Single Stage Coilgun  --  News

20, October 2003:
     Fabricated a lighter and shorter projectile, 13 grams at 3.7 cm.

1, October 2003:
    Say it ain't so!  Yes, balsa coil stick mounts are no more.  The particular balsa wood I have does not hold its integrety when glued to dual locking reclosable fasteners.  Therefore, 1/4 inch thick wooded slabs will be used for coil stick mounts.  Not only was basla stripping, but also it began to warp with lengths approaching my new standard coil stick mount length of 13 inches.  Whether I use 1, 2, or 3 coils, all coils are now mounted atop a computer case on the standard 13 inch wooded slab.
15, September 2003:
I-rms vs. I-peak
     I-rms is the maximum continuous current through the main channel.  I-peak is the maximum pulse or surge current allowed to flow within a period of time.  Though the pulse time actually depends on the induced rise of temperature, many devices are assigned a limit of 1ms to 8ms, 8ms is standard for diodes.  Naturally, the small timings and huge currents of capacitive discharge circuits forces me to only consider the I-peak of my switching devices, SCR and IGBT.  What is interesting about I-peak is the difference in I-peak to I-rms ratio between SCRs and IGBTs.  SCRs have a high ratio of approximately 10:1.  IGBTs ratio is much lower at 2:1.  Not only is the favorably high ratio of SCRs good, but also the price of SCRs are much lower than that of IGBTs.

          Example:  600v @ 500A-peak SCR priced $2.50   yields 166A / dollar
                            600v @ 120A-peak IGBT priced $2.50   yields   48A / dollar
    Knowledge has been attained at the expense of anti-monetary gains in the form of SCR expenditures, IGBT extinctions, and sublimations of other high but not high enough amperage hogs. 
Balsa Wood
      Balsa wood, Ochroma lagopus, a prevalent building material in model airplane construction needs no introduction to the model hobbyist.  Its popularity has vastly grown with the LIFTER projects enthusiast.  Now, a new domain for its fertilization is the Coil Gun realm.  Physically, balsa wood is great because it absorbs shock and vibration well and can be easily cut, shaped, and glued.  Financially, balsa is incredible because it is cheap! 
      Prior to balsa here is how fixtures were made.  First, coils were tied down by fastening the coil to a wooded surface plane by means of ordinary masking tape.  Not only did this use excessive amounts of tape, but also allowed the coils to bounce around the wood.  Such coil movements subtracted from the projectile's kenetic output.  This futher lead to undesired sensor movements and inaccurate detection times.  Second, as a means to ease the changing of coils, screws were driven into the same wooden surface as a make shift vise.  But this only caused many wholes and still jerky coils. 
    Appended video examples of  the single coil in action. 
Single Stage Coilgun -- Results and Videos

 Source Energy      Joules            V          Farads   
                                  1.216 KJ      400v       15,200 uF

                                  2.432 KJ      800v          7600 uF

 Terminal views    Bank 1:  400v + 400v = 800v @ 3800 uF   Bank 2:  = Same
                                  Bank 3:  (2)   x  400v = 400v @ 15,200uF
 Projectile :            Kinetic/ Source   Volts   Eff           Velocity      Weight      Length       Dia.     Stages      Date          
           # 1               25 J     2,432 J    800v   1.0 %       49.0 m/s     26 g         7.6 cm       8 mm    1              01  Sept  2003
           # 2               ?? J     2,432 J    800v   ?.? %       ??.? m/s     35 g         4.8 cm       8 mm    1              01  Sept  2003
           # 3                 8 J     2,432 J    800v   0.3 %       35.0 m/s     13 g         3.7 cm       8 mm    1              20  Oct    2003

# 10     WIP     41 J    2,432 J     800v   1.7 %       23.6 m/s    147 g       16.2 cm    12 mm     1              04  May   2005
       # 10                 22 J    1,216 J     400v   1.8 %       17.4 m/s    147 g       16.2 cm    12 mm     1              02  May   2005
       # 10                 24 J    1,216 J     400v   2.0 %       18.1 m/s    147 g       16.2 cm    12 mm     1              02  May   2005

  Trigger :                 SCR                                                             Qty      Price                   Mfg.    
                                SK040R  1000v  40A  520A surge                 6        $2.75 each        Teccor
SK065K  1000v  65A  950A surge                 4      ~$5.00 each        Teccor
                                S8070W   800v  70A  950A surge                 4      ~$5.00 each        Teccor

  Coils :                   #   1  Dimensions (in, out, length) 1.0 cm, 4.2 cm,  7.6 cm
                               # 10  Dimensions (in, out, length)  1.30 cm, 4.6 cm, 13.5 cm

  Quick Videos:  # 1  No target and loosly bound          # 8  Plastic Jug test
                            # 2  No target and tightly bound          # 9  Can with large coil loosly bound
                            # 3  Can test                                       #10  Large projectile tightly bound
                            # 4  Can test up close                        #11  Large projectile Box test
                            # 5  Potato/Can test 1
                            # 6  Potato/Can test 2
                            # 7  Potato/Can/Box test                                                                           
Single Stage Coilgun -- Construction

I found a local source for dirt cheap capacitors; specifically these large capacitors cost $7 to $8.  Though a cap at 3800uF would produce a shorter peak discharge pulse, I use these glutinous bad boys because I must make use of whatever is readily availiable.  Hence the birth of a series combination for a 800V at 3800uF Bank.

Potential Energy
½ * C * V² = Joules
½ * 7600exp(-6) * 400² =  608 Joules
                             x    4 = 2432 Joules

* 400 VDC @ 7600 uF   (4), max surge 475 VDC
12 AWG copper wire is wound by hand around a steel rod, which also is the projectile source material.  This arrangement achieves very close, 0.5 mm, projectile - coil coupling.  A few layers of tape wrapped around the rod circumvents tight fittings.  Coils generaly undergo a strong contraction force during circuit discharge.  However, these coils retain a constant coupling because cyanoacrylate super-bond adhesive is applied to each layer, raging from 4 to 10.  Lack of contraction enables the use of metal, glass, or flexable tube barrels.  The terminals are terminated with either ring connectors or 12 AWG stranded wire with ring connectors.

 * 12 AWG solid wire
 * Super-bond adhesive
 * Terminal block
 * Spade connectors
 * Ring connectors
 * 12 AWG stranded wire

Three pieces of balsa glued together constitutes an LED form.  IR photo diode and IR photo-transistor are inserted into the two in-line facing holes.  Sensor housing may be tapped above a coil's entrance/exit hole, or placed  on a transparent  barrel.  If barrel is not transparent, then sensor housing is positioned over a cross section hole of the barrel.

 * Balsa wood - 3 sections
 * IR-LED       
 * IR-phototransistor
 * Bias resistors
 * Comparator
 * Vref resistors
Voltage Charger-Pentupler
Lengthy charge time is a thing of the past thanks be to this AC powered 850VDC generator.  In fact, very long charging times was one of the main reasons I halted my coilgun project way back in 1997.  Now, I have to be carefull when charging capacitors because even with 2.4KJ the charge time is within 2 seconds. 

* Capacitors (5)  330V @ 600uF
* Diodes (7) 1000V @ 6 A rms, 80 A surge     
* Relay (2)  120VAC @ 40 A

The diodes are placed anti-parallel across each coil.  This arrangement protects  both the capacitor and the silicon switch from the induced high reverse voltage (back emf) when the coil current has ceased by snubbing the emf down to (-.7v).  For my arrangement, 2 diodes in parallel caused 1 to sublimate, and of course  the associated Boom sound is included.  Actually the sound is more like
Diodes 1000V @ 6 A rms, 80 A surge
* Ring connectors

The terminal block is the intermediate connection between coils, switches, diodes, and capacitors.  Placed in series, I have 16 strips total to share for future 6 coils.  Many preliminary coils are terminated with portions of a terminal block.  Those portions are fabricated with a circular saw.
* 8 strip terminal block rated 30A (2)
* Fastening scews.

