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New member, but long time enthusiast - with a plan.

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Ragnarok

Fri Apr 20 2007, 12:14PM

Registered Member #659 Joined: Fri Apr 20 2007, 09:14AM
Location: SW Hertfordshire, UK
Posts: 75

I wasn't certain that this was the right place for this thread (as it's a cross between an introduction and a plan), but it seemed most appropriate, and I apologise to any moderators that think otherwise.

I have tried to research around the net of arriving here, but there will certainly be stuff I have missed on my tour of the major sites, so please bear with me.
That said, I shall introduce myself.

I'm David - currently at 18 years of age, from the UK, and still studying my A-levels, with intent to go and study engineering at university if my grades suffice.

Over the last year, I've developed an interest in all things that acclerate the relatively mundane to ballistic velocities using various homemade do-hickeys.
My mother however knows this "hobby" by several different terms, including "Distraction from school work", "Highly worrying" and "Potentially dangerous". Questions similar to: "How the hell did you blow a hole through plate steel?" are not uncommon around my house.

Mostly, this hobby proves to be semi-advanced pneumatic cannons (if you wish, I can provide images of these) that fire various items of vegetable matter (occasionally other items), but there have been a pair of coil pistols built from what I could salvage from a gamut of disposable cameras.

They were unreliable and slow to charge, with a worrying tendency to give me 300V electric shocks, had no form of electronics involved whatsoever - other than the flash charging circuit, and could barely fire through a sheet of paper, but the most important thing to me was they proved to be something new and exciting, and a fresh challenge to make and build. (I am also fairly proud of the portable design. Although the muzzle energy was only about 0.5 J at it's best, the whole thing was only about 8" long, 5" tall, and 1.5" wide, with a proper grip and trigger.)

The several hours I spent carefully winding coils in the mess I refer to as a bedroom were when I decided that coilguns were something I wished to continue with.

After the pair of pretty complex air cannon projects I have lined up to drain a fair chunk of my rather limited resources, I would relish the chance to build a proper working multistage portable reluctance coil rifle with proper electronic control and timing, so much so that I already have a large number of fairly optimistic ideas for what I would like to achieve from it.

Ideally, my (probably unrealistic) aims are:
- about 12 ft lb (16.3J) muzzle energy, to be on par with most air rifles. I realise this is optimistic, but I have seen references to a few coil guns that can manage a bit over this. In the end I am not overly concerned about total length.
- semi-automatic operation, with a reasonably fast charge. (5 to 10 rpm would be more than adequate for me. In fact, 3 would be fine. No thoughts on magazine size yet.)
- reasonable accuracy (I have some ideas about how to work on this, but I want to research further before I conclude it possible)
- portable
- multi-stage design
- either 6 or 8mm bore, as these are the most accesible steel rod sizes to me.

Now, as I often say, my electronics skills could be trumped by a drunken monkey, which means that when I get around to building, I will almost certainly drive you insane with questions of how to get a charging circuit built, and other similar issues.

However, although my skills may not be that great (although I do have an all round basic knowledge of CGs), I'd like to think I'm dedicated enough to complete this project, and my air cannon building skills should transfer across to at least some areas of the construction.

So, this said, I'd like to know whether my plans are too hopeful for a first time 'proper' CG builder - albeit one with quite a lot of mechanical skill and knowledge (and if they are too complex, what should I change?), or hear any of your suggestions for what would be a better use of my time and money.

PS: I seem to have an unnatural ability to cultivate anger and hatred for me in any forum I join. I'm hoping I can escape that here with any luck.
And I do try to type straight, but the occasional misspell might grace my posts.

uzzors2k

Fri Apr 20 2007, 12:34PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Welcome to 4HV! I'm sure you'll be well received. Anothercoilgun made a multi-stage portable coil gun which may interest you.

Everything is documented, so there's your whole project done.

Take a look at some multistage designs and get an idea of how the triggering works. For charging I would use a boost converter or a ZVS driver running a suitable transformer. Either one should give excellent charging times. I have never built a multistage coil gun before, so thats all the help I can give, but there are coil gun pros here who can help you further.

Ragnarok

Fri Apr 20 2007, 12:51PM

Registered Member #659 Joined: Fri Apr 20 2007, 09:14AM
Location: SW Hertfordshire, UK
Posts: 75

Thanks!

A lot of my ideas were spawned by the ACG site, but even after looking around, I'm still stuck on some of the electronics. I probably need to hunt down someone at school (teacher or student - doesn't matter really) who actually understands it, and get them to explain how it actually works.

That's part of the problem with a lot of it really - I'm not content with just building something/using an equation, I wouldn't be happy if I hadn't at least tried to understand why it was that way as well. (I'm just too curious I guess)

Other than the basics, I could probably do with some tutoring on coil optimisiation, what voltages to use (As far as I know so far, the higher the voltage the better, at least when properly timed and the components can survive it? As long as you don't shock yourself of course), and other assorted matters.
I've found a few sites, but the barrage of information didn't sink in very well. I suppose it might just be a case of printing some stuff off and reading it at a more manageable pace. Oh well.

EDIT (to follow the rules of not double-posting within 48 hours): Sorry if this is nothing new, (a quick search found no reference to it) but I had a thought some weeks back about getting projectile spin like demonstrated in rifled firearms. The idea probably has more problems than I know of, so if you find any please say.

Observations of the ammo fired from my early designs gave a realisation. Any ferromagnetic round that goes through even a low-power coilgun will pick up quite a strong magnetic field. Not massive, but notable. Maybe enough to pick up a paper-clip or two.
Now, its a logical assumption that a more powerful coilgun will create a larger magnetisation in the projectile. Given that the round now has a (semi-)permanent magnetic field between it's ends, this can be used like in the Faraday motor. Although his motor ran a wire around a magnet, this process presumably can be reversed to spin the magnet instead (by Newton's 3rd law).

So, after the projectile has left the main accelerating stage, by running a current carrying wire (fixed in postion) parallel to the projectile's motion, then the magnetised projectile should start spinning along it's axis.

A single wire wouldn't do much, but I think there should be a way of coiling the wire back on itself to increase the field's strength and efficency - much is done for a basic transformer with a doughnut core (but using a non conducting core instead for these purposes). The wires closest to the projectile should affect it much more than the reverse effect from the wires looping back further from it.
Chucking a hefty current through that lengthways coiling should with any luck do the job and create a spinning and stable projectile.

I can see potential issues with the magnetisation changing within the round when subjected to the new field direction from the lengthways coil, but I don't know for certain how fast the magnetisation would be changed, or how it would change. Perhaps one of you might know? (or you might even spot a far bigger mistake instead)

PS: The real reason for this thinking was that I was wondering if a coil rifle could be comparable to an air rifle for power and accuracy. So far, it seems possible.

uzzors2k

Sun Apr 22 2007, 09:13PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

Well, the electronics of a multi-stage coil gun aren't too complicated. Basically its setup to fire each coil when the projectile is in firing position in the coil. IR/light sensors are often used for this. The chargers are various transformer, or DC-DC converters. You might want to read here about the basics of DC-DC converters. As for coil gun optimization, I use the calculators at The magnetic gun club. Our HVwiki has some good stuff too.

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