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I have had a long-time interest and fascination with railgun technology and for a long time I have wanted to build a small-scale, simple railgun as a scientific experiment. This railgun is designed to use a capacitor as the projectile.

I want to point out that I am not an electrical engineer nor do I have a background in working with electronic components nor with building things with electronical components. I do have a self-taught understanding of basic circuit design and how some basic electrical components work, such as batteries, resistors, diodes, and capacitors.

I am seeking design advice on the best type of capacitor that I should buy for this simple railgun. I have recently been doing a lot of online research on capacitors, and at this point, I am rather confused by all the various types, sizes, and specifications.

My goal with this simple railgun is to try to launch a small capacitor that will travel at least six meters in distance. I am planning to use four D-size batteries to charge up the capacitor.

I am thinking that to achieve this goal I will need to use a low-weight capacitor, say one weighing 3 ounces or less, yet one that will produce enough current for a long enough time to accelerate the capacitor to the point that it travels at least six meters in distance.

Below is a conceptual design drawing I made to illustrate the working principle of this simple railgun:

enter image description here

What would be the best capacitor to use for a railgun that uses a capacitor as the projectile?

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  • $\begingroup$ Cap as projectile? Why would you expend a charge storage device that has pretty miniscule energy storage? I suggest you read up on the magnetic bits of en.m.wikipedia.org/wiki/Railgun 6 meters should be easy enough with a permanent magnet... a D battery is 1.5V.Capacitor energy is .5*Cap*Volts^2... $\endgroup$
    – Abel
    Sep 12, 2023 at 2:43
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    $\begingroup$ Shiva Star - buts that's how I roll;) "Shiva Star was also used as a dense plasma focus driver in the mid-80s, and as an experimental magnetic driver for conventional projectiles in the late-80s." en.wikipedia.org/wiki/Shiva_Star. Separately, accelerations of 100 billion g were obtained 30 years ago. Not sure where the mark is currently. $\endgroup$
    – Phil Sweet
    Sep 13, 2023 at 22:56
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    $\begingroup$ Oh, the fun part is designing the switch that dumps a few megajoule in under a microsecond. $\endgroup$
    – Phil Sweet
    Sep 13, 2023 at 22:59
  • $\begingroup$ @PhilSweet, I didn't know about the Shiva Star system. I would love to see a live test firing of that system if it's still in operation. Also, I see a problem with my design.... leaving the capacitor on top of the rails in the charging phase will cause the capacitor to move down the rails. I will have to add in a locking mechanism to keep it locked in place while charging. $\endgroup$
    – user57467
    Sep 14, 2023 at 16:20

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There are new-technology capacitors available now that can store large amounts of energy; they are called ultracapacitors and have capacities of order ~farads.

Before you go out to buy some, however, I have the following recommendations.

First of all, go find you some data on a capacitor's energy storage capacity on a per gram basis, for each major type of capacitor on the market.

Then calculate the projectile "muzzle velocity" which will yield a 6-meter flight length, in the earth's gravity. From this, derive the energy release required on a per gram basis to accelerate a projectile to that velocity.

Now, assuming a 6-volt charge in all cases, you should be able to equate the required energy release per gram for launch to the energy stored in the capacitor per gram and see if it is possible to self-launch a capacitor projectile 6 meters.

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