Coil Gun
How does a coil gun work?
To get you a mental image of how this works, imagine a magnet. Now place a small metal ball next to the magnet. The magnetic force from the magnet will pull the ball towards it. Now imagine that you can turn that magnet on and off. So the ball is sitting next to it but does not move. You turn on the magnet. The ball is attracted to the magnet and starts moving toward it. Now you turn the magnet off and the ball just keeps rolling alot.
This is the basis of a coil gun. But where do you get a magnet that turns on and off? This is where the coil of wire comes in. When current is run through the coil of wire it becomes an electromagnet. So it can be turned on and off at will. Usually it is just turned on for a few miliseconds, so that the projectile is pulled toward it and the magnet turns off right as the projectile passes through so that is will keep going.
The $0 Coil Gun
The Barrel: I lathed this simple barrel out of a peice of PVC bar I had laying around. As you can see it is fairly simple. Don’t have a PVC bar and a lathe? Just use a straw or anything plastic. You could even make your own barrel out of paper.
Power Source: The power source for this coil gun is two capacitors that I pulled out of an old CRT monitor. They provide much more umph than a single camera flash cap.
Charging Circuit: I used the same circuit used in disposable cameras to charge the coil gun. It takes about 20 seconds to get a full charge. I made some modifications to the circuit such as adding wires that is is easier to start the charging and for firing off the caps.
Coil: The coil is about 20 layers of magnet wire. This is probably too much and I would recommend not making it as big as mine. You can get good quality magnet wire from motors, such as the ones in microwaves.
Trigger: Touching the two wires together :p
In Conclusion: In the end I could shoot a bb about 20 feet straight up into the air, which made me happy and proved that a coil gun worked. The next step: A bigger coil gun of course 
Pictures
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Formulas
| Capacitor potential energy |
| E = 1/2 * U2 * C |
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E = Energy of capacitor in joules U = Voltage of capacitor in volts C = Capacitor capacitance in farads |
| Coilgun Output Energy |
| E = 1/2 * m * v2 |
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E = Output energy in joules m = Mass of projectile in kilograms v = Velocity of projectile in meters per second |
Related Books
Adventures from the Technology Underground
