More on Electromagnetic Pulsed Guns & Launchers

Some basic info on coilguns and other EMP launchers:

There are 2 basic types, distinguished by the force they use to accelerate a projectile. Reluctance and Induction. Reluctance-based designs utilize the attractive force between an energized coil and a ferromagnetic slug. Induction-based designs used induced eddy currents in the projectile that repel the magnetic field in the coil. They both have advantages and disadvantages. As of yet, I have only built inductive type launchers and believe more velocity can be had with this design.

Until I get up some more info a great place to go detailing the differences between coilgun type is http://www.coilgun.eclipse.co.uk/coilgun_basics_3.html (be sure to use the arrows at the bottom for more info).

Some other great places to go about coilguns are FastMHz.com and Magnetic Gun Club

Here are some 3D pics and animations I have created about coilguns. Although designs can be very similar, these were modeled after reluctance-based design.

	A 3d model of a simple 4 stage gun. All stages are the same. This design is sometimes used with IGBT (or similar) controlled switches to vary the pulse length.
	Varying size coils on this design helps shorten the pulse length as the projectile passes through each coil at a greater speed. This is necessary on designs that cannot control the pulse length by switching or by capacitor size alone.
	Here is a partial cut-away view of a single stage of a coilgun. The projectile and LED (for optical triggering) are visible.
	The same model as above, but this also includes a simple magazine for the shells and a bolt style action.
	Movie clip of this model - partial fly around with working action showing the gun loading and firing. AVI file 10 seconds long, 2.5MB

Here is some info I am compiling on the pros and cons of the 2 main types of coilguns. The list is not complete yet, nor is my knowledge on either...

Since most of my work has been with the inductive type I will go into more detail on the pro's for that design.

Inductive coilguns primarily fire aluminum projectiles because: need to be a good conductor as your trying to induce current in it just like a transformer, needs to be non-ferromagnetic, and aluminum is very light weight so you can attain much higher velocities. Reluctance guns need ferromagnetic projectiles which are usually steel, which is very heavy compared to aluminum. Also eddy currents are a problem unless an effort is made to reduce them by methods such as slotting, but ultimately there will still be some losses. The same is true for a barrel if it is conductive. Pulse control is much more critical on reluctance guns because the EM field must not be present once the projectile reaches the center of the coil or it will experience 'suckback' as it tries to leave the other side. Since inductive type guns start at the center or further, and are repelled, the pulse length isn't nearly as critical as you have a maximum repulsion typically at its starting point and there should never be any suckback. Only a possible loss of efficiency would result from too long a pulse length. Another neat feature of an induction launcher that uses a flat 'pancake' style coil (or similar) is that you can put on any size or shape projectile, so long as it has an aluminum (or similar) base that is up against the launching coil. I have launched hard drive disk platters, copper rings, brass gaskets, and soda cans all from the same launcher... you dont have very much flexibility like this with a reluctance gun.

Thats it for know! I hope to get more stuff up here for everyone!

This webpage originally born on 2-27-02. Last updated on 7-16-06