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Rail Guns – the stuff of science fiction writers for more than a century (Jules Verne, for example) – are rapidly becoming the stuff of science fact! Whether catapaulting aircraft off the deck of a carrier without steam, propelling a projectile with such force that it does huge damage without any explosive warhead . . . or even launching satellites without rockets (still in the future – or is it?), electromagnetic force is changing conventional wisdom even as we speak! Rail Guns and Electromagnetic Launchers By Dr David Maddison T here is a surprisingly long history behind electromagnetic launchers, going back to the mid-19th century. In 1844, a Mr Benningfield (first name unknown) invented an electric gun called the SIVA or Destroyer but little is known of what became of it as there was no further mention of it after 1844. An advertisement for a demonstration of the device said “Officers consider that this invention will, in great measure, supersede Gunpowder, and say that it is very much more to be feared than any Engine of War in use. The balls were projected in a continuous stream at a rate of more than 2,000 per minute, each ball having force 14 Silicon Chip enough to kill at a greater distance than a mile with certain aim, and continue from year to year at a cost far less than gunpowder, although with more force.”. In 1845, in The American Journal of Science and Arts, October edition (page 132), Charles G. Page described a “magnetic gun” in which “Four or more helices arranged successively, constitute the barrel of the gun, which is mounted with a stock and breech. The bar slides freely through the helices, and by means of a wire attached at the end towards the breech of the gun, it makes and breaks the connexion with the several helices in succession, and acquires such velocity from the action of the four helices as Celebrating 30 Years siliconchip.com.au Benningfield’s electric gun from an advertisement of 1844. Although little is known of it, the claims made certainly seem ambitious. to be projected to the distance of forty or fifty feet.” In 1901, Norwegian Kristian Birkeland is credited with having invented the coil gun. A magnetised iron projectile was pulled through a series of solenoids, with a system to disengage power to the coils as the projectile passed through them. A later version used a coil instead of an iron projectile and a novel method of switching in which the inductance of the projectile coil was matched to the drive coils so that the back-EMF of the drive coil matched the voltage of the projectile coil so that switching would occur at zero current. However, there seems to be a similarity with this invention and the 1845 one mentioned above. The results were disappointing though, as a velocity of only 100 metres per second was reached with a 10kg projectile fired from a 4m long cannon; much less than the predicted 600 metres per second. Nevertheless, a projectile range of 1km was achieved. A major problem was be- At left is the drawing from Kristian Birkeland’s 1904 US patent entitled “Electromagnetic gun”. Figure 1 shows the cross section of the barrel illustrated in an unusual downward pointing orientation and the coils in cross section. Note the projectile contained within the barrel. Full patent document at siliconchip.com.au/link/aag6 Below is Birkeland’s Electromagnetic (Coil) Gun. siliconchip.com.au From the Earth to the Moon, an 1865 novel by Jules Verne, tells the story of the Baltimore Gun Club (a society of weapons enthusiasts) and their attempts to build an enormous ‘‘space gun’’ to launch three people in a projectile with the goal of landing on the moon. Given the date and the lack of scientific knowledge, some of Jules Verne’s assumptions and calculations are surprisingly close to reality. ing able to supply enough power to the device. The above mentioned devices were based on solenoids but the rail gun we know today was invented by Frenchman Louis Octave Fauchon-Villeplee in 1916 who called it an electric cannon. Its power source was batteries. His initial working model had a two-metre-long barrel and was intended to accelerate a 50g, 270mm projectile to 200 metres per second, for which a required current of 5000A at 40-50V was calculated. In experiments a current of 600A was achieved which could drive a projectile through 80mm of wood at 25m, the limitation apparently being generating the large currents required. The work was abandoned after World War 1. In 1920, Fauchon-Villeplee described a rail gun designed to propel a 100kg projectile at a muzzle velocity of 1600 metres per second, over a distance of 120km. The instantaneous