Re: Yet another coil gun prototype
V2006, Sat Oct 27 2018, 09:50PM

It is possible that 50 volts would be an acceptable voltage. The model for 100 volts was successfully tested by me:

Re: Yet another coil gun prototype
Zuckerstange47, Tue Oct 30 2018, 04:16PM

My plan is to go near 100 V and use multiple coils with 1mm-wire, 9 rows and 10 layers. The first shots utilized only 40 V because I did not have a fitting step-up converter then (still I do not have 100V-capacitors, so I will not put the plan into practice soon).


The current version is much more powerful than the one on the last video. I did attach the second light barrier, so the display shows the speed and the energy after each shot. Also the wiring at the coil is much better.
Yesterday I shot a 128g-nail (because I cannot find the small projectile anymore), which was measured at 0.88 joule at about 40V. Today I connected another step-up converter and went up to 46 V with a new 20g-projectile, which resulted in a speed of about 9.9 m/s and 0.98 joule (if my math is correct).

Now I need to design something to catch the projectiles safely




When I click you first link @V2006, I am forwarded to a page asking for my youtube-login data, but I do not see any video. I noticed that before, as I watched your videos in the past.

Re: Yet another coil gun prototype
V2006, Tue Oct 30 2018, 09:49PM

1 mm wire is very small - it is better to increase the cross section

Re: Yet another coil gun prototype
Zuckerstange47, Tue Oct 30 2018, 11:33PM

I will think about the wire size, what kind of wire are you using? I remember reading somewhere in this forum, that wire above 1mm would be almost impossible to roll up properly, so that might have been the reason why I chose this diameter.

However that may be, here is another video I just made. At the end there is also an old shot, that I made about one day ago.

Re: Yet another coil gun prototype
V2006, Thu Nov 01 2018, 09:07PM

Take at least 1.5 mm or 1mm but with two wires
and better than 2 mm and more

Re: Yet another coil gun prototype
Tomspol, Sat Nov 03 2018, 09:58AM

Hi, I like how your project is made modular but I would recommend you to make all the power wires as short as possible especially that mosfet connection. Also you might achieve better results with coil with the same length as the projectile and place that light barrier on the other end of coil and switch it off when projectile reaches it. I would also like to ask where did you buy the acrylic tube? Anyway I'm looking forward to new updates.

Re: Yet another coil gun prototype
Zuckerstange47, Sat Nov 03 2018, 11:56AM

I will make the wires shorter in the next versions, this is not meant to be highly efficient, yet.


Why should the coil be the same length as the projectile? Could you give me a hint towards the pysics behind it? I was thinking about using a much longer, heavier projectile, to be able to transfer more energy because of longer influence of the magnetic fields, especially in the later coils.
I read, that the best results would be achieved when the length and diameter of the coil would roughly be identical; If you double the length of a coil, the magnetic field strength is halved (provided the length of the wire stays the same), right?
In case there are no/few experiments on that matter, I might try to build two coils with different length/diameter-ratios and test the resulting speeds... but I assume that the analysis will be tricky, when also bringing the energy consumption into accout.

When calculating coils with a thicker wire I had the impression that (striving for the same amperage as a thinner-wired coil) the time for the magnetic field to strengthen would be much longer. When comparing a 1mm to a 1.9mm wired coil, the time to reach 90% of the maximum current rises from 3.8 ms to 21 ms. Also the time for the current to go to zero after deactivating the coil should be much longer, so in conclusion the coil would have to be activated earlier and deactivated some time before the projectile reaches it's center, to prevent retardation after exceeding the center? I am not sure if the results of my calculator are dependable, and my physical knowledge might be not sufficient to interpret it correctly, but I have the feeling that the advantages and disadvantages of different sizes of wires about even themselves out (with much higher costs and weight when using thick wires).

What do you mean by placing the light barrier on the other side of the coil? So that the projectile interrupts the light before reaching the coil (to get reproducable starting positions?)? At the moment, the projectile is placed before the coil manually, and the magnet is turned off when the projectile reaches the first light barrier behind the coil. The second coil is only for measuring the speed.

Maybe it would be the best to start from scratch (apart from the wooden wall), because there are so many thing I would like to change. Then I would do a much more stable mount for the unmeant moving parts, that would allow adjusting the distances of the components easily; meter the voltage of the capacitors by the ESP32, so the energy consumption after each shot could be displayed, and so on...



I bought the tube in a german shop "Holzmaus" (=Wood/lumber mouse) that has a large variety of tubes (but also other materials and forms):

They only deliver to Germoney, Austria, the Netherlands, Luxembourg and Belgium.

Re: Yet another coil gun prototype
Tomspol, Sat Nov 03 2018, 02:02PM

I'm sorry, I didn't write it right. I meant placing light barrier on the beginning of the coil such that when you load the projectile into coil the light beam is interrupted. When you fire the projectile starts moving and when its whole in the coil (if the projectile has same length as coil) it clears the light barrier and coil is switched off. It looked like if you have the light barrier behind the coil the projectile is being pulled back before it reaches the light barrier. But on second thought it pretty much depends on length of projectile.

From my experiments I've got the impression that identical length of coil an projectile would be better than coil with large diameter and longer projectile. But I might be mistaken, it would definitely deserve more look into.

I'm not quite sure what do you want to achieve by increasing wire diameter. You could increase current through coil just by using higher voltage.

Re: Yet another coil gun prototype
Zuckerstange47, Sun Nov 04 2018, 07:03PM


You are right about the placement of the light barrier, another advantage would be that the triggering might be more exact, when using a projectile that has a flat back, but a pointy tip. I already thought about that and might change my design in the future. At the moment I am not sure, how to shape the projectile, if it needs fletchings, like a arrow, to get a stable flight... so far, my idea is to hollow out the rear part of the nail to make it lighter than the front.

The increased wire-diameter was a thought based on V2006's reply directly above yours. I think the reason behind it would be to increase the magnetic field strength and the amperage, or the length of the coil to have a longer time of energy transfer. Using a higher voltage would also lead to changing many other parts, like MOSFETs and capacitors, so I think I will stay at 1mm for now.

Re: Yet another coil gun prototype
V2006, Tue Nov 06 2018, 10:43AM





On these videos, the coil is wound with a wire of 2.6 mm (winding diameter 5.5 mm, 3 layers of 20 turns each)

Moisten at least 1.5 mm - it will be much better than 1 mm - you will immediately see.

Re: Yet another coil gun prototype
Zuckerstange47, Thu Nov 08 2018, 01:49AM

I tried to use the ESP32 as some kind of oszilloscope (not sure though, because I do not own an oszilloscope nor used one before) to measure voltages while and after activating the coil.
The top graphs show the capacitor's voltage for two activations, the first starting at 40V, the second at a lower voltage.
The bottom graphs display the voltage over the coil (the first with an initial capacitor's voltage of about 19V, the second with 30V). I don't understand why the first datapoint and the ones after deactivating the coil are 4095 (the maximum value that the ESP32 can give out) and not zero as I expected. Also I am not sure what to make with the data, but I am happy that the measurement worked.

My interpretation is, that the coil takes at least about 2000 microseconds to get full amperage after activation, but when considering the overlaying drainage of the capacitors the maximum would be farther to the right when having a constant power source. From my calculations the current should reach about 50% of the maximum in about 1500 microseconds and 90% in almost 5000 microseconds. I do not know if my interpretation and calculations are correct, but they seem to harmonize well enough.


(Unfortunately the ESP32 cannot measure voltages accurately, the output is quite noisy and imprecise, but a least it is good enough to make out a trend. I only saved a reading, when the difference to the last saved measurement exceeded a specific value, so it would be possible to get a higher resolution in regard of the time - I chose a coarse resolution because I had to read the values manually from the small blue screen).

Re: Yet another coil gun prototype
V2006, Thu Nov 08 2018, 12:54PM

Looks impressive. But as practice shows, any calculations are significantly different from the facts.

