5. General Pinball Knowledge

This section of this project is where I am going to explain some of the deeper concepts of electromagnetic pinball systems. I am going to attempt to answer all the questions I had when I started and hopefully your questions as well. If you have a question that I have not answered, please feel free to reach out to me at the email in my bio.

Q: What are the differences between pinball systems?

A: From the earliest days of pinball there have been three major companies leading the field: Gottlieb, Bally and Williams. Although the basic concepts of each companies systems are the same, the execution has slight differences. One of the biggest differences is in the solenoids that each company uses. Williams, for example, tended to use solenoids rated at 50v while Bally operates at a much lower voltage of 15 volts. These companies also cahnged their systems over time. While this is an electromechanical system, pinball machines now are solid state meaning that there are many less mechanical systems and much more computation power used.

Q: Why is the flipper wired different than the bumper?

A: To understand the difference between the flipper and the bumper, I first need to explain how a solenoid works in a pinball machine. A solenoid in a pinball machine is simply a metal tube with wire coiled tightly around it and a metal rod in the center. When there is current flow in the coil, it induces a magnetic field that either pushes the metal rod out or pulls it in. This is a sudden dynamic movement that requires quite a bit of power and continuous running of 50v through the coil is enough power to eventually burn the coil. With the pop bumper, it only turns on when a ball hits it and since the ball gets immediately launched away the bumper is never on long enough to be at risk of burning. If you were to hold down the flipper button, however, there would be continuous flow across that could potentially burn the coil out. To prevent this, flipper coils are actually two coils stacked together: a thick gauge one and a thin gauge one. The thick gauge wire is low resistance high power and the thin gauge wire is high resistance low power. The low resistance coil goes before the high resistance coil with a center tab in between the two. That center tap is connected to the closed leaf switch initially which is connected to ground so that when we first hit the flipper button, the current flow can skip the higher resistance coil and only go through high power coil creating the dynamic movement we need. When the flipper extends, though, a small hammer moves with it and pushes the leaf switch open. This means that the only path to ground is now through the high resistance coil. This lowers the power enough that the coil won't burn but keeps it high enough that the flipper can hold in the extended position.

Q: What do NOC and NCC mean?

A: NOC stands for normally open contact and NCC stand for normally closed contact. This simply describes the steady state behavior of a switch in the system. If a switch is by default off, it is normally open (NOC). If a switch is by default on, it is normally closed (NCC). This pinball machine has examples of both. The leaf switches of the pop bumpers are NOC meaning that we want them to be open unless a ball hits so that we know when to fire the bumpers. The leaf switches of the flippers, however, are NCC since we need the center tap to be connected to ground until after the flipper is fired.

Q: What is a flyback diode and what is it for?

A: A flyback diode is a safety measure for our mechanical components. Without it, the solenoids would damage pretty much everything they're connected to and eventually themselves. In short, the solenoids are just large inductors. The relationship between the rate of change in current in an inductor and the voltage and current is: dI/dt = V/I; When we turn the solenoid off, there is a large and fast change in the rate of change of the current but current can't change instantaneously in an inductor. So, as the power in the system attempts to dissipate, the voltage peaks for an instant, sometimes to thousands of volts which is enough to damage most components in a system. The flyback diode prevents this by create a forward bias when the contact is opened, sending most current across it and protecting the rest of the system from experiencing a voltage peak.