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Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
Well it might help us if we know were you live. I dont think you'll have much luck finding steel rods on mars . Around here it is available in any hardware store, lowes, home depot, or can be substituted with bolts, drill bits, pins (not little needles - pins for hitch recieves and suff) or various junk in my garage probably has steel rod pieces in it - or at a scrapyard.
I am sure a hollow point with sharp edges will do some damage to soup cans and such. And looking at it from a ballistic standpoint, a coilgun bullet is quite a bit different than a normal bullet. A full metal jacket bullet would be most similar to a cg bullet, and it is pretty darn rare to see a hollow point FMJ being used. Riffles dont often use HP either, simply because there is no need - HP's were designed for handguns to get the bullet to mushroom at much less energy as compare a riffle round wich will mushroom even with a pointed tip. A steel cg bullet is not going to mushroom, and for hunting there would be two routes to take; penetration or maximum shock. A pointed bullet would get you max penetration, and a flat or wadcutter (term used mostly in pellet guns and shooting competitions) would get you maximum shock. For example, small game arrow tips are flat to knock out the animal or simply deliver a huge enough blow to kill them. I have shot a ground hog with 3 pointed arrows and didnt kill it, however I have taken many deer with pointed tips (and some sharp blades). The hollow point that rupidust posted will have properties of both because it is slightly dommed and has a sharp edge it will have slightly less shock and more penetration than a flat nose. But more shock and less penetration that a pointed tip. Heck to be honest it might be a pretty darn good design, just depends on the application.
Registered Member #342
Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20
You say I can find something like this at a scrapyard? Im in Texas btw. hmm.... I wonder If theres one here in town....Would a junkyard have the rods? hmm....Im not too concerned about the hollow points. I thought that would be just neat, but Im trying to get the projectile first. then I figure things out from there.
Also I asked about the charging circuit...and I think rupidust responded... does a charging circuit really cost 22 bucks? or could I possibly build one cheaper...
(im guessing that youre trying to make a profit too):-D
I wish I could roll back the clock back to when I was in high school...I took three years of this stuff, and I can barley remember anything....
Thanks for the help guys...
On another note, Ive got some calculated values so far. I have a Peak current density of 555 MA/m^2. Is that enough to limit heating? Im reading on the Magnetic Club site, and they say the current density should be higher that 1000 MA/m^2. Another thing, does a wire length(of the coil) of 44 feet sound accurate, or is that too long? Im going to try a single stage first...so that what these numbers are for. Ive got a projectile velocity of 35.24 m/s. My Peak current is 600A, with a voltage of 220v. How can I calculate how efficient my coilgun circuit is?
My 4th set of calculated numbers gives me something I like, and may just go for it. 150V, 600A, a coil length of 1.5" and 4 layers of 36 turns of 18 gauge wire each. Projectile velocity at 28.5m/s. I think that sounds way better, and more possible on my first try, then the first set of numbers...but my question about Effieciency and heat limiting still stand are yet to be answered.
Registered Member #194
Joined: Fri Feb 17 2006, 07:52PM
Location:
Posts: 19
I know Yohan gets mad when noobies ask about how to make a coil gun
I don't recall ever getting mad when someone asks a well thought out question that didn't already have the answer posted somewhere in another thread.
Like this one:
does a charging circuit really cost 22 bucks? or could I possibly build one cheaper...
If your target voltage is <170vdc you can build a charger for about $2.00 and plug it right into the wall. How? Just rectify the 110vac coming out of your home wall outlet.
And this one:
just slotting it might reduce eddy currents, but it wont necessarily increse the speed or efficiency
Could not be more false. Eddy currents bad. Efficiency good. Getting rid of eddy currents boosts speed by reducing drag and increases efficiency which =
For steel rods - Home Depot - Lowes - Any hardware store - I would go with cold-rolled steel. It's easy to work with and very cheap.
What have you chosen for a barrel material? What are your questions for efficiency and heat limiting, specifically?
Registered Member #342
Joined: Thu Mar 23 2006, 08:27PM
Location: TX, USA
Posts: 20
[quote]
I don't recall ever getting mad when someone asks a well thought out question that didn't already have the answer posted somewhere in another thread.
I found a previos thread...
... that has to be the most ignorant post I've seen out of you yet.
This forum is dedicated to those in search of knowledge and you create a "Coilgun for Dummies" post. Shame on you.
Sorry, I may have misunderstood.
What have you chosen for a barrel material? What are your questions for efficiency and heat limiting, specifically?
I might go with aluminum, tho I may stick with steel. Still doing the research so I dunno which is better. As for heating limits, according to the Magnetic club site, the inductance should be over 1000uH, All of the calculated inductances so far in simulators have been way below that. Is that good or bad?