Re: Yet another coil gun prototype
Plasma, Tue Nov 13 2018, 06:54AM

Zuckerstange47 the second and forth graph looks like you increased the resistance, ssmaller wire diameter maybe, that is forward emf after switch off, switched off current before the coil I think,
Nice work.

Re: Yet another coil gun prototype
Zuckerstange47, Wed Nov 14 2018, 09:42PM

Plasma: I do not understand why it looks like I increased the resistance, as my knowledge is very limited. To me, the first and second look almost the same. The only change between the shots was that the capacitors were not charged as much on the second and forth graph.

My next planned steps are to tidy up the construction. I designed a simple PCB to produce multiple, more beautiful light barriers easily (on the image the coil and a spring-type terminal block is overlayed).
Also I am printing an apparatus to help making coils, based on a previous design of mine (that is shown on the other images). The new one will be more stable (I hope) and the distance-adjustment should not lose it's setting by mistake, when rotating the pipe.

Re: Yet another coil gun prototype
Shrad, Thu Nov 15 2018, 08:01AM

if you need ultra fast detection, a small laser module and a reverse biased PIN photodiode will be top gear

Re: Yet another coil gun prototype
Zuckerstange47, Mon Nov 19 2018, 12:14AM


I think the ones I am using are fast enough for my experiments, but thank you for the information nevertheless.


My current big problem is that I cannot build coils the way I want to. Does anyone have a tip for making a good transition between one layer and the following one? In the last image one can see that I finished the first layer, wound from right to left, and consequently want the wire of the first winding of the second layer to stay between the two leftmost windings of the first layer. Maybe the end plates (black disks) should be mounted in a more rigid way, so that the wire cannot slip into the gap...? How do professional coil-winder solve this problem?

I am afraid that my new winding-machine was printed in vain

Re: Yet another coil gun prototype
DerAlbi, Mon Nov 19 2018, 11:51PM

Ger: Orthozyklische wicklung
En: orthocyclic winding

Re: Yet another coil gun prototype
Zuckerstange47, Mon Nov 19 2018, 11:57PM

Okay, I partly found a solution, but the result is still very bad. I put the coil between some nuts on a threaded rod, and adjusted it in the way that the number of windings on the first layer was right. The second layer looks okay, too, but later ones look a bit messy and probably I missed some windings. At the end I had 3 meters too much remaining on the spool (assumed the sellers specification was correct), but the outer diameter of the coil was the one my coil-calculator had generated.
The winding-procedure was not pleasant also, because rotating the printed parts seemed to result in tightening the nuts, and so the resistance got stronger after each turn, and now I got several blisters on my hand. That was one reason why I changed the first winding machine's design (the pink one) in the first place...

I do not want to unwind this thing again, but at least I learned a bit from it: Next time I will measure the wire length beforehand and mark it every meter or so. Also I might print something to have a better grip on the rod and turn the complete thing instead of clamping the pole and only turning the coil with the printed parts. I suppose the coil will work in an acceptable way even if it looks ugly, but at least I would like to know how much wire I used, and how many windings I made.










@DerAlbi: The Orthozyklische Wicklung looks very promising, but because of tight tolerances and the need for a very precise positioning of the wire it seems to be impossible to implement for me. Have you succeded in realizing this technique?

Re: Yet another coil gun prototype
DerAlbi, Tue Nov 20 2018, 12:41AM

Well.. lets just say: i got so far that it seemed plausible with better equipment
I have built a 3d printed winding machine too (fully automatic) but it was way too flexible. Today i know what would need changing, and can tell you right now that your setup will never succeed. Inconsistent wire tension is the first issue - not only is the force unknown, but it will vary over time.
So what works in your case is to use a small stiff plastic piece and manually lay down every turn. But even that will result in wild winidng after a few layers. Try to make the coil former either exactly n*WireDiameter or (n+0.5)*WireDiameter, anything in between will fail. Use the highest wire tension the wire allows (can be calculated) which helps with laying down the wire consistently. Your picture shows kinks in the wire even after the wire tensioner - this may never be the case. Straighten the wire through a pulley labyrinth and pull it really hard. 1mm diameter must be pulled with around 5kg equivalent (50N). It can withstand 17kg before breaking. So dont hesitate.

However I have found that there is no substantial loss in performance of the coil, if wound wild. It is really more a cosmetic thing. Keep going. Dont invest too much time in printing. Its too far from viable.

Re: Yet another coil gun prototype
V2006, Wed Nov 21 2018, 08:14AM

Very beautiful. But with such an investment of time and labor, I would have wound it up manually a long time ago. And thicker wire

Re: Yet another coil gun prototype
Zuckerstange47, Thu Nov 22 2018, 12:01AM


Wow, I can hardly imagine how long that machine took you to make. You do not have any images/videos of it, or do you? Did you construct it for mass facturing your coil gun?

I will not try to get perfect coils anymore, the wild winding style should be sufficient, but of course I still want to make some improvements. The last coil created the problem that I could not remove it from the acrylic tube without damaging the coil (see photo), even though I had several layers of paper wrapped around the tube to prevent this from happening. On the next try I will have stronger printed limitation-discs that can be slides without deformation, and I will take more care of the paperwork. Is this a common problem?

I only changed a little bit on my winding machine: The two pink big cog-wheels are directly connected to the nuts on the threaded rod (melted into it), so I can move the complete rod instead of just the central part like last time to prevent it from clogging up. Also I improved the wire routing and other minor things, but I know it is still very primitive. At least the conversion was fast and simple. Unfortunately I do not have enough wire to test it at the moment.


I guess you might be right, but I thought the procedure would have been too complex for a two handed person like me without some helping device. In the end my machine is just a mounting for the rod and a clamp for the wire, so I have to confess that a lot of time was wasted.

Re: Yet another coil gun prototype
DerAlbi, Thu Nov 22 2018, 01:23AM

It was during the time i was new to CAD and 3D-Printing. It took about 10 weeks i guess. But i also wrote the software for the stepper motors, the wire tension system and the PC (usb) user interface where i could program the machine. I have the machine still in my room, but i dont plan to ever use it again - its not in shape for a photo. I didnt had full automatization in mind, but just to get a high quality coil (which i didnt get from the machine). It was basically a hind-winding machine, where my hands executed stepper motor sequences. Once refined i could ususally play sequences that wound 2 layers failry quickly.

Your coils look fine. You might want to make the sides of the coil former aluminum to make the sides stiffer. Put a layer of this brown packaging tape on it and treat it with vaseline (this makes the epoxy not stick to the sides). For the inner coil former i recommend POM plastic rods (get some from ebay). Epoxy does not stick to POM plastics.
Then use epoxy that does not hardens quickly. 1h minimum - better 3h to give you time to work. After every wound layer apply epoxy with a brush (you can clean the brush with acetone afterwards). Dont use too much epoxy or it will ooze out. After you are done, heat the coil up to 80 - 100°C which is easy by running current through it. You can use step-downs from ebay that can deliver 20A or more ; Heat the coil with high power, then let it sit at 10W power consumption to keep it warm.
With high temperature your epoxy will cure fast after you are done winding. It should give you very good coils and disassembly of the coilf ormer wont rip apart the coil.

That said, your coil shape seems a bit weird. They are very short and fat. Got such a short projectile?

Re: Yet another coil gun prototype
V2006, Thu Nov 22 2018, 09:04AM

Zuckerstange47, I can send you my coils.

Re: Yet another coil gun prototype
Zuckerstange47, Thu Nov 22 2018, 06:20PM


Thanks for the thorough advice! As Epoxy I was using "UHU Endfest", which has a very long hardening time. On the subject of the short coils: "Tomspol" wrote that ealier (14 posts above), too, but I did not understand why the coil should be of the same length as the projectile. From my little knowledge a shorter coil should have a stronger magnetic field, but I would like to be corrected if that is wrong. My plan was to make two different coils as a short-term objective and test which one works better.




Thank you for that offering, but I would like to make my own ones ("the route is the goal"). I already wasted too much time on the machine to stop making coils now Furthermore I already got new wire today.

