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When to go public / ask for support | Coilgun | crowd funding


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Old 04-12-2017, 08:00 PM   #21
Belargo
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Quote:
Originally Posted by DerAlbi View Post
Hmmh. This is a question that has been asked before and its still not answered - at least to my knowledge and its by no means stupid but rather interesting to discuss.
First of all one has to discuss the mechanism: i agree with your proposal that an electric motor would be the way to go. Having a guidance system in place that gives the projectile spin during acceleration is not going to happen. The friction is way too high - which in a conventional gun is totally fine as this builds up pressure, but in a coilgun it just killing the little efficiency it has.
My thoughts about this are again precision related. I think a rotating projectile inside the rails would be comparable to a worn out bushing - if the fit isnt tight (which it isnt!), its not going to be pretty - it will result in wobble or chaotic movement as the rotating projectile collides with the rails...
So my guess is that it will actually worsen the projectile behavior in some way because the rotating motion is feeding unknown initial conditions into the system.
Another thing is a reliable and practical solution, but this is nothing i will even touch until i know the problem is actually real.
I know it sounds frustrating and very wrong from an engineering point of view, but "fingers crossed". You catch me on the one and only thing i am uncomfortable to make any predictions on.

I think Niels Bohr said it best: "Prediction is very difficult, especially if it's about the future."
I just looked up how fast bullets typically spin, and those numbers are truly frightening - somewhere around 300.000 RPM. If this is really necessary to stabilize a projectile in flight, this indeed might cause more problems than it will solve.
I wasn't thinking about the guidance system making the projectile spin, that friction would indeed be horrible.
Rather, would it be possible to make the dowel spin by using the magnetic fields of the acceleration coils? That way there would be no need for an additional motor.


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Old 04-12-2017, 09:10 PM   #22
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Unfortunately i dont know any technique to give an iron dowel pin spin as long as the dowel pin is the rotor itself.
But bullets are faster. They follow supersonic aerodynamics which is very different from subsonic scenarios. I dont think its a valid reference..
It could very well be that the projectile may be unstable but the path of flight is still straight.. which will be ugly as hell but somewhat acceptable..
I really need to see that in action


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Old 04-12-2017, 10:23 PM   #23
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As they say, the proof of the pudding is in the eating.
Shoot 'em up, and lets hope they fly true and straight without the need for any fluid dynamics shenanigans.
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Old 07-16-2017, 11:30 AM   #24
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Hi guys, just a quick update for anyone who was interested... i am still working on the coilgun and i had a lot of progress!
The hardware (electronics) are finished, tested and it looks very good - everything within spec right now. This means that its very possible that the prototype of the coilgun will be capable of 2 shots per second with 20J kinetic energy. (trust me, its a lot given the form factor)
I also have redesigned the case again and it will look somewhat better - yet i feel it will be inherently ugly. I accept that for now.
I also gained confidence that the case will withstand the stress of a shot and that the barrel-less design (required by German law) will work perfectly - it exceeds my wildest dreams to be honest
Also the sensor system that tracks the projectile position works better than expected.
My biggest problem right now is to wind coils that have a decent quality. The prototype will be copper based (a bigger design will be aluminium based to reduce weight) but i am unable to make nice inductors :-( I need rectangular copper wire which is not easy to get in small quantities. Making prototypes sucks.
All in all it still looks very good. There is still a lot of work to be done.. i guess in a few months i might be able to report the first shot, and early next year the software should be done (i have tested the low level stuff, but havent done any functional software design yet).
I all takes a lot longer than expected.. i have started to work 40h/week since i lost so much money on this project..

Anyway.. if anyone is interested in images of electronics.. i can take some
For now i guess most people will be interested in the "barrel-less" design according to German law since this is actually a mechanical design thing . This is just a look through 2 of what will be 8 acceleration coils.
So anyone who feels like a lawyer may judge now if this thing is "tubular", guides the projectile and so on..
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Old 07-16-2017, 02:39 PM   #25
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I am looking forward to updates on this project. Please keep us posted and Good Luck with your development.
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Old 07-17-2017, 08:06 AM   #26
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If the ball has clearance to the wall, there is no problem with the German law. A barrel must apply "a certain amount of guidance" (ein gewisses Maß an Führung), otherwise it isn't a barrel.