power developed in the barrel would be 3.4GW at an average current of 3.55 million amps. The gun assembly with generators was to be mounted on railway bogies and would have weighed 1000 tonnes. The power was to be produced by a homopolar generator and was designed to fire one shot every 20 minutes, consuming 60kg of petrol. The gun was not built due to lack of funding. The June 1932 issue of “Modern Mechanics and Inventions” magazine mentioned two scientists whose work in generating pulsed ultra-strong magnetic fields was seen as the basis of an “electric cannon”. One was P.L. Kapitza (a Nobel Prize winner) of Cavendish Laboratory, Cambridge University and the other was T.F. Wall. It is not known where this work went in respect of a gun but a dramatic image of the hypothesised gun was produced for the magazine. In 1933, a Texan by the name of Virgil Rigsby invented a coil gun intended to be used as a “silent machine gun” but the military had no interest in it. It was patented in 1934. The first plans to actually use a rail gun for military service came from Joachim Hänsler in 1944, from Germany’s Ordnance Office. Theory was developed and a device was built using batteries as the power source but it was never employed. The device was able to propel a 10g mass to 1000 metres per second. This was a good speed but not much better than could be developed with chemical propellants at the time. Further rail gun developments came from General Electric in the USA, accelerating a 45g projectile to 550 metres per second in 1957; R.L. Chapman, D.E. Harms Celebrating 30 Years December 2017  15 Virgil Rigsby with what we would know as a coil gun today. It used 17 coils and a timing mechanism, similar to that used on car ignition systems at the time, was used to sequentially activate the coils. This picture is from November 1936 Popular Science, but there was also an earlier version that appeared in the June 1933 Popular Mechanics. “Modern Mechanics and Inventions” magazine from June 1932 showing a proposed “electric cannon”. and G.P. Sorenson accelerating 210mg to 9.5km/s in 1963 and D.E. Brast and D.R. Sawle accelerating 30mg to 6km/s (21,600km/h!) in 1964. The Australian contribution In 1970, J.S. Adams, at what was then the Defence Standards Laboratory in Melbourne, accelerated a 300mg projectile to 3km/s. The first large-scale rail gun in the world was built by John P. Barber at the Australian National University in the early 1970s and one experiment accelerated a 3g projectile to 5.9 km/s. Its power source was a homopolar generator facility designed by Sir Mark Oliphant. The homopolar generator (see box) could deliver 500MJ of energy with current pulses of up to 1.6 million amps. A variety of rail guns were built with bore sizes from a few millimetres to 20mm, with lengths from under a metre to several metres and input currents of up to 400,000A. The success of the Australian work led other major organisations around the world such as the US Defense Advanced Projects Agency (DARPA) to establish advanced rail gun research programs in the latter half of the 1970s. Another Australian rail gun was at what was then known as the Materials Research Laboratory of the Department of Defence at Maribyrnong in Victoria (an institution where the Author used to work). The research program was general in scope and was about studying the science of these devices with launch velocities up to 10km/s and input energies of up to 500kJ or more. Unfortunately, the rail gun seems to be another area in which Australia was once a world leader in a technology that was not pursued. Advantages and disadvantages of electromagnetic launchers Rail guns and coil guns have the advantage of greater What is a homopolar generator? A homopolar generator is a now uncommon type of DC electrical generator which uses a rotating disc in a perpendicular magnet field to generate a potential difference between the centre of the disc and its rim. The homopolar generator used at ANU to power the railgun had the disc in the form of a heavy flywheel that could store enormous amounts of energy which could be quickly discharged in the form of a current pulse into the railgun or other experiments it was connected to. For details of the homopolar generator used in ANU, readers are referred to “The Big Machine” at siliconchip.com.au/link/aag7 The generator was in use from 1962 until 1985 after which it was dismantled. This author is privileged to have seen this device. Image credit: Australian National University: University Photographs, ANUA 226-895-2 16 Silicon Chip Celebrating 30 Years Mark Oliphant (in lab coat) demonstrates the homopolar generator to the GovernorGeneral, Sir William