Re: Yet another coil gun prototype
V2006, Thu Nov 22 2018, 09:12PM

OK. Good luck

Re: Yet another coil gun prototype
Zuckerstange47, Thu Nov 29 2018, 05:51PM

I just realized that I might not be able to build a coil gun the way I planned to, because I did not read the fineprint on some component's manual (and as mentioned earlier I am a newbee on the subject of electronics).
When looking at the datasheet I thought my MOSFET could be used for switching 209A @ 75V, but when looking at the "Maximum Safe Operating Area"-Graph it seems that the 209A (continuously) are only permitted at a voltage of about 1.4V, and that only 0.5A can be switched @75V for a time of 10ms. Is my interpretation correct?

PS: Attaching the file did not work...


There is the image:

Re: Yet another coil gun prototype
DerAlbi, Thu Nov 29 2018, 06:05PM

Well, if your mosfet is on, then there is just little voltage drop across the mosfet (since Drain sopurce is virtually shorted), so the specs make sense. Also if your mosfet is off (Drain-Source not "shorted"), which allows the 75V across drain.source, then NO current will flow, so you are below the 0.5A rating as well.
The only critical thing is, switching from On to Off. There is a transition period where there is actually 200Amps AND 75V across the mosfet. the faster you switch the shorter the time. And you will switch faster than 10µs. So dont worry about the 10ms rating.
However the energy from the coil must go somewhere. The current will continue to flow even if the mosfet is off. A freewheeling diode wont conduct instantaniously but it will also take time for it to "turn on". This effect (forward recovery) does not exist in Schottky diodes, but they often dont have a beefy current rating and only 2x overload safety - in contrast to silicon diodes which suffer from slow forward recovery but are much more resistant to overloading.
Why am i telling you that? The time it takes the diode to take over the current is time that the mosfet spends in the transition state between on and off - this is what is (mainly) shown in the SOA diagram.
Honestly, just try and see what happens.

Re: Yet another coil gun prototype
V2006, Thu Nov 29 2018, 09:05PM

Zuckerstange47 My offer is still valid.
Buy coils from me and become the first designer on this miserable planet.

Re: Yet another coil gun prototype
the_anomaly, Thu Nov 29 2018, 11:29PM

Zuckerstange47 My offer is still valid.
Buy coils from me and become the first designer on this miserable planet.

The joy of learning is in the journey not the final result. Zuckerstange47 is learning by doing.

Re: Yet another coil gun prototype
Zuckerstange47, Fri Nov 30 2018, 12:37AM


I guess my question must have been really stupid I am very grateful for your patient explanation!
For the switching to be as fast as possible I was thinking about using a MOSFET-driver for each MOSFET. My driver has a rise time of about 35 ns for my MOSFET, so I assume that should be fast enough.
As a suppressor ("Schutzbeschaltung" in germon, is this the right word?) I am using a Zener diode (1N 5908, 5V, 1500W) and a diode (P600M, 1000V, 6A) but I have not figured out how to calculate the time for the transition state.
Does your last suggestion indicate that I will notice the MOSFET beeing destroyed if my suppressor it not good enough, or do you mean to see the result on the oscilloscope (which I do not own)? So far there were no defects on my prototype (as far as I know).

( Zener and diode:
)




I do not really understand what the designer-part means, but my coil construction line is ready for production




Exactly!

Re: Yet another coil gun prototype
DerAlbi, Fri Nov 30 2018, 08:05AM

Dont worry about the life of your mosfets right now. They will blow anyway at some point, so just buy enough instead of being overwhelmed by complexity.
1.5kW-Zener: sounds sketchy. at 5V that gives your 300A, but a (is it really a Zener or is it a TVS?) Diode will suck up that heat energy in its silicon - once that gets hot enough it will die.
TVS diodes with 1.5kW will never dissipate the 1.5kW, its only a theoretical rating because a pulse load is assumed. This pulse load (Transients) arent supposed to be longer than 10µs at some points.
There are people who built Coilguns with Zeners and it worked, but i think you need to use a much bigger Zener.
For a start, you can simply use a normal diode in forward conduction and see where it gets you. But try your Zener first. But check it after every pulse.
Regarding your switching speed: dont worry. Knowing the usual Coilgun setup, the actual switching speed of your mosfet wont be an issue. The time it takes for the current to stop flowing through the mosfet is another issue. I guess your mosfet will be fine.
Just try. Post a picture of your setup first ^_^

Re: Yet another coil gun prototype
V2006, Fri Nov 30 2018, 09:08AM

Zuckerstange47 The part is a coil of unique design.
But everything else is possible
There are no more such coils on this planet.
Better learn from the best tutorials
Good luck

Re: Yet another coil gun prototype
DerAlbi, Fri Nov 30 2018, 09:42AM

WTF.
V2006.. sometimes... i am just not sure if you are a troll or actually that ...... weird.

Re: Yet another coil gun prototype
V2006, Fri Nov 30 2018, 05:37PM

DerAlbi mutually))
here 15 years they write the same thing
I just wanted to help

Re: Yet another coil gun prototype
V2006, Fri Nov 30 2018, 05:45PM

they have been discussing the same thing here for 15 years - mosfet , diode ...
I wanted to help

Re: Yet another coil gun prototype
Plasma, Sat Dec 01 2018, 11:08AM

This might help limit the damage to the MOSFET,,a diode will only protect against forward emf not back emf. If you place a capacitor and resistor in series and then parrellel across the coil it will asobe the spike if it has a large enough storage

Edit picture isn't showing

Re: Yet another coil gun prototype
V2006, Sat Dec 01 2018, 12:33PM

I know it.
I wanted to say that in the discussion of small details, the very essence was lost here
So you can do another hundred years the Electromagnetic Projectile Accelerators
No success
It's not like you think
You lost the essence here the Electromagnetic Projectile Accelerators

Re: Yet another coil gun prototype
DerAlbi, Sat Dec 01 2018, 03:18PM

The essence of the hobbyist coilgun is learning electronics. Communicating about effects in electronics and how to read datasheets, understand the SOA and so on, is therefore extremely on topic. And everyone has to learn it again and again, that is natural.

The essence of a professional coilgun is very different. Its technically a linear reluctance motor which is very complicated. Its metic is power densitiy - nothing else matters; the often discussed efficiency is only the means to achieve a good power efficiency.
So "Shots per second" * "Kinetic Energy per Shot" / "Device weight" gives you a number in Watt per Kilogram. This is generally the figure of merit a motors engineering is judged on.
I have never seen you having any credible scientific description of what you achieved except shaky 240p camera footage shooting at a door or tin cans. Actually, seeing t´any built in action is the least interesting thing: numbers are the only thing that counts in the professional league. I didnt find anything relevant from your side until now.
I dont really understand how you complain about the state of things.
It seems strange to reply to Plasmas "put a snubber circuit around the mosfet" (thats what he tried to say - just paraphrasing for better google words ) with "i know it" as if the thread was made for you.
Generally you hijack a lot of threads and post your coilgun videos that are without any information or relevance to the thread.
The spam in one of your previous posts for example linked to 2 videos: and .
Whats the point?
Do you think that video without any numbers or description of how its built or what exactly is innovative is any contribution to the community?
All anyone sees is that something moves. How is that any superior to what Zuckerstange is trying?
Please make your own thread, provide the world with the wonders you engineered there and please provide real numbers including the procedure how you obtained them. If you have done anything ground breaking, people will acknowledge it.

Re: Yet another coil gun prototype
Zuckerstange47, Sat Dec 01 2018, 03:25PM


I have been using the zener + diode for about 20 - 50 shots with no problem so far, but the voltages were not very high yet. I will post an image when I plan to change the setup.




I cannot upload pictures as well, thats why I used this uploading service last time:

(It belongs to the blender 3d-software community)

I would be very interested in learning more about that topic.

