“Belly” Fruit Machine

Built by Brian Leach in October 2008

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See also my original 1980 attempt at an fruit machine.

The fruit machine casing

The base of the machine consists of four 12½” angle girders with the slotted holes facing downwards. The machine while being 12½” deep is 13½” wide. This is achieved by adding extra strips (at the front they are 4½” long) between the horizontal angle girders and the base of the vertical angle girders.

At the front the vertical angle girders are 18½” and at the back they are 24½”. 5½” or 3” strips are placed diagonally between all the girders to strengthen the machine up.

Additionally 13 holes back from the front of the machine there are two more vertical angle girders for mounting internal parts. The one on the right hand side is 24½” while the one on the left is 18½”. The one on the left is shorter because of a reel mechanism re-design resulting in inadequate space!

The reel face of the fruit machine is 6½” high and goes back 2½” at the top. The side strips at the top of the machine are made of a 9½” strip and a 2½” strip with one hole of the 2½” strip projecting giving 10 in length.

In general 12½” x 2½” butted strip plates are used to cover the machine normally. At the top where the machine narrows on the side there are two 9½” strip plates at the back, arranged one on top of the other and just below there are two overlapping 5½” x 2½” flexible plates side by side. There is a 5½” by 1½” flexible plate next to the 9½” strip plates and then three triangular plates fill in the rest. At the top there is a 3½” x 2” plate and at the bottom a 3½” x 2½” plate. This leaves a small gap near the bottom which is filled by a 2½” x 1½” plate with the 2½” edge bolted to the strip placed diagonally up the side of the frame. This can all be seen in figure 1.

The viewing area for the reels is made out of 7½” flat girders horizontally with 4½ strips dropping vertically. Behind this there are 5½” x 2½” transparent plates and only the top half of these forms the window in order to obscure the centre hole.

The coin entrance has at the base a 2½” flat girder only bolted on the slotted holes such that a 2p piece can just enter the machine. To make the opening narrow two 1½” flat girders are mounted internally from the vertical strips each side and they are in turn connected to 1½” angle girders. The fish plates and the washers merely obscure the slotted holes of the angle girders.

The coin payout box needs careful design because any Meccano plate would rapidly be scratched by people removing coins. Therefore it is made of 4½” strips bolted to a 5½” x 3½” flat plate beneath. For easy removal of coins it is very important there are no parts or lips for the coins to snag on, so in front of the front most 4½” strip there is a 4½” flat girder connected to the 4½” strip with obtuse angle brackets. There is no lip between the strip and the flat girder.

The reel mechanism

Two hub discs are used for each reel with eight fruits per reel giving 512 permutations. Commercial fruit machines have between 16 and 24 fruits on each reel giving 4096 or 13824 permutations respectively. This is difficult to do with standard Meccano parts. The hub discs have eight hole bush wheels on both sides to minimize vibration. Do not oil the axle rod carrying the reels as it reduces randomness of movement. Randomness is achieved by a compression spring for each reel. From left to right there is a fixed collar; the compression spring; the reel itself with the two bush wheels which are not connected to the rod and then another fixed collar.

The sensing mechanism for which fruit on the hub disc is on is made by placing double brackets (11 and 11a) on the spokes of the hub disc (see figure 4). 1 from the axle rod are the brackets for the bars, at 1½” there are the brackets for the bells and at 2” the cherry brackets. A bracket stops the sensor from moving towards the hub disc and means the reel is not on the respective fruit.

The sensing arms for each reel have couplings on them (63 or 63d). Figure 5 shows the middle reel sensing arms. The sensing arms for bells and bars are all connected to a horizontal slider so the slider can only move if all the reels are showing the same item. For cherries it is more difficult. There is a horizontal slider for each cherry. The left reel cherry slider can move whenever the cherry for that reel is up. The middle reel cherry slider can only move when the cherry for that reel is up and the left reel cherry slider has moved along. The right reel cherry slider can only move when the cherry for that reel is up and the left and middle reel cherry slider have moved along. The joining of the cherry sliders is achieved by ½” pulleys and can be seen in figure 4.

The horizontal sliders are kept retracted by spring cord (see bottom of figure 4). From the horizontal slider to the spring cord there is a coupling with a 2” axle rod in it, then a strip coupling followed by a 2” slotted strip and then a double arm crank. Tension springs connected to the cam mechanism allow the rods to move to the right if they can. The cam consists of an eight hole bush wheel and a 1½” narrow strip with a threaded pin at the end. The threaded pin has a pulley without boss kept in place by a collar. It is important the bush wheel does not slip so a rod with keyway is used on this rod and the rod adjacent to it.

