Project on Emp

Topics: Capacitor, Magnetic field, Coilgun Pages: 34 (9076 words) Published: December 4, 2012
Electromotive Force Projectile Accelerator Proposal

Why build an Electromotive Force Projectile Accelerator (EFPA)? Electromotive Force Projectile Accelerators have the ability to accelerate without using any sort of propellant. In addition, EFPA’s can be built with no moving parts, an attribute that makes them highly reliable and silent instruments. The basic EFPA uses a voltage source and a combination of circuitry to accelerate an object to a desired speed. This is what makes EFPA a fairly unique device. An Electromotive Force Projectile Accelerator demonstrates many of basic concepts of magnetic machines. An EFPA is an example of an electromagnetic coil/solenoid. Such appear practically everywhere, from car door locks to doorbells and from diskette drive ejectors to fuel injectors. The only difference is that most solenoids limit the range of travel, and usually have a spring return. An EFPA is also an example of a simple linear motor. What is the overall scope of work required for this project?

The basic theory of operation is as follows: voltage is applied to a coil (usually it is a multi layered coil), the current ramps up and a magnetic field is established in the coil. Once this magnetic field is established the projectile, which is made up of ferromagnetic (iron) material magnetizes and experiences a force towards the center of the electromagnetic coil (solenoid). A large current is forced through the coil, creating a magnetic field and attracting the ferromagnetic projectile. Capacitors are charged up over a few seconds, and then all of their electrical energy is released extremely fast. In an EFPA the energy is released into a coil of wire. This creates a powerful magnetic field which causes any ferromagnetic object in the coil to accelerate. When the projectile passes through the coil, the current is switched off and most of the magnetic field collapses, allowing the projectile to keep moving. Since the coil is wrapped around a thin wall of plastic tubing and the iron projectile is inside the tube, it will accelerate along the tube towards the end coil. As all the energy from the capacitors will be released in a matter of milliseconds, the coil should ideally be turned off by the time the projectile passes its center and exits the other side of the coil. If the current is collapsed properly the projectile will hold a resultant velocity and will exit the coil with a specific amount kinetic energy.

What obstacles and risks will this project face?
Ideally, 100% of the magnetic flux generated by the coil would be delivered to and used on the projectile, but this is often far from what actually happens due to the common air-core-solenoid / projectile construction. Since an air-cored solenoid is simply an inductor, the majority of the magnetic flux is not coupled into the projectile, being stored instead in the surrounding air and tube. The energy that is stored in this field does not simply disappear from the magnetic circuitry once the capacitor finishes discharging and much of it returns to the capacitor while the circuit's current is decreasing. As the EFPA circuit is inherently analogous to an LC oscillator, it does this in the reverse direction, which can seriously damage polarized capacitors such as electrolytic ones, which are substantially cheaper and smaller for a specific capacity compared to other types.

Relatively simple designs made by hobbyists have a low efficiency output. EFPA’s are remarkably inefficient. Many designs are doing well if they have 1 or 2 percent of the energy in the capacitors converted into kinetic energy of the projectile. Some of the energy is lost because the projectile is first pulled into the coil, and then if the magnetic field has not collapsed before passing through the center of the coil, it will be pulled back into the coil, slowing the projectile down. The way we can resolve this is to shorten the pulse, which can be done in two ways: ■ Use fewer...
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