Hello everyone, how do you do? this is project How-ToDo, my name is Konstantin and today I want to show you how I made this portable coil gun. I make it just for fun, so I don't have a goal to build the most powerful pistol, actually I don't even make any calculation before assembly.
Step 1: Theory
At first let's refresh the theory in memory. How does coil guns works? We charge a capacitor with high voltage, usually about 400v, and then discharge it to coil of copper wire which is located on the barrel, when a current flowing through the coil it create a powerful electromagnetic field and bullet made of ferromagnetic, retracting in the barrel, capacitor discharging very fast so ideally it lose all energy when bullet will be right on the middle of the coil, and bullet continue to moving by inertia. Before we step into the assembly I must warn that you have to be very careful working with high voltage, it could be dangerous.
Step 2: Circuit
I will make a coil gun with only one coil, because it's extremely simple compere to device with few coils, you need to synchronize all coils, use some kind of sensors to detect position of the bullet, also multi-stage device simply would not fit in the form factor of the pistol, even now body is completely filled. As a basis were taken such kind pistols, and because I have a 3d printer, it's logical to print a body on it.
Step 3: 3D Model and Components
I start with a 3d model as usual working in Fusion 360, all files are HERE in case someone wants to make it. I tried to put components as compactly as possible, by the way there are very few of them, 4x 18650 battery giving a total of approximately 15V, in their holder in the model I made a sockets to installing cooper foil jumper to have a serial connection of batteries. Next is boost converter (Ali or Amazon) Increasing the battery voltage to about 400V to charge a capacitor, capacitor itself (Ali or Amazon), in my case 1000uf 450v and coil. Small parts like thyristor (Ali or Amazon), 1.5v battery to operate it, button, you can place anywhere in the body, glue it to the wall, I didn't make a specific space for it. For the barrel you need a non-magnetic tube, I will use the body of a ballpoint pen, it's much easier than print it on a 3d printer and then try to ideally polish the inner walls.
Step 4: Coil and Handle
I wind a 19 gauge copper wire (Ali or Amazon) turn to turn, put a layer of electrical tape after each layer of coil, I didn't count how many layers I made, just before it's completely filled. I decided to make a handle of wood, although of course it was possible to print it, but I personally like working with the wood.
Step 5: Printing and Painting
When the model is ready, I start printing, almost all the details I did with a 0.8mm nozzle and only the button holding the barrel with 0.4mm, printing took about 7 hours. I ran out of filament, so I only have pink PLA, despite my love for this color, in this case it is probably not the best chose .. After printing, I carefully clean off the details from the supports, then I went to the store to buy the primer and paint, initially I wanted to use acrylic paint, but it's refused to hold even after primer, also from what I red about painting PLA, there are special spray paints that will perfectly hold without primer, but I have not found one. Of course it turned out not so well, but bear in mind that I hung half out of the window, painting and trying to do not drop down something, especially camera. Let's say that an uneven surface is such a style and in general, it was planned.
Step 6: Handle
While the printing was going on and the paint was drying, I was working on a handle, I did not have a suitable thickness lumber, so I glued two pieces of old parquet, when it dried, I give it a rough shape with a jig saw, by the way, I was surprised that the cordless jigsaw without any difficulties cuts 4cm of wood .. further, with the help of a dremel and a saburrtooth bit I round the corners, because of the small width of the workpiece, the handle turns out not quite as desired, but I tried to cover this inconvenience with ergonomic design. Next working with bit with sanding paper, then handheld 400 grid, and as usual layer of danish oil. Fix the handle with a screw in pre-drilled channel. Finish, with sandpaper and small files I make sure that everything is closed, held, clinging as needed.
Step 7: Electronic Part
Now we can go to the electronic part, first of all I install the power button, then I make the battery holder, for this I cut the copper foil into strips and glue it under the battery contacts, connecting them in serial, always checking that there is a good contact between battery and foil. When this is done, you can connect the high-voltage module through the button, capacitor to the module, and even try to charge it, I set the voltage to about 410V. To discharge it to the coil without loud clapping and sparks, it is necessary to use a thyristor, which works like a switch, it closes by applying small voltage of 1.5V to the gate electrode, unfortunately my boost converter has an middle point, which does not allow without special tweaks to take voltage from the already installed 18650 batteries, so I just took a AA battery, and a small clock button serves as a trigger, commuting currents of hundreds of amperes.
Step 8: Thyristor and Charge Indicator
This would be the end, but two thyristors that I have can't withstand such current, so I had to order a more powerful guy 70TPS12, it can withstand 1200V and 1100A in the pulse, and because project frozen for a week anyway, I bought details to make such kind of a charge indicator, it can work in two modes, lighting only one diode and moving it, or lighting a bar of diodes, I prefer the second option, the circuit is pretty simple, but if it is difficult for you, you can buy an assembled module (Ali or Amazon) and adding a couple of Megaohm resistors on the input you can connect it directly to the capacitor. The new thyristor, as planned, easily passes powerful currents, and the only one moment it is not closing. So before the shot, you need to turn off the charging so that the capacitor can be completely discharged and the thyristor would come to its original state, this could be avoided if the converter had a half-wave rectifier, I tried to remake the existing one, but it did not give any success and I skip it, keep in mind.
Step 9: Bullet
Next, you need to make bullets, as I said before, they need to magnetize, running through the construction shop found these wonderful dowel nails, they have a diameter of 5.9mm and perfectly go into the barrel, it remains only to cut off the cap and sharpen the top a little bit, the weight of the bullet is 7.8g, unfortunately now I have nothing to measure speed. Finishing assembly gluing body and the coil.
Step 10: Finish
Well, now we can test it, this toy easily make holes in aluminum cans, goes through cardboard, and in general felt pretty powerful, although many people say that the coil guns are silent, it slams a little when shot even without a bullet, while large currents passing through the coil, even it's fraction of a second, it heats up the wire and slightly expands it, I think if you filled the coil with a resin, you can partially get rid of this effect. As a result, I want to say that this project was really interesting to do and I would like in the future to make something else like that, maybe a multistage coil gun ... That's all I got for today, thank you for watching, see you soon!
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