Two pieces of light-weighted wood glued together having a whole driven near each end equipped with counter sinks secured to a wooden surface by two flat-head screws, is a simple coil-stick.  The coil is fasted down with either tightly wrapped tape or reclosable fasteners.
* Balsa wood

Cans are simply screwed from the base down into my desk.
* Screws
* Targets  BYOPC (bring your own potato and can)



SCR Bank
If an individual SCR does not suffice or survive the subjected pulse currents, other SCRs constructed in parallel increase the surge current rating.  All Anode leads are removed, Cathods soldered together as well as the Gate leads.  Then the SCR Anode tabs are soldered.  The tabs may be left intact during testing but are cut down to minimize its required PCB space when installed into portable coilguns.

* SCR Teccor SK040R  1000v @ 40A, 520A surge
* SCR Teccor S8070W    800v @ 70A, 950A surge
SCR Teccor SK065K   1000v @ 65A, 950A surge
* Solder & Soldering Iron
* Reservoir of cold water
* Wire cuters

This perforated can has amassed more lawyers than holes. Presently, it is busy drafting a subpoena along the lines of abduction, displaced purpose, and bombardment without provocation. As figured, The CFA (Can Food Association) has decided to back this can with great support. All the legal hoopla will boil down to who's rights supersede. The cans right to peacefully lay dormant indefinitely just after expelling nourishment. Or my right to use my energy gained from said nourishment to impale cans with repetitive, rapid rotating rounds of steel.
Source Energy

Potential :  2,432 Joules
Capacitor: 400v @ 7600 uF, QTY 4
     Bank 1: 400v + 400v = 800v @ 3600 uF
     Bank 2: 400v + 400v = 800v @ 3600 uF


Projectile # 1

25 Joules Kinetic Energy
Velocity =  43.8 meters/second
Weight   =  26 grams
Length   =  7.1 centimeters

800v 40A-rms 520A-surge
Brand  =  Teccor
QTY     =  6 in parallel for Banks 1, 2
Cost    =  $2.70 each

Hand wound 6 layered
26 turns of 12 AWG wire
Equipped with terminal mounts
Coil-Stick mount 

Two strips of balsa glued lengthwise having a hole driven near each end..  Each hole counter sunken to  give flush surface.  The coil-stick mount is secured to a wooden surface by two flat-head screws.
* Balsa wood
* Screws

Cyanoacrylate Adhesive

This is a generic bottle used to hold together coils, coil mounts, screw bolts, and SCRs. Basically, this is the liquid form of duct tape.

7600 uF 400 VDC,  max. surge 475 VDC

½  *  C  *  V²                       =         Joules
½  *  7600exp(-6)  *  400²  =   608 Joules
12 AWG copper wire wound by hand around a steel rod, which also is the projectile source material.  This arrangement achieves very close, 0.5 mm, projectile - coil coupling.  A few layers of tap around the rod prevents tight fitting.  Generaly, coils undergo a strong contraction force during circuit discharge.  However, these coils retain a constant coupling because cyanoacrylate super bond adhesive is applied to each layer, raging from 4 to 10.  The terminals are terminated with either ring connectors or 12 AWG stranded wire with ring connectors.
 * 12 AWG solid wire
 * Super bond adhesive
 * Spade connectors
 * Ring connectors
 * 12 AWG stranded wire
The housing is a wooden dowel sized to match coil diameter.   Three wholes drilled: one across the diameter to except LEDs, the other through the plane surface to except the projectile. This whole is 25% larger than projectile to allow for a slight mismatch with coil breach.

 * Wooden dowel
 * IR-LED       
 * IR-phototransistor
 * Bias resistors
 * Comparator
 * Vref resistor
The housing is a wooden dowel sized to match coil diameter.  The four linear gauges excepts two V-shaped metal springs.  The metal is procured from a mechanical ink pen.  This simple mechanical contact reduces the component count down to a current limiting resistor.

 * Wooden dowel
 * Spring metal        
 * Current limit resistor
1000 V 6 Amperes
4 in parallel

* Ring connectors

Voltage Tripler

Input    = 120 vAC (rms)
Output = 510 vDC(peek)

* Diodes 1000V 6A (4)
* Capacitors 330V 600 uF (3)
* Relay
The Penetrator

Steep pointed angle designed for the purpose of penetrating steel sheet metal and food cans.
Coil #3
Hand wound 4 layered 18 turns of 12 AWG solid copper wire.  Equipped with 12 AWG stranded speaker wire and ring connectors.