#221 Better than GreatScott's Coil Gun? A true story, how-to not do it

I should have been warned some viewers on our sama project were against a gun on the tank but I did not listen this video shows what happened and how I was punished gritty youtubers here is the guy with the Swiss accent with a new episode and fresh ideas around sensors and microcontrollers in Switzerland every adult man is in the Army and has its gun at home maybe this is the psychological reason for my choice but I'm not a psychologist I'm an engineer so let's start with the story if you look at the discard channel of the summer project you see that there are many possibilities to build a gun for a tank but there is one favorite for an electronics engineer a decent coil gun sometimes also called railgun running purely on electricity you could call it also the Tesla of guns viewers of great Scots Channel know that he did such a gun and I did not want to repeat it here I wanted of course more keep in mind his build was 5 volts and 12 amperes for all of you who do not know how such a coil gun works it consists of a coil and an iron bullet and it works like this solenoid here if current flows through the coils a magnetic force pulls the iron towards the middle of the coil and it stays there as long as the current is applied if the current stops the coil force fades away and the iron is moved back by the spring not exactly a gun lovers of the film No Country for Old Men know however that it is possible to kill people using a similar principle anyway let's stick to the story if the inner iron runs free and you stop the current in the right moment it continues on its way and it leaves the coil on the opposite side and if the current is high the result is a fast moving projectile as a rule of thumb more current and more turns on the coil results in more speed and more current needs more voltage of course when I saw this instructable I knew this is much closer to what I want it uses a capacitor to store 400 volts and a thyristor to switch the current this should provide the needed current but the gun on the tank has to be remotely controlled not manually so we have to enhance it and now the sad part of the story begins I ordered the components as described in the instructable a DC to DC converter which according to its datasheet should be able to output 400 volts and unfortunately exceeded its specifications a 100 micro farad capacitor for 450 volts some copper wire and a thyristor thyristors are the working horses of high-voltage switching the one I used was called 7 - TPS 12 and it's datasheet says it can deal with more than 1,200 volts and 70 amps which is not the full truth if you read the small print you see it supports up to 1,100 amperes for a short time that is the stuff electric dreams are made of it only needs a short trigger of 1.3 volts on his gate and then it starts to conduct simple and efficient so I started to print the inner part of the coil and called the copper wire using my electric drill this is quite efficient and leads to a very tight coil which is good for our purpose then I connected the parts now I have to confess something important since my years of study I never touched high voltages anymore with good reasons as you will see when I finished the wiring I can 12 volts to the DC converter and really the voltage on the capacitor started to increase to nearly 400 volts as promised in the description on Aliexpress then I did some research on the PC and did not look at the bench suddenly a noise like a gunshot from the bench but it was not my coilgun it was one of the capacitors of the DC converter which exploded the smell was awful and Dave Jones would talk about magic smoke I have to say I did not feel any magic in the smoke and I also did not see any hallucinations like Steve Jobs when he consumed LSD so please do not expect a new iphone from me after cleaning up the mess I did some measurements and discovered that the converter was able to produce much more than 400 volts and the output capacitors are only rated at Chinese 400 volts if you know what I mean so one of them exploded after a few minutes this was the first victim of this project and because it was the capacitor of the negative rail it did not stop my ambitions and I was able to continue after buying some decent nails and cutting the end off I wanted to try the thing without thinking too much I used the second rail of my bench power supply to provide the trigger voltage to the thyristors the effect was a spark and a loud noise when the smoke disappeared I saw that I killed the second part of my bench power supply since then it shows 50 volts and over current and I cannot change that anymore and the size of the flash told me that the thyristors also did not survive why did this happen unfortunately naive as I am with these high voltages I connected the thyristors to the high side which was in this case the wrong side you can imagine how annoyed I was about forgetting to check everything before powering up as usual I had or a few thyristors more and corrected the circuit and because I learned something I used a 1.5 volt battery to power the gate I did not want to sacrifice another valuable equipment of my lap and really it worked the bullet moved quite fast out of the toilet and because I wanted to measure the current I connected a 1 ohm resistor between the capacitor and the coil on the low side this time otherwise I would have to mourn my valuable oscilloscope according to Ohm's law this resistor also called shunt resistor shows one volt per ampere and because the action is so fast I had to use the oscilloscope to see what happened here we see that about 130 amperes circulated through the coil and the whole thing just took a few milliseconds cool what limited this current looking at the diagram we see a capacitor a