At the right hand end of the five horizontal sliders (figure 3) there are the reel sensor payout switches which go down to the payout mechanism. The electrical contacts are insulated by putting a collar at the end of the slider rod and then an insulated fishplate is bolted to a hole of the collar. Another collar is placed at the other end of the insulated fishplate and a contact screw goes through the hole of this collar. A terminal nut on the inner side of the collar has a wire connected to it. The insulated fishplates have to be arranged alternately below and above the rods to stop them snagging each other.

The sliders should be oiled as the tension springs may not be strong enough to cope with friction.

It is possible to see the reel hammer release cams in figure 6. Each cam consists of a six hole bush wheel and a number of 1” triangular plates connected around it with fishplates in-between the triangular plates to strengthen it up. Finally double brackets are connected to the ends of the triangular plates. The number of brackets is different for each reel, so the reels stop one at a time from left to right. The left hand reel has five double brackets, the middle six and the right seven.

The hammers which stop the reels consist of 5½” slotted strips bolted to a eight hole bush wheel as the pivot. The hammer is an angle bracket (12a) with two angle brackets (12) connected either end. These angle brackets bolt to the slotted strips in the slotted area so it is possible to adjust the hammers position to line up each reel. The bush wheel also has bolted to it a 3” narrow strip which goes to the cam.

An EM1 motor is used to turn the reels and the timing mechanism. The initial gear chain is 3:1; 3:1; 3:1 and then goes to a universal coupling.

Then to the reels it is 1:1; (two 57-tooth gears); 1:2 and 4:1 giving a ratio of 54:1.

To the reel hammer cams it is 4:1, 4:1 and 5:1, giving an overall ratio of 2,160:1 allowing for a 15 second cycle. To get to the horizontal slider cam there is the same 4:1, 4:1 gear chain and then there are two sets of bevel ears to get to the correct level then a 5:1 and a 1:1 ratio.

Payout probabilities

Now for some complicated maths made easy. It is 2p a play. For each reel the table gives the fruit on display and how many of that fruit there is on the reel.

On average if after 512 plays and 1024p put in, all 512 combinations come up, the percentage payout = (384+192+96+120+80) / 1024 = 85.2%.

The remaining fruits are two plums on reel one, three plums on reel two and three lemons on reel three. The change on the last reel means there are never three of a non-paying fruit.

Coin mechanism

The idea is to reject as many coins as possible. Since the machine takes a UK 2p piece all other UK coins should be rejected and this begins with coin insertion. The only coins with a diameter greater than a 2p coin are the 50p and 2 coins. The height of the opening (see figure 1) is less than these coins therefore stopping entry. A 1 coin is too wide to go down the chute (see figure 7) which consists of four 2½” narrow strips sandwiched between 3” flat girders. The flat girders are joined to the frame with ½” reversed angle brackets. This allows for some adjustment of position.

This leaves 1p; 5p; 10p and 20p coins still needing to be rejected. This is achieved by the coin testing mechanism in figure 9. The mechanism consists of a counterbalance. It is tricky to construct because there must be no screw heads near the coins. In order to do this a face plate is connected to the shaft. This face plate has angle brackets (12b) bolted to it to hold the 2p coin while the counterbalance rotates, but then an extra face plate without boss (109a) is placed after the angle brackets to obscure the screws. On the right hand side there is a statically mounted face plate without boss. The bolting of the plates occurs well away from where the coins enter and exit. A threaded boss is used to provide the weight for the counterbalance.

A correct 2p piece turns the counterbalance forwards and the coin drops in front of the two 2” strips at the base of the picture. A coin which is too small falls between the two angle brackets and drops behind the two 2” strips.

The face plates are kept close to each by a compression spring on the shaft just to the left of the bossed face plate. If there is an underweight coin resting on the brackets then the face plates need to be moved apart which is achieved by pushing the rod from the right hand end. The coin then falls behind the 2” strips.

Below the counterbalance (not pictured) there are two 3½” x 2½” flexible plates and are spaced ½” apart at the top, but taper down to a vertical coin accept chute and a coin reject chute. Closest to the machine frame the chute is a 5½” x 3½” flat plate. 3” x 5½” flat girders form the other side and are spaced away from the flat plate at the top and bottom by a washer, a 5½” narrow strip and another washer. The use of flat girders means there is a vertical channel where the coin switch 2½” insulating strip can stop the coin from dropping.

The coin pool

The coins are held in two cylinders placed one on top of the other. The base of the bottom cylinder can be seen in figure 2 just to the right of the payout tray. The cylinders can have no bolts attached to them or the coins may jam on the bolts. The cylinders are kept in place gripped at the back by a 1” motor tyre. A 1” bossless pulley loosely bolted to the flat plate keeps the 1” motor tyre from moving about. Bolt ends are just about allowed to go through one of the holes in each cylinder to hold them in place. The bolts are mounted on the back flat plate. Thin washers are useful here to make sure the bolt ends to go just far enough into the cylinders.

The cylinders are gripped left and right by girder brackets. At the front the cylinders are pushed onto the flat plate by the motor tyres at the rear.

The wedge at the base dispenses two coins at a time. It must not be too thick as it may jam against the base of the third coin in the stack which is still partly in the cylinder. Too thin and it may only dispense one coin. Two much vertical play and it may again jam against the third coin.

It was found that three 2½” flat girders sandwiched together make a very good wedge. Since the flat girders can only be bolted at one end it is very important they are not warped. The wedge must only move horizontally. There are side guides, each made out of two 5½” narrow strips with spacing between them to allow a static locking 1” corner bracket to go in-between them. At the back (see figure 12) two more flat girders bolt onto the wedge and slide pieces are used to allow the wedge to reciprocate.

Variation in part thicknesses may cause problems here. Thin washers can prove very useful. Two cylinders allows for about 65 coins to be in the coin pool. This means the chance of the fruit machine running out of money due to multiple payouts is very small. I estimate somewhere around 100,000 to 1.

Warning: Do not load the coin pool with more than one coin at a time. They can jam in a vertical position and be very difficult to get out.

The payout mechanism

Figure 8 shows a 6½” rack strip just underneath the lower of the two 5½” angle girders. It slides along a 12½” strip by slide pieces (must have side holes) connected to a 5½” rod through the slide piece side holes and then short couplings on the rod join to the rack strip. The rack strip moves along breaking connections to the motor that drives it for each possible payout. Breaking the single cherry contact stops it ½” along; the two cherry contact 1”; the three cherry contact 1½”; the three bell contact 2½” and the three bar contact is 5”.

The vertical payout shaft (see figure 11) rotates once for each 4p paid. A gear chain is needed to ensure the correct payout for every ½” the rack strip moves. Rack strips have 6 teeth for every ½”. When meshed with a 15-tooth pinion, the pinion rotates 0.4 of a revolution for each ½” moved. A 1:5 and 2:1 gear chain ensures the payout shaft turns once. A tricky thing is to get everything to reset once the payout has been achieved because the payout shaft when turning the other way will payout. To stop this there is a cam on the payout shaft which locks the shaft at a certain point in one direction only. However this would jam the motor, so there is a friction drive in this direction (figure 9 centre left). When paying out, a ratchet drive (figure 9 centre right) overrides the friction drive. Any slippage in the friction drive in that direction would reduce the payout.

From right to left the parts for the ratchet and friction drive are:

1. A bell crank connected to the rod with a 1” corner bracket connected to the slotted holes of the bell crank. A pawl on a pivot bolt is on the far end of the bell crank and a 2½” rubber band goes from the pawl hole to the centre hole of the corner bracket.
2. Next there is a ratchet connected to a socket coupling and then a 50-tooth gear which is driven from the next rod by a 25-tooth pinion. All these are free to move on the rod.
3. Next there is a 1” pulley with rubber ring connected to the rod.
4. Then a 8 hole wheel disc with four bolts attached to it provide the friction drive.
5. On the other side of the 8 hole wheel disc there are two short threaded pins bolted on.
6. The threaded pins go to a 8 hole bush wheel and a compression spring is sandwiched between the wheel disc and bush wheel.
7. The bush wheel connects to another socket coupling and then another 50 tooth gear which is driven from the same rod as in 2.

The five payout slider switches which can be seen in figure 10 are constructed as follows. A 2½” insulating strip is pivoted at the centre hole. Underneath a coupling (part 63) forms a collar for the axle rod and the other end of the coupling is bolted to the strip. A 1½” angle girder is bolted the other side with one hole of the girder jutting out. The slotted holes of the girder are vertically positioned and a 1½” wiper arm is bolted to the slotted holes. The bolt nearest the axle rod has a terminal nut on it to allow a wire to run off it. Five contact studs are placed on ½” x ½” angle brackets and are placed along a 7½” strip at the front of the picture. The switch for two cherries is so close to the other switches that it has to be constructed upside down and above the others. The top 5½” angle girder in the picture has five threaded pins with compression springs on it. The compression springs go against a set screw on a collar to make sure the switches close circuit when not being operated.