Slim, October 1954. siliconchip.com.au Just what is a Rail Gun? A rail gun comprises two parallel electrically conductive rails bridged by a conductor connected together by a moveable armature. A DC current is applied to the rails and flows through the armature and the resulting magnetic field causes acceleration of the armature, which is also either the projectile or pushes on one, down the rail and out of the device. Often the armature has to be given a start by compressed gas, for example, as if the current is applied when it is stationary it might become welded to the rails. A plasma, which is electrically conductive, can also be used as the armature in some implementations of the rail gun. The Lorenz force drives the armature along the rails. In any inductive loop, which is essentially what the rails and armature are, the Lorenz force acts to push the components apart via opposing magnetic fields. If one part of the inductor is free to move, in this case the armature, it will be driven along the rails in a direction determined by the polarity of the power. If the current is high enough with a fast enough rise time, it can be ejected at great velocity. The US Navy has advanced rail guns under development although deployment seems to be considerably delayed. Two contractors are involved in development, BAE Systems and General Atomics Electromagnetic Systems (GA-EMS). The Navy’s short term goal is a weapon in the 20MJ to 32MJ range that can shoot a projectile 50 to 100 nautical miles with a repetition rate of at least ten rounds per minute. The amount of energy represented by 32MJ is the same as 4.8kg of C4 military explosive. It is also about the amount of energy behind a 10.5kg projectile with a velocity of Mach 7 (8644 km/h) although much less than that, maybe 50%, will be delivered to the target. By way of comparison, a tank’s 120mm gun can generate 9MJ of energy at the muzzle and a cruise missile like the Tomahawk can deliver 3000MJ of destructive power to a target from 450kg of explosive. While some weapons might be more destructive with the amount of energy delivered to a target, rail gun projectiles are Driving Current Magnetic Field Projectile (Above): railgun schematic showing how opposing magnetic forces are established when a current flows, forcing out the projectile. You can demonstrate this effect at home as explained in the link in the text box. (Right): simulation of magnetic field lines in a railgun at a certain instant in time with the electrical potential on the rails shown as different colours. siliconchip.com.au very fast in comparison to conventional weapons, are cheaper and can be launched in greater numbers with a fully developed operational system. An important consideration limiting the employment of shipmounted rail guns is the amount of electrical power required. The Zumwalt-class destroyers of the US Navy are the only non-nuclear vessels that have sufficient spare power available for a rail gun. A rail gun capable of propelling a projectile to the desired range would required 25MW of available power to charge a capacitor bank or other pulsed power system. The Zumwalt destroyer can produce 78MW while a typical naval vessel only has 9MW spare. Existing vessels would have to be fitted with extra power systems if rail guns were to be retro-fitted. GA-EMS has three rail guns under development. The 3MJ Blitzer, the 10MJ medium range multi-mission rail gun system and the 32MJ Advanced Containment system. A live action video of the Blitzer rail gun in operation can be seen at “Blitzer AUSA 2016 ” siliconchip. com.au/link/aah3 In August this year (2017) it was announced that GA-EMS had completed final assembly and factory acceptance testing of a 10MJ (megajoule) medium range multi-mission rail gun system in preparation for transport to a proving ground in Utah. This weapon is a third generation design with a fifth generation pulsed power system. It is designed for a fairly small footprint on ship and mobile platforms. The system was previously tested with projectiles accelerated at 30,000g and the projectiles had two-way communication with the ground station. In the current phase of development of this rail gun there is a focus on the gun’s fire repetition rate. Another version of the rail gun is one in which a plasma (hot electrically conductive gas stripped of its outer electrons) is fired rather than a solid projectile. HyperV Technologies Corp. has developed some of these devices. The plasma rail gun is not designed to operate in air but in a vacuum or near vacuum. It is intended to be used in various types of nuclear fusion reactor projects, laboratory astrophysics experiments and in thrusters for