Re: Yet another coil gun prototype
V2006, Sat Dec 01 2018, 06:23PM

DerAlbi : it will take another hundred years and you will not do anything

Re: Yet another coil gun prototype
Zuckerstange47, Sat Dec 01 2018, 07:13PM



Your links do not work, again.

I modified them here:







Anyhoo, I do not understand why this link-posting is happening right here, and also in the comments of many youtube videos, that are distantly related to the topic.

Re: Yet another coil gun prototype
V2006, Sat Dec 01 2018, 07:23PM

Zuckerstange47 Thank you

Re: Yet another coil gun prototype
DerAlbi, Sat Dec 01 2018, 07:24PM

And what do those videos show in particular? Some coilgun shooting.. so what?
What efficiency? What device weight? What shot rate? What projectile energy? There is none of the really important information in those videos.
2kJ @ 100V with 400mF... is exactly zero information except how much money you put in. Everyone can do that and accelerate some projectile with this energy.
I am not sure what i have not done and what exactly will take 100 years. My coilgun is finished and as far as i know with 27W/kg my linear accelerator has the best power density in the world (regarding the devices powered from capacitors), but i love to hear other results..

Re: Yet another coil gun prototype
V2006, Sat Dec 01 2018, 11:22PM

DerAlbi
you have no such video
money spent many times less than you spent
for the money that you spend, I would do even better

coefficient of performance not less than 30%

projectile energy not less than 600 joules

*2kJ @ 100V с 400mF

device weight:

Re: Yet another coil gun prototype
DerAlbi, Sun Dec 02 2018, 01:45AM

Sry, i dont find a weight nor shot rate
I found however that your projectile weight is given as "370 to 480g" which is an uncertainty of 20% for the weight alone. How is that even possible?
Your build uses a very big projectile. With such a design it is not complicated go get into the 3 digit energy range. You can think about it as if you have built a bigger and heavier motor: more iron and copper, more power, but also more weight. The tricky thing is to get more power out of the same build volume and materials. Also it is not difficult to put a lot of energy in the projectile as long as the projectile is fat and slow. Small projectiles at high speed is there the engineering begins.
I dont think you can compare my goals with yours. I have a magazine, automatic reloading, quite some complicated software and a complete case for my gun - it also adheres to local laws and is battery powered for as much as 200 shot per battery charge. I dont think that you have any idea what it took to get to this state, so sorry if i ignore your comment on my resource spending.

May i ask what you think you have done differently to anyone else to get the performance you see? (except building a really big gun)
You criticize that everyone builds the same stuff and there is too little development in the community..
Hands down, what is your invention here? (beside the size)
Can your technology be scaled down to achieve a 100J version with an 8mm diameter 30mm long projectile? If you build a small, light and compact demonstrator, i would be impressed!

For a start: is it an SCR-design, or resonant, or halfbridge?

Re: Yet another coil gun prototype
V2006, Sun Dec 02 2018, 08:51AM

DerAlbi
370 до 480 г - optimization experiments
370 г. - for 10300 J (450 V) optimally
for 2000 J (100 V) optimally 550 g
I can do everything
but I have almost nothing
if i lived in dresden and had that kind of money like yours i would do everything
my material base is outdated
with modern material base everything is possible
8mm diameter 30mm long projectile - also possible
but this is unnecessary complexity
diameter of 12 - 14 mm will be more optimal

Re: Yet another coil gun prototype
V2006, Sun Dec 02 2018, 08:57AM

here you can understand that the velocity of the projectile is great



370 gramm, diametr 22 мм, long 145 mm

Re: Yet another coil gun prototype
DerAlbi, Sun Dec 02 2018, 11:59AM

Ok, you totally misunderstand why i spend resources. You think that it spend all this time to get a 20J gun and find that pathetic - i get that; if you phrase it like this, you are right. But you totally miss the point of my build.
As far as i can tell from everything you say you have scaled up your coilgun and got a very big and powerful device - maybe the strongest hobbyist coilgun in the world currently.
Scaling up is a matter of resources - i totally agree and understand why you think you could have done better in different circumstances. You spent your resources to get to 600J; but scaling up is the most trivial thing to do in a coilgun. Nothing changes, everything just becomes bigger and with this, naturally things become stronger and up to some point also more efficient.
But you have not built anything new or innovative - its just big. You seem to use the optimization routine every hobbyist uses and you also seem to use the same concept as everyone else uses.
If your goal was to create the ultimate big gun, you succeeded, but this was far away from my goal, so dont compare us.
My gun is the smallest possible with high shot rate and decent output energy with scalable concepts behind it. I broke several usual design rules of coilguns and reinvented a lot of components to get the most energy transfer out of the least volume and weight.
I am sorry to say, but having had those ideas was more a matter of sleeping, walking and shitting than the fact that i spend all my money on the gun. Money made the quality possible, but the performance is not a budget issue. This is about engineering skill and creativity and understanding the device in depth, not scaling up the known concepts.

So i really do not understand your criticism that the community is not moving forward: scaling up has nothing to do with evolving the technology. The last time this forum has seen something truly innovative was the member "Yandersen" with his resonant foil capacitor design.
If you could spend more money, i am quite certain you would get in the kJ-range quite easily. But it would still be the basic SCR design. How would that move the community forward? Kinetic kJ-range coilguns had been done, so whats the point of scaling? New concepts (that are in reach for hobbyist) is what we would need. My design unfortunately isnt suitable for hobbyists.

Re: Yet another coil gun prototype
V2006, Sun Dec 02 2018, 02:03PM

Ok DerAlbi send money - i will make a small model
there are plans to make a small model
but there are no more capacitors
there are no wires either
in general, there is nothing
in the presence of investments I will do everything

Re: Yet another coil gun prototype
the_anomaly, Sun Dec 02 2018, 04:21PM

Ok DerAlbi send money - i will make a small model

This is a forum for sharing information. You can post a thread in the Sale and Trade forum if you wish to sell anything.

Re: Yet another coil gun prototype
DerAlbi, Sun Dec 02 2018, 11:01PM

in the presence of investments I will do everything

This is exactly my point. You will never get investors if everything you show is the capability of scaling without improving. You had capacitors, you had wires, you decided that the best you could do was scaling. If you could do more you would have done so. A good system is not about money, its about concepts. I ask you about conceptual improvements, but i never get an answer. It seems like you simply optimized an large scale SCR design and thats it.
Dont get me wrong: its an impressive gun with 600J kinetic, but from a technical standpoint it has been done - way bigger in some publications.

I could send you IGBTs (15x IXGK320N60A3 with their legs cut of, but you can solder wire onto them, they still work) and diodes (15x P600G) for free, if you like. I would even pay for shipping, i really understand your frustration, i have the same problem, but on a different level (my tools also were never good enough for the quality i wanted). But you would need to build the IGBT driver circuit on your own. Can you do this?

Re: Yet another coil gun prototype
V2006, Mon Dec 03 2018, 01:24PM

I have two devices - a small one for 600 Joules kinetic (2000 Joules, 0.4 Farad, 100 Volts)
and a large at 1600 Joules kinetic (10300 Joules, 0.1 Farad, 450 Volts)

If I do not get investors, then this miserable planet will never make progress
if I tell you everything - everyone can do it - what will I get from this?
IGBT it's good
but we need modern capacitors

Re: Yet another coil gun prototype
DerAlbi, Mon Dec 03 2018, 05:09PM

Oh boy, you are a mess.
I really do get it, it depends really on luck where you are born and what access to education and society you have. Digikey parts are the same price for many regions, but income is not. For me, ordering part hurts a bit, but for others it is outright impossible to get industry quality supply. You seem like a very frustrated person blaming your problems on others and showing even jealousy which i understand, but i think that it is not a way forward.