Also, I got two ques. Anyone know where I can find the legal limit of a projectile velocity out of a gun? And, how fast or how slow a projectile needs to be in order not to have problems injuring someone ( or shooting it through a wall)? Thanks!
As for the charging circuit, I need a small mobile circuit, that can run on AA batteries. turning 18vdc into 150vdc.
Registered Member #194
Joined: Fri Feb 17 2006, 07:52PM
Location:
Posts: 19
Sorry, I may have misunderstood.
You did misunderstand. Read it again. That post was directed at an existing member who was counseling a newbie.
I might go with aluminum, tho I may stick with steel. Still doing the research so I dunno which is better. As for heating limits, according to the Magnetic club site, the inductance should be over 1000uH, All of the calculated inductances so far in simulators have been way below that. Is that good or bad?
Conductive barrels are not good. I don't care if you slot them or not. The eddies can still spin up in a slotted barrel and jack your efficiencies. Look into polycarbonate. There are several other suggestions in the archives as well.
1000uH is huge...take the MGC with a grain of salt. The coils we used for our fastest and most efficient model ranged from 5u to not more than 500u with the armature at TDC.
Also, I got two ques. Anyone know where I can find the legal limit of a projectile velocity out of a gun? And, how fast or how slow a projectile needs to be in order not to have problems injuring someone ( or shooting it through a wall)? Thanks!
I wouldn't worry about that. I'll be quite impressed if you get a velocity even 30% of a low caliber air rifle.
As for the charging circuit, I need a small mobile circuit, that can run on AA batteries. turning 18vdc into 150vdc.
Why mobile? Why 18v? Do you realize how simple it would be to modify an AC wall plug to get your 150vdc? Perhaps you should do that first to at least get the gun calibrated and working well. Then, after you've learned a bit more, venture into power supply design. Or just pay the $22 bucks...
After reading your posts, I can see that you haven't been through the archives yet. So I'll tell you what I tell every other new forum member. READ!!!! It's all in here. We'll help you if you get stumped.
Registered Member #32
Joined: Sat Feb 04 2006, 08:58AM
Location: Australia
Posts: 549
Okay, the original swipe at Yohan was definitely pushing it, now let's cool things a bit. The issue in the last thread was cleared up as far as I know.
wrote ...
A. Be respectful. This includes everyone: other members of the forum, moderators and administrators, other people on the internet, and any other person, living or dead. Making false statements that are damaging to another person's reputation is not allowed. Insults, threats, and harassment are prohibited!
wrote ...
F. Let the moderators do their job. If you're not a moderator, you shouldn't be accusing new members of not having read the rules, or of not Googling properly. You certainly shouldn't be making people feel unwelcome by acting hostile. If there's a problem with a post, report it to a moderator, and let them handle it.
In short, don't make personal remarks and don't tell others what to post. If you have a problem, tell a mod.
Registered Member #194
Joined: Fri Feb 17 2006, 07:52PM
Location:
Posts: 19
With regard to small and mobile:
With a battery powered charger, the life of your charger is limited to the amount of energy stored in your batteries. Depending on the size of your capacitor bank, you may tear through a pack of AA's in one session. This can get expensive.
To obtain the velocities that you had mentioned in previous posts, you're going to need a fairly large capacitor. i.e. >>470uf especially if you're operating at 150vdc. Reason? The energy in your capacitors is .5CV^2...typically we use a small capacitance, larger voltage to get the energy you need to obtain the velocities you want. In this case, your V is relatively small so your C will need to be larger. If your C is large, you're going to have a small, mobile white-hot charger (if not properly sinked as aahz mentioned in his boost converter post - awesome little circuit btw )
It's your decision, but until you get it tuned, it would be wise to use the quasi-free energy coming from the wall outlets of your college/home. (quasi-free as long as you don't pay the e-bill )
EDIT: OR....use rechargeable AA's!!! Seems a bit redundant though...
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Well, then you could just build a crossbow with a winch for loading. That would cut out all the pesky electronics and it would be 50 times more efficient too. Try not to go too far off topic folks.
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New Gauss Rifle
. Around here it is available in any hardware store, lowes, home depot, or can be substituted with bolts, drill bits, pins (not little needles - pins for hitch recieves and suff) or various junk in my garage probably has steel rod pieces in it - or at a scrapyard.
150V, 600A, a coil length of 1.5" and 4 layers of 36 turns of 18 gauge wire each. Projectile velocity at 28.5m/s. I think that sounds way better, and more possible on my first try, then the first set of numbers...but my question about Effieciency and heat limiting still stand are yet to be answered. 
