Electronics > Projects, Designs, and Technical Stuff
Everything wrong with amateur railguns and how to make them better
<< < (6/8) > >>
German_EE:
Some may question the wisdom of this thread but I do not see a problem, sometimes you feel the need to build something a little out of the ordinary. Elsewhere on the board you will find my quest to build a 100A meter shunt that is accurate to 6.5 digits, an almost impossible task, but as the quality of German TV is so low I need something to occupy my mind.

If our friend here wants to build a railgun and shoot off lumps of metal at speeds approaching Mach 1 then I wish him luck, just send me a link to the Youtube video showing first firing.  :popcorn:
Honda Rider 271:
Research continues. Since the propulsive force in a railgun is equivalent to current squared there is a current / time discharge  "dead zone" where railguns in fact suck. My calculations lead me to believe that anything below 100KA for <1ms will definitely suck. With the logarithmic discharge curve of a capacitor bank you need to stay in the higher part of the voltage range for the entire shot to extract good power. ~500kJ expended energy is about where fun things start happening with regard to hyper velocity shots. Anything less simply can't sustain a high enough current for long enough to get >1km/sec with a realistic armature. This implies a ~750kJ total energy cap bank if you want voltage to remain at half when discharge is finished.

You can calculate this yourself with F =.5L'*I^2 with L' being the inductance gradient of gun (.5uH/meter a common value). https://scholar.colorado.edu/cgi/viewcontent.cgi?article=1184&context=asen_gradetds also has relevant data.

In other words, a capacitor bank is probably out of the question. Now I need to learn more about how I could reasonably charge a giant inductor with nearly 1MJ.
Marco:
At constant resistance losses are also I^2'd, so I don't find that a convincing argument in and of itself.

I imagine that with increasing voltage/current the resistance of the arc between the rails and armature drops though.
Honda Rider 271:
At low currents, for very short periods of time, your armature + projectile (if any) needs to have extremely low mass (<1G) to be accelerated to KM/s even with extreme conductivity. There are too many problems trying to pass gigantic currents through or behind a really small object, and in addition, the rails need to be a certain minimum distance apart meaning your low mass object now needs to be low density to fill the space between the rails. Even if you could make a good low power design with small rail gap, really small directly conducting armatures that are non superconducting have too much resistance. Extremely low mass plasma-armature payloads will probably have difficulty surviving. What could be used as a resilient extremely low mass low density plasma-driven payload? It is possible to accelerate plasmas by themselves to several KM/s with relatively low energy since the mass is extremely low.
13:

--- Quote from: Honda Rider 271 on December 27, 2019, 01:02:34 am ---Injection system:

Pneumatic injection seems easiest. Ideally the charged cap bank will be switched to the open circuit of the rails and triggered by the projectile making contact. I'm not sure how much efficiency will be lost with armature switching vs using a big thyristor.

--- End quote ---

I would try to stay away from a pneumatic injection system. The rail erosion will limit efficiency and lifetime of the gun. To get around this you could use a solid state switching scheme made of SCRs. There are quite a few "cheap" SCRs on Ebay that are sold as NOS because the seller can't find the data sheet.
Navigation
Message Index
Next page
Previous page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod