PINBALL TROUBLE- SHOOTING (PART 4)
By Russ Jensen
The final type of pinball 'load' to be discussed is the motor. Motors have been used in pin-games over the years for a variety of purposes but the most common use was the so called 'score motor' used in most post-war electro-mechanical machines Before we discuss these however, the other less frequent uses of motors will be described.
Late in 1933 Bally came out with a game called ROCKET which was the first game to have an electrically operated coin payout mechanism. This began a boom of payout pingames, which peaked in the mid thirties. Most of these payouts used an electric motor to power the payout device. Many of these devices had a rotating drum that had brass contact strips of various lengths around its periphery that completed circuits with contact 'wipers.' These contacts were part of the circuitry that controlled how many coins would be paid out for a particular 'win.' Most of the earlier payout machines were battery operated and therefore used DC motors, but later games used AC motors.
Another use of motors in pin- games was for 'animation.' An early example of this was Chicago Coin's DUX (in 1937) which had a small motor in its backbox which, through gearing, slowly rotated a disk with pictures of ducks painted on it. These pictures were alternately visible to the player through a window in the backglass painting. Other uses of motors to provide movement of objects on the playfield or behind the backglass can be found in later machines.
Another type of 'animation' using motors, found primarily on machines made in the sixties and early seventies, is the ‘moving target.' In this case a small electric motor beneath the playfield, by the use of a gear/cam arrangement, caused a playfield target to move back and forth across a small playfield area The motors used in these animations were generally small 'synchronous AC motors’ of a type somewhat similar to those used in home phonographs.
The so called 'score motor' was first used in a few machines (primarily by Exhibit) around 1940/41, although a few earlier machines, such as the DUX game just described, used variations of the same idea. In the Exhibit machines, the earliest units consisted of a small AC motor, with a speed reduction gear train, which turned a shaft. Connected to this shaft were two metal disks (called 'cams') with indentations around their outside edges. These disks were mounted one above the other on the shaft and rotated with it when the motor was running. The lower disk had a series of 20 'hills' and 'valleys' around its outside edge. A 'cam follower' lever rode on this edge and therefore rose and fell 20 times for each complete revolution of the disk The follower on the 'impulse cam' operated an electrical contact set ('switch') which thus 'closed' and 'opened' 20 times per revolution. The other cam had 4 notches in its edge 90° apart. It also had a follower and a set of switch contacts, which were normally closed, but which opened whenever the follower fell into a notch (4 times per revolution of the disk).
The lower disk also had four 'slots' through it about halfway in from the outside edge and 90° apart in the disk’s rotation. A solenoid coil was mounted on the unit in such a way that its plunger (with a rounded tip) protruded through one of these slots when the motor and the solenoid were both un- energized. When current was applied to the solenoid, the plunger was retracted and disengaged from the slot in the disk The movement of the plunger also operated a pair of switch contacts which applied power to the motor as long as the plunger was 'in.' This operation caused the disks to rotate and the end of the plunger 'rode' along the face of the disk (even though current was subsequently removed from the solenoid) until it encountered the next slot. At that point it dropped into that slot, opening its switch contact, and thus stopping the movement of the disk and the motor.
Each time the solenoid was energized the disks made a 1/4 revolution and stopped. During each of these 'cycles' the set of contacts operated by the cam follower on the lower disk closed ('impulsed') 5 times and the contacts associated with the upper disk 'opened' one time for a brief period. The notches on this disk were arranged in such a way that this latter action occurred just prior to the end of each 'cycle.'
The 'score motors' common to most pingames since World War II were somewhat similar to the early model just described. The motors, gear trains, and cam disks were essentially the same although some score motors had three or more cams instead of two. The use of cam followers to operate switches was also similar except that several groups of switches (mounted on brackets around the cams) were sometimes operated by the same cam. The switches were in 'stacks' similar to those used on relays. A detailed discussion of switches will appear in next month's article. Many times one or more of the cams also had 'studs' mounted at various locations projecting from the top and/or bottom surface of a cam disk. These studs also operated sets of switches that came into contact with them during the cam’s rotation.