In your videos, you are charging your capacitors with a light bulb. I can tell you outright, that it is impossible to bring the world forward with this level of technology; yet i understand that my critique is pointless because you simply cant do better with your resources. Still, any level of serious engineering is currently years away from you, even if you had resources - just to learn how to use the resources. [Doing simulation (circuit and FEM), make PCBs, programming, 3d printing, milling...]
I honestly dont see how you ever could get investors with your current mind set. You need more references for your engineering skills. Also you really should not write sentences like "but we need modern capacitors" because this implies that you think that your technological improvement might depend on other technological improvements that are not in your hands further saying that you havent actually done more than scaling.
The fact that you criticize important semiconductor effects as overhead to the topic speaks for it self.

The issue that repels me the most is currently the impression that you dont even know what you dont know and flourish in that ignorance. Without that knowledge you cant even appreciate or recognize or replicate engineering work leading to frustrated sentences like "i could do better than you with your resources" without knowing what you judge.

Your build with the 30% efficiency is impressive - no doubt! I analyzed your youtube audio and the claimed 50m/s is plausible. But if the 30% efficiency would be the result of a ground breaking new optimization, scaling to 1.6kJ kinetic should not reduce efficiency to ~16%, if that optimization would be systematic and repeatable.
For me it looks like you just pushed more energy in the bigger gun, went deeper in saturation and got reduced efficiency. And the 30% efficiency with your dimensions is far from impossible, so i dont see any mechanics that are worth supporting right now.

Your projectile weighs 20x more than mine, and you push 30x more energy. So with the same iron you push 1.5x more energy than i do. That is not impossible in terms of scaling: the bigger you build a motor the easier it is to get better efficiency. Keep in mind that my goal was more complex than just energy transfer: i tried to reduce weight as well (and have a full functioning stand alone system with high shot rate)

I am really open for you because i see that you have enough passion to be frustrated. But in your position your only chance is to be open about your achievements and be honest and detailed. Keeping this technology to your self is not a way forward to be recognized. First we need to discuss if your gun is really the result of some good idea or if it is just up-scaling.
If i really missed something and you keep everything to your self and die with your secrets, then the world indeed will not go forward. On the other hand, if you are open and we find that everything you think is special about your gun can be explained by already known effects, then maybe that will lower your frustration too. Your mind set - being a frustrated, unrecognized talent - is damaging in the long run.

@mods: i know that currently the forum software is currently a bit kaputt. We are hijacking Zuckerstanges thread, but V2006 is something that deserves attention. Sorry if you grind your teeth if the admin tools are not functioning right now, but i hope you can cut out out posts later on. Damage is already done, so we might as well continue here.
@ Zuckerstange: sry auch an dich ^_^

Re: Yet another coil gun prototype
V2006, Mon Dec 03 2018, 08:28PM

I had no money for batteries





even on this miserable planet is full of ways to charge capacitors

100 volts proved to be more efficient than 450 volts

I spent almost three years in prison
when I came out I saw that nobody did anything
and none of you will do anything
the inhabitants of the earth have deceived themselves "Doing simulation (circuit and FEM), make PCBs, programming, 3d printing, milling...]"

if it interferes Zuckerstange - write to my thread
or e-mail **link**

Re: Yet another coil gun prototype
DerAlbi, Mon Dec 03 2018, 10:57PM

Thanks, you made a pretty clear picture now.
I am sorry to say that i dont see that you have a working theory about coilguns. Lowering the voltage to get better results is a tuning step, but from a system view always wrong. If you need to lower the voltage you have too much capacitance and too thick wire in your coil.. Your goal should always be to minimize current, because that is what causes heat. And maybe you wouldnt need better capacitors, because losses in ESR matter less...
Maybe you deceived yourself getting away without theory and simulation

Just out of curiosity: what do you expect from others? What is the progress you demand??

Re: Yet another coil gun prototype
V2006, Tue Dec 04 2018, 09:32AM

I have working theory about coils
I have everything except money and happiness))
I do from what is available
There were 450 volt capacitors
And there were 100 volt capacitors
I just have no other capacitors
Previously tried 900 volts and even 1350 volts - meaningless
And my coils do not heat at all
In one Israeli university undertook to calculate my parameters - they didn't succeed
completely different results were obtained
apparently, without receiving my layouts, no one will understand anything
I don't speak English well
progress is 200 meters per second and above

Re: Yet another coil gun prototype
DerAlbi, Tue Dec 04 2018, 10:15AM

Make a detailed drawing (dimensions of your coils, coil distance and so on, also the projectile..) also prepare capacitor values , turn count, DC resistance, wire diameter and switching points (positions or timings). I will conctact you via email and invest the time for a simulation. I can also have a look on what you think is special. If you dont trust me, then dont. But nothing will come from nothing. If its just an upscaled SCR design, it should be manageable. I had good experiences with simulation.

Re: Yet another coil gun prototype
V2006, Tue Dec 04 2018, 10:48AM

Ok. Write to my e-mail

Re: Yet another coil gun prototype
Zuckerstange47, Wed Dec 12 2018, 03:31AM

I was reloading the thread for days, without noticing that the conversation moved to another thread

Instead I will continue updating my stuff: Yesterday I got PCBs from China to build light barriers. They probably are not perfect, but I like the result. The barriers are meant to be clamped on two threaded rods so that they cannot move when accelerating a mass, yet it should be possible to reposition them easily.
I bought them from the manufacturer shown on the parcel in the image.






Even though most of you might know about buying PCBs, the process was new for me, and maybe it could be interesting for others, too, so I will give a short summary: I learned about the shop from numerous youtube-tutorials on the topic, it seems to be the cheapest source for getting such products. The designing process can be done directly in the browser window ("EasyEDA.com") and the basic knowledge about using the software can be aquired in about 1-3 hours.
I bought 10 PCBs (the minimum quantity, I guess) in the cheapest finish (2 conducting layers [even though I only used one], 10x10cm) with four light barrier boards on each PCB, so I got 40 all in all (probably too much actually). The costs are 2$ + shipment and paypal currency exchance charge, which resulted in about 9,50 Euro for me (0,24 € per light barrier board). This way it was much easier to make multiple light barriers, with a much nicer looking result, compared to the ones I made using perfboards.

Re: Yet another coil gun prototype
V2006, Wed Dec 12 2018, 08:35AM

Great choice.

Re: Yet another coil gun prototype
Zuckerstange47, Sat Dec 15 2018, 12:59AM

I cleaned the machine up, because there were too many cables hanging about, and installed the new light barriers. I also soldered a new perfboard with MOSFET, driver, diode and zener - the previous version had an external MOSFET-driver which was responsible for lots of ugly cables on the table.
The much more stable mounting for the light barriers and coil is new, too, and the parts can finally be fixed by nuts.



Like I said before, I would like to experiment with different coil-designs before moving on. The plan is to charge the capacitors to a specific voltage, and try to get the fastest shot by varying the starting position of the projectile and of the light barrier that deactivates the coil (the first barrier moved to the other side of the coil to be able to work with longer coils, as Tomspol suggested on page 1). Also I would note the remaining voltage after the shot to bring the energy-consumption into the equation. I am not sure if this is a good approach, I am open for suggestions.


@DerAlbi: If I understood right, you indicated that my "Schutzbeschaltung" might not be the best solution. I made a sketch of my circuit containing the diode and zener. Maybe you could tell me if this is correct, or what I should change. I used the following explanation for making the circuit:

At the moment I am only testing with relatively low power, but I plan to raise it some time and then I would install multiple MOSFETs and drivers in parallel.




Photos:







Ciruit (Germon language!):

Re: Yet another coil gun prototype
ShieldExperiments, Sat Dec 15 2018, 04:28AM

Dang, you Germans always seem to make beautiful coils!

Zuckerstange, I'd reccomend just going for it with the zener + diode for a while, and run it until it burns out. That way you can fine tune your other variables while you save up for a better snubber.

That's not to say you can't get away without a proper snubber, if you're willing to sacrifice some efficiency you can even get away with just using a straight diode and a higher voltage tolerant MOSFET.

But really, I'm impressed, and listen to DerAlbi - He's the real expert here, not me, and I wish you well on your adventures into this interesting field. Just don't be surprised when I steal all of your best ideas ;)

Re: Yet another coil gun prototype
Zuckerstange47, Sat Dec 15 2018, 01:54PM




Thank you very much!