spacecraft. Projectile Current Force Rail BAE Systems prototype railgun on display on the USS Millinocket. A GA-EMS railgun was on display at the same time. Note these were on static display only and not installed on the ship and no testing has yet been done at sea, though it had been planned to do so by now. BAE Systems 32 MJ railgun at the Naval Surface Warfare Center in Dahlgren, Virginia, USA. You can watch it in action at “Electromagnetic Railgun - First shot at Dahlgren’s new Terminal Range” siliconchip.com.au/ link/aah4 Celebrating 30 Years December 2017  17 A concept from General Atomics about how a railgun might be used as a battlefield weapon. In direct fire mode a projectile can reach the horizon in six seconds, in indirect fire mode the projectile is launched into space and can reach a land target 370km away in six minutes. safety for their users, since no potentially hazardous propellants and explosives are needed, which simplifies the supply chain and strict storage and handling requirements. Much higher projectile velocities can also be achieved compared with conventional guns. This leads to great destructive power by kinetic energy alone although some proposed projectile designs have terminal guidance and even small explosive charges. Another advantage of rail guns in military applications is the relatively low cost of the projectiles compared with a guided missile. But a significant disadvantage of all launcher designs is the requirement for large generators and pulsed power supplies. The mass driver can theoretically achieve high enough velocities for launching materials from Earth to space or from objects in space where electricity may be the only power source, eg, from solar panels and where no chemical fuels are available. Note that by using chemical propellant guns of a very special design it is also possible to launch materials into space from Earth. Google “Project HARP”, which stands for Super High Altitude Research Project, [siliconchip.com.au/link/aah6]. By the way, this is quite different to, and should not be confused with, the now-defunct HAARP project (HAARP: Researching The Ionosphere), featured in a 2012 SILICON CHIP article (siliconchip.com.au/Article/492). Also see the Jules Verne Launcher [siliconchip.com.au/link/aah5]. 18 Silicon Chip The coil gun A coil gun, also known as a Gauss rifle, uses one or more coils mounted on a common axis to accelerate a projectile down the central axis of the coil assembly. It is important that when multiple coils are used that there is a proper sequential activation and deactivation of adjacent coils or the projectile will become trapped. If one coil is used the projectile must be inserted at the proper location within the coil body. (Imagine a magnetic object put into the central axis of an electrically-energised coil, it would simply oscillate back and forth under normal circumstances.) A rail gun requires a projectile or armature to be in contact with rails but in a coil gun the projectile does not nec- Representation of a coil gun. The projectile has passed through the first set of coils which have been deactivated and is being pulled and accelerated toward the middle coil which has been activated. Having passed through the middle coil, which will then be deactivated, the third coil will be activated and the projectile accelerated toward that. Diagram source: ZeroOne. Celebrating 30 Years siliconchip.com.au A General Atomics Electromagnetic Systems 32MJ Advanced Containment railgun system in test configuration. essarily need rails and can be suspended by the magnetic field, although in some designs the coils runs along a track. Coil guns are much more simple to construct than rail guns due to fewer practical difficulties and are a popular choice among hobbyists. Some links are provided elsewhere on hobby projects. In 1978 a Soviet scientist by the name of V.N. Bondaletov, using a coil gun, achieved a record for acceleration by accelerating a 2-gram ring to 5km/s over a distance of just 1cm. Applications suggested for coil guns including firing projectiles into space, military mortars (one project that was funded by DARPA has projected mortars twice the range of conventional ones) and Electromagnetic Missile Launcher (EMML) for launching Tomahawk cruise missiles. These projects do not currently appear to be under active development. The Chinese are said to be developing an active protection system for tanks based on a coil gun. The mass driver for space launch Electromagnetic launch systems have been proposed as a cheaper method of getting materiel into space since in a conventional rocket launch most of the mass of the Flight Body launch vehicle is