Making Music with a Coil Gun, Part 1
In the search for mirthful and magical ways to make music, I ran across an interesting article about a small coil gun. The author has written a piece up about making the coil gun using pretty simple components [discovered via the kind folks at Hackaday] which I found most instructive.
This got me thinking about a novel way to make mechanical music - use a coil gun to fire balls at objects which produce a tone! Done properly it should be possible to launch the balls silently, which is so much more appealing than using a pneumatic system (with the accompanying noise) to fire the projectiles.
Doing some quick Googling on the subject turns up a lot of fun stuff, and dangerous too! Lot’s of folks who are interested in coil guns also seem to take interest in Tesla Coils, rail guns, and potato cannons. Sounds like a fun crowd to run with, huh?
I decided to do some modeling of the coilgun to help me understand the physics of the problem. You can find lots of sources on the web that talk about the coil size vs. the projectile size, switching the current for the coil, using multiple coil stages, etc etc. For my purposes I wanted to understand if a single coil could be used with satisfactory results.
Fortunately, there is a very useful magnetics modeling program by the name of FEMM available under the Aladdin Free Public License, and apparently enough people have used it to investigate coil gun magnetics that the author has kindly included a sample file for a coilgun model. Yay. Since there’s nothing like a picture to help you wrap your brain around something, I made an animated GIF file which shows the forces on the ball as it enters the coil and travels halfway down the length of the coil. Click on the thumbnail below to see the full size animation (warning: 2 MBytes!):
This is a pretty interesting animation. It certainly confirms a lot of the reading I had done, and spurs me to cogitate upon the control system for applying the current to the coil. See how the field pulls and pulls at the ball as it approaches the coil? But then notice that, as the ball enters the mouth of the coil you begin to get magetic fields tugging backwards on the ball, which would slow it down during a real launch. It’s clearly important to switch off the current before the ball reaches the center of the coil in order to impart the most kinetic energy to the ball. More on this as it develops in my imagination. Drop me a comment if you’ve got some good ideas to share. 
I’ll keep you posted as to my progress!
Mirth Maker
