To make a simple gun using magnetic propulsion. This gun uses a coil, a relay, two capacitors, a switch and a power supply.
How it works
An iron projectile is placed in one end of a hollow coil.
When ilde, a capacitor is charged through a relay. When a switch is pressed, the relay changes position, and the capacitor is recharged into the coil. Also, the relay makes sure the power supply is not short circuited.
The projectile is being dragged into the coil, and before it reached the center, the capacitor has been drained, and the projectile continues out of the coil.
Here you see the coilgun, coil and relay at the left, the switch at the back, all mounted on two capacitors. The gun can shoot both ways:
A little video of my coilgun:
Here is the diagram of the gun:
The projectile can be anything made of iron, cheap nails with small heads are good.
The hollow coil is made with 0.5 - 2 mm isolated cobberwire, try different thicknesses and rounds for best result. Wound it around a non-metal pibe, with an inner diameter suitable for the chosen projectile. The space between the projectile and the pibe must be as little as possible, so the coil is as near as possible, and the stearing through the pibe is good.
The two capacitors are electrolytic and comes from a retired power amplifier. They are at 22.000uF each, and is coupled in parallel, so the total capacity is 44.000uF. The more applied voltage and the more farad, the more power in the gun. Make sure to polerise the capacitor correct, and make sure not to exceed the voltage limit.
The relay is a SPST - Single Pole Single Throw, and must be strong enough to deal with the high current.
The power supply is a DC supply, and do not need to be very strong, it just takes more time to charge the gun. You can messure the voltage on the capacitor, to see when it is fully charged. In this case, it gives 24 volt and 0.5 amp. The higher the voltage, the more power in the gun, but again, make sure not to exceed the capacitors voltage limit.
Problems
The initial placement of the projectile in the coil is very important, and it seems that the best placement is just inside the coil, not in the middle, and not outside it. About 1/3-1/4 inside. Try for yourself.
A simple way to meassure the velocity, is either to point the gun upwards and compare the heights, or shot at a cardboard and compare the heights of impact.
My tiny relay burns together from time to time, and I manually have to break the terminals apart. So, a bigger relay would be good. In fact, a high current thyristor would be the best solution, and there is a lot of really heavy DIY coilguns on the internet.
The capacitors must be emptied into the coil before the projectile reaches the center of the coil, otherwise the projectile would be attracted backwards and loose velocity. The time it takes depends on the capacitors and the resistance in the coil. So, the thicker the wire, the shorter the recharge time. Also, the wires used to connect the components carrying the high current, must be much thicker than the wire in the coil.
And of course, the size and weight of the projectile is important, and again, try different sizes.
An idea to make the projectile spin, is to mount a small magnet on a fast motor, and let it hold and spin the projectile, when shooting.
If you want to know more about more advanced diy coilguns, I will recommend Barry's Coilgun Design Site where you will find lots of ideas and theory.
Finally some pictures:
