguns from e ver becoming man portable; the weapon would simply be too heavy and unwieldy for any unaugmented soldier to carry, much less employ effectively. However, they would make an ideal vehicle and support weapon. The Traveller version of the VRF coilgun fires 4000 rounds per minute, and each pull of  the trigger unleashes a hundred-round burst. It is supplied ammunition in 1000-round hoppers, and typically vehicles sporting the weapon carry over 30 interconnected hoppers for it. COILGUN FIREARMS Tech Level: 15 These are the gauss guns, gauss rifles, and gauss pistols often referred to by a number of  science fiction sources. Coilgun rifles and pistols would represent a quantum leap forward in small arms lethality and capability. Even though with their shorter barrels they wouldn’t be able to come close to the performance of the larger, more powerful versions of this technology, they would still be significantly more powerful than any equivalent modern firearm. They would not only be able to shoot their rounds much at a much greater velocity (a theoretical maximum of 8500 mps in an atmosphere), they could also do so with a greater  rate of fire and significantly increased range. Powering such weapons while making sure the energy source is not bulky or heavy enough to act as a detriment to handling the gun is always an issue with this technology. However, its is assumed that by the time coilgun firearms become practical, so too will  power sources compact enough to be incorporated into the guns. One possibility are compact, high-efficiency EPGs, with the tailored explosive charge incorporated into the individual round. Other possibilities include flywheel generators carried in backpacks or   belt packs, and disposable superconductor batteries and/or ultracapacitors built into the  base of a coilgun’s ammunition magazine. Recoil will be a problem that would have to be addressed in coilgun firearm design. These weapons may in fact be deliberately designed to be under-powered to a degree in order to make them easier for an unaugmented soldier to handle.

Heat regulation is another issue, but because these weapons would be smaller and use less power, heat build-up in the coils may not become a significant factor, at least to the  point where it would risk degrading weapon performance. Still, the weapon’s barrel after  firing would be a very bright infrared source, and if used often enough in a short period of time might even start glowing red-hot. A compact recyclable coolant system would be ideal, perhaps with a recharge of the chemicals needed included in the weapon magazine. Combined with air cooling and radiator fins, heat buildup can be handled readily. So even though coilgun rounds would be lighter and smaller than conventional rounds, the need to couple them with an explosive charge for the gun’s EPG, as well as working a coolant recharge into each ammunition cassette, would mean that their magazines may actually prove just as large and heavy than a modern gun’s, if not more so. A coilgun that does not use EPGs would be significantly quieter than modern firearms, as there is no explosive charge needed to propel the round. The projectile would still create a loud report as it breaks the sound barrier, but the gun’s coils can be powered down to subsonic performance if stealth is necessary. Running is such a "quiet mode" would result in greatly reduced performance, but on the plus side the weapon would make virtually no noise when fired.

Help fund more PowerLabs research? Project Introduction: After my move from Brazil to study in the US I had to leave behind all of my ongoing  projects, including the 3kJ single stage coil gun and my 7kJ multi stage coil gun  prototype, both of which were incomplete (the multi stage coil gun was crushing the glass coil forms I was using as barrels and the 3kJ gun had barely been started). Not counting small prototypes I built as a kid, this is my 4rth Coil Gun project (I have worked with 1.5, 3 and 2.6kJ systems before), and although this research is nothing new to me I have come up with some theories over the years as my science and engineering education progressed and am hoping to test these ideas on a new gun platform with the objective of creating my most efficient and powerful gauss gun / linear coaxial magnetic accelerator yet. The basic platform used here (busbars, barrel, SCR clamp and polycarbonate structure) was built in one afternoon when I arrived at the machine shop and found that the non metals center was closed so that the tables could be re-varnished. It is being built entirely from left over materials from the Rail Gun research and the Solid State Can Crusher.

