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How to build railguns and coilguns, continued ...
   How Electromagnetic Guns Work

Anyone who has played with magnets knows they have two poles, north and south. Opposite poles pull toward each other, while like poles each other push away. These forces of push and pull drive all electric motors, including electromagnetic guns. Furthermore, all electric motors use electromagnets, which use electricity to turn on and off their magnetism.

Newbie Note on Magnets --->>

The idea behind electromagnetic guns is deceptively simple. Depending upon the type of gun, magnetic fields may push it out a barrel, pull it out, or combine push and pull. One type, the coil gun, also uses electromagnets to levitate a projectile above a track, the same way Maglev trains levitate.

There are two main kinds of electromagnetic guns: railguns and coilguns.

How Railguns Work

A railgun’s barrel consists of a pair of parallel conducting rails. Inside this barrel (which is mostly open to the air), a movable armature is wedged between the rails. To fire the railgun, you place a projectile resting on the front of the armature. Next a pulsed power supply (for example, a charged capacitor bank or homopolar generator) applies DC current to one rail at the beginning of the barrel. This current travels up the rail to the armature, across the armature, and down the other parallel rail. This completes the circuit, which fills the gun’s barrel with a magnetic field contained (so we hope) behind the armature. The pressure of this field, (the Lorentz force), makes the circuit expand. This expansion shoots the armature out of the barrel.

The projectile of the fastest railgun ever tested achieved 5.9 km/sec (21,000 km per hour or 12,700 miles per hour). By contrast, even the most powerful conventional cannon is only able to fire projectiles at 1.5 km/sec (5,400 km per hour or 3,400 miles per hour). Even one of the world’s most powerful rifles, the M16A2 semiautomatic, fires bullets at a mere 3,000 km per hour (1,840 miles per hour).

Railgun technical challenges --->>

How Coilguns Work

The coilgun is based on electromagnets and is a form of a linear induction motor.  In this sort of electrical motor, current flowing through a wire creates a magnetic field and this causes something to move.

The barrel of a coilgun consists of one or more electromagnet coils. Inside the barrel is a bucket with its own electromagnet coils that react to the coils in the barrel. Unlike the armature of the railgun, which conducts current from one side of the barrel to the other, the coilgun bucket only touches the barrel enough to draw a the current to keep its own coils powered as it flies out the barrel. The barrel’s coils are powered on and off depending upon where the bucket is as it flies. Each coil creates its own magnetic field. The fields between the barrel and bucket either push or pull the bucket to the next coil, depending upon the gun’s design. But timing is everything: if the projectile reaches a coil when it’s turning on, it speeds up. If the coil is turning off, it slows down. If the coil energizes too soon or too late, it slows the projectile instead of accelerating it.

So far, coilguns have been way slower than railguns. Despite this, researchers at places like Sandia National Laboratories in Albuquerque, NM continue to work on them. Big advantages of coilguns are that they can fire large projectiles quietly and without a muzzle flash. If your objective is to pound your enemies with a mortar, it’s a good idea to make it hard for them to figure out where to shoot back at you, so a coilgun mortar could come in handy.

Also, a coilgun can be built to be really long, even hundreds or thousands of km long. The advantage of a long coilgun is that it could slowly speed up its payload, for example people who want to fly into space. There already is a passenger system in commercial operation today that is basically a coilgun. I'm talking about the Shanghai Transrapid maglev train, which carries passengers between Pudong Airport and downtown Shanghai. The Transrapid in Shanghai has a design speed of over 500 km/h (310 mph) and a regular service speed of 430 km/h (267 mph).

Maglev train

Coilgun Technical Challenges --->>

The seeming simplicity of these guns is why a lot of very intelligent people have flubbed building hypervelocity versions of them. How frustrating that even little kids can build slow versions of railguns, and a coilgun-based Maglev train carries people every day in Shanghai -- yet getting to truly awesome hypervelocities is really, really hard. The failures of people who dreamed of building hypervelocity systems had nothing to do with their intelligence and knowledge. Their failures were caused – in my humble opinion – by the fact that the materials we have to build electromagnetic guns don't make it easy. In a little bit you’ll see what I mean.

More --->>


       © 2013 Carolyn Meinel