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Everything wrong with amateur railguns and how to make them better

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tautech:
Further interesting video:

Honda Rider 271:
The Naval railgun is completely different scale of project with repeat fire requirement...by the way it unloads a projectile weighing SEVERAL THOUSAND TIMES more than I'll be working with. Mine will be at most a few grams. Budget is a few thousand usd. At this scale 1km/s should be doable with under 100kJ. Many small railguns firing a few grams to kilometers a second have been built in university labs.


--- Quote from: mzzj on December 27, 2019, 08:54:18 am ---Where the f** did you get this idea from?

--- End quote ---

Is this a nice way of correcting whatever I got wrong but you forgot to include that part? Please be helpful. I am trying to learn.

edit: Powerlabs had a more powerful version of the gun with 100kJ cap bank on their youtube. No idea how fast it went. Looks like it was too powerful for the design:

tautech:
What experience do you have in ballistics ?
Are you a current reloader of traditional powder propelled firearms ?

Even this ^ is a big learning curve to get consistently accurate results despite the 100+ years of reloading knowledge available.
IMHO rail gun territory is beyond the capability of even a well equipped and knowledgeable mechanical and electrical engineer, however good luck and keep us informed of your progress.
There's a few keen shooters here that I'm sure would be interested in your developments.  :popcorn:

T3sl4co1l:

--- Quote from: i_am_fubar on December 27, 2019, 08:25:06 am ---I wonder how much that cable bundle twitches when It fires. Serious current there. How much you figure? 10s of kA?

--- End quote ---

They use "kickless cables", so called because they don't... you know. ;D

A rather obscure type, but it's just another style of transmission line.  With both poles brought along in the cable, there's no net external magnetic field, or force.  They're typically made of zillions of twisted pairs, inside a jacket.  Very low inductance (a bigger priority here), or more generally speaking, very low impedance because it's so many transmission lines in parallel.

I've used some not-quite-wrist-sized stuff before, measured less than 200nH for a 2 or 3m length.  Water cooled, good for one or two thousand amperes.  Understandably, they were prone to arcing breakdown, as the combination of close clearances (both terminals come out at each end, in this case separated by about 1/8" of G10) and immersion in water isn't exactly a recipe for success.
Example: https://www.flexcable.com/all-products/resistance-welding/kickless-cables

Tim

David Hess:

--- Quote from: Honda Rider 271 on December 27, 2019, 07:37:11 am ---Unless I misunderstand the pulse forming network is basically what I'm trying to do by putting an inductor (or inductors) in series with the cap bank. Right?
--- End quote ---

In the extreme case, the capacitors and inductors form a distributed element transmission line so the discharge pulse has a lower peak current, limited by the impedance of the transmission line, and a discharge time controlled by the electrical length of the transmission line.


--- Quote from: tautech on December 27, 2019, 09:48:26 am ---What experience do you have in ballistics ?
Are you a current reloader of traditional powder propelled firearms ?

Even this ^ is a big learning curve to get consistently accurate results despite the 100+ years of reloading knowledge available.
--- End quote ---

Most shooters and firearms are not accurate enough that reloading presents any limitation to accuracy.

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