Multiple Stage Coilgun

08, May              2005:   7-Day CG Cannon
02, May              2005:   Cannon ??
29, January        2004:   4 Stage Coilgun
27, December   2003:   Move to portable after dig from whole
20, October       2003:   Short projectiles prove difficult to attain high Joules
01, October       2003:   Migration from soft to hard
15, September  2003:   First multi-stage videos

15, September 2003:
   Appended video examples of the multi-stage coil in action.
1, October 2003:    Migration from soft to hard
    Say it ain't so!  Yes, balsa coil stick mounts are no more.  The particular balsa wood I have does not hold its integrity when glued to dual locking reclosable fasteners as seen in video clip # 9 of the Single-Stage page.  Therefore, 1/4 inch thick wooded slabs will be used for coil stick mounts.  Not only was balsa stripping, but also it began to warp with lengths approaching my new standard coil stick mount length of 24 inches.  Whether I use 1, 2, or 3 coils, all coils are now mounted atop a 24 inch wooded slab.
20, October 2003Short projectiles prove difficult to attain high Joules
     Fabricated a lighter and shorter projectile, 13 grams at 3.7 cm.  Shot from a Single-Stage coil, the Kinetic output is a meager 8 Joules.  This projectile does not yield the high Joules I expected because the LC discharge pulse period, which is fine for the 7.6 cm projectile, is too long for such a short projectile.  As a means of rectification, I divided 3 capacitors each with own coil into 3 stages for a total source of 1.824K Joules.  Now, the output of the 13 gram 3.7 cm projectile has increased to 19 Joules. 
27, December 2003 Move to portable after dig from whole
      Started the construction of a Two-Stage or Three-Stage portable coil accelerator, each stage using a 608 Joule capacitor.  Presently, voltage amplification is the hurtle keeping me from crossing over from the drawing board to a fully assembled and functioning unit.  My boost converter is capable of charging a 608 Joule capacitor to a full 400v within 20 seconds.  What bothers me is the exorbitant 36v needed for this rate of charge.  I was planning on using 24v, but the lengthy rate of charge was not acceptable.  What frightened me was the exploding diode during charging.  I have had parts explode in my face and moved on.  Success again will be mine after I conquer this hurtle as I have conquered the others in this project.
29, January 2004:   4 Stage Coil Gun
      Increase in velocity and joules with the addition of another 608 Joule stage.  This 4 stage model is driven with the same 2.432K Joules of energy as my first single stage model.   Videos are appended  to demonstrate what this truly means.
02, May 2005:  Cannon ??
     The goal, achieve 100 Joules kinetic energy using caps, wire, and scr(s) that I already have.  The task, do this in 7 days.  Once done, I can name this the 7-day CG Cannon.  After this time, work will continue on the Cannon but will not be included as part of the 7-day CG Cannon. 

      I own a good stock of high energy caps and wire spools of all gauges.  These have remained idle for too long.  The good part of their comeback is than when these neglected components once again grasp their freedom all in their path ought to step aside because they shall do so with a mighty roar.

     100 Joules from my usual short 9 gram projectiles proves difficult.  So in light of this new goal I will use longer and larger projectiles.  The end velocity is sacrificed for the high end energy.  A 100 Joules 147 gram projectile travels at 37 m/s.  My caps possess huge uF values at 7,600 uF each.  Connected in parallel, the pulse widths will be long, so the projectile must be equally as long else it will be slowed down by the negative force (suck back).  As the projectile increases velocity in successive stages, the caps will be placed in series for higher voltages and shorter pulse widths.  Dividing the uF by 2,  7,600 uF / 2 = 3,800 uF, the pulse widths are now shorter yet are still relatively long because the projectile is moving much faster.  To counteract excessive pulse widths, the stage detectors are placed farther away from the coil entrance.  Doing so wastes the initial current rise in the coil at the sake of not wasting current decay on an existing projectile, meaning the earlier the bank discharge, the less the negative acceleration (suck back).

Projectile properties:
*  Mass 147 grams, 16.2 cm and 1.3 cm diameter.
*  Demeanor: intimidating.

