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:

Rods:
13x Black/green rod
10x Silver/white rod
5x Blue rod
3x Dark grey/yellow rod
1x Tan rod (strengthend)
http://www.knexusergroup.org.uk/acatalog/knex-part...

Connectors:
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
http://www.knexusergroup.org.uk/acatalog/knex-part...

Gears:

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!)
http://www.knexusergroup.org.uk/acatalog/knex-part...

Other:
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
http://www.knexusergroup.org.uk/acatalog/knex-part...
http://www.knexusergroup.org.uk/acatalog/knex-part...
http://www.knexusergroup.org.uk/acatalog/knex-part...

! 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