Re: Yet another coil gun prototype
DerAlbi, Sat Dec 15 2018, 05:32PM

As elected King Albi of the Coilgun-Nation, i hereby declare that no coilgun shall exist with way shorter or longer coils than the projectile length; on this miserable planet.
Punishment shall be received on violation and executed by the majesty him self. A shot with no less than 2.5J to the thumb-nail must be suffered in addition to a 2 weeks arrest, strapped to the workbench where the offense was thought out.

But in seriousness, you asked for a reason the last time this was mentioned.
Go to Wolfram Alpha, and plot the function: "-x^3 * exp(-abs(x)) from -10 to 10"

This is how the force curve of a coil looks like (roughly). The left side, the force is positive, so the projectile is accelerated, at 0 (it correspondents to the the projectile center is at the coil center) there is no force, and than suckback kicks in. The time one experiences negative force, the current better already reached 0. This is not the actual force curve, but the force that you would measure if the current was constant.

If you have a too short coil, the "humps" move further apart (you have a larger area around x=0, where the force is 0, because as soon as the projectile tip exits the coil, there is pretty much no force anymore. The same is with a too long coil: as soon as the projectile is fully inside the coil, there is also no force anymore, resulting in the same force function shape.
The reason, the force-curve changes with the shape is because the force is related to dL/dx. The more the inductance changes with the projectile movement, the higher the force on the projectile.
But as soon as the projectile penetrates a too short coil completely or a projectile is completely inside a too long coil, the inductance does not change anymore, so no force.
Having the coil as long as the projectile results in the best possible force shape.

However there are positive side-effects to violating the rule:
Too short coils: they have a good material-to-force ratio (bot not better as optimal coils with projectile = coil). The timing is more forgiving because if the pulse is too long, you dont immediately run into suckback. Still, it decreases efficiency, after all you have a too long pulse, but shot performance does not suffer.
Too long coil: is the most useless design one could make in terms of material-investment (on this miserable planet). You have the same forgiving timing behavior (no immediate suckback). But all the portion of the coil that is longer than the projectile can be considered as additional resistance. Such resistance can be beneficial: on Barry's site he experimented with the (over/critical)damped LCR-circuit to shape the current waveform. This is what happens if you build a way too long coil. But you can save the copper (and weight) and use a resistor instead.

Still dont violate the rule. Remember the punishment!

Regarding the Zener:

I'd reccomend just going for it with the zener + diode for a while, and run it until it burns out.

I would fully agree. However, please dont be ignorant and at least know that you will damage your capacitor with this circuit. Electrolytics happily withstand -1.5V reverse polarity but you subject them to maybe -15 to -20V.
If you dont care about the life of your capacitor, then this is ok too - they will still last a while. But dont abuse capacitors, and later decide to put them into a bigger capacitor bank. While one failing capacitor (inner short circuit) is likely to be ok, if additional energy is delivered from the outside things can become messy.

Re: Yet another coil gun prototype
Zuckerstange47, Sun Dec 16 2018, 04:53PM






I plotted the curve, but I do not understand, how the formula is derived (I nevertheless believe in the king's word). From my experience I was of the opinion, that a force should exist until the projectile's center of mass reaches the center of the coil, independend of its lengths.
I hope I can confirm your rules by experimentation, but unfortunatelly I am too stupid to make coils. Yesterday I tried to make the most simple coil (35 windings in length and 4 layers), but failed in many ways. The calculated length of wire differed very much from the real one and I could only take the center pipe away afterwards by heating the coil up and by destroying the pipe (even though I used grease). I probably have to do many more coils until I learn to not make as many mistakes...

In terms of Schutzbeschaltung I will have a look at snubber circuits someday, because I do not like to damage the capacitors. Until then, I will just keep using my diodes.




The graph:

Re: Yet another coil gun prototype
DerAlbi, Sun Dec 16 2018, 08:58PM

The formula is not derived from anywhere, it is the result of plotting a FEM analysis and finding a model function that the data can be curve-fitted to. The actual model function would be more complex, but this simple form conveys all the features that are interesting for now.

From my experience I was of the opinion, that a force should exist until the projectile's center of mass reaches the center of the coil, independend of its lengths.

This is technically correct. But just because there is a force, does not mean it is significant.
See, the function plot shows you the force. The force at any given moment is a description how much your projectile is accelerated at this point (under constant current). The velocity is the integral of the acceleration - the summed up acceleration for every moment. Even this is a bit more complicated, the basic thought is, that the area under the curve is an equivalent of how much work the coil can do. This area is maximal if the coil length matches the projectile length.


Do not obsess over coil quality. Even very ugly coils show basically the same electrical data as perfect coils. The failures I see in your coils happens if your setup is not rigid enough. The pressure of the layers force the sides apart, then the wire falls deeper into the valleys and an unrecoverable winding defect propagates. The more it escalates, the harder it is to wind further.

Re: Yet another coil gun prototype
Zuckerstange47, Sun Dec 16 2018, 10:04PM

I had a lot of problems winding the coil: At first I marked every meter of the wire to be able to measure the total length, but when I should about reach the 2m mark, I could not find it any more. I did not even find the 1m mark, which afore I had seen on the coil clearly, so I thought the glue had dissolved it somehow, so I started anew (later I found the 2m coincidentally). I then marked it with masking tape instead.
On the next try I suddently noticed that the starting piece of wire was pulled into the apparatus and got wound onto the coil, too, because the wire-tension was too high. Also I once handled the wrong turning wheel, which resulted in the three nuts (on the side of the green part) to unscrew. I think the rigidity should not be a big problem.
Maybe I will do another coil later today, perhaps I will encounter even more accidents then .

Re: Yet another coil gun prototype
DerAlbi, Sun Dec 16 2018, 11:12PM

Why do you measure the length of the wire?
Measure the resistance of 10m of wire, (with a 5A current source and a voltmeter) and then do the same with the final coil. I dont see how wire length is critical to a coil.. its more turn- and layer count..
What is your thought behind that ?

Re: Yet another coil gun prototype
Zuckerstange47, Wed Dec 19 2018, 02:10AM



I probably did not put much thought into it. For comparing a long and thin to a short an thicker coil I thought it would be interesting to use the same wire length.
My second coil is finished now, here are some photos of them together with the projectile (which is about as long as the longer coil).
The making of the second coil was much easier than expected, due to my gain in experience and also because I used a device that automatically releases a portion of wire when needed from the spool (I constructed it from parts of a 3d printer and a pen). It is visible on the last image.





Also I attached the light barriers and started reprogramming the esp32.



[Edit: Continuity]

Re: Yet another coil gun prototype
DerAlbi, Wed Dec 19 2018, 06:54AM

Wire length is not really a metric that makes sense to use. It is basically the same thing as making the resistance constant while changing other parameters (except the wire diameter). However resistance is always a parasitic in a coilgun.. so why would you focus on parasitic, instead of the actual parameters that matter I think you get the point.

[Edit: Off topic content removed]

Re: Yet another coil gun prototype
Zuckerstange47, Thu Dec 20 2018, 06:09PM


I thought it would be a good idea, because with a fixed maximum switching current of the MOSFET, the resistance of the coils should be identical. But I think I understand, that it does not make much sense, yet I do not know how else to make a "fair" comparison.




Do you know what will happen to the capacitor, when it fails because of the missing snubber? Will it just stop working, or might it explode? I thought I heard a fizzling sound after my last shot, but the capacitors do not look different from before ...

Re: Yet another coil gun prototype
DerAlbi, Thu Dec 20 2018, 06:58PM

Hahaha
That is soo good. The typical Coilgun circuit ruins capacitors, and mostly no body knows or even notices it, because before serious damage is done, most have given up. It was always my suspicion (because it must be true) but no one ever confirmed.

