How Pinball Flippers Work: The Physics of Solenoids and Electromagnetism

In 1947, a mechanical engineer named Harry Mabs changed pinball forever. He didn’t add more bumpers, didn’t redesign the playfield, didn’t even change the rules. He simply gave players the one thing they’d never had: control.

Before Mabs’ invention, pinball was a game of chance—players could only nudge the machine and hope. But with his new creation, the “flipper,” players could finally strike back at the ball with precision and timing. The engineering principle behind this revolution wasn’t a motor, a gear, or a spring. It was electromagnetism—the same force that powers everything from MRI machines to electric guitars.

Digital pinball machines like the AtGames Legends Pinball Micro continue this 78-year legacy, using the same fundamental physics that Mabs pioneered. Understanding how solenoids convert electrical current into the satisfying thwack of a flipper reveals why this technology has remained virtually unchanged for nearly eight decades.

The Solenoid: Electromagnetism in Action

At its core, a flipper solenoid is beautifully simple. Picture a coil of copper wire wrapped around a hollow plastic tube—this is the bobbin. Inside that tube sits a movable iron rod called the plunger. When electrical current flows through the coil, something almost magical happens: the copper wire transforms into a magnet.

This transformation follows Faraday’s Law of electromagnetic induction. When electrons move through a conductor, they create a magnetic field perpendicular to their direction of flow. In a solenoid coil, each loop of wire contributes its own magnetic field, and when thousands of loops work together, the result is a powerful, focused electromagnetic force.

The iron plunger experiences this force immediately. Iron is ferromagnetic—its atoms align readily with external magnetic fields. When the coil activates, the plunger doesn’t just feel a gentle pull; it gets yanked violently into the bobbin’s core with the force of a small car braking from 30 mph. This happens in milliseconds, faster than your eye can track.

Why Not Motors?

The question arises: why use solenoids instead of electric motors? Motors are ubiquitous, reliable, and well-understood. They power everything from ceiling fans to electric vehicles.

The answer lies in the nature of the motion required. A flipper needs to rotate approximately 60 degrees in roughly 20 milliseconds, then return. A motor produces rotational motion, which would require gears, belts, or cams to convert into the flipper’s angular sweep. Each mechanical interface adds complexity, wear points, and latency.

A solenoid, by contrast, produces linear motion directly. The plunger shoots straight, pulling a linkage rod that rotates the flipper via a simple lever. No gears to strip, no belts to slip, no conversion needed. The electrical signal from the flipper button translates almost instantly into mechanical force.

Speed comparison: A typical DC motor might take 100-200 milliseconds to reach full speed, even without a load. A solenoid delivers peak force within 10-30 milliseconds. In a game where reaction time determines survival, this difference is everything.

The Two-Coil System: Power Meets Endurance

Early flipper designs used a single coil, which created a fundamental problem. The coil needed enough power to flip the ball aggressively—a requirement that meant high current and strong magnetic fields. But if the player held the flipper button down (a common situation during gameplay), that same high current would flow continuously, turning the coil into a heater.

The solution engineers developed was elegant: two coils in one package.

The high-power coil handles the initial flip. When you press the button, full current rushes through this coil, generating maximum electromagnetic force. The flipper snaps up with authority, capable of launching a 2.5-ounce steel ball several feet up the playfield.

But here’s where the engineering gets clever. At the end of its stroke, the flipper hits a switch called the EOS (End of Stroke) switch. This switch doesn’t just tell the machine the flipper has reached its limit—it fundamentally changes how the flipper operates.

When the EOS switch activates, it redirects current away from the high-power coil and into the low-power coil. This second coil generates just enough magnetic force to hold the flipper in place, but with a fraction of the current. The flipper stays up without overheating, ready for the next ball.

When you release the button, both coils deactivate. A small spring—often overlooked but crucial—pulls the flipper back to its resting position. The entire cycle, from button press to flipper return, takes less than 100 milliseconds.

Heat: The Enemy of Electromagnets

Every pinball technician knows the smell of a burned-out coil. It’s an acrid, distinctive odor that means one thing: someone held the flipper button too long, or the EOS switch failed, or the machine’s power supply wasn’t properly regulated.

Heat is the Achilles’ heel of solenoids. The copper wire in a flipper coil has very low resistance—often just 2 to 10 ohms. At 50 volts (a common operating voltage), this means currents of 5 to 25 amps. Even at 50% efficiency, that’s hundreds of watts of power concentrated in a coil the size of a golf ball.

Most of this energy becomes heat. Under normal operation, the flipper activates for milliseconds at a time, giving the coil time to cool between hits. But hold the button down continuously, and the temperature rises rapidly. Copper wire insulation melts at around 150°C. A sustained high-current flow can reach this temperature in seconds.

