1. Rail gun and Coil gun
Complete explanation of the pure electrically driven and electrically controlled weapons.
Presentation by
Salil Tembe

2. Contents of part 1 What are rail guns?
How can I propel a projectile using ONLY electrical current?
How far does the projectile travel?
How much impact is possible with such a weapon?
What should I do if I want to make one myself?

3. What is a Rail gun?
A rail gun is entirely electrical weapon which fires a conductive projectile along a pair of identical metal rails. Rail guns use rolling or sliding contact. High current is made to pass through the rails and the projectile. The electromagnetic force produced is so strong that the projectile is driven right through the two rails.

4. How to propel a projectile using only electric current?!
As seen earlier, the rail gun has two rails parallel to each other. The projectile is conductive and it is in contact with the two rails all the time until it leaves the end of the rails. Extremely high current flows through the projectile creating an enormous amount of force. This force drives the projectile out towards the trajectory.

5. How much force?
The force generated by the rail gun is so high that you can see plasma explosion behind it!
The explosion is caused because of intense electric current, friction between the rails and the projectile.
Video link:

6. Lets do some calculations
The magnitude of the force vector can be determined from a form of Biot-Savart law and a result of Lorentz force. Considering the distance between the rails as d, the permeability constant as µo, the radius of the rails (considering the rails are circular in cross section) r and the current flowing through the rails I. From the Biot-Savart law it can shown that the magnetic field from distance s from a semi-infinite current-carrying wire is : 𝐵 𝑠 = µ 0 𝐼 4𝜋𝑠 ∅ The magnetic field between two rails when distance is s, equation is as follows: 𝐵 𝑠 = µ 0 𝐼 4𝜋𝑠 1 𝑠 + 1 𝑑−𝑠

7. Average magnetic field along the length of the rails
𝐵 𝑎𝑣𝑔 = 1 𝑑 𝑟 𝑑−𝑟 ( 𝐵(𝑠))= 𝐵 𝑎𝑣𝑔 = 1 𝑑 𝑟 𝑑−𝑟 ( 1 𝑠 + 1 𝑑−𝑠 )𝑑𝑠 𝐵 𝑎𝑣𝑔 = µ 0 𝐼 4𝜋𝑑 𝑟 𝑑−𝑟 ( 1 𝑠 + 1 𝑑−𝑠 )𝑑𝑠 = µ 0 𝐼 2𝜋𝑑 log 𝑑+𝑟 𝑟 Therefore by the Lorentz law of force 𝐹=𝐼𝑑 𝐵 𝑎𝑣𝑔 = µ 0 𝐼 2𝜋𝑑 log 𝑑+𝑟 𝑟 Some other assumptions are also done to make the equation more accurate. This applies only to the circular rails, but for practical applications the shape of the rails and the projectile must also be considered.

8. Railguns as weapons
Railguns are used as weapons, but the projectiles used are non- explosive. It is currently possible to propel a projectile at 3500 m/s i.e. ~11500 ft/s i.e. Mach 10 at sea level. For comparison, M16 rifle shoots only at 930m/s or 3050 ft/s. This shows that a projectile shot from a railgun has equal energy as compared to a explosive projectile. Since the projectile is shot at a higher velocity, there is less bullet drop as compared to regular projectiles.

9. Railgun as a weapon The rails need to be clean as new!
Main disadvantage of railgun over regular explosive guns is that, with railgun rapid fire is not possible. After firing several rounds there is massive wearing on the rails. This causes development of resistance to flowing current. Resistance means increased loss of energy, this means loss in efficiency and drop in current. This leads to state when the projectile cannot be fire until the wearing is fixed.
The rails need
to be clean as new!

10. ACCURACY
On 31st january 2008, US Navy tested a railgun which could fire a projectile at approximately 2520m/s and delivering 10.64MJ of energy. It is estimated that a 5800m/s muzzle velocity can hit a 5meter target over 200 nautical miles (~370.4 kilometers) while firing at 10 shots per minute. So much power was provided by 9mega joule prototype capacitor bank and solid state switches constructed out of high-energy-density capacitors.

11. Random mesurements from a normal railgun
The huge spurts of curent surge upto 40 to 50kA in ~7 milliseconds.
The moment capacitor banks are released, extremely high current flows through the rails driving the projectile straight out towards the trajectory.
These graphs are not a manipulation, but an actual result of an experiment.

12. Continued graphs…
Since the resistance of the rails and the capacitance of the capacitor bank remains pretty much constant throughout the experiment, the discharging time is always around 7ms.

13. Coil GUN
Another example of a electrical gun is a coil gun. Having a single low resistance coil, driving the magnetic projectile through the barrel at sufficient speeds. But it is not so powerful as compared to the Railguns.

14. Simple coil gun
A simple coil gun has a low resistance coil wound a non magnetic hollow barrel. The projectile used to shoot is completely magnetic. It must be taken care that the projectile placed right behind the first coil.

15. Understanding the basics
When we apply current from a capacitor bank, having low resistance coil used, there is a huge surge of current. This current is the necessary current for driving the projectile out of the barrel towards the trajectory. Now when we apply high current, we have a region of highest magnetic influence a shown in the animation.

16. Region of magnetic influence
The region of magnetic influence has the highest degree of magnetic flux present. When we close the circuit, high current from the cap. Bank flows through the coil, and at this instance the magnetic flux is at its peak.

17. timing
When we don’t cut off the current at right time, the projectile gets attracted towards the center of the coil’s length and it doesn’t move ahead because the magnetic flux is strong enough to hold it. So, to make the projectile move forward, the current must be cut off at right time. When the projectile reaches the middle of the coil’s length, supply current must be cut off. Because of this projectile moves smoothly out of the barrel attaining good muzzle velocity.

18. Timing control systems
One precise way to stop the coil current is by using an infrared or light sensing circuit near the coil. As the bullet reaches the center of the coil’s length, it is seen by the infrared/light sensor. A signal is generated which switches off the current supply. Another way is to have a capacitor bank which can deliver extremely sharp spikes of current within very small amount of time.

19. Power?
The power delivered by the coil gun can almost be equivalent to the power of a hand gun. A simple home made coil gun is sufficient to break a wall if made properly. Here is a picture showing a 2KJ cap. Bank.

20. Want to make one?
You can construct a simple coil gun out of simple materials you might have got at your home. This site explains very well how to construct a EXTREMELY powerful coil gun. Coil gun making a world wide hobby and there are numerous blogs and websites dedicated to this subject. You can also follow -> heaven for high voltage stuff. I had already made one coil gun a year ago, but didn’t consider improving it, but whenever I get time I am working on this (seriously). You can find OVER 9000 videos on uploaded by several hobbyists and engineers.