the rocket body with relatively little payload. An electromagnetic launcher leaves the launcher device on the ground ensuring that most of the flight body is payload. Electromagnetic launchers have been proposed to launch materials A concept for an electromagnetic launcher to launch payloads into space from the side of a mountain. Image source, Ian R. McNab, 2003. siliconchip.com.au from the Earth, Moon and other bodies such as asteroids. In the case of a launch from Earth there is a significant problem of high velocities required to launch objects into orbit of greater than 7500 metres per second. This means long launch tubes, high energies, high acceleration of 1000G or more and aerodynamic heating of the flight body. The high acceleration means that only robust payloads such as water, solid metals, fuels and other items that can easily sustain a high acceleration without damage can be utilised. Certainly, humans are out of the question for launch by this method. The high velocity also requires some sort of cooling system and heat shield attached to the flight body. For launches from the Moon and asteroids of mined raw or refined materials the low gravity and lack of an atmosphere means that lower accelerations can be used and aerodynamic heating of the flight body is not an issue. There have been several concepts of using a mass driver for space launch. Mass Driver 1 was an early constructed prototype mass Evacuated Launch Tube Containing Railgun Accelerator ~10MWe power plant to provide launch power High (2-3km) mountain on or near the Equator Celebrating 30 Years December 2017  19 ACCELERATION TUBE LAUNCH EGRESS TUBE HATCH PLASMA EMPTY SLED WINDOW PROJECTILE Y-AXIS Z-AXIS (VERTICAL) X-AXIS PROJECTILE MAGLEV SLED Launch ring concept. This has an underground accelerator ring and an above ground launch ramp. driver designed to launch materials from the lunar surface to the fifth Lagrange point. This is an area of stable orbit between the Earth and moon where it has been proposed to build space colonies and where objects will remain in place without station keeping. The device was built by students at the Massachusetts Institute of Technology in 1976/77 for around $2000. It had 20 drive coils, a “bucket” (armature) in which the payload was contained and four copper tubes through which the drive current, supplied by car batteries, was carried. The bucket was electrically connected by brushes to the rails and a microswitch was activated as the bucket passed each coil causing the energising of the appropriate coils in sequence via capacitor discharges which propelled the bucket via the Lorenz force. An acceleration of up to 33g could be achieved. There is also a 2006 concept from LaunchPoint Technologies who developed the Launch Ring concept. This design comprises a circular evacuated ring with a linear motor and a sled containing the launch vehicle held without contact with the ring by magnetic levitation. This is accelerated around the ring multiple times until it has reached a velocity of 9000 metres per second at which point it is diverted to a ramp built up a hill or mountain which is located at a tangent to the acceleration ring. It was estimated that the launch vehicle would reach the required velocity in about one hour. Multiple sleds could be maintained within the ring allowing multiple launches in sequence. The egress window would have a plasma window at the exit point to prevent air entering into the evacuated system. Conceptual designs were created for both superconducting and non-superconducting systems. A later more cost effective concept was also developed but details have not been released. See siliconchip.com.au/link/aah7 LaunchPoint Technologies Launch Ring. The launch tube would be built up the side of a mountain while the acceleration tube would be buried in the ground. higher maintenance and shorter service life; the inability to launch light aircraft such as drones and a high thermal signature and energy requirement due to the large amount of steam that has to be produced for a single launch – a typical figure is about 600kg. These systems are also very heavy and take a lot of space in the ship. EMALS uses a linear induction motor to propel a carriage attached to the aircraft along the launch track. Linear induction motors are also typically used on magnetic levitation trains and also the tracked train servicing the terminals at the JFK Airport in New York and are a well-established technology. EMALS consists of six main systems comprising: • Prime Power Interface that connects the ship’s power to the energy storage generators; • Launch Motor in the form of a linear induction motor; • Launch Control System