Coil Gun for Newbies: Learning Electromagnetic Propulsion

There’s something attractive about coil guns, especially big ones. It’s probably the danger; between the charge stored in banks of capacitors and the flying projectiles, big coil guns can be lethal to experiment with. But there is a lot to be learned from how coil guns work, especially if you build this 3D-printed entry-level coil gun.

For the coil gun newbie, [Great Scott] does a fantastic job of explaining the basics. Pulsing the coil at just the right time will suck a ferromagnetic projectile into the coil core and let momentum fling it out, and multiple coils used correclty improve performance.

His gun is a simple pistol design with two coils, optical sensors to tell when the projectile is centered in each coil, and an Arduino to coordinate everything. The results are not spectacular — he uses only a modest amount of current — but the gun still works. [Great Scott] points out how a capacitor bank could be used to increase the current, but for the sake of keeping it simple he leaves that as an exercise for the builder.

Many coil gun and rail gun builds have made it to our pages over the years, including his ridiculously powerful gun that uses a capacitor bank so large it needs its own car. We like this build for its simplicity, its approachability, and the excellent explanation of its function.

25 thoughts on “Coil Gun for Newbies: Learning Electromagnetic Propulsion

  1. I really have a problem, when someone suggest to use main voltage directly, like in the video at 6:44. I’m worried that a kid will try it out and get seriously injured.
    BTW: Cody’s Lab also tried a coil-rail-gun, but seriously flawed, almost something for the fail of the week.

    1. I have a book from the 1940s. It’s for boys and contains articles on how to make electrical things, including a hot dog cooker. Many of the projects use main voltage. It used to be assumed that kids were smart enough to observe safety precautions. . .

  2. When you want to turn off a coils magnetic field fast you don’t want to use a flyback diode, with only ~0.7V across the coil current decays very slow. Much better to use an avalanche rated fet and let the voltage fly up to Vbrdss

  3. The only way a ‘coil gun’ would achieve any kind of accuracy approaching a smooth bore musket is by firing a ball bearing. Any elongated projectile must have spin to stabilize it or it will begin to tumble end over end. The longer it is, the faster the spin required. You could compensate by using a hollow steel tube with a lead insert at the front end (the shuttle cock effect). But I’ve yet to see a coil gun design that can impart spin on a projectile.

      1. Another way is to form the driving coils slightly oval in shape, and cut two slots along the opposite sides of the projectile.

        Start the projectile 90 degrees off the coil, and the coil will twist it as it pulls in, imparting a spin as the projectile aligns with the field.

  4. Although I’m a little bit surprised about the 3D printed design that had no trigger and no holes/cutout for the sensors.
    But I would really like to say that I really liked the opening of the video. I made the way it worked very clear very quickly, great job in explaining that.

    Now regarding the sensor, it is a reflective sensor, very sensitive and you want to detect a nail only a few mm away or the other side of the barrel just a few extra mm away. How would the sensor know when to stop sensing… it doesn’t, so don’t expect the sensor to do that. Sure you can dim the amount of IR but that is not the way to do it.
    If really must use this type of sensor (reflective) then make a hole on the opposite side of the barrel and cover that hole with non reflecting black paper and your sensitivity problems would be greatly reduced.
    But there is another reason no to use this type of sensor. Because if it fails (not sensitive enough) you cannot detect this until it is to late. You need an emitter and sensor on opposite sides, this way they always see each other unless they are obstructed by the projectile. No false reflection problems. And if the sensor is broken, chances are that it is broken before you press the fire button, you can detect that situation and sound a “sensor defect alarm” and refuse to fire.

    As a bonus to do some statistics on your performance I would like to suggest the following addition to the design. Since you have 2 sensors and a microcontroller already in your design, you can determine the speed of the projectile very easy. Al you need to do is add a display (or a speaker and some speech software to pronounce numbers). The distance/time to travel is the speed. Knowing the weight of the projectile you can calculate the energy. With that information it is easier to notify improvements when doing changes in your design, even the starting location of the projectile could be an issue, then there are the timing parameters, voltage over the coils, max current, etc. So much possible variables to tune/try out.

      1. Lol, some of us try to improve the presented projects instead of simply bash them. :)

        Constructive criticism is always better than ‘not a hack!’ Or ‘could’ve done it with a 555!’.

  5. hasn’t been updated in many years, but – I myself made a few projects back in the late 90’s early 2000’s inspired by Sam Barros works over at http://www.powerlabs.org/ quite some time ago. Including my own take on a lunchbox gauss gun. For anyone new to this, his projects are still worth looking at.

    1. Screw those guys SERIOUSLY!

      10 years back (yes that long ago) I created a thread where I attempted to explain that it wasn’t necessarily important to either
      A.) get a longer/larger coil
      B.) Build a bigger capacitor bank.
      C.) _I_ fricken suggested a coil around a another coil that would fire in a timed sequence. I even used MS Paint to explain how multiple layers coils insulated and offset would increase the velocity imparted.

      Also search hackaday for more railgun technology posts. You’ll find the one where you don’t need a 100 mile launch strip for space borne delivery of cargo and personnel.

      Screw those guys!
      Seriously! That’s how I really feel!

  6. here’s a good example of electromagnetic propulsion using pinballs. This pinball game is called ‘Getaway’ and was released back in 1992. One of the goals to get more bonus points is to get as many pinballs in the steel electromagnetic racetrack located near the back of the playfield. And this also makes use of optocouplers to detect the pinball position. The first 15sec of the video shows how to get the pinball in there.

    If I ever make a coil gun, I would use pinball coils , ready made for you, and steel pachinko balls. The perfect combination in weight and diameter. The inside diameter of the common pinball coil matches the diameter of the pachinko balls

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