Make a Pinball Machine

Pinball machines are designed and built around available mechanisms. The design of the mechanisms has not really changed from the 1960's. I have discovered that they can only be obtained from a few suppliers all based in America. They can also be found in used condition on e bay, again usually from America. Buying single items can mean that the postage costs are high. So I usually buy new from the suppliers such as pinballlife.com and marcospecialaties.com. I make sure that I order all the items for one machine at the same time so that I only pay postage once.

So lets have a look at some of the mechanisms. I will just include the ones that are used on the Alice machine. Pop bumpers, Flippers, Shooter, and Ball Return. On the two most recent machines I have also used Slingshots, Targets, Ball Eject, Drop Targets and Rollover switches (animations and information on these are in the e-book).

The photo above is of a pop bumper assembly and its "spoon" switch.

The animation illustrates how a pop-bumper works. The “mushroom” (shown in black) is waiting to be hit by a ball. When it is hit , it is tipped over at an angle and its lower point, which sits in the “spoon” switch, closes the switch. This action applies 30v to the coil. The solenoid then pulls down the conical ring which strikes the ball and sends it across the play-field. NB there are two springs which are not shown in this animation (too difficult). One which raises the solenoid plunger and one which holds up the “mushroom” .

The photograph shows a Williams flipper mechanism. They are handed, one left hand and one right hand.

The animation illustrates how the flipper mechanism operates. The solenoid coil contains two windings connected in series. The primary winding, being of low resistance and drawing about 2 amps , provides the power for the “bat” to strike the ball hard and send it up the play-field at speed. The secondary coil of a higher resistance is initially shorted out. When the flipper button is operated, the primary coil is energised from the 30volt supply and the plunger enters the coil and forcefully rotates the mechanism. Towards the end of its travel a switch is opened which removes the short from the secondary coil. This reduces the current through the two coils but holds the mechanism in position until the flipper button is released. The above sequence prevents the coil from overheating and possibly burning out if the flipper button is held closed. This electro mechanical arrangement obviates the need for any computer control of this device.

These mechanisms are very reliable and robust and are easy to set up. However the bat shaft is connected to the rotating arm by a clamp and as the shaft is smooth the clamping bolt has to be tightened very firmly in order that the bat does not slip out of position when hit it hits the ball.

Of course we need something to send the ball up the pinball play field. The “shooter” predates the first pinball machine. It was a feature on bagatelle machines. Unfortunately, as with modern motorbikes where the kick starter has been replaced with a start button, some machines have dispensed with the shooter. We’ll be having virtual pinball machines next!

This is a ball return mechanism. It is mounted on the top surface of the play-field. It requires a rectangular hole in the play-field to allow the bottom end, where the ball rests, to be below the surface of the play-field in order that the ball may drop into position.

After passing between the flippers or being lost down the “drains” at the sides of the play-field, the ball is directed, via guide rails, into the bottom of the “ball return” mechanism. When the "New Ball" button is pressed, the coil is energised and the ball is driven over the hump of the ramp and ends up in the entry lane ready to be struck by the “shooter”.

The Williams mechanisms such as pop bumpers and flippers are designed to operate at about 30 Volts. I chose The TDK-Lambda LS150-36 power supply. This has a rated output of 36V at 4A and is adjustable between 32V - 40V. As you can see the mains input terminals are similar to the low voltage output terminals and there is no clamp for mains lead. There was a flimsy clear plastic hinged cover over the terminals but it got knocked off and I lost it. It is also easy to drop screws, nuts etc. through the open mesh case. Because of these features I recommend that you enclose it in a non conductive box with a clamp for the mains lead. Because the mechanisms only require full power for a fraction of a second each time they fire, the power supply does not get hot and requires little ventilation.

Here is the enclosure that I made.

We now need to consider the design of the pinball machine's play field. This is a photo of the play field for "Alice". At this stage it has three pop bumpers and two flippers installed. Most of it is made of plywood, which is the traditional material used for play fields. Under the triangular "islands" are rubber bands (about 6mm dia.) stretched around plastic posts. These form the bumpers. Pinball parts stockists hold a number of sizes of these bands and also the posts.

This drawing shows the dimensions that I typically use for a pinball machine. They are not the ones used for "Alice" but they are very similar. They are the dimensions that I used for a later machine, “Galapagos” . The width of the play-field is the same a standard sheet of plywood (in the UK). The thickness is 12mm. The diagram shows the main holes and slots that I drilled and routed through the thickness of the play-field board. This view is from the top of the play-field, when mechanisms and electronics are fitted to the rear many more holes are needed and will be positioned when the components are placed in position. Care is needed to ensure that these rear holes do not penetrate the front surface.

The top sets of holes and slots are for the guide posts and roll-over switches.

The lower set (circled) are for the pop-bumpers. Dimensions for a set of holes for a pop-bumper are given later.

The lower triangles represent the rubber “rings” that form the bumpers, and the hole positions for their support posts.

The slots within the triangles are for slingshot mechanisms

Most important perhaps are the position of the holes for the flipper bats. If the holes are too far apart then it is too easy to loose the ball as it falls between them into the “drain”. Too close and the call cannot or seldom falls between them. On the next machine I reduced this 150mm dimension slightly so that it was not too easy to loose the ball.

This photo show the play-field being drilled

From the dimensioned drawing that I had produced I marked out the position of holes and slots using a long rule, a set square and pencil.

