Making Music with a Coil Gun, Part 2

I was pretty pleased with the results of the animated GIF file in my previous post on this subject. I like the visualization of what is happening with the magnetic fields as the ball approaches the barrel of the solenoid. And a numerical table that I had output confirmed what I had read elsewhere: after the ball enters the barrel to a depth approaching the radius of the ball, the ball begins to experience some forces opposite to the direction of travel of the ball.

What I saw visually in the first simulation made me want to see more, so I did a couple more simulations. Here are two good examples, one small, one large, depending upon what you’d like to download:

Small Large:

Watch closely as the ball enters the solenoid barrel. Observe two things:

see how the intensity of the magnetic forces at the edges of the ball vary. You can watch the forces opposite to the direction of travel as they “bloom” off the rear of the iron ball.

as the drag forces grow until the red areas are about equal in area, the forces cancel each other out.

According to the simulation data, the location at which the ball experiences the most forward force is (as expected) when the ball is between 2/3 and 3/4 of the way into the throat of the barrel. This image nails down the exact position:

OK, so I’ve confirmed what I had read. What next? I think I’ll see about modeling a solenoid with a collapsing field, as when you switch off the current. If I can get that model to work then I should be able to apply those concepts to the ball and coil configuration, and hopefully be able to predict the ideal position at which to shut off the current to the coil so as to achieve the greatest velocity of the iron ball out of the barrel of the solenoid (at the opposite end of the solenoid, of course).

Check back for more!

Mirth Maker