Build A Coil Gun Controller And Launcher Part-1
Launch Control
Build A Coil Gun Controller And Launcher
Andrew’s educational system works as a controller and data recorder for a dual-coil coil gun.Use the LM3S811-based controller to experiment with various aspects of the coil gun,including timing and voltage control.You can also measure the real-time voltage and current.
Acoil gun is an electromagnet thatcan fire metal projectiles like a regulargun, but without any explosives, loudnoises, or moving parts, apart from theprojectile itself, of course. Energy constraints limit such a gun’s use as ahandheld weapon, but the largest,most powerful coil gun is capable ofmoving a lot of mass. Some peoplehave even proposed using coil guns forlaunching payloads into space.My interest in coil guns is educational.I teach a course in circuit analysis,which is full of equations and abstractconcepts, at Grand Valley State Univer-sity in Grand Rapids, MI, so I know wellthat a practical design project goes a longway to help bring the hard stuff down toEarth. A coil gun is a perfect project formy course because it doesn’t includetoo many parts and it demonstrates thebehavior of basic components such asresistors, capacitors, and inductors. Plus,it’s much easier to get young engineersexcited about a coil gun than it is to getthem enthusiastic about a typical intro-ductory circuit, such as an LED flasher.
I built a two-coil coil gun launchercapable of operating at up to 60 V and25 A (see Photo 1a). I also constructeda controller/datalogger for the launch-er that features a Luminary MicroLM3S811 microcontroller (see Photo 1b).Since finishing the project, I’ve success-fully used the design—which includes alot of protection circuitry that makes itas “student-proof” as possible—as a lab-oratory demonstration/experimentationplatform. For instance, in April 2007, my students followed my lead by designingand building their own coil guns. Wethen held a competition to see whichgun could shoot a projectile the farthest.
COIL GUN BACKGROUND
Like any electromagnet or solenoid,a coil gun comprises a wire-woundcoil and a ferromagnetic movablearmature, or slug. But while electro-magnets and solenoids limit the rangeof motion of the slug, a coil gunenables it to move freely and eventu-ally exit the coil, thus becoming a projectile (see Figure 1). So, if you’ve everwound wire around a tube to build anelectromagnet, you’ve built half of acoil gun. The other half is either atiming or feedback circuit to turn theelectromagnet off at the right time.
When a current is applied to the coil,the projectile is attracted to the center ofthe coil, no matter which side it startson. Thus, if you just turn on the coilcurrent and leave it on, the projectilewill quickly come to rest in the middleof the coil. That isn’t what you want atall! If you can time it just right, howev-er, and turn off the coil when the projec-tile has reached maximum velocity onits way to the coil center, it will shootout of the coil gun in an impressive dis-play of electrical-to-kinetic energy con-version. Figure 2 illustrates this process. The coil current creates a magneticfield around the launching tube, whichmakes the projectile start to move (seeFigure 2a). In Figure 2b, the projectilehas started to move and continues to accelerate. When the projectile reachesthe center of the launching tube, turn offthe coil current, as shown in Figure 2c,and the projectile’s inertia will contin-ue to propel it out of the open end ofthe launching tube.
By CIRCUIT CELLAR THE MAGAZINE FOR COMPUTER APPLICATION #216 July 2008
No related posts.
Related posts brought to you by Yet Another Related Posts Plugin.
No tags for this post.