IEEE Spectrum December, 2007 - 48

RESOURCES
hardware they have. "As a game developer, you can't change the
hardware," Saulnier says. "You must find out what it's good at
and maximize it, very much like working with a satellite system
you shoot into space, or a utility system, where approval cycles
are long. You have to work with those constraints."

launched her own firm, 1st Playable, which focuses on kids'
games-a natural for her, as she was by then a mother of two.
Titles include a spin-off of the Cabbage Patch franchise and a
mind bender called Puzzle Quest. She keeps up the energy level
by having her staff of 35 share an open space.
She signed on as a member of the IGDA board with a particular interest in encouraging women to join the field. Her choice
of position with IGDA reveals her professional pedigree: "I'm
treasurer because I made the mistake of asking about the numbers," she jokes. "But for me it's second nature. I'm an engineer.
Numbers are interesting."
n

getting proDucts to market in good shape can also be
a challenge, due to the complications surrounding software
updates and patches. Although networking makes it possible
to patch a console game, there's always a potential for disaster.
"You don't want to make it that easy to patch a system, because
an ill-intentioned person can take the system down," Saulnier
says. "Video-game quality standards are high and extremely AbouT ThE AuThor
tightly managed because the stakes are high."
contributing Editor DAvID kuShNEr blogs for Spectrum online at
In April 2005, after Activision, a video-game publisher http://blogs.spectrum.ieee.org/gizmos. In this issue, he also wrote
in Santa Monica, Calif., bought Vicarious Visions, Saulnier "Playing Dirty," about how one man turned virtual dross into gold.

Why? Because you just plug
it in, aim...and fire
By pAul WAllich

tools & toys

A gun that uses moving electrons
instead of messy chemicals to throw
a slug has been a staple of speculative fiction since the days of Edison
and Tesla-and not only of fiction.
Electrically operated projectile
launchers-variously known as gauss
rifles, railguns, and mass drivers-have
both fascinated and frustrated military
researchers the world over [see "For
Love of a gun," IEEE Spectrum, July].
So of course I jumped at the chance to
build one.
After skimming the Web for sources, I
settled instead on a design from the optimistically titled book Mechatronics for the
Evil Genius, by Newton c. braga (Mcgrawhill, 2006), and nipped out to my local
electronics shop for some parts.
These shops aren't what they used to be.
There was a drawer for silicon-controlled rectifiers (Scrs)-I'd need one for a fast, highcurrent switch-but it was empty, and the
clerk said there were no plans to restock the
item. on top of that, the biggest capacitor on
the rack offered a piddling 4700 microfarads.
I was lucky to get a transformer, a few packets
of resistors within shouting distance of the
values I needed, and some wire that just might
be suitable for winding a coil.
Even online the pickings were slim: most
vendors cater to buyers willing to place bulk
orders with plenty of lead time, not writers
60

IEEE Spectrum | December 2007 | NA

switch to charge the capacitor, waited with
bated breath for it to reach maximum voltage,
then touched the firing contact.
Tick.
I closed the circuit again.
Tick.
The scrap of metal inside my magnet coil
moved perceptibly each time, but that was
about it. I guess my concerns about the danger of this home-built electromagnetic cannon
were overblown.
It turns out I should have spent a little
more time jotting calculations on the back
of an envelope. That 22 000-µF capacitor
stores a little more than 1/50 of a joule for
each volt of potential across it. At the 15 to
20 volts my slapdash circuitry was willing
to generate, a perfectly efficient transfer of
energy would propel a 25-gram projectile at
a blistering 3 meters per second. My toddler
can throw harder than that. but I wasn't getting 3 meters per second. I might not even
Quick On THe dRaW:
...for power, that is.

ShAyNE LyNN

Build Yourself
An Electric Gun

on deadline. I finally found an outlet that had
22 000-µF capacitors and the Scr I needed
and promised to deliver them fast. Then I got
the soldering iron and heavy-gauge wire out
of the basement and went back to wiring the
rest of the circuit and winding my solenoid.
When the capacitors and the Scr arrived,
I was eager to get everything hooked together.
on the incoming side of the circuit, I had a
12-volt transformer (to make sure I didn't kill
myself), a fairly hefty diode to transform ac
into pulsed dc, and a 10-watt, 50-ohm brick of
a resistor to limit the charging current for the
capacitor so the wires wouldn't melt. on the
output side, I had my coil-160 turns wound
around a transparent plastic tube, chosen
so I could see the projectile move-and the
Scr with a push-button switch controlling
voltage to the gate. (you can also substitute
a photoresistor for the gate switch, to trigger
the Scr automatically.)
I plugged in the transformer, threw the

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Table of Contents for the Digital Edition of IEEE Spectrum December, 2007