The gear chain from the PDU (which is set at the 6:1 ratio is) 3:1 (bevel gears), 4:1, 2:1 (25-tooth pinion and 50-tooth contrate wheel). From there to the rack strip it is a 25 tooth pinion to a 25 tooth contrate wheel to allow the drive to go vertical and then 5:1 and then a 15-tooth pinion to the rack strip. To the payout crank it is 2:1 either via the friction drive or the ratchet and 1:1 to the payout shaft using bevel gears.

The fruit machine arm and mechanism

The arm is two 9½” angle girders followed by two 2½” angle girders going away from the body of the fruit machine. Couplings in the slotted holes of the angle girders provide the slight change in angle required. The arm employs a cylinder piece at the top for the player to grip.

Unfortunately Meccano is not strong enough against heavy handedness so normally a warning is displayed about gentle use of the arm. However the following rules allow for a fairly strong arm.

Do not rely on bolts gripping rods, they will slip. My method from the arm to inside is as follows. A coupling has 2” x 1½” strips bolted to both sides of it and a 1½” rod in it. The strips and the coupling are bolted to the base of the arm.

The end of the strips and the rod connect to the end of another coupling at right angles. This coupling is at the end of the main shaft. The coupling is connected to a socket coupling and is bolted in place through the two screw holes in the coupling. There is no freedom of movement anywhere here.

At the other end of the socket coupling there is a bush wheel. To avoid slippage, two collars are bolted through their centre shafts to both holes of the socket coupling. The screw holes of the collars are bolted to the bush wheel holes. Plenty of washers are needed here to make sure it all lines up.

The bush wheel has 2” strips connected to it which in turn connects to three tension springs to bring the arm back vertical. The higher tension replica springs are best here.

Some damping of the arm is needed. A 1” pulley with a rubber ring is sandwiched to the support for the main rod.

A 3:1 gear ratio is employed from the main rod to a rod which has the motor start contact. This means even if the arm is pulled horizontal, no damage will occur.

Circuit diagram

See Figure 14. Note that for simplicity in the diagram only one of the five reel sensor payout switch/payout slider forward switch circuits is shown. If you have a AC motor with reversing capability (such as the EU1072 motor) then this is very good for the payout motor because with just two connections it can be made to go forward and backwards. Never allow both connections to be made at the same time or the motor will burn out very quickly. For DC motors a double pole relay can be used to switch the poles of the power supply. I used four standard Meccano relays, two for forward and two for reverse. Alternatively use two power supplies or a transformer with two independent outputs.

The cycle of putting in a coin to payout

1. Insert and test coin. An incorrect coin will either not fit the entrance hole or will go straight down the reject chute to the payout tray. A correct 2p coin operates the counterbalance and goes down the acceptance chute.
2. If the coin is accepted, the coin operates the coin switch (figure 2 middle right).
3. Start the reel motor. The player pulls the arm which operates the arm switch which when coupled with the coin switch mentioned in point 2 starts the motor to the reels and timing mechanism. The timing mechanism has about a 15 second cycle before shutting off.
4. Ensure the reel motor stays on. In the 15 second cycle there is the reel timer short duration off switch. Within about half a second of the motor operating this switch is set on, which means the arm can be released without stopping the motor.
5. Retract the reel payout sensors. On the previous play a cam has been used to work out the position of the reels. This must be retracted to allow the reels to turn properly. The cam completes its cycle and the sensors retract. The retraction operates the reel sensor cam switch which makes an electrical connection to the payout slider rewind. The payout slider rewind ensures the payout slider is reset before the payout. The previous play means the payout slider needs resetting if there had been a payout (see 9). Once the payout slider has rewound the payout motor is stopped by the payout slider rewind switch.
6. Start the reels turning. Each reel has a hammer which stops the reel in one of eight positions. The hammers are lifted by cams at about the same time so the reels can start turning. The reels are only connected to the input shaft by compression springs so they speed up slowly and gain randomness.
7. Get the coin to coin pool. There is a reel timer short duration on switch on the 15 second timer shaft which sends a pulse to the coin drop electromagnet (see figure 10 top right) which allows the coin to drop into the coin pool (or if it is full into the overflow box).
8. Stop the reels. Each hammer for each reel is quickly lowered when the cam for the reel completes.
9. Engage the reel payout sensors. Near the end of the 15 second cycle the cam operating the payout sensors engages. Any payout makes a contact on one of the five reel sensor payout switches. The payout slider now moves until the relevant payout slider forward switch is broken by the movement of the slider.
10. Stop the reel motor. The reel timer short duration off switch does this (see 4).