Project Description and Goals: Coil Guns, (also known as "gauss guns", or "coaxial accelerators", or "linear  electromagnetic accelerators") are extremely easy to make, a fact that explains their   popularity on the Internet and as a science project in general. Basically, all one needs to  build a coilgun is to wrap a couple turns of wire around some type of tube and run electricity through that wire with a piece of iron inside the tube. However, as with most things, when it comes to making a coil gun that performs well, that is, converts a significant portion of the energy stored in the capacitors into kinetic energy, even the best designs -the ones on this web site included- achieve at best a meager couple of % efficiency. Although a comparison with conventional electric motors and transformers, which can perform at efficiency levels as high as 90% and above, is not appropriate since they are completely different devices, some governmental institution coil gun designs have been quoted as achieving efficiencies as high as 26%, which makes it very obvious to me that there is something seriously wrong with the current amateur designs. It is clear that the problem lies with a very low degree of power coupling between the coil and the projectile, which can be remedied by a smaller coil/slug ratio, thinner barrel walls, and a tighter fitting projectile, however several other factors are probably playing a role, such as the permittivity and magnetic saturation of the projectile material and the general fine tuning of the device. Solving the first problem can be achieved through the use of a more optimized coil/projectile design, although this will bring with it a power  switching problem. Solving the second issue will now be possible through the use of a chronograph, which will make it very easy for the efficiency to be calculated and changes in efficiency quantified. I also hope to gain access to specialized magnetic materials so as to maximize the energy transfer potential of my Coil Gun .

Parts: Energy Storage: When Mr. Parler from Cornell-Dubilier provided me with 40 capacitors for my Rail Gun research I kept the 3 leftovers as possible replacements in case some of  the capacitors from the bank were destroyed from over current. These capacitors have  been sitting around for almost a year now and I decided that it was time to put them to some good use. The exact specifications for this 3-capacitor bank are (as measured): 2019uF, 22.81mOhms ESL. The bank can be charged to a peak voltage of 1300V, limited  by the SCR being used. The stored energy on the bank is 1706Joules at that voltage, which I have found to be an appropriate value for a single stage (WARNING: It only takes 16Joules to kill a human by electrocution: high energy capacitor banks should only  be handled by professionals!). The capacitors are inter connected through 1/16inch thick  oxygen free pure copper bus bars that I had left over from the Rail Gun project. It is very interesting to note that at only 2.7 kilograms and measuring 23x16x8cm (9 1/4x6 1/4x3in) this capacitor bank stores 19% more energy than my first coil gun capacitor   bank, which contained 10capacitors the same size as these, 30% more energy than one of  the stages used in my 7kJ gun, which weighted just as much, and 38% less energy than the 3kJ coil gun capacitor bank, which weighted almost 7 times as much containing 20 non pulse rated capacitors! Coil Barrel: Although for a future multi stage gun it would be highly desirable to have transparent barrels so that optical sensors could be easily moved along the gun for 

optimization experience has thought me that glass and most plastics are too soft to maintain good structural rigidity as a thin tube when a solenoid wound on them is pulsed with more then a couple hundred joules. Metals are ideal having a high strength to weight ratio but they suffer from severe eddy current losses in coil gu n duty. My solution was to utilize a very thin (.001 inch wall thickness) brass tube (brass has the second lowest coefficient of friction of any metal, second only to Bronze.), and slot it with a 1/16" mill  bit so as to eliminate eddy current losses. The current barrel has an inside diameter of  5/16" (.79cm), a common size for finding metal rods for, and also larger than my  previous 1/4" diameter barrels, in the hope that if magnetic saturation is indeed one of the causes for poor performance this will help alleviate it. In order to fully eliminate the eddy loss problem it may be necessary to insulate the projectile.

Coil: The coil was wound on a precision turned stainless steel form, slid out and then inserted into the slotted brass tube. By winding the coil outside of the coil form I can ensure that the turns are tight and accurate without deforming the coilform. The coil is 8cm long (3 1/4") and 2cm dia (3/4") and consists in 115 turns of AWG12 polyurethane insulated (Class A Type T-1 105C) magnet wire.

I currently have the facilities to manufacture most types and sizes of high precision/high  performance coils and coil barrels for Coil Guns and other applications. If you are looking for a small quantity of custom coils contact me and we may be able to work out a deal.