Also the law says the projectile must be pushed through the barrel (" durch einen rohrförmigen Lauf getrieben"). If I understand this correctly, your device actually pulls more than it pushes, right? This fact alone may render the "barrel" issue irrelevant.
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Old 07-18-2017, 06:22 PM   #27
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Haha thanks for your support Jörg :-)
unfortunately you are incorrect regarding the push vs pull-issue. Technically, yes i pull.
But when i asked the BKA about what i should do (do i need a permit or whatever) they told me explicitly:
Quote:
Der Begriff „getrieben“ ist stets weit auszulegen, da auch bei einem glattwandigen Schrotlauf der Schrotbecher lediglich hindurchgeführt wird, ohne dass hier ein Geschoss in die Felder eines gezogenen Laufes eingepresst wird
I am not sure if they got the point however there is no chance to argue ^_^

Additional to the WaffG there is a document where its regulated how to interpret the WaffG document - its called WaffVwV (Waffengesetz Verwaltungsvorschrift). Within some WaffVwV barrel-related paragraphs are:
Anlage 1 Abschnitt 1 Unterabschnitt 1 Nummer 1.1
Anlage 1 Abschnitt 1 Unterabschnitt 1 Nummer 1.3.1
and probably more but i am not a lawyer nor am i patient enough to read all through that stuff. I did actually read in some document that the "getrieben"-word covers all kinds of applied force so a broad interpretation is within their right afaik. The stupid thing is that i am pretty sure that this was stated within the WaffVwV but i cant find that clarification again. Strange. :-/

Anyway, i go with a black-orange color theme. My printer is running hot!
..and i kept the white test print in the shot just to show you that the case was reworked a bit.. on the right you see how the capacitors now kind of bulge through the case which increases sex appeal a lot.. i hope.. The grip houses the battery, the 210W-capacitor-charger and touch sensors for power-mangement. I am finalizing the design now...
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Last edited by DerAlbi; 07-18-2017 at 06:43 PM.
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Old 10-06-2017, 08:16 PM   #28
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I know, i know its been a long time, but i have made some progress. The case has developed quite a lot; i am still working on the upper hull, but it will never be pretty (its not fitting right, i know - its a nightly print to see how the design coarsely will look).
I have some problems with the reloading mechanism.. this is what took the last 2 weeks and will take the next week too :-(. Maybe i have a video when it works. The 2 shots per second i am going for is really hard to realize. The electronics is fine, but the mechanical stuff.. well lets say i notice my inexperience :-(
The electronics are still promising - havent found any problems (but the high power stuff was never operated yet) and the firmware is developing fine. The user interaction is as planed and it turned out very cool: accelerometer is checking the movement of the case to wake up the electronics, touch sensors check if the gun is held in a hand (even detects if its left or right hand and how tight you grip) and this can ready the gun. So no On-Switch. Refilling the magazine drum will also work as hoped.
One big design mistake are my status-LEDs (next to my trigger finger). They are red/green indicators but they are completely blocked from sight when i hold the thing, so.... well. Smile and keep going ^_^ No big deal.
My biggest issue is still the looks. I dont like it. I never will. The form factor was a stupid idea. Too late to change. I have learned that the many parallel edges on the design make it look boring/strange. Even if i could change that i would run into limitations with the 3D-printing. Its a very different process from injection molding and it has different constraints.
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Last edited by DerAlbi; 10-06-2017 at 08:24 PM.
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Old 10-06-2017, 09:58 PM   #29
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Startin' to look like something. I don't mind long pauses.
Keep us posted.
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Old 10-11-2017, 12:21 PM   #30
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Looks a bit clumsy though very futuristic! Not too bad at all! Very very thrilling experiment you got there!


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