How Slots Work

Originally, slots were installed in casinos for the entertainment of casual players. Unlike traditional table games such as blackjack or dice rolling, slots required no gaming knowledge and anyone could participate by placing a very small bet.

The idea proved to be a huge success – slots eventually came out of the fringes and became the most popular and profitable game in town, bringing in over 60% of annual gaming profits in the world.

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The technology of slots has also changed greatly over the years. The classic mechanical design has been almost entirely replaced by computer-controlled machines. But the game remains the same. Players pull the handle to spin a series of reels (usually three) with pictures on them. Winners and losers depend on which pictures are lined up with the paylines, which are located in the middle of the viewing window. If each reel shows the same winning picture along the payline, you win (some single pictures are sometimes winners too). The amount you win – the payout – depends on which pictures fall on the payline.

In this article, we will learn what makes the reels move in modern slot machines and in the old mechanical models. We’ll also learn about the factors that determine the chances of winning on a slot and look at some popular variants of the traditional game.

How Slots are designed

The classic slot machine design uses a carefully designed gear and lever configuration. The central element is a metal shaft that supports the reels. This shaft is connected to the handle mechanism that moves the object. A braking system stops the spinning reels and a sensor communicates the position of the reels to the payout system. A coin detector initially registers that coins have been put in and unlocks the brake so that the handle can be moved.

There are many different ways of arranging these elements, and manufacturers have tried dozens of methods over the years, so we will focus on one representative design. The basic design consists of three reels mounted on a central shaft. The central shaft also supports three disks with slots which are connected to the three reels. A second shaft below the central axis supports a kicker, which is a piece of metal consisting of three paddles. The kickers are lined up so that they push against the slots on the three discs. The second shaft also supports a series of attached plugs which are teeth locked into the slots on the disks.

Both the kicker and the stopper are attached to springs which hold them in a spare position. The kicker is fixed behind the disc and the stopper rests on the disc, locking them into place.

These parts do a lot of work when you pull the handle on the slot machine. We will find out exactly what happens in the next section.

A person pulls the handle on a slot machine and a series of events occur. This is an outline.

  • The handle rotates a hook mechanism that grabs the kicker and pulls it forward (towards the player).
  • A latch on the other end of the kicker grabs the control cam piece and rotates it forward. This rotates a series of gears attached to the control cam. The 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.
  • As the control cam turns forward, it releases the spring loaded cam plate across the rear of the machine.
  • The control cam also pulls the plug away from the disk with the slotted opening. As the kicker continues to move, it pushes the stopper against several catches on the cam plate. These hold the stopper in place so that the disc and reel are free to rotate.
  • As the handle continues to move the kicker, the kicker paddle pushes the disc forward briefly. As the handle is pulled all the way back and the kicker has passed the disc, the bottom of the hook mechanism moves upwards to the tilting surface. The tilt causes the hook to turn forward, thus releasing the kicker.
  • The kicker spring pulls the kicker backwards at a good speed. The kicker paddle hits the notch on the disc, causing the reel to spin rapidly.
  • While this is happening, the control cam is slowly returning to its original position. When it does return, it pushes the cam plate backwards, thus releasing the stop. The different catches fixed to the different stops are positioned so that the cam plate will release one stop at a time. Each stop pops forward and locks into a slot, holding the reel in place.

This is what it looks like from the player’s point of view. The player pulls the handle. There is a click and the three reels start to turn. Then the three reels stop abruptly, one at a time, followed by the expenditure (if necessary). The “one stop” part creates suspense. If the first reel stops on the progressive bonus symbol, you must wait for the next reel to stop to see if it is the progressive bonus, and finally the third. If all three show the correct symbols, the player wins.

Traditional mechanical slot machines eventually produced motors that worked on a similar principle. In a motor, the reels are spun by the motor and the stop is usually activated by the solenoid, but the game is played in essentially the same way. Motors have a more sophisticated currency handling system, as you would see in a vending machine, as well as a more flashing light and sound display.

In both types of system, once the reels have stopped, the slot machine needs to read whether the player has won or lost. In the next section we will examine some of the systems used to make this decision.

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