The noise comes from is hydrogen forming. The capacitor will degrade over time, but i dont think it will have serious consequences. One fully charged ELECTROLYTIC capacitor on its own will never explode [dont apply that to high energy foil capacitors]. The energy stored per weight is less than (or around) 1 Joule per Gram of capacitor weight.. This energy is easily consumed by the thermal capacitance of the involved material. Even if only a small part of the capacitor fails (as short circuit) it is not different from an external shot circuit which is obviously fine. Capacitors explode when they fail and there is a constant supply of energy - like in a power supply.. if one capacitor is shorted, it may heat up and this continuous heat up can build up pressure that leads to explosion. The same is true for a very large capacitor bank (but not for a small one), if you parallel many capacitors.
As far as i know you can test the health of your capacitor mainly by measuring its leakage current.
What you do is, putting a 1k-Resistor (a high power one, or a low power one with a diode in parallel) in series with the charging circuit. Then you measure the voltage drop across the 1k resistor and wait until it is below sqrt(C*V) in µA (this is a typical value from the datasheet).
First you charge only to low voltages, then you increase the voltage up to the maximum rating.
This process is known as "reforming" the capacitor on this miserable planet..

If you have a bathtub, read about capacitors:

Re: Yet another coil gun prototype
Zuckerstange47, Thu Dec 20 2018, 08:13PM

What I noticed is that the voltage drops constantly after the capacitor was charged (about 10-20 seconds from 10V to 9V, roughly estimated). I guess that is a sign of damage as I did not see that behavior before.
I will try a reformation like you said (but without the math part ), starting at a supply voltage of 3V...

When saying the "typical coilgun", do you mean that most people construct their coilguns in a faulty way? Maybe many of the coilgun-makers do not have much more knowledge than me, who only started tinkering around with electronics by getting kicked into touch with the Arduino platform without having a professional background on this topic. Btw: How did you end up being king, did you study this? I hope this question is not too personal or off-topic, again... you do not have to answer

Re: Yet another coil gun prototype
DerAlbi, Thu Dec 20 2018, 08:53PM

When talking about the typical coilgun, i mean the SCR design. People like to think up ways to make the current drop faster after the capacitor is discharged to avoid suck-back, but most circuits actually reverse polarity on the capacitors. That is a common flaw, but as said, most people dont notice damages - even if, they dont know what is normal or not; a coilgun is a pretty forgiving project, it will almost always work and deliver results. Also, most coilgun builds are made from scrap parts anyway.. a damaged capacitor is not really a problem and damaging a capacitor takes time (many shots).

Some leakage current is always ok! Discharging from 10V to 9V in 20sec when a 10MOhm voltage meter is connected is actually quite ok.
As said, try to measure the leakage over a 1kOhm resistor. If the voltage drops below 5mV, then you are good. Leakage increases with the applied voltage. Electrolytics have their aluminium oxidized - the oxide layer is the insulation that gets damaged. If it just gets thinner, it will still work as insulator at low voltage, but becomes leaky at high voltages.
Just put it in your calculator: if you have 10.000uF and 50V, you get sqrt(10mF*50V) = 0.7 put µA behind it, and you are done. Now 0.7µA is a very low leakage current, there is always almost an offset to this, like 3..5µA. so anything below 5.7µA (or 5.7mV over 1kOhm) is healthy.

I did not study coilguns I studies electric engineering at university, but that teaches nothing about practical application of knowledge. It helps to get an engineering thought pattern if you do project at home however. During my university years, i took mostly curses that had nothing to do with what i do at home - just to get the broadest knowledge possible. I learned about information technology, wireless data transfer modulation schemes, error correcting codes, encryption, network behavior, game theory and so on. For some time I was an analog IC designer and worked with 28nm and 45nm IBM technology and now i am the R&D department of a company that builds 5G base-stations. Nothing about coilguns here
I just read a lot, try to distinguish good from bad arguments and i really like to play with simulation. It is very important to learn all the equivalent circuits of all components - all the different level of precision and complexity the component possesses and when to apply which model. It takes a lot of project to learn how to apply models and one should never give up; even if something does not work, the simulation must be brought to a detail until it shows the same problem.
I think the "king" part was a joke and i really do not consider myself as this. I think, i simply have wasted the most money and time on a coilgun. This builds up experience that others do not get, if they change the project after 5 months or if the are stuck with a particular design. I also tend to be a very active user here, because there is not much coilgun community left. I think young people are not into technology anymore; swiping screens is all they can do. So i help anyone i can here (who is interested in following engineering methods)
My coilgun is a very different design so i actually have no practical experience with most of what is discussed here (the SCR design). Everything I know about it is from simulation and the involved math, and seeing patters in the result of the work of others. So take everything with a grain of salt.

Re: Yet another coil gun prototype
Zuckerstange47, Sat Dec 22 2018, 06:42PM

Thats interesting information about your background - now I understand how much effort it must have taken to get a solid foundation of knowledge. For a moment I had the impression you considered yourself old, because of talking about the "young people", but incidentally I just read another post about your "rail"gun (in an airgun-forum), where your were described as a "young engineer". I hope to see the video about your design, that was announced there, some time, or have you stopped the project completely? In this thread I was confused that the subject switched towards tripling the energy to reach 60 joule...
Is this just an great dream by your uninformed video-partner, or is it a realistic goal?

Concering the leakage my measurement must have been wrong, because the capacitors were still connected to the inactive circuit. Now I don't see the pointer of the multimeter move at all (it is an analogue one, I do not know how many ohms it has). I already did a lot of reforming, but I am not sure how big the steps of voltage-increase should be, but I guess it probably is not that important.

Re: Yet another coil gun prototype
Zuckerstange47, Sun Dec 23 2018, 11:36PM

Today I started comparing the two coils and destroyed the coilgun, twice. After doing 19 shots with the shorter and 9 with the longer coil, I could not recharge the capacitors anymore. When starting the recharging process, it resulted in drawing a big current from the power supply, until it was turned off (even when the charging-switch was deactivated again). After swapping the MOSFET (luckily I had installed it on a socket) it was recharging and shooting just fine.
But two shots later something else smelled burnt, and I don't know what it is at the moment, I will have a closer look at it in the next days. What I know is, that I cannot charge the capacitors anymore when using the usual circuit, but I don't see why and the indications are different from the first time (the multimeter pointer goes up to 1V as long as the charging-supply is turned on, even when the MOSFET is unplugged). Outside the circuit the capacitors do charge perfectly.

However, the resulting speeds of the two coils were very similar, but the shots were not sufficient for an objective comparison. Strangely the speed trap gave faulty results from time to time, but only about one or two for the short coil (that was tested first) and about 50% of the measurements of the second coil. With that I mean that the results make the appearence of beeing wrong, but maybe even more were. Perhaps I should install two speed traps and check that the results are identical...
The speed of the projectile using the short coil was about 8.5 m/s (up to ~0.77 Joule) that was confirmed by many shots that were all done with capacitors charged to 30V. I learned from that experiment, how important the starting position is to incease efficency - previously I only reached about 1 Joule with a much higher voltage.
The longer coil resulted in a resulting projectile's energy of about 0.86 Joule, which was only achieved twice (because of the MOSFET-failure) with a higher efficency than the shorter coil (but I have not calculated it). The last shot with the new MOSFET was displayed as "2.32 Joule", and it felt relatively strong in my hand ( ), but I do not trust that one.

So, the next problems are to repair the coilgun and to think about, why the speed measurement is wrong so often, and if the longer coil could be the reason for the failures. Also I am having the snubber in my mind.

Re: Yet another coil gun prototype
DerAlbi, Tue Dec 25 2018, 10:28PM

My project is currently on ice. Without money, i cant do anything. (on this miserable planet!) I also would need a partner or 2.. to really get a good thing going. Complicated.

To help you with your problems, we need schematics of your gun and your charger.
It sounds like the negative capacitor voltage swing strains your charging circuit (maybe the rectifier diodes?) Give more detail about the current state of things.
Please with as much detail as possible (Mosfet types, Diode types, Resistor vaues, capacitor values, nominal in-out-oltages and so on; which component has a heatsink?)