I used a small pillar drill to drill the holes. This has the advantage over a hand held drill, that the holes are always vertical. As can be seen I swung the drill head 180 degrees around from the base and counterbalanced it with a weight placed on the base.

I used a router to cut the slots in the play field. I found it easy to make mistakes with the router as it is difficult to see where the cutter when being operated. I used a guide “fence” clamped to the play-field board. I made pencil marks on this to show where to stop at the ends of the slot. When using the router it is necessary to increment the cutter depth and do several runs rather than cutting the full depth in one go (which would cause overheating and smoke!)

The illustration shows the dimensions that I used for fixing the pop bumper and its spoon switch.

The cross section at the top shows the dimensions of the spacers which I had to use to obtain the correct positioning of the pop bumper and its switch. I understand that the pop bumper is made to mount in a play-field that is half an inch thick and this usually has a thin printed plastic sheet, the play-field graphics, stuck to it. In the UK the standard thickness for a similar sheet of plywood is 12 mm and also I do not use the plastic sheet as I paint the graphics straight onto the play-field. This may all sound a bit pedantic, however the positioning of the switch is critical for correct operation of the pop bumper. The switch’s “cup” (on the end of the spoon!) Has to be centred on the tip of the “mushroom stalk” but not quite touching it. All this is not so difficult on a mass produced machine as the holes will drilled accurately by an NC machine.

In order to get my pop bumpers accurately positioned I made a drilling template out of a sheet of mild steel (shown in the illustration). I used it to drill 3 mm holes and then opened them up to the hole sizes listed .

I am thinking for future machines that I may design some adjustment device for the switch. Ideally the switch needs to operate if the ball just slightly nudges the mushroom’s skirt. However there must be no danger that the switch sticks in the closed position.

This photo holes for the pop bumper and those for the "Upper lanes", a subject that I will cover next.

The illustration shows 3 “upper lanes” at the top of the play-field. They have plastic lane guides with rubber bumper rings and are each illuminated by an led which is mounted on a post. In the centre of each lane is a slot in the play-field. A roll-over switch is mounted under each slot with its arm protruding through the slot.

The lane guides here are Stern/Sega type. And the posts are Williams/Bally type.

As can be seen in the section (lower left) the posts, 4 of them, are fitted into two rectangles which are sandwiched together. The holes in the top piece are sized so that the posts are a “push fit” into them. An led is mounted on the top of each pillar with its legs with attached leads inside the pillar. This assembly is fixed to the underside of the play-field with wood screws and the pillars are thus inserted through clearance holes in the play-field and appear inside the lane guides to illuminate them.

I realise that I have now strayed onto the subject of switches and lighting. With an electromechanical machine it is difficult to do much with lights other than to have them alight all the time that the machine its switched on. When the ball passes over a rollover switch it closes the switch for only a fraction of a second so that a light connected would only flash for that time. With a computer controlled i.e. solid state (ST) machine any lighting sequence is possible. (details in my e-book). I will talk about LEDs next though.

I have chosen to use leds throughout my pinball machines. In comparison with filament lamps they are brighter for their size, do not get hot and are long lasting.

As leds are diodes they will only pass current in one direction. They have different length legs and the longer one is the positive one.

When using a filament bulb (that is in essence a resistor that gets very hot) all you have to worry about is supplying it with the voltage that is designed for. However an led is a bit more complicated.

To achieve the correct voltage and hence the correct current an appropriate resistor should be connected in series with each led. A series of leds can then be connected in parallel, each with its own resistor, if they all need to be operated from a single switch. To calculate the resistor required, simply subtract the diode’s Vf (see the LEDs data sheet) from the supply voltage and apply Ohms law to calculate the value of the resistor.

So if Vf is 2V and my power supply is 5v then the resistor needs to use up 3v. In order that 25mA flows through the resistor into the led then the resistor value should be 3 divided by .025 i.e. 120 ohms. I have standardised on this value of resistor regardless of the colour of the led and its been fine. All bright and no failures.

As previously mentioned, each led requires a resistor in series with it . The illustration shows how I have dealt with this.

The left led illustrates how I have cut both LED legs short but left one longer to indicate that it is the anode (+) connection. I have then soldered on a resistor to the leg.

The middle illustration shows that the leg and the resistor encased in small diameter heat shrink sleeving in order to insulate it from the cathode (-) leg.

The right illustration shows the two legs and leads encased in larger diameter heat shrink sleeving.

There's not much to say about the circuit on an simple electromechanical pinball machine. It's just basic connecting up power to the coils and lighting via the relevant switches. The only slightly more complex example is the flipper mechanism. I have talked about that in earlier in regards to the animation.

As you can see from this illustration, I constructed a very simple but rigid cabinet. It has, for example no security and no provision for a coin operated mechanism. It can be assembled and dismantled very quickly. This simplicity was possible because the machine is only used as an art exhibit at a gallery or in my home.

The legs are made from 68mm x 33mm hardwood and are fixed to the 8mm thick plywood side panels with M8 “coach” bolts.

An 8mm thick plywood base panel is screwed to rails on the side panels. (The power supplies sit on this panel as does a 13 amp multi socket into which they are plugged).

The play-field rests on rails on the side panels at an angle to the horizontal of seven degrees. It is hinged to a rail that spans between the panels at the rear.

Thanks for taking the time to read my Instructable, I hope that you found it helpful. If you would like to know about my other machine or download my ebook, Pinball Design, on how to build more complex machines then please visit my website. www.pinballdesign.com

May 2020 : My new ebook Animated Arduino is now available to download now via www.animatedarduino.com