SoylentNews is people
SoylentNews
posted by
cmn32480
on Saturday November 14 2015, @07:45PM
from the i-so-want-to-try-this-at-home dept.
from the i-so-want-to-try-this-at-home dept.
This is the most powerful mobile electromagnetic railgun built by a non-government. A railgun is a device that accelerates a conductive projectile using extremely high current and electromagnetism. No explosive powder required. Just batteries. This page shows many of the steps required to make one.
The gun is portable, but the power supply is not. Still, cool project.
This discussion has been archived.
No new comments can be posted.
DIY 250 lb Giant Mobile Railgun, 27,000 joules.
|
Log In/Create an Account
| Top
| 32 comments
| Search Discussion
The Fine Print: The following comments are owned by whoever posted them. We are not responsible for them in any way.
It's not reality that's important, but how you perceive things.
(Score: 0) by Anonymous Coward on Sunday November 15 2015, @02:31AM
It's the same amount of energy as a 25-watt light bulb burns in three hours.
(Score: 0) by Anonymous Coward on Sunday November 15 2015, @03:27AM
its actually about 18 minutes for a 25 watt bulb (27000 j / 25 (j/s)) = 1080 s / 60(s/m) = 18 m ;
3 hours is 270 kJ
(Score: 2) by captain normal on Sunday November 15 2015, @03:45AM
Did you see all the 9 volt batteries they used. Seems like it would be better to transform the voltage from a deep cycle or two golf cart batteries. In any case I want to see more specs. I want to build one...you never know when the zombie invasion will begin.
When life isn't going right, go left.
(Score: 2) by shortscreen on Sunday November 15 2015, @08:32AM
Well I guess they needed 400V to charge up the capacitors. To use a 12V battery they'd need an inverter.
I didn't watch TFV (gotta conserve bandwidth), how long does it take to accelerate the projectile? In other words, how much current is required to power the railgun directly? Now I'm imagining something like two pieces of angle iron and a car battery launching a piston pin. Maybe I need to brush up on the applicable physics...
(Score: 2) by c0lo on Sunday November 15 2015, @09:05AM
Why? The resistance of the slug will be around 10-3Ω, you get get thousands of amps at volt level. And the magnetic field scales with the amps, not volts.
What matters most is how fast the capacitors can discharge - that where the capacitors' internal resistance comes into play.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by deimtee on Sunday November 15 2015, @10:16AM
The internal resistance is important, but you need the high voltage to overcome the inductance of the setup.
If you cough while drinking cheap red wine it really cleans out your sinuses.
(Score: 2) by c0lo on Sunday November 15 2015, @12:16PM
One-loop coil that expands.
Hmmm... need to get to Maxwell eqs, I'm too lazy for this at the moment
Let's simplify. The inductance of 1 rectangular loop of 1200mm (max len of gun) X 20mm (slug size) with a 10mm wire is 0.6e-7H [eeweb.com].
Assuming:
;
results in an V=L*di/dt=0.6e-7H*1.6e+5A/s=9.6e-3V.
Doesn't seem too high of a value to overcome
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 0) by Anonymous Coward on Monday November 16 2015, @12:14AM
That is only the inductance of the gun. Capacitors and the wiring carrying the current to the gun also have an inductance.
But the main problem with your calculation is that you assume the current rises steadily as the projectile accelerates. You actually want the current to go to max as fast as possible, 6 ms is really slow.
(Score: 2) by c0lo on Monday November 16 2015, @02:58AM
Double it then. You'll still be in the 10mV ballpark.
Actually no, I don't want a Dirac delta pulse in current. I don't need the rails be deformed by too high forces and I'd be happy to keep the ohmic loses at a minimum (they scale with I2).
What I'd be the most happy with: the entire energy in the capacitors bank being transferred in its entirety to the slug as uniform as possible over the entire length of the rail until the slug escapes the "muzzle".
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford
(Score: 2) by shortscreen on Monday November 16 2015, @03:38AM
What about the total energy stored in the capacitors though? They were rated for 400V. If they aren't charged to 400V then they won't be able to store 27kJ anymore unless more capacitors are added.
(Score: 2) by c0lo on Monday November 16 2015, @12:08PM
Yeah, but if I'm right, those $2600 [imgur.com] on 6000uF capacitors were such a waste.
For around $800 [aliexpress.com]. one could store 15 x 3000F x (2.7V)2/2=164kJ in a capacitor bank - Maxwell supercapacitors behave well in burst discharge and have quite a large number of charge/discharge life cycle.
https://www.youtube.com/watch?v=aoFiw2jMy-0 https://soylentnews.org/~MichaelDavidCrawford