Power Switching, triggering and protection circuit: Since I am already foreseeing power switching problems with this gun as higher and higher coupling coefficients are experimented w ith I decided to use the largest solid state switch I could possibly get my hands on: a 1000Ampere, 1200V SCR. It will handle a 14kA, 1300V pulse, which may be just what is needed for a projectile to be fully accelerated in a distance of under one inch. I am currently looking for similar units; if  anyone knows of a good supplier please E-mail me. This SCR is mounted on a custom machined aluminum heat sink as the previous one I was using for it was unnecessarily large and hea vy. Contact me if you need a custom machined SCR clamp. The SCR will be protected from the CEMF produ ced by the collapsing magnetic field in the coil by two large MOVs and an ultra fast 2000A peak diode. The trigger circuit is still  being designed but will be capacitive in nature. Capacitor bank Charger: Again here I am using the same one as the Rail Gun (what do you expect from a device built in one afternoon!): Variac feeding a MOT with a full wave  bridge rectifier. This crude prototype will have only one resistor which will serve as both current limiting for the PSU and as a discharge device. The temporary rail gun charger  will eventually before a permanent charger for my coil gun experiments after the rail gun is switched over to a solid state high speed charger.

Completed Device: Here is a photo of the device are it currently stands, with the coil uncon nected and minus charger, trigger and SCR protection circuit. Check this page back often as it will be continuously updated until the gun is ready, and click on the image for a higher resolution one.

Results: The gun has been completed, and it works! I finalized the design so that I could show it on my presentation on electromagnetic accelerators -which mainly focused on the Rail Gun- for "The Daily Planet", on The Discovery Channel. It works well, with only a few  bugs to sort out; mainly the coil is moving backwards with the recoil of firing and this is

disconnecting it and wasting energy. Also the back EMF is sufficient to blow all the diodes on the power supply and charge up the capacitor bank in reverse to over 100 volts, so a back-emf protection circuit is a must. I expect some more high power tests and videos soon, including chronograph results and optimization. For now, enjoy this low  power test video (capacitors charged to +- 1kJ). Video

This chronograph will be used to measure the velocity of the projectiles to within 99.5% accuracy soon. Links: You can see my older Coil Gun Research on the PowerLabs Gauss Gun Page. For a more spectacular kind of linear electromagnetic accelerator be sure to check out the PowerLabs Rail Gun Research. Greg's Coil Gun Page Email: [email protected]

My Homepage X-Gun: 3-Stage Optically Triggered Coil Gun Big Gun: High Energy 3-Stage Coil Gun Permanent Magnet Repulsion Coil Gun still in the making Event Counter: High Speed Clock to Determine Projectile Velocities Results: Check out some quantitative coil gun results on the high energy coil gun Introduction The concept is pretty easy to understand unless your name is Kurtz or Matt. An electric current is passed through a hollow coil of wire inducing a magnetic field in the vicinity of  the coil. Anything "magnetic" that is near the coil experiences an attractive force towards the center of the coil. If the current through the coil can be switched on and switched off  at just the right time, the magnetic object can be accelerated right through the hollow coil

towards a target or another coil system. A series of these coils and switches may be arranged on a linear barrel to produce a coil gun. The Projectile The projectile can be pretty much anything that will stick to a magnet and fit in the barrel.  Nails, screws, segments of clothes hanger all work ok. Long stuff works well, round stuff  does not. The more it sticks to a magnet the better. And remember, the lighter it is, the faster it will go! The Barrel The barrel's job is basically just to hold things in a straight line. When choosing a barrel it is important to take several factors into account. If you want to use optical sensors to trigger additional coils, you're going to want something that is essentially transparent to the light that your sensors use. Glass and plastic are have low absorptivities in the infrared region and work well. Metal barrels restrict the field experienced by the  projectile because eddy currents are produced in the conductive barrel material (unless you can find a metal that is not conductive!) You must also think ab out the forces that will be acting on your barrel. When the coils are energized, they compress and will smash a glass or plastic barrel if your gun is really juiced up. The Coils The coils must be made of magnet wire to produce the large magnetic field you need to get the projectile zooming. Magnet wire is used to make electromagnets (like relays) and electric motors. An excellent source of magnet wire are microwave cooling fans. The fans are easy enough to get out of the microwave, but getting the wire out of the fan motor is a bit tricky to do. The wire is wound on a coil around a squarish coupling made of iron sheets. You can remove a few of the iron sheets with a small flat screw driver and a hammer. After several of these sheets are removed, the entire coil of wire can be dislodged leaving you with a hundred feet or so of nice wire. With significantly more effort, the thick magnet wire in the main microwave transformer can removed utilizing the same technique of transformer destruction. Getting the wire is the tough part, next you just wind up the coils. The coils don't need to be wound in any certain direction for  good coil gun action. The size of the coil influences the magnetic field it puts out. Usually the larger the coil, the larger the field for a given current it's passing. But the longer your coil is, the more resistance and inductance it has. This is going to cut down the current it will pass at a given voltage, so there is an optimum coil size/length. The Capacitors The capacitors store and release the crapload of energy you need to get your projectile moving. Since the magnetic field is greatly dependent on the current you can pass through the coil in a small amount of time, you are going to want as much voltage as you can manage across your coils and capacitors. So the capacitors you use are going to depend on how you're going to charge them up. With a only a 9-Volt battery as a power  supply, capacitors rated for any more than 9-Volts are just a waste. If you are going for  low voltage, you'll need a lot of capacitance (several thousand uF). Or if you go the high voltage route, you need a lot less capacitance at a higher voltage rating. Capacitors out of 

camera flash circuits work especially well for this application because they were designed to discharge rapidly through the flash tube. Flash capacitors are typically rated for 300350 working volts at around 200-500 uF which is plenty for a fun coil gun. Depending on the properties of your gun (coil size, operating voltage), increasing the capacitance of  your capacitors could actually SLOW down your shooter. If the capacitance is too high, the coils will be energized too long and they will slow down the projectile or even  prevent it from passing at all. So where am I supposed to get capacitors from flash circuits you butt-licker? Well I guess you can con the people at the mall photoshop into giving you disposable camera carcasses. I find them in a the trash or at goodwill. The Capacitor Charger  You can charge your capacitors with any DC source, a computer power supply box, a car   battery charger or a cactus (according to McGuyver). To achieve some major high voltage, you're going to need to make or steal a high voltage power supply. An easy one to make is the transistor driven flyback transformer power supply. The parts are pretty easy to come by and you can't beat the output voltage of up to 20,000 volts! Here's the link to the high voltage flyback transformer information flyback. You do need to be careful when you use this kind of charger on your capacitors as it could easily surpass the voltage rating on your caps so you need to monitor the capacitor voltage while charging. I recommend a cheap analog VOM for this because you can dedicate it and also a digital VOM would get fried if you accidentally overloaded it! Also, the flyback circuit will only give you 1-2 mA, so if you are making a big gun, say > 1500 uF total capacitance you are going to want a more powerful supply or you will spend all day trying to charge up your  caps. Switching Components If you only have a one coil system, you can fire it with just a switch with a high surge or  current rating. If you plan on having more than one stage or coil, you'll need a way to switch on your capacitors quickly at just the right time. In order to get the switching speed you'll need for a nice gun, you'll need some silicon products. Most coil gunners who employ the capacitor design use SCR's (Silicon Controlled Rectifiers) to dump the capacitors through the coils. The SCR stays open (no current flowing) until it receives a signal of positive voltage to the gate terminal. Once it gets gate signal, it c onducts in one direction until the current drops down below the threshold current level for the specific SCR. There is no stopping the SCR after it's begun conducting, so it's ideal for cap acitive discharge circuits which stop themselves (when completely discharged). SCR's are sold  by their voltage and current maximum ratings. When choosing and SCR, make sure that you won't exceed its maximum voltage rating and choose a SCR with as high of a surge current rating as possible. Most SCR's can handle a lot more current as a short surge than what they are rated for. So to save money, look for the surge ratings rather than the nominal current rating. The currents passing through the coils are quite substantial. At 300 volts and a coil resistance of only an ohm or two, more than a hundred amps will be  passed through the SCR for a brief time. Transistor Driven Circuit:

