The Railgun:
For when you need 
that extra bit of firepower...
ALL ONGOING WORK CONCERNING THE RAILGUN PROJECT CAN NOW BE FOUND HERE. THE PAGE BELOW REMAINS TO PROVIDE BACKGROUND.
Amongst others, Sam Barros at Powerlabs.org does some wonderful work which has inspired many to invent, design and engineer fascinating projects of their own. One of the more interesting amateur projects is the linear accelerator, affectionately named the "Rail Gun."
The process of designing, experimenting and tinkering with novel ideas is a testament to humanity's inventive and altruistic spirit. It should always remain as a core pillar of the American spirit. Recently the work of two young men from Colorado Springs came to the attention of us here at Fortscribe. Like Perankhscribe, these individuals love to experiment and have a passion for this interesting form of electromagnetic propulsion. Fortscribe would like to help them in their endeavors as prodigies don't always get the support they deserve. Fortscribe has supplied them with a variety of components needed in the production of a rail gun. As they develop this device, Fortscribe will document the creation step by step so that others can be inspired to learn and create their own projects.
*Please note that the developers of this section wish to contribute their scientific creativity and should not be associated with the political agenda found elsewhere on the site. You may find their own documentation of their work at http://rp181.110mb.com/ Please refrain from attempting to contact them on matters unrelated to the content below. *
JOURNAL OF A RAILGUN DEVELOPER:
BUILD LOG: Click here to go to our ongoing build log that tracks the building of this device as well as offering a more in-depth look at the various aspects components. Otherwise, please read below for more background...
THE CONCEPT WE WILL EXPAND ON
-Animated video showing earlier work that will be expanded on.
WHAT WILL BE CREATED
-With some supplies from Fortscribe and the tireless efforts of the building team - Bigger, badder and a whole lot more firepower. (Or if you have to be technical: over double the capacitance, a large increase in the strength of the magnets and a revamped injector system. Minor tweaks like silver plated rails also add a finer touch.)
A SEND OFF FROM PERANKHSCRIBE
-Perankhscribe introduces the building team and sends them some of the supplies they will need.
BACKGROUND:
Theory:
A railgun works due to electromagnetic fields present around any conductor carrying a current. The magnetic field of an infinitely long wire is given by the Biot-Savart law:
B = µ0*I/2
Where I is current in amperes, and µ0 Is the magnetic constant, 4π × 10−7. The result is plotted below.
The linear relation means that theoretically, in an ideal world, the same efficiency with a 500kJ bank should be possible with a 5kJ bank. This is counteracted by environmental forces, such as friction. The graph also shows large amounts of currents are needed to get a considerable field in a straight wire. When a conductor is looped, the magnetic field inside the coil is stronger, and the outside weaker. A railgun is essentially a 1 turn coil.
The armature in a railgun must be diamagnetic, meaning a material that takes on the same magnetic field that is present. Two similar magnetic fields repel, causing a material, if allowed, to move. In this case, the armature is a sliding contact. As the armature is “pushed” down the rails, the current continues to “follow” the projectile, constantly repelling the armature, a long as there is a current.
Obstacles
Circuit values
In order to get even a rough estimate of what is involved, some circuit parameters need to be obtained. The main factors determining the force on the projectile are circuit resistance, and circuit inductance. With these, RLC calculations can be made, and the circuit roughly modeled.
Rail calculations:
Resistance: 8.71124*10-5 ohms per rail
Inductance:0.465168993 nh
Rail resistance:
R=C*L/S
Where R is resistance, C is resistively of copper by volume, L is length, and S is the cross section of the rails.
C=1.7241*10-8 ohms/m
L=.3048m
S=0.000060325 m2
Rail inductance:
Lt=L*2+Lm
Where L(t) is total inductance, L is single rail inductance, and Lm is mutual inductance.
L=0.23258362 nh
Lm =1.75253E-06
L=P*D/(2п)*(ln(2*D/(W+H))+.5+(.447*(W+H)/2*D))*105
Where L is the inductance of a single rail, P is the permittivity of free space, D is the rail length, W is the rail width, and H is the rail height.
P=1.25664E-06
D=0.3048 m
W=0.0254 m
H=0.003175 m
Lm=(P*D/2*п)*(ln(2*D/S)-1+S/D)
Where Lm is the mutual inductance and S is the rail separation.
S=0.0127 m
Capacitor bank calculations:
40x 400v 3900uf capacitors.
Estimated ESR (datasheet value): .040 ohms
Parallel ESR: .001 ohms
ESL: unknown
Bus:
Length: 28”
Width: 2”
Thickness: .5”
Resistance (same method as above) (anode) .0000310866 ohms
(cathode) .0000828976 ohms x2
Inductance: 1.0289759nh
Interconnects:
2x 00 AWG cable 2 feet long each
1000’ 00 AWG resistance: 0.07793 ohms
Total cable resistance: 0.00031172 ohms
Estimated cable inductance: 1.146586374 nh
Totals:
Resistance: 0.0015999502 ohms
Estimated resistance with projectile: .00351972
Inductance: 2.4399759 nh
Resonant frequency: 0.126475039 hertz
1/(2pi*sqrt(LC))
HIGHLIGHTS OF THE PROJECT:
For a device that creates propulsion through electromagnetic fields, it should not surprise one that when designing the circuitry to power and regulate a railgun, much finesse is needed. In order to achieve optimal results however, equal, if not greater care must be given to the mechanical design of the rail gun. Before we delve into the more intricate aspects of this design, we would like to start by discussing some of the challenges that will need to be overcome.
The most common and difficult to remedy problem is the rail repulsive force. As students of physics should be aware, two currents running along an anti-parallel path will exert a repulsive force upon one another.
Fig 1) In this illustration, the light green arrows depict current flow, the blue the magnetic field, and green the force. The grey block is the armature, and the brown are the rails. Notice that the anti-parallel current flow creates a repulsive force between the rails.
While large currents are necessary to generate a substantial propulsive force, as larger currents are generated, the increasing repulsive strength threatens to rip the rails apart. Therefore any successful rail gun design must support these high loads. This is done in several ways. First, we use some extremely durable and resistant materials like garolite. Secondly, we orient the rails perpendicular to the support bolts. As the rails repulse one another, these bolts help support the load.
This is enough, as long as solid armatures are used. As this is a research prototype, plasma and hybrid armatures will be tried, so the enclosure must support those loads too. If the rails are held perpendicular, this leaves the side walls to take the plasma pressures; a design is needed to take both of these forces. Two possible designs were evaluated.
The first design utilized wedged shaped pieces, to transfer the load, and hold the pieces locked in place. This design has the advantage of minimal flex, with direct transfer of energy. Disadvantages include excessive waste to machine, and excessive copper that will not be used.