SpudFiles

rp181 wrote:Naa, I don't want a injector at all

Why not? I'm given to understand that a good injector makes a big difference when it comes to performance.

It actually does not. Yes, It does give more power because of the imparted energy, and increases efficiency a very small amount. A injector just adds a whole new system. It also makes good projectile contact hard, It has to be loose enough to slide. Thats why the NAVY uses a hydraulic press to push the projectile in.

rp181 wrote:Thats why the NAVY uses a hydraulic press to push the projectile in.

The NAVY has a slightly larger capacitor bank

Why not have some sort of flexible/spring loaded bush at the sides of the *cough* projectile as contacts?

edit: temporary blink in the brain-finger interface

by sides of the capacitors, if you mean the projectile, then yes, i have thought about it. This is why i didnt:
- much harder to make, i had enough trouble getting a V projectile with a band saw =p
- lower contact area - this is going to make alot more plasma, and an ideal railgun should have no plasma
- higher resistance - the spring would be the main conductor through the projectile, and unless its very thick, it would probably just vaporize

It would actually probably be a good idea to make the actual rails on springs, and being pushed inwards, but the way the garolite was machined, it would be impossible to incorperate, and i cant machine it (school probably could, but no way im going to risk it).

Don't spring the rails! Even if you can get accurate machining to do so.


Those cables that separated, even though they were zip-tied? Same thing will happen to your rails, making contact-pressure lower and rail/projectile erosion worse.

In fact, shorten those cables as much as you can, twist them together, and anchor them really well-- like with conduit clips screwed to a board every 3 inches or something-- to reduce inductance. . . you'll get a faster rise-time and therefore better energy transfer. Use the PVC version of conduit clips. . .

Also, might I suggest that instead of the 'bandsawn' projectile you mentioned above, a piece of appropriately sized aluminum U-channel with some form of insulating, non-compressible filler inside the U might be a better projectile. (Easy way: make tape dams on the open sides and fill with 5 minute epoxy. Or body filler, but body filler tends to be more compressible/flexible.) You'll need to remove the anodizing on the hardware-store variety of U-channel, of course. . .

Under NO circumstances use the same material for rail and projectile--galling and severe rail wear will result. Also, using a projectile with a lower melting point than the rails will tend to reduce rail erosion.

A thought just occurred: 'spring' the sides of the u-channel outward a bit, then fill with silicone RTV . . . there's your 'spring' for your projectile. Figuring the right amount of distortion will take some cut-and-try, but hey, you'd be looking for excuses to play with this thing anyway, right?

Rubbing down the rails with a thickish coat of graphite between shots might be worth experimenting with, too. . . The oil carrier on the most common forms of anti-seize tends to insulate, and might make erosion worse rather than better.


Edit: Stupid spelling mistakes, and an ommited comment on projectile material. No point in double posting. . .

rp181 wrote:It would actually probably be a good idea to make the actual rails on springs, and being pushed inwards

I'm going to argue otherwise - given the rails are under considerable electromagnetic forces which push the rails apart during firing, I doubt spring-loading them is a good idea - they'll likely start resonating, and you'll almost certainly just ensure internal arcing and rail damage.

Same material for both the projectile and rails works very good. The erosion if abit more, but efficiency goes much higher. A person reached 12% with no injection (there was a sacrificial SCR), and a .25" copper projectile. Power was 20kJ.
For the projectile with springs, I thought jason rollete had a good idea. He does a standard U projectile, and then drills a hole in the tail. A close fitting carbon rod is put in, with a spring connecting to the carbon.
Im not really worried about the rails separating, I hammered the rails in, so there is no wiggle room. Also, the plastic is very stiff. I was tightening a bolt too much, and the bolt broke in half, the plastic had no damage what so ever.
The corrosion shield i put is made for conductive joints. It is a petroleum based product with copper in it. After the shot, It seems all the copper is gone, and the oil is still there.

@jack:
Its more your projectile's compatibility with the Injection and Rails that makes a difference. Since i can only go 50 PSI, I had to keep the projectile loose. In the end, I got it so the injection would push the aluminum right to the end of the rails, then stop.

Later i plan on trying augmented rails (ND magnets), series and parallel agumented, and injection with sulfur hexaflouride, or atleast helium.

and injection with sulfur hexaflouride, or atleast helium.

sulferhexafluoride is a very heavy gas
helium is a very light one
Do you want light or heavy?!

I'd inject with 500 psi if I were you. MOAR power.

A person reached 12% with no injection (there was a sacrificial SCR), and a .25" copper projectile. Power was 20kJ.

Sounds interesting.
Got a link?


Edit @ Rag:

What does the scouter say about his spudbux level?

Ha. You've been saving that for months, haven't you?

what if you forced it then their with a small pneumatic ram it could serve as a breech aswel.;

_Fnord wrote:Ha. You've been saving that for months, haven't you?

Not really, I was more expecting to have to use it for JSR's post count - but never one to avoid a daft joke, I thought "Hell, why not?"

Here:
http://4hv.org/e107_plugins/forum/forum ... 45561.post
It doesn't say 12%, but i was talking to him a little while back. Make sure you look at his high speed video.

I said sulfur hexafluoride because it is a very good arc suppressant. I plan to increase injection power as bank power goes up.
@maggot:
That would work, if the ram moved fast enough.

that is in fact near the speed of the electron flux...not gonna happen ^^. Pneumatic injection is good because it pushes the aluminium (or whatever-metal-you-use) sparks out of the gun, enhancing its durability. (btw, any chance of a chronograph speed estimation?)

That is totally awesome! Just one question, and I'm not sure if you've answered this already: Are the capacitors you're using specially designed for being rapidly discharged?

@ CpTn
You wish =) How much pressure do you think just the sparks cause? I don't know, but alot more then 50 PSI =p Look for the cloud of smoke in the video.
@turbo
There as far from pulse rated as you can get. Pulse capacitor's are expensive, these are the cheap alternative.