On the Score Motor circuits page simple scoring circuits were animated to illustrate how a Score Motor is used to add various numbers of points. This page demonstrates instead how the Score Motor is used to control a simple sequence of events.
Each time a player loses the ball before the end of a game the pinball machine must do at least two things: advance the ball count and return the ball to the player, typically by kicking it from the Out Hole to the Shooter Lane. These two things are done sequentially under the control of the Score Motor. The circuit animated below illustrates how this is typically done on a Williams pinball machine.
On the left side of the schematic drawing is the score motor sequence chart and timing diagram. The sequence chart indicates when each of the score motor cams activates its switch stack. For example the first row of the chart shows that the Index cam on the Score Motor activates its switch stack while the motor is at rest at 0 degrees while the second row shows that the #1 cam activates its switch stack when the Score Motor has rotated 30 degrees. Below the sequence chart is a timing diagram that shows the state of devices in the schematic as the Score Motor turns and simulation progresses.
On the right side is the circuit that drives the ball return sequence. At the top is a Step Unit that drives the Ball in Play lights. The simulation starts with the Step Unit in position 1 which indicates that Ball 2 is currently in play.
Below the Step Unit is the circuit for the Out Hole relay coil which is activated by a switch under the Out Hole behind the flippers on the playfield, represented here by a push button switch in the lower left. The Out Hole relay Lock In circuit is controlled by a switch on the #5 cam of the Score Motor.
Below the Out Hole relay circuit is the Ball Unit S.U. (Step Up) solenoid circuit. This solenoid advances the Ball Count Unit when it deactivates.
The Ball Release solenoid circuit below that is what kicks the ball from the Out Hole back to the shooter lane so the player can launch the ball back onto the playfield.
At the bottom of the schematic is the circuit for the Score Motor which is activated by the Out Hole relay and remains active through the end of the score motor cycle with its own Index cam switch.
Animated Ball Return circuit
(Tip: Start the video above then pause it. Then use the slider to move forwards and backwards to various times in the simulation.)
The circuit simulation starts when the ball in play drains into the Out Hole (represented here by the Out Hole push button) which closes the switch under the Out Hole. The Out Hole switch activates the Out Hole relay which in turn closes a switch that starts the Score Motor.
The Score Motor (specifically a Williams Score Motor) turns for a while activating switches unrelated to this circuit until it reaches 60 degrees into its 180 degree rotation. At this point the #2 cam activates the Ball Count Step Up solenoid by closing a switch on the #2 cam and completing the path through the switch on the Out Hole relay that closed when the Out Hole relay activated at the start of the simulation. Notice that in the Timing Diagram reflects this change as the line for the Ball Unit S.U. solenoid changes from inactive (or grey) to active (or green).
Although the Ball Count Step Up solenoid activates at 60 degrees, the Ball Count Step Unit doesn't advance from position 1 to position 2 until the Step Up solenoid relaxes at about 75 degrees. That is also reflected in the Timing diagram as the Ball Unit line changes from position 1 to position 2 at the same time as the Ball Unit S.U. line changes from active back to inactive.
The Ball Count Unit video demonstrates how activating the Step Up solenoid only stretches a spring and moves the advance arm into position. It's not until the solenoid relaxes that the spring and advance arm alone do the work of moving the Step Unit from one position to the next.
The Score Motor continues turning uneventfully until 120 degrees into its rotation when a switch on the #4 cam closes and completes the circuit to the Ball Release solenoid which kicks the ball from the Out Hole into the shooter lane. At about 135 degrees the Ball Release solenoid relaxes.
Once the ball is removed from the Out Hole by the Ball Release kicker the switch under the Out Hole opens which opens one of the circuits keeping the Out Hole relay active. This indicates that the situation requiring the help of the Out Hole relay has ended.
The Out Hole relay remains active however until the Score Motor has turned 150 degrees and a switch on the #5 cam opens to finally deactivate the Out Hole relay. This transition is shown on the last line of the Timing Diagram.
At this point all that remains is for the Score Motor to continue turning until it reaches its next Index or home position at 180 (or 0) degrees where a switch on the Index cam opens to cut power to the Score Motor and forces it to stop.
When examining this or other Williams schematics keep in mind that the cam number specified on the schematic often indicates the order in which the switches are activated. In this example even without studying the motor sequence chart you can reasonably assume that the Motor 2 switch will activate before the Motor 4 switch, and that the Motor 5 switch will activate after both of them.
Follow these links to other animated schematic diagrams: