Railgun from 2006
Friday, April 21.
We planned on testing the railgun. The velocity meter was built (see below) and a few people gathered around (we didn't advertise) but the projectile was a little too large. It got stuck between the chambers.
Velocity meter
Below are a few photos of the railgun under construction. Here's the capacitor that we'll use. To get an idea of the size of the capacitor, you can compare it to the end of the rail gun, and the Variac (both are to the left of the capacitor). Here's the electronics, as of 2/27/06 Railgun from ~ 1997 The railgun Mitch Rappard, Mike Passer, and many others have been working on is built! We have the railgun fully assembled, and it works! The projectile speed is not quite what we expected, but we have some ideas we are going to try to increase it. Theory The theory behind the railgun is not overly difficult. It revolves around the simple equation: F=ILXB. The F stands for the force which will be acting on the bullet, the B is the magnetic field, I isthe current through the rods (rails) and L is the length between the rods. Using the 'right hand rule' one can see that the force will push the bullet along the rails and out the end of the 'gun'. Below is a diagram depicting how it will work. The velocity of the bullet goes as: L'*i^2*t L' is the inductance of the rods v = ------ i is current, t is durration of current pulse 2*m m is mass of the 'bullet' Obviously, increasing the current is the best way to go about increasing the velocity of the bullet. We also decided to use rare earth magnets to get some 'free' magnetic field to help out with the force. Implementation Our railgun consists of two copper rails that are 1/4'' wide and 5 1/2'' long. The 'bullet' is really a graphite disk that is 3/4'' by 3/64''. To get a large pulse of current, and thus increase the velocity of the projectile, we use a capacitor bank of 15 Photo Flash Capacitors in parallel to hold the charge. Photo flash capacitors were chosen primarily due to their quick discharge rate. The total capacitance of this capacitor bank is 3 mF since each capacitor is 200mF. Once a switch is thrown, and the charge is released, we expect around 3,000 amps to flow into the railgun in a time span of about 100 ms, but will have to confirm this through experimentation. Below is a rough schematic of the power supply and how it connects to the railgun. The variac takes the 115 volts from the plug in the wall, and allows us to change it to only 30 volts. A 10 X transformer that we found laying around in the physics dept. collecting dust is used to bring the voltage up to 300 V. (Since it was the only transformer we could find, we had to use the variac to bring the current down to 30 volts.) A bridge rectifier takes the AC from the transformer and converts it to DC (note: a resistor follows the bridge rectifier to keep the transformer from frying). Once the capacitor bank is charged, a switch is thrown (a starter solenoid from a car) and the current flows through the railgun, causing the projectile to fire. Here are some pictures we have taken of the railgun. Railgun, switch and capacitor bank Our capacitor bank All the parts of the railgun
Below are a few photos of the railgun under construction.
Here's the capacitor that we'll use. To get an idea of the size of the capacitor, you can compare it to the end of the rail gun, and the Variac (both are to the left of the capacitor).
Here's the electronics, as of 2/27/06
Railgun from ~ 1997
The railgun Mitch Rappard, Mike Passer, and many others have been working on is built! We have the railgun fully assembled, and it works! The projectile speed is not quite what we expected, but we have some ideas we are going to try to increase it.
The velocity of the bullet goes as:
L'*i^2*t L' is the inductance of the rods v = ------ i is current, t is durration of current pulse 2*m m is mass of the 'bullet'
Below is a rough schematic of the power supply and how it connects to the railgun.
The variac takes the 115 volts from the plug in the wall, and allows us to change it to only 30 volts. A 10 X transformer that we found laying around in the physics dept. collecting dust is used to bring the voltage up to 300 V. (Since it was the only transformer we could find, we had to use the variac to bring the current down to 30 volts.) A bridge rectifier takes the AC from the transformer and converts it to DC (note: a resistor follows the bridge rectifier to keep the transformer from frying). Once the capacitor bank is charged, a switch is thrown (a starter solenoid from a car) and the current flows through the railgun, causing the projectile to fire.
Here are some pictures we have taken of the railgun.
