Understanding the Physics of a Coilgun: A Beginner's Guide

[jlefevre76]

Hey, I've seen a few posts on this without any responses I really thought helped (at least help answer my question).

So, I was hoping somebody on the forums here could help walk me through the basic physics of a coilgun. Basically, how could you characterize the magnetic field inside the inductor/solenoid in such a way that it's averaged or gives an approximate value? Also, how do you characterize the projectile as a charge, when it isn't actually charged (if that makes any sense). I know the force is the cross product of the magnitude of the charge times the vector v (which for the life of me I can't find what that represents in any material I've seen online), crossed with the magnetic field.

If anybody can walk me through the equations on this, I'd appreciate it. I only took one course in electronics and magnetism years ago, so if you explain it to me, you might need to walk me through one equation at a time, and one variable at a time.

 

[berkeman]

Hey, I've seen a few posts on this without any responses I really thought helped (at least help answer my question).

So, I was hoping somebody on the forums here could help walk me through the basic physics of a coilgun. Basically, how could you characterize the magnetic field inside the inductor/solenoid in such a way that it's averaged or gives an approximate value? Also, how do you characterize the projectile as a charge, when it isn't actually charged (if that makes any sense). I know the force is the cross product of the magnitude of the charge times the vector v (which for the life of me I can't find what that represents in any material I've seen online), crossed with the magnetic field.

If anybody can walk me through the equations on this, I'd appreciate it. I only took one course in electronics and magnetism years ago, so if you explain it to me, you might need to walk me through one equation at a time, and one variable at a time.

The projectile is not charged -- it is ferromagnetic. The coilgun is just a series of solenoids that are pulsed to keep accelerating the ferromagnetic projectile down the barrel:

http://en.wikipedia.org/wiki/Coilgun

.

 

[jlefevre76]

Right, which is what I stated (or at least was trying to). How do the force equations change when you have a ferromagnetic projectile in an inductor instead of a charged particle or object? Any quick links anybody can throw at me? I just need a way of approximating the force on a magnetic projectile in a magnetic field created by an inductor/solenoid. This is probably a stupid question, but I honestly have not touched this stuff in years and was just hoping for a quick link to some decent learning material on the subject, or for somebody to just post the equation that tells how the forces related to the magnetic field and the magnetic projectile. Does that help clarify?

 

[berkeman]

Right, which is what I stated (or at least was trying to). How do the force equations change when you have a ferromagnetic projectile in an inductor instead of a charged particle or object? Any quick links anybody can throw at me? I just need a way of approximating the force on a magnetic projectile in a magnetic field created by an inductor/solenoid. This is probably a stupid question, but I honestly have not touched this stuff in years and was just hoping for a quick link to some decent learning material on the subject, or for somebody to just post the equation that tells how the forces related to the magnetic field and the magnetic projectile. Does that help clarify?

Reference [9] at the wikipedia article has a pretty complete mathematical treatment, but it may be more complex than you are looking for...

 

[jlefevre76]

I'll take a look at it, thanks for the help.

 

[jlefevre76]

That helped quite a bit, but I was looking for something more along the lines of this:
http://www.ece.rutgers.edu/sites/default/files/capstone13/CoilGun-FinalReport.pdf
(I post this in case anybody finds this post in the future and wants the same thing. Not that the link berkeman gave wasn't any good, this is just a little bit closer to the basic/newb kind of easy to understand analysis I was going for.)