The EOS switch prevents this catastrophe by reducing current after the initial flip. But if the EOS switch fails (and mechanical switches do fail—contacts pit, springs weaken, wires corrode), the high-power coil stays energized. The result is predictable: a burned coil, a non-functional flipper, and a machine out of service.

Solid-State Evolution

In the early 1990s, pinball manufacturers finally addressed this chronic weakness. Instead of routing high power through mechanical switches, they introduced computer-controlled flippers.

Williams/Bally’s Fliptronics system, introduced in 1992, changed everything. The flipper buttons now triggered low-power optical sensors—no mechanical contacts to wear out. The machine’s computer controlled the high-current path directly, using transistors instead of switches.

This design offered several advantages. First, the buttons themselves became vastly more reliable. Optical sensors have no moving parts to fail. Second, the computer could monitor flipper position and adjust power dynamically. If the EOS switch failed, the computer could detect the anomaly and reduce power automatically. The flipper would still work, just with reduced strength.

Third, and perhaps most interestingly, computers enabled new gameplay possibilities. Some modern machines weaken flipper power during certain modes, creating additional challenge. Others vary power based on game state, helping new players while challenging experts.

The Sound of Physics

Close your eyes during a pinball game, and you can diagnose the machine’s health by sound alone. The sharp clack of a flipper hitting a ball is distinctive—a combination of steel meeting steel and the mechanical shock of the solenoid’s plunger hitting its stop.

This sound tells a story of physics in action. The plunger accelerates from rest to several feet per second in milliseconds, then stops abruptly against the coil stop (a metal bracket that limits the plunger’s travel). The kinetic energy has nowhere to go but into sound and heat. A healthy flipper makes a clean, sharp sound. A worn flipper—whose coil stop has developed a divot from millions of impacts—makes a duller, muffled sound.

Players can hear other physics too. The thwack of a well-timed flipper shot resonates differently than a weak nudge. The slight hum of a held flipper (caused by the low-power coil’s electromagnetic field vibrating at 60Hz) tells you the machine is powered and ready.

Maintaining the Machine

The beauty of solenoid-based flippers is also their vulnerability. They’re simple enough to repair with basic tools, but they require maintenance.

Coils eventually burn out—insulation degrades with thermal cycling, and the wire can short-circuit. Linkage mechanisms wear, creating play that reduces flipper precision. Springs lose tension, slowing the return stroke. The EOS switch contacts pit and carbonize, eventually failing to conduct.

A well-maintained machine gets its flippers rebuilt every few years. The process involves replacing the coil (if it shows any discoloration), the coil stop (if it has a divot), the linkage parts (if they’re worn), and the EOS switch (if contacts are pitted). For a machine that sees heavy play, this is routine maintenance.

Home machines, played less frequently, can go years between rebuilds. But even light use causes wear—every flipper activation is a tiny mechanical event, with forces concentrated on small contact points.

The Future of Flipper Physics

Digital pinball machines like the the digital pinball machine face a different challenge. They can simulate the physics of solenoids, but they don’t need to replicate the mechanical limitations. A digital flipper never burns out, never needs a coil stop replacement, never requires EOS switch adjustment.

Yet something is lost in translation. The tactile feedback of a physical solenoid—the slight delay between button press and flipper movement, the sound of the plunger, the vibration transmitted through the cabinet—creates an experience that pure digital simulation struggles to match.

Some high-end digital pinball machines now incorporate haptic feedback, using solenoids to simulate the feel of real flippers. This seems paradoxical: using the same technology that causes maintenance headaches to enhance a machine designed to avoid those headaches.

But it makes engineering sense. Humans are physical beings who experience the world through force, vibration, and sound. A flipper that feels “right” engages our proprioceptive senses in ways that pure software cannot. The physics that Harry Mabs harnessed in 1947—the immediate conversion of electrical current into mechanical force—remains the most efficient way to create that sensation.

Engineering Elegance

The pinball flipper solenoid represents a kind of engineering perfection. It does one thing—convert electricity to linear motion—and does it extremely well. The design has persisted for 78 years not because engineers are conservative, but because the solution is genuinely optimal.

Motors would add complexity. Hydraulics would add maintenance. Pneumatics would add bulk. The solenoid, for this specific application, is unbeatable: simple, fast, powerful, and repairable.

When you press that flipper button and watch the ball arc toward your target, you’re experiencing the same electromechanical principle that Mabs engineered in 1947. The copper coil, the iron plunger, the linkage rod, the return spring—all working together in a dance of physics that has remained essentially unchanged for nearly eight decades.

That’s not stagnation. That’s elegance.