■ FIGURE 12. Completed pistol
grip with fire switch mounted.
■ FIGURE 13. Aluminum covers
and side panels.
you find one that works well.
■ FIGURE 14. Capacitor bank,
side panels, and trigger
Firing and Velocity
bank over 800 volts unless you
have installed an SCR that can
handle it. The control panel
and circuit board can been
seen in Figure 16.
A 1/2 inch projectile can
be cut from a piece of . 30
diameter cold rolled steel and
then filed on one end for a
more aerodynamic shape. I
found that iron crossbow/
archery tips (available at Wal-Mart) make ideal projectiles
for this type of coil launcher.
Three of the different projectiles that I have used with
success are shown in Figure 17.
If you decide to fabricate
your own projectiles, then experiment
with different sizes and weights until
Set up a proper backstop when
you are ready to fire the launcher and
always wear eye protection when
operating the device. The velocities
listed in Table 1 were measured with
a commercial chronograph. The
projectile used for the measurements
was an eight gram crossbow tip like
the ones shown in Figure 17. The
EM- 15 coil launcher stays well below
the legal velocity limits in Canada and
the US, but because of the projectile
weight, it should still be considered
dangerous. Regular firearm handling
precautions should be taken.
■ FIGURE 15. The adjustable breech is
ideal for experimentation with different
types and initial positions of projectiles.
■ FIGURE 16. Side
view of control panel
and circuit board.
■ FIGURE 17.
EM- 15 coil
The EM- 15 coil launcher design
can be used as a starting point for
more advanced experimentation.
Improvements can be made to the
charging circuit, capacitor bank,
accelerator coil, and barrel design
to achieve higher velocities. Try
designing a system with multiple coils,
capacitor banks, and a switching
device. A capacitor bank configured
for higher capacitance and higher
voltage can be used, but be sure
to replace the SCR with one that
can handle the increased voltage
A design using a microcontroller
to coordinate the switching, charging,
voltage monitoring, and display would
make a multiple coil design much
easier to implement. The smooth bore