Re: Yet another coil gun prototype
V2006, Wed Dec 26 2018, 08:59PM

fur DerAlbi: Daher müssen Sie etwas tun, um Investitionen anzuziehen. Ab 1600 Euro werden Sie nicht weit gehen. Die Bewohner dieses miserablen Planeten geben überall Geld aus. Müssen Sie sie in die richtige Richtung schicken.

Re: Yet another coil gun prototype
Zuckerstange47, Thu Dec 27 2018, 04:43PM





Thank you for your offer! After it stopped working, I uninstalled the perfboard containing the MOSFET and noticed, that there was an electric continuity between two connectors, that should not be there. Not until motivated by your post I started working on it again and measured a resistance of about 50 Ohms between those connectors. I do not know how the circuit could have changed it's own, but this conductance could not have been there before. I then took a box cutter and cut beween the perfboard pins which seemed to be the reason for the continuity and the problem was solved!
Afterwards I made six shots, which went very well and the speed-measurements were plausible, too (so I assume that they also might have been wrong because of the hardware-failure). I varied the projectile's starting position and reached 0.94 Joule, which is a new record for my 37 mF capacitors charged to 30V (they were discharged to 18.1V by the shot).

Then I wanted to take another shot, but this time I charged to 45V: The result was that the projectile accelerated intensly but was then sucked back and came to a stillstand after about 5cm. The capacitors were completely discharged, so I suppose something broke while the shot was on the way. Now I have the same problem as before and cannot charge the capacitors. I will disassemble it again, soon.

My components are (circuit image appended):
MOSFET: Toshiba TK72E12N1, S1X, N-Ch, 120V, 179A
Driver: MIC4420ZT, 6A, Hi-Speed, Hi-Current Single MOSFET Driver, 10.000pF load Drive
Diode: P600M, 1000V, 6A
Zener: 1N5908, 5V, 1500W
Capacitors: 22 mF and 15 mF, 50V

The charging circuit is a step up converter with a resistor in series. It is only connected before the shooting procedure takes place, using a switch. I do not use heatsinks, but I noticed there must have been some heat at the soldering of the MOSFET mount, as the white, printed PLA had a brown spot there.
Would it be possible that a spark originated there and melted the soldering tin again, so that the short circuit occured and the coil could not be turned off?


I will try to upload the circuit image again, this time I marked the position where there was an electrical conductance with a resistance of about 50 Ohms.



On the subject of your coilgun, I think the marked might be too small for the high price of a commercial product (1500 $€ when I remember correctly) and most potential customers or investors will not really understand what it is about. When seeing the post of the weapon-expert, who had seen your prototype, I had the impression, that even he did underestimate the effort you put into it, or would have to be done to triple the energy output.



PS: I think I can still not append images here, so:



PPS: Now I am measuring only 10 Ohms instead of 50, but I do not see were the two lines are connected. Maybe I should just rebuild the board completely...

Re: Yet another coil gun prototype
DerAlbi, Thu Dec 27 2018, 06:29PM

StepUp: a step-up converter will be short circuited by any load that demands a lower voltage than Vin. So if you supply 12V to your Step-Up, your capacitor cannot be discharged below 12V or excessive current will flow from your 12V supply.

If your board goes bad from the shots, try to make a better build. You are lucky that the components are not blown - respect your luck and give your components a suitable work environment; they have earned their place with their spirit.

What you delivered was a layout, not a schematic. Schematics are the language to describe the circuit intention. Your schematic looks like this:
(drawn with LTSpice)
A layout is a physical representation of the circuit. As you can see, some stuff from your layout didnt make it into the schematic: Control and the -12V make no sense; -12V is in fact Gnd. :-/

If you see a short circuit between Source an Drain of the mosfet, first make sure that there is no gate voltage. A pull down resistor [2.2kR between gate and source (the outer pins of the mosfet)] would be good.
Also note, that you cant measure as long as the capacitor or coil are connected, because they force a voltage between Source and Ground that annoys your resistance meter.
Check your diodes too. Maybe they are already blown. If the Zener is shorted, it would create weird effects for sure. (depending on how high resistive your layout is)
If you measure, try to reverse the polarity of your measurement. Only if both readings are consistent the effect you see is actually a resistive short circuit. Anything else may be a junction.

Re: Yet another coil gun prototype
Zuckerstange47, Sat Dec 29 2018, 12:40AM


I do not exactly understand this, is this connected to the reforming of the capacitors? When I did this, I directly connected the supply that can be tuned from about 0 up to 18V, and only used the step-up for the higher voltages. When charging to shoot the coilgun I of course used the step-up, but I stopped charging, when the multimeter showed the desired capacitor-voltage. Does this seem possible? (For that reason there is a push-button between step-up and capacitors, that does not seem to be included on the picture you made.)


Concerning the damaged circuit I realized that I forgot to remove the MOSFET when measuring. Now I know that the MOSFET is destroyed, again (but there is no short circuit on the boards soldering this time). Do you think this is due to the heat, or because the circuit is not good enough? I thought that the heat transfer would not be quick enough when the MOSFET is only switched on for 5 to 8ms at a time, so that a radiator would not matter. But after thinking about it, I got to the conclusion that I might be wrong and I have no clue about the speed of heat dispersal in a MOSFET.
I did measure the Zener, too - it seems to be okay. It starts conducting at about 6.5 V, just like a new one does. The diode is good, also.


The resistor beween gate and source is installed now, and I will care about the cooling next.

Re: Yet another coil gun prototype
DerAlbi, Sat Dec 29 2018, 02:37AM

Your intuition concerning the cooling is correct. Any power component that actually gets hot in a coilgun is basically dead. The thermal capacity of the mosfet is enough to swallow the heat. If you need a heatsink, then something is wrong. (Except if you shoot in rapid succession, then you need some thermal considerations)

If the mosfet is dead, there are multiple reasons:
1) too much current (who would guess)
2) excessive avalance energy: high voltage peak after mosfet shutdown. You think that you have the free-wheeling diodes, but they do not work instantaneous. It takes time for a diode to become conductive and in that time the mosfet burns all the energy in the coil, until the current path is finally redirected. Slow diodes (and the P600 is a dog slow diode!) are not the only reason - the diodes, depending on how they are soldered/layouted form an inductor (with a single turn). Any inductive current path resist current change - so the sudden expectation that there should be flowing current through the diode path, is a bit too simple - the current needs to build up slowly.. and during this time, your mosfet avalanches (drain source breakthrough due to high voltage spike).
3) bad gate drive: if the gate drive is inductive (long wires to the gate), the gate may overshoot and undershoot during turn on and turn of. This can be so bad that the gate is destroyed (due to excessive voltage)! After all, the wires are an inductor, the gate is a capacitor - what you have built is an oscillating circuit. To suppress this, people use a gate resistor. Such resistor lowers the quality factor of the oscillator so it wont oscillate anymore. Your mosfets internal gate resistance is about 2 Ohm already, if you have really bad layout, you might add 4.7Ohm in series with the gate.
Gate ringing can also cause parasitic turn-ons after turn of (if the gate voltage oscillates so much that the peaks of the voltage waveforms are high enough to turn the mosfet on again). If that happens, the mosfet is extremely under stress.

Regarding the step-up: dont get confused. My main point was that you need to take into account the circuitry that is connected to your capacitor. If there is a switch that is always open when you shoot, then this is ok. If the capacitor charger is always directly connected, then there can be issues. (but not necessarily)

Re: Yet another coil gun prototype
Zuckerstange47, Sat Dec 29 2018, 04:34PM

I calculated the current and discovered that it is too high, indeed. Strangely the measured resistance of the coil is only about 50% of the one that I calculated before winding it, so that I underestimated the flowing current.
Now I shortened the wire that connects the gate driver to the microcontroller and added a resistance, but I will not shoot in this configuration anymore. I want to research about snubber circuits and rethink the whole thing first.