to control the current to the Launch Motor in real time; EMALS (ElectroMagnetic Aircraft Launch System) Traditionally, aircraft are launched from aircraft carriers using a steam catapult. These are effective and reliable but have a number of disadvantages, including uneven acceleration leading to excessive forces on air-frames and therefore 20 Silicon Chip EMALS launch motor in land-based experimental installation. Image credit: General Atomics. Celebrating 30 Years siliconchip.com.au “Below deck” view of EMALS equipment. Image credit: General Atomics. EMALS energy storage system in land-based testing. Image credit: General Atomics. • Energy Storage System that provides power to the Launch Motor for two to three seconds during the launch process and is recharged between launches; • Power Conversion System that is a solid state system that converts power from the Energy Storage system to the appropriate voltage and current to drive the shuttle along the Launch Motor and • Energy Distribution System that delivers power from the Power Conversion System to the launch motor via a system of cables and connectors. Like other linear induction motors, EMALS use a row of stator coils along the track. These are energised only in the vicinity of the shuttle as it is propelled down the track to minimise losses. EMALS can launch a 45,000kg aircraft 91m down the length of the track to achieve a launch velocity of 240km/h. A key to the operation of EMALS is an energy storage mechanism. Ship power is used to spin up a series of four disk (flywheel) alternators which are discharged during the launch process. A maximum energy launch will reduce the speed of the rotors from 6400 RPM to 5205 RPM. It takes 45 seconds to recharge which is faster than a steam catapult can recharge. The maximum energy launch represents 136kWh of energy or about the same as four litres of petrol. EMALS offers lower maintenance and staff requirements, lower life-cycle cost, reduced thermal signature, increased capabilities to launch lighter unmanned aircraft and future heavier aircraft and with reduced weight and volume. EMALS also offers flexibility of installation so can also be used on a variety of ship sizes. The United States Navy has an EMALS system operational on the USS Gerald R. Ford (CVN 78) and will next have one operational on the USS John F. Kennedy (CVN 79). Associated with EMALS but a separate system is the Advanced Arresting Gear (AAG) system. This system has only just finished development after many delays but is currently installed on the USS Gerald R. Ford and will When is a “Rail Gun” not a “Rail Gun ” There are various devices which have been called “Rail Guns” over the years which have nothing to do with the electromagnetic devices we are talking about here. We show two of these below. There are the railway-mounted heavy artillery pieces of both world wars. The 800mm German Schwerer Gustav (WWII) is the largest gun ever made and used in combat, and could fire seven tonne shells a distance of 47km. Another type of “rail gun” which you may encounter uses custom-made rifles (using conventional ammunition), designed for competitive shooting where the emphasis is on ultra-high precision. See siliconchip.com.au/link/aah8 Built in 1941, Germany’s Schwerer Gustav (English: Heavy Gustaf) rail-mounted monster. See siliconchip. com.au/link/aah9 Unlimited class railgun for competitive shooting – not to be confused with the electromagnetic variety. Image source: siliconchip.com.au/link/aaha siliconchip.com.au Celebrating 30 Years December 2017  21 Resources “The Big Machine” article about the homopolar generator built by Sir Mark Oliphant at the Australian National University which was used to power the world’s first large scale rail gun: siliconchip.com.au/link/aahb A very nice and clear explanation of the physics of a moving bar in a magnetic field which is relevant to the rail gun can be seen at “Electromagnetic Induction: Induced EMF in a Moving Bar in a Magnetic Field” siliconchip.com.au/link/aahc Another video explaining the physics is “Rail Gun example” siliconchip.com.au/link/aahd and “U.S. Military’s Most Powerful Cannon - Electromagnetic rail gun - Shoots 100 miles - Mach 7” siliconchip.com.au/link/aahe Advanced Arresting Gear, below deck view be installed in other carriers of that class such as the USS John F. Kennedy. Energy is absorbed via water turbines and induction motors. Videos to watch: “Fighter Lands on Next Generation Carrier USS Gerald R. Ford for the First Time” siliconchip.com.au/link/aahg and “USNI News Video: Sailors Describe First Fighter Landing, Launch on USS Gerald R. Ford” siliconchip.com. au/link/aahf The US Department of Defense