These later units did not employ the solenoid to start and stop the unit. One of the cam operated switches was used to keep power to the motor (once started by an external circuit) until the motor completed its 'cycle.' Some units were designed such that each 'cycle' was 1/4 revolution (as in the early unit previously described) and others made 1/3 revolution. In the latter case the lower cam had 15 'lobes' and the other cam(s) had only 3 notches. Still others made ^2 revolution per operating 'cycle.' The motors on these units were normally operated by the game's AC 'coil voltage' (usually 25 to 50 volts). Some units (primarily in ‘one balls’ and 'bingos') used 110-volt AC motors.
Some method was generally employed to identify the various cams and switch positions on schematic diagrams. Somewhere on the diagram, pictorial information was generally provided indicating the configuration of the score motor and the function of its various cams and switches, also providing a method of cross-referencing the switch symbols in the circuitry to actual score motor switches. In many cases pictorial views of each 'switch stack' and the functions of each of its switches were also indicated. Often pictorial drawings of each cam were also provided.
The switch 'numbering systems' generally employed used either a number or a letter to identify each cam. Letters were used in most cases where the cams were stacked vertically (as in Gottlieb machines) and this configuration usually also used ‘studs' mounted on the cams. The lower cam (which was the 'impulse' cam) was labeled ‘A,' the studs on its upper side 'B,' the next cam 'C,' and its studs 'D.' Some units employed a second set of studs on the top face of the top disc which were longer than the other studs and this level was labeled 'E.'
On this type of score motor the stacks of switches operated by the cams and studs were mounted on brackets at four or five locations around the cams. These locations were generally numbered '1,' '2,' ‘3,’ etc. and their actual position on the unit was depicted on a pictorial drawing on the schematic as were the 'levels' 'A,' 'B,' etc. It should be noted that these 'position numbers' normally had no particular significance as far as the order in which the associated switches operated in time during a motor ‘cycle.' Each bracket (at a particular position) could have mounted on it switch stacks which were operated by cams and/or studs at one or more levels. Any cam or stud could therefore operate switches at one to all of the positions ('1,' '2,' etc.); the 'cam notch' or stud thus operated switches at each position at a different time within the unit's 'cycle.'
Each individual switch 'stack' could be called out on the schematic by a reference such as '1A' (switch at 'position 1'operated by the ‘impulse Cam’ at ‘level A') or '3D' (switch at 'position 3' operated by the studs at 'level D'). It should be noted that this numbering system made no distinction between multiple sets switches in the same switch 'stack.' This could only I done by noting the wire colors associated with each set of switch contacts.
Another common score motor configuration employed cams (usually 6 or more) mounted on a horizontal shaft turned by the motor and gear train. One cam ('impulse' or 'IMP') generally had ten lobes in ten groups of five. The other cams normally had ten notches, each on opposite sides of the cam. One these cams was referred to as the 'Index' cam (often abbreviated 'IND'). This cam was mounted on the shaft such that its notches lined up with the gaps between the groups of 5 lobes on the 'Impulse Cam.' The other cams, which were generally numbered '1,' '2,' '3,' etc., were each positioned on the shaft so that their notches occurred at various intervals after those on the 'Index Cam' ('1' occurring first, '2' next, etc.). Therefore when the motor was running the switches operated by these cams operated in sequence following each other in time according to their number. The 'cycle' for these units was 1/2 revolution of the shaft. (NOTE: This relationship between 'cam number" and timing does not apply to 'control units' on 'one-bell' and ‘bingo machines.)
In addition to the cam position notation (IMP, IND, 1, 2, etc.) the individual switch sets within the ‘switch stack’ operated by each cam were designated by letters with 'A' generally being the switch in the stack physically closest to the cam itself, 'B' next, etc. The notation to identify a particular switch on the schematic circuit for example might be' I ND A' (the switch operated by the 'Index Cam' and closest to that cam in the stack or '3B' (a switch operated by 'Cam 3' which is the second switch in that cam's stack). Cam '3' would be the third cam to reach its notch after the 'cycle' is started (the 'IND' cam being at its notch when the motor was stopped between cycles of the unit).
