Rapid Fire Coilgun


Magazine Spring


   Rapid fire was first realized using slinder 12v 2.3AHR sealed lead acid batteries.  Starting from 12v, I added more 12v packs for a total of 5 equallying 60v.  With each addition, the total supply voltage under pulse load steadily decreased.  HIgher voltages for a fixed coil resistance draws more current.  If a single 2.3AHR pack does not supply enough pulse amperes, then 5 packs will be more insufficient because they require 5 times more current consumption.  Once the voltage drop of a 60v suppply during a pulse load drops to 30v,  it is time to find another way.

   Larger 12v 7AHR sealed lead acids provide a better performance.  I need a high pulse ampere qualifying supply in the area of 400 amps.  Here is where 12v Lawn and Garden batteries come to play.  I am using Energizers rated at 300 cranking amps.  The supply nolonger drops, meaning my coils are driven with more current, the actual V / R current as it should be as opposed to the (V - Vdrop) / R current.  For a 100v bank the current will be just over 200 amps for my coils.  After I complete 100v test for 2 to 3 coil stages, I just might ante up!

    100.0   Volt power source
      00.5   Ohms Coil
 = 200.0   Amps DC Max

* 12v Lead Acid battery  x  (?)
* Automotive battery charger


   The Injector is a high power solenoid designed to push the projectiles out from the magazine into the coil breach.  The armature/piston is made out of the same steel as the projectiles but of a slightly smaller diameter.  The length is twice as long as the coil so that when the armature is magnetically sucked in to its max insertion point, there is > 1/4 length of armature protruding out of the injector coil.  This 1/4 length of steel is what produces the work on the projectile.

combination of armature, coil, spring, and housing mixed with pulsed voltage produces a hard hitting injector.  The injection force must be strong to counter act the tension extered on the projectile from the magazine spring.  The initial projectile speed must be fast to prevent jamming in the accelerator breach.

* Coil  22 AWG magnet wire
* Steel armature core 5 cm x 0.5 cm
* Action Spring, music wire diameter 0.020"  -  0.025"  length 36"
* Birch Plywood 1/16  -  3/32 inch thick

The magazine holds all the projectiles in a vertical linear array and is comprised of a box, spring, plate, and follower.  Plate prevents the spring from popping out the bottom of the box.  Follower provides a floor plain between spring and the first inserted projectile.  First generation followers are made from plywood ca-glued to the top of the spring.  Second generation followers are made of sheet metal.  The metal, width equal to spring width and length slightly longer then spring, requires no glue for its excess length is folded under the top of spring and crimped on with pliers.

Magazine 2

Magazine 4

* Birch Plywood 1/16  -  3/32 inch thick
* CA Glue Medium or Thick   (Cyanoacrylate Adhesive)
Magazine Spring

    This spring assures that a continuous projectile supply is available for the injector.  Though its formation is simple, hand made by needle nose pliers, the much time consumed to complete one spring makes this step in the rapid fire building tidious.  Single inline magazines require 2 springs, Dual magazines require 4, and my latest Triple magazine requires 6 springs.

    If any one of the many bendings of the wire results in a portion of the spring being too large, the spring will bind in the magazine, instantly halting the continuouse flow of projectiles.  This link, just as every other link, is one important link in the chain. 

* Music wire diameter 0.032" - 0.039"  length 36"
* Needle nose pliers

1500 uF 250 VDC, max surge 275 VDC
½ * C * V² = Joules
½ * 1500exp(-6) * 250² = 47 Joules

The TRW site in Manhattan Beach California sponsors a traditional Swap Meet on the last Saturday of each month, which features all matter of sellers ranging from ham radio to computer products, old and new.  One gentleman sells these photo caps by the bucket full for less than .50 cents each. His motto is, "The bigger the pile, the bigger the smile."

Banks  47J and 94J

Banks 375J

300 CA
Lead Acid
First generation injector.  The construction did not last long.  Over time the force chiped away on the plastic barrel until it finally shattered.  For when shattering never came to pass, barrel deformation under the coil heat stud in its proxy.