shunt resistor the thyristor and the coil the total resistance is 400 volts divided by 130 ampere equals around 3 ohms 1 ohm comes from the shunt which is quite a lot the other come from the internal resistor of the capacitor the thyristors the wires and the coil itself you can imagine that the current was even higher when I removed the shunt resistor because of my misfortune we can see how an electrolytic capacitor is built if we look at its remains we see that it's connectors are quite thick and the bigger capacitor has even thicker connections by the way this is the cap of the capacitor still more or less intact I found it a few metres away from the explosion I also had to add a switch to shut the DC converter down as soon as the capacitor was charged the IRA stirs only stop to conduct at very low current levels so it just stops conducting if the capacitor is completely discharged but with the running were too connected to the capacitor it never discharged is completely which created a short through the coil and kept the thyristors always on this switch on the primary side of the DC converter solved the problem at least I had now a working gun and I wanted to try it out outside the house for that I used the same quadcopter battery I used in the tank in the final version this should also power the gun when I connected the DC converter to the battery it's 15 ampere fuse melted immediately now you know why I love my assortments I quickly replaced the fuse I had to add a 1 ohm resistor in series with the battery to limit the current now it worked and I was able to do the tests with a battery as a power source I was a happy man at least as long as I suppressed any thoughts about my poor power supply but the whole thing still only worked manually with a 1.5 volt battery as a next step I had to connect it to the ESP 32 on the tank but wait you know I love my ESP boards especially the newer ESP 32 and I learned something from my previous experiments 400 volts are dangerous for electronics parts especially with a noob at the controls so I went into my esp8266 box and searched for the board with the least value for me not an easy task because I loved all of them I wanted to start by automating the trigger which needed at least 1 point 3 volts according to the data sheet the 3.3 volts of the ESP should be ok for that said and done I wrote a small sketch which triggered the gate pin for a few milliseconds I also connected a USB isolator between the ESP and my computer it is the same which should edit the video later on so I did not want to destroy it it worked somehow and the thyristor was triggered then I heard the sound that the USB connector of the ESP was unplugged evidently my esp8266 port had died a nearly silent death I do not exactly understand how this happened but maybe the thyristors created a short voltage spike on the gate or the high current changed the potential of the ESP let's count the casualties a dead power supply a completely destroyed capacitor two dead thyristors I do know more recall how the second one the height and a dead esp8266 this was definitely enough for one day's work and I had to change strategies completely I wanted to isolate my electronics entirely from the high voltage parts for such cases I have a few optocouplers in my lab I did some tests with them but did not manage to get the gate triggered without additional transistors so I gave up because I anyway had to use a relay to switch the primary side of the DC converter I decided to use one of those ready-made modules also to trigger the gate the last step was to measure the voltage across the capacitor to decide if the gun is armed how do you measure 400 volts with an ESP you create a voltage divider you can use the following formula I did not need an exact result here so I choose 410 kilo ohms and 810 ohms like that the voltage should always be below one volt the sketch is very simple I need a button as an input and two output pins want to switch the DC converter and one for the trigger the output of the voltage divider is connected to the ADC of the esp8266 you see I still used a backup esp8266 and not the ESP 32 because I was not entirely sure if it will survive if we have a look at the sketch we see that we first switch the relay for the DC load on to do that we have to pull the into lo the charging process starts and we measure the voltage as soon as the voltage reaches the desired level the weapon is armed and we wait for the button I used the readily available flash button on the board connected to GPIO 0 or D 3 as soon as the button is pressed the thyristor is triggered for 100 milliseconds and the gun fires now the charging can start again so finally the prototype is ready this project created the biggest cemetery of dead parts and devices in the history of this lab and I'm not sure when I will work with high voltages again and I'm also not sure if this concept ends on the tank it seems to be quite dangerous for noobs like me in such moments where things get a little costly I'm glad I have loyal supporters on patreon and people who use the affiliate links in the video description thank you for your support without you it would be difficult for me to do what I do now bye you

Channel: Andreas Spiess

Views: 220,718

Keywords: How-to, hack, coil gun homemade, projeect, lorawan, arduino project, arduino, greatscott, electronics, nodemcu, guide, wemos, do-it-yourself, iot, smart home, esp32, esp32 tutorial, Rail Gun, esp8266 datasheet, esp32 datasheet, esp32 project, summer project, diy, powerful, beginners, hobby, esp8266 project, coil gun diy, how to, coil gun, esp8266, simple, esp32 weather station, coil gun powerful, wifi, coil gun project, rail gun diy, eevblog, ttgo, rail gun project, rail gun powerful

Id: yKL9yqsJFtI

Length: 14min 59sec (899 seconds)

Published: Sat Sep 01 2018