"The basic ideas presented here should enable a person to understand the operation of any such unit after carefully examining its operation and construction."
The purpose for score motor units in games was to provide 'timing' for operations which had to occur in a certain sequence with respect to one another. The switch contacts on the score motor unit were ‘opened’ or 'closed' at various times within the motor's operating 'cycle' as previously described. Several types of timing functions were provided by these switches.
One function common to almost all score motor units (except some very early units as were previously described) was that of the 'motor run switch.' One of the switches was connected to provide electric power to the motor itself as long as it remained closed. This switch was 'open' when the unit was 'at rest' (the cam follower operating it being in a notch on one of the cams, often the' Index Cam'). When power was applied to the motor from any external source the motor operated and the cams began to rotate. As soon as the cam follower operating the 'run switch' left its notch the switch closed also applying power to the motor such that when the external source of power was removed the motor continued to operate until the 'run switch' was again opened by the next notch on the cam. This action thus established the operating ‘cycle’ of the unit.
Another switch function common to all score motors was the 'Impulse Switch (es)' which 'closed' and 'open- ed’ 5 times during each motor ‘cycle' thus providing 5 impulses to the game's circuitry. These were used to provide multiple scoring (ie 5,000 or 50,000) when certain playfield 'targets' or other objectives were achieved. If a score multiple other than five was desired then 'impulses' could be fed through contacts on one of the game's relays which would only be closed during the period of time in which 3 (for example) ‘impulses’ from the score motor occurred. Other motor contacts were used to accomplish this as described below.
Many switches on score motors were normally closed and opened only for one short period during a motor ‘cycle' (when their cam follower dropped into a notch on the cam). These could open at various times during a 'cycle' usually at the same time as the 'impulse' switches were going through one of their 5 impulses. One could call these five possible times during a cycle TIME 1,"TIME 2,"TIME3,"TIME4,'and 'TIME 5' (each corresponding to one of the five impulses from the impulse switches).
The purpose of these switches was to turn some device 'off at one of these particular times during a motor 'cycle.' If, for example, only 3 impulses were desired (to score 3.000) a normally closed switch which opened at 'Time 3' could be used to turn off a relay (as previously mentioned) after the 3rd impulse had occurred An example of this type of ‘relay hold on circuitry will be described in a subsequent article. These normally closed switches were sometimes used to 'eliminate' one of the 5 impulses. This was accomplished by wiring one of these switches 'in series' (more about that next month!) with the impulse switch such that the impulse occurring at the time this normally closed switch was open could not pass through, but passing the other four impulses.
The other common switch function on these motor units was a normally open switch, which would close one time during a motor cycle (when a cam follower was in a notch on a cam). These switches would usually close at the same time as one of the five 'impulses' from the 'impulse switch' as in the case of the normally closed switches just described except that the normally open switches would close at the same time, as a normally closed switch would open.
These switches were used to provide single impulses at specific times during a motor cycle and were often used to provide an electrical impulse to reset coils on a relay bank, stepping switch coils, etc. It should be noted that in some cases both these normally open and the normally closed switches were configured to operate slightly before or after one of the impulse switch closures by the 'impulse cam’ instead of exactly 'in time' with it.
The foregoing discussion of score motors attempted to describe the most common configurations of these units. Many variations however were used by various manufacturers over the past 40 or so years. The basic ideas presented here should enable a person to understand the operation of any such unit after carefully examining its operation and construction.
This concludes the discussion of the pinball components that act as 'loads' in the basic electrical circuit The third and final part of this basic circuit, the ‘switch,’ which has already been alluded to frequently in these articles, will be described in detail next month.
Russ Jensen discusses pinball components and their method of operation. Read his informative article on switches in the May issue of "The Coin Slot."
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