The most powerful mobile electromagnetic railgun built by a non-government

You can see the wires jump--that's inductive magic in action. To get any sort of quick magnetic pulse into the railgun, you need high voltage[1] and low transmission line inductance; neither of which are satisfied here.

A guy I know works on high power pulse mode lasers and they achieve ridiculous rising edges with thin twisted pair wire. Lots of resistive loss but hey at least the current rising edge is nice and fast.

[1]: a few kilovolts.

The delay between the first flash from the gun and the entry hole appearing is 4 frames at original fps. At 30 fps, that gives flight time between 100 and 130 ms.

I estimate that the distance from the gun to the car door is around 10 m. That gives speeds on the order of 100 m/s (200 mph).

Energy depends on the mass of the projectile. At these speeds, 27000 joules would require mass in the range of kilograms, which is obviously not true. Still, it seems feasible to me that this gets better than highway speeds.

Edit: also note that these are high speed camera recordings.

Nearly lost an eye when a kid I was paired up with in science class made that mistake. The cap blew off with a loud bang, and I was left with a perfectly symmetrical round bruise just above my eyebrow.

I never forgave him. Not for nearly blinding me, but because he was happy to let everyone believe it was me who had made the mistake!

They made us dismantle it as it was unsafe - so we re-use the capacitors and made a tesla coil.

Humphrey Davy (the discover of Al) originally use aluminium (1808) but, later, switched to aluminum (1812); the latter spelling became his preferred spelling. The British objected to the -um variant, and insisted on -ium. Davy (himself) seemed to consistently choose the -um variant after 1812.

When the mass production of Al became feasible (another great story!) the inventor (... or, most effective capitalizer, I guess), used the -um variant; this happened in North America. Since that was the effective product name, it became the most commonly used variant in North America.

Now, which is correct? The answer is: both! While I only have a few examples to look at, the dictionaries I have admit both spellings are used, and note which spelling to use in which circumstance, i.e., aluminium in Britain, and aluminum in North America.

In fact, for some programs if your English locale is US then 'aluminum' is recognized as the proper spelling, and 'aluminium' is marked as 'misspelled'. However, switching your locale to UK, the opposite is true!

Paraphrased, can't remember the source

I think this is true for all institutions. Change need to be first enabled and then forced. This is because institution is not a solid thing, it's a while loop. A process that needs to feed itself to exist. So it has natural inertia to stay the same.

I think democracy is enabled by efficient taxation of businessmen. So you no longer need aristocracy as middlemen to collect taxes.

It's enforced by necessity of defense. You can motivate peasants to defend "their country". But you have to let the vote for it to feel theirs. This worked at an age when you needed lot's of fingers to pull lots of triggers. There was proof of concept: https://en.wikipedia.org/wiki/War_of_the_First_Coalition

Looks like weapons technology and general resentment against conscription is enabling whatever comes after democracy.

Here is my problem, or my main problem, with this line of thinking. America is founded upon the idea that individual liberties are basis for all other liberties, and while I can understand the reasoning that the national security apparatus finds the shifting sands of power from nation states to individuals a potential security threat, they have embraced this thought process without bringing it to the people in an upfront manner as should be properly done in a constitutional representative democracy. This model of thinking, at least in the USA, is a complete rewriting of what we consider our government should be, and a rewiting that is happening with no informing the people, and one that will most certainly have more unintended consequences than anyone can yet imagine.

I am certain of one thing, and that is the worst things will befall those who so eagerly trade liberty for security, at the hands of those who promise to protect.

If the projectile is too large, then you will get all of the energy out of the capacitors, but the slower motion will result in a lower back EMF, and consequently most of the energy will be dissipated resistively, probably mostly in the arc between the rails and the projectile.

If the projectile is too small, then almost all of the power in the circuit will be reactive, but the projectile will leave the barrel while the capacitors are still mostly charged.

Calculating this is somewhat complicated by the fact that the voltage across the projectile will be highest as it leaves the barrel, because that's when it's cutting the maximum amount of magnetic flux per millisecond; but that's exactly the point where the voltage across the capacitors is lowest, since that's when they stop discharging.

Maybe you could remedy this problem by using a flywheel-driven homopolar motor instead of capacitors. Failing that, probably the best you can do is discharging the capacitors to something like half voltage, transferring three fourths of their energy into the arc and the projectile.

Your two arcs, assuming a length on the order of millimeters, are going to suck up minimally 50 or so of your volts, which is one reason to use higher voltage — so that the relatively fixed voltage drop across the arcs doesn't hurt efficiency so badly.

https://en.wikipedia.org/wiki/Tesla_%28unit%29 suggests that the maximum field you can reasonably expect to achieve across the rails is on the order of 500 milliteslas. If you were going to keep using 400 volts, discharged down to 200 at the time of exit, then the optimum would be to have a back EMF at 500 milliteslas of about 150 volts at whatever the muzzle velocity is. 150V / (500 mT * 20mm) = 15 km/s, about Mach 45 and about twice the speed of, say, the International Space Station.

Okay, so if we have, say, 15kJ of projectile energy at 15 km/s, how massive is the projectile? 15 kJ / ((15 km/s)²/2) = 130 mg. One difficulty with this is that small, light projectiles slow down more from air resistance, which is significant when you're talking about flying fast enough to suffer ablative erosion from turning the air in front of your projectile into plasma.

So, you're right. 22 grams means that the capacitors finish discharging far too early, so almost all the energy would be dissipated in the resistance of the arc. Except actually I think most of it ends up in the flapping cables, which weigh a lot more than 22 grams. You could probably get a noticeable improvement in the penetration just by tying the cables to boards so they can't flap around and generate so much back-EMF of their own. (They'll still generate a significant amount due to self-inductance, which you can reduce but not eliminate by tying the opposite-direction cables very closely together.)

But wait! What if the magnetic field is weaker? Achieving 500 milliteslas is pretty hard, after all. MRI machines have a field on the order of a tesla, which creates hazards of its own, though that's mostly due to the field being distributed over a large volume. If it's only 50 mT, then you need the projectile to be going ten times as fast to build up that same 150 volts of back-EMF: 150 km/s. And that, in turn, means that your sweet-spot weight goes from 130 mg to about 40 mg.

You could improve the situation for massive projectiles, at the expense of arc losses, by using a lower voltage and higher capacitance. And of course a stronger magnetic field would help too, but I don't think that's very practical.

I don't know, maybe I've missed something in my calculations here. You'd think that barrel length would enter into it somewhere, for example.

He also mentions he's an engineer and has designed/built weapons that have actually been used lethally, so I get the feeling he knows what's he's talking about, professionally.

[1] https://www.reddit.com/r/DIY/comments/3s4o4j/diy_250_lb_gian...

How so? We purport to be a "free country" and part of that entails the right to own weapons. Just because some people spazz out with irrational fear every time the hear the word "gun" doesn't mean that the rest of us have a problem. Consider that, by far, the vast majority of firearms owned in the US will never be used in the commission of a crime. I don't have the numbers in front of me, but somebody worked out the math and based on existing statistical trends, it's a minuscule percentage of firearms that will ever be used to commit a crime.