*  Wind coil
*  Solder SCRs and Diodes
*  Build Capacitor Chargers 400v system and 800v system
*  Connect SCRs, Diodes, Capacitors with Barrier Terminals
*  Test
*  Repeat process for second stage
*  Repeat process for third stage
*  Document, film, photograph, and publish
08, May 2005:   7-Day CG Cannon
    The cannon may now be officially dubbed 7-Day CG Cannon.  Both the goal and the task have been reached.  100 Joules kinetic energy surpassed at 127 Joules - 41.1 m/s within 7 days.  Because of all my prior experience designing and building coilguns, very little time was spent on figuring how the system should be laid out.  Actually, majority of the time was spent soldering and procrastinating.  There were days where the soldering seemed to never end.  Other days I did not feel like working on the project at all.

Diminishing Capacitance
    Each stage's pulse width should be decreasing as the projectile accelerates.  To modify the width I can decrease the two factors by which the pulse is governed, capacitance and inductance.  Each of the 3 stages have approximately the same inductance due to equal coil dimensions, therefore inductance will have to remain a constant.  I also wish to keep the coils the same length and layers for now for simplicity.  Capacitance on the other hand is something not only I can control but must control.
    Stage 1, 15,200 uF from 2 parallel capacitors, produces the longest pulse width.  This long pulse width is acceptable because the projectile has yet gather a high velocity.  Stage 2,  7,600 uF from (2) parallel 3,800 uF banks, produces a shorter pulse width.  By now the projectile has gathered a decent speed requiring stage 2 to impart on it a shorter pulse width.  Stage 3 has the lowest capacitance at 3,800 uF.  Its pulse width is the shortest and must be so else the projectile will experience a huge negative acceleration (suck back) as its center mass passes the center of the coil. 

S i m p l i c i t y
    First, how is all this energy being controlled?; with SCR(s) and a simple gate switch.  The implemented device is neither expensive nor large, and requires neither exotic connections nor clamps.  The ratings are 800v or 1,000v 70A or 65A rms, respectively, with 950A surge.  Paralleling, Anode to Anode, Gate to Gate, and Cathode to Cathode, permits the combined device to control a current larger that the individual parts.  The 400v stage uses a 3 stack SCR bank for up to a 2,800A surge.  The 800v stages use a 4 stacked SCR bank for up to 3,800A surge.
    Coils are hand wound.  No change here.  As usual the wire is rapped around a rod of equal diameter to the projectile with the addition of a few layers of tap to aid in the coil removal and gap creation.  During the layer formation, thin cyanoacrylate adhesive (ca glue) is applied and sprayed with adhesive accelerator.  Mounting the coil sturdy enough for this high level of energy discharge would seem to be difficult, but its just the opposite.  I use either clear super strength packaging tape or painters masking tape for its ease of use and ease of removal.  The tape is simply rapped around the coil and the coil rail mount a few times.  The many small grooves impressed on both the rails and tape by the coil windings generates a strong zipper strength.  I prefer packaging tape for its beautiful plastic tensile strength.  I do not prefer Duct tape because of the messiness once removed and, being stretchable, it gives over time.

  Mounting the parts together is the responsibility of the Barrier Terminals.  A torque screwdriver, parts, and firmly soldered ring/spade quick connect crimps finishes up the job.

7-Day CG Schematic

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Teccor (Little Fuse) Part # S8070W

Ratings per SCR:
Volts         = 800v
Current     = 70 Amps
Surge       =  950 Amps ~ 10 milli seconds

Teccor (Little Fuse) Part # SK065K

Ratings per SCR:
Volts         = 1000v
Current     = 65 Amps
Surge       =  950 Amps ~ 10 milli seconds


Teccor (Little Fuse) Part # S8070W

Ratings per SCR:
Volts         = 800v
Current     = 70 Amps
Surge       =  950 Amps ~ 10 milli seconds


Kinetic           = 127 Joules
Velocity         = 41.1 meters per second
Mass             = 147 grams

Source Total = 4,508 Joules  

Stage-Voltage      Joules      System          
Stage 1 = 400v    1216 J        400v
Stage 2 = 760v    2195 J        800v
Stage 3 = 760v    1097 J        800v

CG 188
Dubbed  -  Throw Away
Source Energy:     188 Joules
Capacitors:            250v @ 1,500 uF, Qty 4
Bank 1:                  250v + 250v = 500v @ 750 uF
Bank 2:                 
250v + 250v = 500v @ 750 uF

Kinetic Energy:      4 Joules    -      2.1%
Projectile:              9 grams, 3.0 cm, 8 mm dia.
Velocity:                 30 m/s (98ft/s)

Drives :                  2 coils
Charge time:         5 seconds
Power supply:       24v NiMH battery  AA