The simple high voltage railgun was tested in May 2005. Previous to firing a current limiting resistor was placed on the railgun and the voltage across the barrel was raised to determine at what voltage flash over occurred. The pulse power supply is capable of operation at 10,000 Volts. However, the railgun suffered flash over at 7,000 Volts. Since an unintentional flashover powered directly by the capacitors is highly undesirable the railgun was never charged to more than 5,000 Volts. This problem would best be resolved by using a high voltage high power switch to energize the railgun when the projectile is in the barrel. Keeping the rails at a high potential and using a moving projectile to switch the circuit is easy, but is certainly not the best option. Using an actual switch to activate the railgun would allow for much higher voltages to be used that what the railgun could withstand open circuited, that is, with no projectile in the barrel. Since even with poor insulation the majority of the current is going to go through the aluminum instead of the air or plastic insulators. I would like to implement a system that still injects the projectile into the railgun at high speed and then switches on the current. This would require a high speed switch capable of transferring power on the order of a few gigawatts, and a control system that activates the switch when the projectile is in the right position. This of course will take some time and money.
With air pressure alone the injector fired the aluminum projectiles at 190 ft/s, at with 80 psi in the air chamber. The railgun noticeably accelerated the aluminum projectile beyond the velocity provided by the air pressure alone. Unfortunately the flash and sparks from the railgun kept the chronograph from measuring the velocity of the projectile with the railgun energized. In order to protect the chronograph from all the sparks, and since it did no good anyhow, we stopped using it. In order to successfully use an optical ballistic chronograph the railgun and testing arrange will need some improvements. The railgun will need to be fitted with a flash suppressor/spark catcher. The chronograph will need to placed as far away from the railgun as possible; and the chronograph will need aluminum foil placed in front of it to reflect flash, catch sparks, but still let the bullet penetrate the foil and pass over the sensors. I think a doppler radar based chronograph would be much more likely to work as well.
The injector is built to fire at up to 200 psi, the limiting rating being the pressure rating of the solenoid. I bought a cheap 12 volt compressor and got what I paid for, it only went to 80 psi on testing day. I would like to use a compressor that can easily reach 250 or 300 psi, but the compressors I've seen that operate in that range are very expensive.
The nylon copper backed projectiles fired about as fast as the aluminum projectiles using just air pressure, although I didn't measure the velocity. Only one nylon plasma projectile was fired with the railgun energized, at 5,000 Volts, 7325 Joules. The copper backing turned into plasma as expected, the projectile came out at some unknown but high speed, and the plastic barrel of the injector and all the paraffin insulating the breech end of the railgun exploded from the plasma pressure.
The pieces used to make the plastic section of the injector only cost about $20 US, so once replaced the railgun will still be usable for solid aluminum projectiles.
Here is a nice picture of the railgun, after the plasma projectile was fired. Click on the picture for a much larger version.
The aluminum projectile fired in the 3000 Volt test shot (see video below) was recovered. The current did noticeable damage to the projectile. The current began to flow well before the projectile was able to make metal to metal contact with the rails. Arcing occurred through the nose of the projectile as it entered the barrel.
For whatever reason one side of the projectile has a longer area of scarring than the other. It is desirable to have the entire projectile in the barrel with strong metal to metal contact before the current begins to flow. While this can be done with a switch to turn on the railgun and with the projectile stationary in the railgun; it seems difficult to achieve with a pneumatic injector. Close up pictures of the railgun/injector interface. Click on photos for larger versions.
Each link lists injector pressure, capacitor voltage, and capacitor energy stored.
Aluminum Test Shot Video at 80 psi No Electrical Power (1152 kB) AlAirOnly.wmv
Aluminum Test Shot Video at 80 psi and 3000 Volts, 2355 Joules (980 kB) Al3kV.wmv
Nylon/Plasma Test Shot Video at 80 psi and 5000 Volts, 7375 Joules (1769 kB) Plasma5kV.wmv
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