Possible enhancements

• The coin tester does not test for magnetic properties but a Meccano magnet could be used. The coin may need to be scraped off the magnet and rejected.
• Disallow a coin entering the machine if the player has already entered a coin. When the coin switch activates it also activates an electromagnet which pulls a shutter down near the coin entrance.
• Disable the fruit machine arm pull if the machine is paying out. It is possible for the player to put another coin in the machine before the payout has completed and they would not get the full payout. This would probably involve a relay in parallel with the payout motor to the reel motor.
• The machine casing could be detachable for easier maintenance.
• The coin pool needs to be mounted at least 1 higher. This allows for more coins to go into the payout tray without jamming the descent from the coin pool.
• The payout mechanism suffers from the problem of the motor taking time to stop. The motor will slow down more quickly the more coins there are in the pool due to friction. Therefore there has to be some lee-way in the coins being dispensed to where the cam stops the payout shaft from going the other way. This makes the payout a bit on the slow side. A centrifugal clutch or an artificial load may improve things.

Other notes

If an American version of the fruit machine is required it can be easily adjusted to use quarters or dollar coins. A European version is best operated with a 2c or a 50c coin. It is important the diameter of the coin is only slightly less than that of the diameter of the coin pool cylinders or they may jam. This means no Meccano part can be used as a token as there are № 1” discs.

If parts come into contact with the coins, use old parts as the coins will scratch them over time.

Acknowledgements

• Meccano Bandit by Phil Ashworth, rebuilt by Ken Wright — inspiration for hinged front panel and to some extent the arm and the coin pool.
• Fruit Machine by Ian Henwood, International Society of Meccanomen — picture of a coin pool.
• How Things Work — The Universal Encyclopaedia of Machines, Paladin Granada books — coin tester.
• ModelPlan 71 Fruit Machine, Philip Drew — removable casing.

11/10/08 SELMEC exhibition

I was very disappointed not to have this finished for the 2008 exhibition. The reel mechanism was fundamentally flawed and the payout mechanism not even started. What folly! After buying my first ever rack strips, I was intent on using them on the fruit machine with a disregard as to whether they were appropriate. Using racks strips to work out what fruit the reels are on was never going to work. It was shown at the exhibition but the reel mechanism hardly worked. After the exhibition it was scrapped

21/05/09

It is working!

23/05/09 Blackheath Rugby Club Great Get Together

A fun 5 hours! There were a few teething troubles. I demonstrated with my own money almost all the time and it was fairly reliable. Two improvements are needed. It needs to be more random. There seemed to be too many cherries and plums coming up on the first reel. I am guessing the hammer shape to stop the reels is wrong and the hammer tends to stop after a threaded pin that is slightly closer to the shaft, also the shaft with the reels on must not be oiled, this reduces randomness. Additionally the switch activated by the coin needs the pivot position changed so there is more force and therefore a better electrical contact.

20/06/09

A video was recorded at the meeting today. This can also be seen on this page and on YouTube. The middle reel is off centre. Caused by a loose bolt.

28/06/09 Charlton Park Great Get Together

Another fun 5 hours. The fruit machine was extremely reliable, needing hardly any maintenance. The only problems were vibration working a few nuts and bolts loose and damage to the arm caused by over-enthusiasm. Cost to me two 2½” strips and a double angle bracket. Apologies were made.

04/07/10 Randomness

A comment at the SkegEx exhibition was ‘is it random enough?'. After looking at the first reel for a few plays it was obvious it wasn’t. So back to the drawing board. Maybe when I’m 75 years old I’ll make another one with a proper random mechanism.

05/07/10 Dismantling

After successful exhibitions at Henley, SELMEC, NELMC and SkegEx it is time to dismantle the fruit machine, taking 6 hours 10 minutes :(.

Specifications

• Total part count: 4388
• Part count less fixings: 1463
• Construction time total: 10 months
• Estimated construction time: 400 hours
• Deconstruction time: 6 hours 10 minutes
• Cost (reference www.meccanoman.co.uk): 1800 pounds

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