Multiple
Stage Coilgun
News
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15,
September 2003: Appended video examples of the multi-stage coil in action. |
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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.
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20,
October 2003: Short 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.
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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.
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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.
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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. Steps: * 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 |
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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. |
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