Introduction: K'Nex Fruit Machine

Picture of K'Nex Fruit Machine

This is a working fruit machine which is made almost entirely from K'Nex. It is so large that it will have to remain in the room (which has a concrete floor) for ever.

The machine pays out in balls, the size of the win being the lowest digit which appears on the three reels (so any combination which contains a zero is a loser).

During the building of it much was learned about K'Nex (Elap had discovered it at a car boot sale only a couple of months before he started) and some PDFs on K'Nex have been produced (see below).

The non-K'Nex bits of the fruit machine are the reel symbols (produced using Microsoft Word and then laminated) and the balls (meant for a child's play pit - Elap didn't have anywhere near enough K'Nex balls, and they are expensive). Also, a weight has been made from a lead-filled K'Nex cage because there were no K'Nex components which were heavy enough.

It probably took about 150 hours to build, spread over two years, and was made up as it was built - there were no plans, but Elap collects old mechanical slot machines and was familiar with the principles. There were a few areas where a redesign was necessary (for example, the handle kept falling to pieces when pulled, and the original pawl and ratchet mechanism was clunky and didn't work very well), but there wasn't a lot of reworking overall.

The return is 85.94% - quite generous for a fruit machine!

The K'Nex pieces were acquired from car boot sales (mainly) and eBay.

Here are some documents relating to the construction of the machine, and some K'Nex tips.


master-splinter306 (author)2015-08-28

Great job !

humor4fun (author)2015-05-13

You sir, are a king among k'nex engineers. I'm not currently adept enough at k'nex engineering to re-build your machine from what you've provided, but perhaps someday I will be. If you ever produce a set of build instructions I'll be certain to hop on ebay post-haste to buy 90,000 parts so I can build one of these myself.

Elap (author)humor4fun2015-05-14

Thank you, kind sir!
I've made three fruit machines so far, the last two smaller than their predecessors, but I made them up as I built them, and they are so complex that it's too late to produce instructions!
Having said that, I am wondering whether it is possible to produce a yet smaller version, for which I would produce full instructions.
Stay tuned...

humor4fun (author)Elap2015-05-14

I look forward to it. In the meantime I am going to start working on a Coin Pusher machine with a goal of 2 or 3 moving tiers. These have always been so much fun for me at the arcades.

Mr._Rodgers (author)2015-04-07

Shouldnt you be out curing cancer or something? this is insane!

Elap (author)Mr._Rodgers2015-04-07

Mark 3 is the latest version...

MisterBukweet (author)2013-06-16

I am almost speechless, that is why I'm typing.. lol.. you my friend are a god... don't expect any tithes though...

lavagod13579 (author)2013-02-11

That is great i hope you complete the machine, because after looking at this im sure it'll be a great piece of ingenuity.

lavagod13579 (author)2013-02-11

Are you considering adding more instructions so someone else could build it maby using PDFs? Because this is very nice work, and took vast amounts of engineering.

Elap (author)lavagod135792013-02-11

The problem is that I made it up as I went along and hadn't come across the Instructables site then.

It would be too much work to explain what I did, and I've forgotten a lot of it!

HOWEVER, I'm experimenting with a smaller version which would use K'Nex ratchets and K'Nex rubber bands and would work with K'Nex balls.

If I succeed, I'll produce step-by-step PDFs, but to be realistic it would be the middle of the year before - and if - I completed it.

daredevil499 (author)2012-12-07

that must have taken forever to build.

Elap (author)daredevil4992012-12-07

I made it over a period of two years, spending about an hour or two a week on it on average.

daredevil499 (author)Elap2012-12-08

wow,The longest I ever spent building something with knex was about 2 1/2 months. I was building a ultra-lightweight helicopter that actually lifted into the air. It actually lifted about an inch. I started working on it again last week. I going to post when I finish

knexpert#10829476 (author)2012-09-16

This brings tears to my eyes, all those beautiful mechanisms working together. Maybe you can make a smaller version of this and post it on instructables:)

Elap (author)knexpert#108294762012-10-06

The problem here is one of scale. Clearly, making a machine which was say 6" high would be impossible because of the relatively chunky size of the pieces.

The larger the machine the more feasible it is. For example, If you want a combination of rods to be a certain length, there are far more combinations of rod lengths to try for a large-scale machine than with a smaller one.

It would be a big challenge to make a smaller version without modifying the pieces, which of course is not allowed!

The reason the machine is the size it is is based on constructing the smallest reels which used eight flexible rods of the same length.