has also given the Indian Navy approval to purchase EMALS and AAG. Acknowledgement: The author wishes to acknowledge the assistance of Andrew Krelle in locating some of the source documents. The rail gun in the Australian Parliament Rail guns have been mentioned nine times in the Federal Parliament from 1984 to 1988. This was mainly in connection to the one that was under development by the then Defence Science and Technology Organisation’s Materials Research Laboratory in Maribyrnong, Victoria and in relation to the then Government’s opposition to the Strategic Defense Initiative of the United States (see below). The questions can be seen here: siliconchip.com.au/ link/aahi Geoff Pryor’s 1984 cartoon about then Prime Minister Bob Hawke’s embarrassment when it was disclosed that he had committed Australia to collaboration on the US “Star Wars” program (Strategic Defense Initiative) through the Australian Department of Defence despite his party’s opposition to it. siliconchip.com.au/link/aahh 22 Silicon Chip Celebrating 30 Years siliconchip.com.au Building your own electromagnetic launcher device – some ideas Building some type of electromagnetic launcher is within the scope of an experienced and responsible electronics hobbyist and there are many plans and videos on the Internet showing how to do this. SILICON CHIP presents these URLs for information only. We cannot advise you on the legality of making a high power one in your jurisdiction, particularly in Australia with its many “nanny state” laws so you would need to determine this yourself. One tip: never refer to it as a ‘‘gun’’– rail or otherwise! Nevertheless, here are a few examples from overseas enthusiasts. While they do not have anything like the energy of a traditional firearm, very high energies and voltages are involved in devices of this kind and they can be potentially lethal. A video safely demonstrating the principles of a rail gun using only cardboard, aluminium foil, glue, 9V battery, a piece of steel rod and two magnets followed by instructions on how to build a small rail gun can be viewed at “How To Build a Railgun Experiment” siliconchip.com.au/link/aahj The author has additional details and other interesting projects at siliconchip.com.au/link/aahk Very simple experiment to demonstrate railgun principles using basic materials of cardboard, aluminium foil, glue, 9V battery, a piece of round metal steel rod and two magnets. The magnets may not be needed if a high enough current is used. A variation of this idea is to use model railway track as the two parallel rails as shown in the video “Lorentz Force Experiment using N-Scale Track (240fps)” siliconchip.com.au/link/aahl and a similar experiment without rail track “Fuerzas de Lorentz (corto) / Lorentz forces (short)” siliconchip.com.au/link/aahm David Wirth and his portable railgun. It uses 3D printed components and is controlled by an Arduino. You can read more at siliconchip.com.au/link/aahn A DIY rail gun by Zebralemur siliconchip.com.au/link/aahq is claimed to be the most powerful built by an individual. It uses 56 400v, 6000µF capacitors. Zebralemur’s home made railgun, claimed to be the most powerful built by a non-government entity. An Instructable on building your own rail gun is at siliconchip. com.au/link/aahr This person makes a coil gun and provides an extensive discussion about the electronics involved. “World Fastest Six Stage Coil Gun Yak Questions Answered” siliconchip.com.au/link/aahs Thinkbotics, a company that supplies to robot experimenters have developed the EM-15 coil gun and their website siliconchip. com.au/link/aaht states that plans will be available ‘‘soon’’. The electronics of the coil gun consist of a voltage step-up transformer converter, a Cockcroft-Walton voltage multiplier cascade, a capacitor energy storage bank, a voltage comparator to set the charge voltage on the capacitor bank, an SCR switching section and a single accelerator coil. Construction details were published in the March 2008 edition of Nuts and Volts magazine, see siliconchip.com.au/link/aahu Here is a video of a home made coil gun siliconchip.com.au/ link/aaho You can read more about this project at siliconchip. com.au/link/aahp Thinkbotics EM-15 coil gun. The CG-42 coil gun. Note the eight coils which are sequentially energised to propel the projectile through. siliconchip.com.au A simple mass driver can be built with plans at this link and there is also a video of the device. siliconchip.com.au/link/aahv Finally, here’s a clever launcher contraption made with rare earth magnets, no power required. “Magnet Gun -magnetic launcher” siliconchip.com.au/link/aahw Celebrating 30 Years SC December 2017  23