Smallest K'NEX Differential




About: Hello! I am mechatronics graduate and have always had a passion for making things. This started at an early age with LEGO and K'NEX. I think it's great to create. From useful stuff to art or toy. The ibles...

This instr is about making a working K'NEX Differential. It uses all original K'NEX pieces, and is the smallest up to date (July 12, 2014).

Here's a video of it working in a 2-speed gearbox, used to add the power of two motors together.

Step 1: Parts Needed

You will need:

13x Black/green rod
10x Silver/white rod
5x Blue rod
3x Dark grey/yellow rod
1x Tan rod (strengthend)

2x 8-way black/white connector
4x 4-way silver/purple 3D connector
2x 5-way grey/yellow connector
1x 4-way green connector
2x 3-way dark grey/red connector
5x 2 way (V-shape) grey connector
4x 2 way (long shape) brown/orange connector


2x Red gear (also may be yellow crown gear)
1x small Blue gear
2x small Dark grey gear
2x small SNAP-ON grey gear (Important: you must have these!)

4x Tan clip (with "nose")
1x Blue clip (without nose, can also be with one)
3x Metallic spacer (1 and a half width)
10x Blue spacer (half width)
16x Black clip with rod end
4x Tyre large
4x Hub/pulley medium
4x Open wheel 25mm

! Non-K'NEX:
Also some isolated wire (used to tie a USB cable together for instance) about 10 cm / 3 inch.

Step 2: Preparing the Differential

Attach 6 "clip with rod end"s to a 8-way connector. Then pull the isolated (not really needed, but looks fancy) wire through the holes of one of the red gears, so they will be attached. Give the ends a firm twist, so the gear and the connector stay close and don't wobble too much.

Step 3: Start Building

I think the pictures speak for themselves. I you have trouble making it, comment below.

The structure becomes strong once the blue rods are attached. The structure around it, will make it even better. This will follow in the next step

Step 4: Making the Structure

Once again, if you face troubles, don't hesitate to comment.

And there you go! differential done. I'm using this in my next K'NEX creation.

I hope you've enjoyed my first instructable, happy building!



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    41 Discussions


    Reply 3 years ago

    The most common use for a differential is inside cars. It enables the rear wheels to rotate at different speeds from each other, while still pushing the car forward, when making a turn. I can't explain better, google it or even better "youtube"-it.

    Apart from car, A differential can also be used to add the power of 2 motors to eachother, with minimum efficiency-loss


    3 years ago

    Technically, a version of this differential out of mini K'nex would be the smallest.

    11 replies

    Reply 3 years ago

    Not yet ;) Altho I doubt K'NEX will make gears so small?
    (would be cool tho, in my opinion)
    or you could design and 3D print something yourself ;)


    Reply 3 years ago

    I have a mini K'nex roller coaster set that doesn't have any big K'nex. It uses a motor with a mini K'nex shaft, and 4x of the lower grey gear in the picture:

    (The top three gears are big K'nex, to show proportion) The K'nex set also has the equivalent of the small gear at the right. But so far, I haven't seen a mini gear with a covered, rounded top.

    Photo on 12-23-15 at 1.10 PM.jpg

    Reply 3 years ago

    You could try it... this differential also doesn´t rely on the fact that all gears have cornered teeth ;)
    if you can make a smaller one, I'll change the title :)


    Reply 3 years ago

    I accidentally made a mistake. I remembered small gears in the set, but I when I looked for them, I couldn't find any. I guess I was imagining things. The set only has the equivalent of the red gear, so without the small gears (equivalent of the normal K'nex grey gear in the pic) a mini K'nex differential won't work.

    However, I did come up with a way to make this build 100% K'nex, and it only takes two mini K'nex pieces. All you need is a Black end-of-the-rod clip, the kind that is all rounded at the top, and a yellow mini rod.

    1: When you are building the differential, you slide the yellow rod through one of the smaller 'lock' holes in the big red gear.

    2: Continue sliding it through one of the 8 black connector holes.

    3: Snap on the black mini clip, between the grey gear and the black connector.

    This yellow rod does the same thing as the string, and the black clip holds it from sliding out.


    Reply 3 years ago

    That's indeed true :) I'll see if can make it my own.
    I'm going to build another vehicle which uses the differential, so I'm going to plan to make new pictures for this instructable as well :) But it will take some time, perhaps months.


    Reply 3 years ago

    But technically - as Linkin_J_Knex pointed out correctly- for this mechanism (with gears) to work, one would need smaller gears then too. And until the present day, they do not exist oficially


    3 years ago on Introduction

    There doesn't seem to be anything preventing the grey gears from slipping around the drive axles. Some of my gears are small enough to have a little friction, but most would freely slip. In fact, my version relies on the fact that these gears slip freely. Am I missing something?

    2 replies

    Reply 3 years ago

    Excuse me for my late reply. Instructables didn't let me have a notification.

    There is indeed nothing that stops the (dark!) grey gears from slipping. Yet, I have found that on rod ends, they tend to have quite some friction (I don't have actualy magnitudinal forces, but I'm guessing it will be a coulpe of Newtons)
    The force of this friction is greater than the slipping force/spring of a 3V motor... that's why this works :)

    Thanks for your comment!


    Reply 3 years ago

    Brain...explodes. xD I think Gworks seems to know what he is doing. I don't even understand how a differential works, or even understand how gear ratios work!


    4 years ago on Introduction

    I have no idea how differentials even work and you make one out of kid's toys from scratch. Very nice