I also have messed around with a transistor switched coil gun (rather than SCR). I figured that with a transistor switcher, I could have a constant DC power source across the coils for a longer amount of time (longer than a capacitor discharging) which would hopefully increase the force that the projectile would experience. This is the design that I came up with. For coil power, it uses a DC power supply constructed from a VARIAC (variable voltage transformer) whose output was then rectified and fed through a large capacitor to take out some of the ripple. So I ended up with a 0-150 Volt DC power supply for the coil  power. I used a break-beam optic sensor so the transistor would conduct the entire time the beam was broken and then stop conducting when the beam had been restored. Here is the system I ended up with transistor driven. But I could never get as much acceleration out of the transistor drivers as a simple capacitor/scr system. I think that I co uld just not get enough juice through the coil operating at only 150 Volts maximum??? Electronic Trigger Circuit If you have more than one coil, the trigger circuit and timing is the most important part of  this project. If the timing is off, you could end up stopping or even shooting your   projectile backwards! I have always used optical triggers so my knowledge on other  trigger systems is essentially zero (Sorry!). But I do have a bunch of stuff on optical triggers. With optics you have a couple of options. You can have your SCR fire when the  beam is broken, when it is restored, or fired at a variable amount o f time after the beam is  broken or restored. Here are some diagrams of optical triggering circuitry. Here is a circuit that manually discharges the first capacitor, switches the SCR's as the beam is  broken, and also a circuit to determine the projectile's velocity (more about this later). Here is another one that fires the SCR when the beam has been restored (after the  projectile passes through). The X-Gun utilizes a modified restored beam circuit which works very well. But don't forget the BYPASS DIODE! Bypass Diode In order to protect your switching units (SCR's) from over voltage cau sed by your coils, a  bypass diode MUST MUST MUST be installed. This diode is placed in parallel with your coil. The polarity is biased so that the main capacitor current cannot pass through the diode, but the "after current" created by the coil can dissipate itself. here is the correct  polarity diagram. Helping dissipate the current as fast as possible also allows the  projectile to exit the coil with maximum velocity so several bypass diodes are commonly used in coil gun projects. Projectile Velocity Determination Measuring the projectile velocity is very important when you want to brag quantitatively to your friends, but is not an easy thing to do! I once tried to shoot it straight ahead and tried to measure its trajectory and back out the velocity from kinetic motion equations. This did not work, as it was very difficult to get accurate measurements. Another method of determining the velocity is electronically. I don't have any fancy expensive equipment so I made this device that I can use to time the projectile through the barrel of my coil gun. The circuit diagram is above in the trigger circuit section. It works like this: I used

another optic sensor and some transistors to charge a capacitor. As the beam was broken with the projectile, the transistors allowed a moderate current from a battery to charge up a 410 uF capacitor. The voltage across the capacitor is proportional to the charge time which is inversely proportional to the velocity of the projectile. In order to calibrate this circuit (don't trust the equations) I set up another identical barrel that is mounted vertically. I dropped the same projectile I use for the gun down the barrel at different starting heights and measured the initial and final voltage across the capacitor. I then used gravitational kinetic equations to determine the co rrect velocity for the different heights. Then the data were plotted with a logarithmic fit. Anyhow, for the projectile that I wa s using, the velocity is approximately 21/ln(v/vo) meters per second. High Speed Event Timer/Counter  In order to more accurately measure the projectile velocity I've opted to make a high speed event timer. The circuit diagram and explanation can be found here. This timer  displays how long the projectile blocks a beam/photo detector. The velocity the projectile is traveling at is simply the length of the projectile divided by the time it blocks the beam. DISCLAIMER  The author assumes no liability for any incidental, con sequential or other liability from the use of this information. All risks and damages, incidental or otherwise, arising from the use or misuse of the information contained herein are entirely the responsibility of the user, have a nice day! Last updated: 6/28/02 Copyright 2002, Greg Miller  http://www.angelfire.com/80s/sixmhz/coolstuff2.html