# Spintropics and Magnetic Acceleration

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1. Feb 19, 2017

### VNV

I have a rather odd question that delves outside of the realm of reality just a bit.

Recently, I've had a bit of an obsession with designing ludicrous weapons. My current venture is a little bugger I call the 20MM Magnetic Accelerator Rotary Cannon. The MARC20 for short.

It's an eight barreled minigun with a twist. Instead of the traditional gunpowder propellant, each barrel is instead a hollow electromagnet that should pull the bullet through the barrel at some velocity.

Were this a single barreled weapon like a carbine or an assault rifle, there wouldn't be an issue here. But this is a minigun with eight barrels. It has rotation.

So, how would a rotation affect a magnetic field pushing a projectile along a narrow tube? The desired RPM is 300,000(I did say they were ludicrous), and the barrels are activated with a pulse of electricity every time the barrel passes the top of the gun, where a pair of electrodes interact and send the pulse down the barrel(theoretically pulling the bullet with it).
Thanks!

2. Feb 24, 2017

### PF_Help_Bot

Thanks for the thread! This is an automated courtesy bump. Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post? The more details the better.

3. Mar 8, 2017

### rkolter

I know I answered this at one point.

You have a few problems with how ludicrous this gun is. II went with 300,000 rotations per minute and put that into a calculator with a 1 meter diameter (I figure this is an emplaced gun - I don't imagine someone carrying this beast) - that gives a linear velocity of 157,000 meters per second. I assumed a mass of 200kg for the sake of argument - at that mass and velocity the gun barrels would experience a centripetal force of about 10 trillion Newtons. That's a 2.2 trillion pound force trying to rip your gun apart. For comparison sake, a flywheel being used for a small battery might weigh 100kg and spin 20,000 rpm in a vacuum. And the flywheel is solid - your machine by nature of what it is, has to have multiple parts. Those multiple parts would be badly overheated - at sea level, for that velocity, the aerodynamic heating would be... if I calculated it right, 22,000 degrees F.

If the gun has 1 meter barrels, then the bullet must accelerate at 5000 m/s for the first second after firing, because the bullet has to traverse the length of the barrel before the barrel comes up to fire again (300,000 RPM is 5000 RPS). The Navy has a hyperkinetic railgun that fires at 8000 feet per second. Video is at the bottom - the problem is that 5000 meters per second is 16,000 feet per second - double the velocity of that rail gun. It is safe to say, the bullets would vaporize if not in the barrel then immediately upon contact with the air outside the barrel.

What you have created is a weapon rotating at 160 kilometers per second, superheated to temperatures that would deform it, firing bursts of superheated plasma at a rate of 5000/second until it violently tore itself apart, sending shrapnel at initial velocities that would put modern rocketry to shame. Your initial target, while the gun held together, would be disintegrated. Your emplacement would soon follow suit.

As for how the rotation would affect the magnetic fields? Probably irrelevant. If you can build this device and operate it safely over the long term, then you have sufficient technology to handle the issues you'd have with the magnetic fields emanating from the gun barrels.

Cool idea though.

Angular and Linear Velocity calculator: https://planetcalc.com/556/
Centripetal Force calculator: https://www.easycalculation.com/physics/classical-physics/centripetal-force.php
Flywheel Information: https://en.wikipedia.org/wiki/Flywheel#Physics
Aerodynamic Heating Calculator: http://www.aerospaceweb.org/design/scripts/atmosphere/
Navy Railgun: http://www.popsci.com/technology/article/2010-12/ [Broken]

Last edited by a moderator: May 8, 2017
4. Mar 8, 2017

### rkolter

Sorry - updated navy railgun link. I don't know what happened with the popsci one.

This thing is what you're trying to put eight of together, rotating at 5000 rotations per second. 8 x 5000 = 40,00 shots like this, per second. Or 8 x 300,000 = 2.4 million shots per minute. Well, not shots like this. Your gun fires its projectiles at twice the speed.