Having said all this, I have an ongoing background task running in my brain on how to make a smaller version...

emilyvanleemput (author)2012-08-17


My mouth fell open...

jameshond (author)2012-05-05

this thing is cool i like it

mrknex3000 (author)jameshond2012-06-27

This is almost as cool as the amusement ball machine thing.

darkkiller545 (author)2012-05-03

Very expensive i guess :p

knexpert#10829476 (author)2012-03-28


Gr3at_Whit3_North_Guy (author)2012-02-16

how does the machine know how much to pay out

Have a look at Reel Construction.PDF. You'll see that each symbol has a slot associated with it; the higher the number, the deeper the slot. The payout tester falls to the depth of the shallowest of the three slots which correspond to the displayed symbols on the winning line. Depending on how far the payout tester falls, levers get lifted so that the right number of balls are released.

LiftAndLove (author)2012-01-31


Tjakka5 (author)2011-12-14

Im rebuilding this machine, only waaaay smaller.
But im wondering, how do you make the wheels spin?

The handle attached to the wheel?
A quick running motor?
A weight on the wheels?
Something else?

Also, how are you stopping the wheels exactly at the good spot?

Elap (author)Tjakka52011-12-14

The reels are spun by using weights and levers - there are no motors.

I'll reply more fully within the next week or so.

Elap (author)Elap2011-12-27

I've added a PDF document explaining how the reels are spun and stopped.

Tjakka5 (author)Elap2011-12-27


That is so smart,
Thanks :D

KNEX-pert (author)2011-12-25

OMVG! That is the most outstanding, most incredible, machine i've ever seen! Collosal! Super job! Five star rating!

Puddock (author)2011-12-04

This is incredible! Great job!

rheath2 (author)2011-11-23

What an incredible machine! Did you use for the angle *556% or did you use angle 4775- scale triganomatry?

Elap (author)rheath22011-11-23

I used a spingleflex unit with a horizontal jigglepoker.

rheath2 (author)Elap2011-11-23

You should know what triganomatry means.

rheath2 (author)Elap2011-11-23

Uhh I'm talking actual words here. =)

The Cannoneer (author)2011-10-31

Quick there any way you can post the mechanism of the machine or post instructions on a smaller one? Im askin this cause its awesome and i want one!!! :)

Elap (author)The Cannoneer2011-10-31

Unfortunately there is no easy way!

I could show you how to make the reels, and how to install them in a frame. I could then show you the principles involved, but because I made it up as I went along I couldn't give you step-by-step instructions (I only discovered the Instructables site after I had finished it).

A smaller version would be much more difficult - there would be fewer ways to make each element of the construction because you are constrained by the number of combinations which could be experimented with.

Also, it is occasionally necessary to reach into the innards of the machine which would not be possible if it were smaller - bits of it would have to be disassembled first.

Let me know whether you want more photos so that you can see various sections in detail. Bear in mind that you will need to be an inventive kind of K'Nexer to build something like this and not just an instruction-follower!

The Cannoneer (author)Elap2011-10-31

oh ok...i understand....can you post a few more pictures of the reels and the mechanism and show me how to how to make the reels, and how to install them in a that ok?

Elap (author)The Cannoneer2011-11-01

I'll see what I can do. Give me a few days.

The Cannoneer (author)Elap2011-11-01


Elap (author)The Cannoneer2011-11-21

I've added a PDF document showing how the reels were made.

jeffeb3 (author)2011-10-19

So a fruit machine? Is that like a slot machine? Like you would find in Las Vegas?

sfeingold (author)jeffeb32011-11-19


Elap (author)jeffeb32011-10-19

Sure thing.

knexpert#10829476 (author)2011-11-10

This thing is so incredible! I've never seen anything this cool!

MegaMetal8 (author)2011-10-29

Why can't you move it forever?

Elap (author)MegaMetal82011-10-29

Because it won't fit through the door and it would never be the same again if I dismantled it and tried to reassemble it!

MegaMetal8 (author)Elap2011-10-30

It doesn't have to be rebuilt??

Elap (author)MegaMetal82011-10-30

You don't REALLY think I'm going to take to pieces after all that work, do you?!!!

MegaMetal8 (author)Elap2011-11-08

Fair enough

natwitt (author)2011-11-05

dude that is one heck of a machine that is sweet haw to balls come out of the machine great job!!!!!!!

mikeasaurus (author)2011-10-28


The video showing the machine in action is amazing!
(you can also embed your video directly into this Instructable using therich editor)

About This Instructable




Bio: Wacky retired chap who just can't resist going to car boot sales; a hoarder. Having retired 14 years ago after working for 33 years ... More »
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