Originally, casinos installed slot machines as a
diversion for casual gamers. Unlike traditional table
games (such as blackjack or craps), slot machines
don't require any gambling knowledge, and anyone can
get in the game with a very small bet.
This idea proved to be a monstrous success -- slot
machines eventually moved off the sidelines to become
the most popular and the most profitable game in town,
bringing in more than 60 percent of the annual gaming
profits in the United States.
The technology of slot machines has also changed
a lot over the years. The classic mechanical designs
have been almost completely replaced by computer-controlled
machines. But the game has remained the same. The
player pulls a handle to rotate a series of reels
(typically three) that have pictures printed on them.
Winning or losing is determined by which pictures
line up with the pay line, a line in the middle of
a viewing window. If each reel shows the same winning
picture along the pay line, you win (certain single
images are sometimes winners as well). The amount
you win -- the payout -- depends on which pictures
land along the pay line.
In this article, we'll find out what sets the reels
in motion in modern slot machines as well as in the
old mechanical models. We'll also see what determines
the odds of winning on a slot machine and look at
some popular variations on the traditional game.
The classic slot machine design works on an elaborate
configuration of gears and levers. The central element
is a metal shaft, which supports the reels. This shaft
is connected to a handle mechanism that gets things
moving. A braking system brings the spinning reels
to a stop, and sensors communicate the position of
the reels to the payout system. A coin detector initially
registers that a coin has been inserted and unlocks
a brake so the handle can move.
There are any number of ways to arrange these elements,
and manufacturers have tried dozens of approaches
over the years. The diagram below shows one representative
design.
Click on the three "click here" areas to
see the different parts of the mechanism animated.
Then read the description below for details
This design includes three reels mounted on a central
shaft. The central shaft also supports three notched
discs, which are connected to the three reels. A second
shaft below the central shaft supports a kicker, a
piece of metal comprising three paddles. The kicker
paddles are lined up so they can push against the
notches on the three discs. The second shaft also
supports a series of connected stoppers, teeth that
lock into the notches on the discs.
The kicker and the stoppers are both connected to
springs, which hold them in a standby position. The
kicker is held in place behind the discs, while the
stoppers are held up against the discs, locking them
into place.
Here's what happens when a player pulls the handle:
The handle rotates a hook mechanism, which grabs
hold of the kicker, pulling it forward (toward the
player).
A catch on the opposite end of the kicker grabs a
control cam piece and pivots it forward. This rotates
a series of gears connected to the control cam. A
spring pulls the control cam back to its original
position, but the gear assembly slows it down considerably
-- the gears act as a mechanical delay.
When the control cam is pivoted forward, it releases
a spring-mounted cam plate extending across the back
of the machine.
The control cam also pulls the stoppers away from
the notched discs. As the kicker keeps moving, it
pushes the stoppers against several catches on the
cam plate. These hold the stoppers in place, so the
discs and reels can rotate freely.
As the handle continues to move the kicker, the kicker
paddles push the discs forward briefly. When the handle
is pulled all the way back and the kicker has passed
the discs, the bottom of the hook mechanism moves
up against a slanted surface. The slant pivots the
hook forward, which causes it to release the kicker.
The kicker spring jerks the kicker backward at a
good speed. The kicker paddles hit the notches on
the discs, spinning the reels rapidly.
While all of this is happening, the control cam is
slowly returning to its original position. When it
does return, it pushes the cam plate back, which releases
the stoppers. The different catches holding onto the
different stoppers are positioned so that the cam
plate will release the stoppers one at a time. Each
stopper springs forward and locks into a notch, holding
the reel in position.
From the player's point of view, here's how it looks.
The player pulls the handle. There is a clunk, and
the three reels start spinning. Then the three reels
stop abruptly one at a time, followed by the payout
(if necessary). The "stopping one at a time"
part builds suspense. If the first reel stops on the
jackpot symbol, then you have to wait for the next
reel to stop to see if it is a jackpot, and then finally
the third. If all three display the right symbol,
the player wins.
Conventional mechanical slot machines eventually
gave rise to electrical machines that worked on similar
principles. In an electrical machine, the reels are
spun by motors and the stoppers are generally activated
by solenoids, but the game basically plays out the
same way. Electrical machines have more sophisticated
money-handling systems, like those you might find
in a vending machine, and flashier light and sound
displays.
In both types of systems, once the reels have come
to a stop, the slot machine needs to read whether
the player has won or lost. In the next section, we'll
examine some systems for making this determination.
Extracted from "How Slot Machines
Work", HowStuffWorks (http://www.howstuffworks.com),
by Tom Harris. HowStuffWorks, Inc., 2005.
