Welcome to my instructable on how to build a k'nex piston! This is my second version, also check out my original K'nex Piston.

This is a video of the K'nex piston version 2 operating.

This k'nex piston converts rotational motion to linear motion. (or vice versa). This piston has a smaller range of movement than the previous version, it is able to retract/extend 51mm (about 2 inches). The original version is able to retract/extend 65mm (about 2.5 inches).

It has always been a challenge to create linear movement with k'nex. But no longer! I have designed a rack gear (something which k'nex should have made a long time ago in my opinion) built completely out of k'nex. A rack gear is a rod with teeth on it which allows a round gear to push the rod back and forth.

This video demonstrates how a rack gear works:

Step 1: The Parts List

These are the parts you will need to build the piston:

109 - blue spacers (many can be substituted for grey spacers)

9 - black clips.

3 - blue clips.

6 - brown clips.

21 - grey clips.

8 - orange connectors.

40 - blue 3D connectors.

2 - white connectors.

6 - yellow connectors.

2 - green connectors.

8 - red connectors.

2 - blue gears.

5 - grey grip gears. ( finally found a use for those things :P )

2 - yellow gears.

2 - red gears.

20 - green rods.

13 - white rods.

39 - blue rods.

6 - yellow rods.

1 - red rod.

3 - grey rods.

Step 2: Starting the Frame

This is the back of the frame which you will start building off of.

Step 3: The Rack Gear(s) Parts

These are the parts you will use to assemble the the rack gear in the next step.

Build though pictures 4 - 9 twice. you will need two of these parts.

Step 4: Rack Gear(s) Assembly

Assemble and mount the rack gear as shown.

Note: There is a small issue with the yellow rods disconnecting from the red connectors in the rack gear assembly. my solution to this was to rap a rubber band around them to hold it together.

Step 5: Upper and Lower Pinion Gears

This version of the piston uses 2 pinion gears to drive the rack gear. This helps keep the rack gear in place and increases power output.

Please read picture notes.

Step 6: Gearing

In order to power both pinion gears from a single input, I built a gear train connecting them. The challenge of this though is that both pinion gears had to spin in opposite directions. building a 3 gear train would have made them spin in the same direction. To make things even more challenging, both pinion gears had to spin at the same speed, which required a symmetrical gear design. So I had to design a symmetrical 4 gear train to solve this problem.

Connect 6 blue rods to the blue and red connectors.
Add the 2 red gears to the blue rods on the red connectors.

Step 7: Gear Supports

These gear supports hold the gear axles in the proper position to keep the teeth of the gears interlocked.

Step 8: Final Assembly

Just add the spacers and the final structural panel.

Congratulations on completing the K'nex Piston V2!

Thanks for viewing my instructable! Be sure to check out my other instructables!
If you post an instructable which uses something from one of my instructables, let me know, I'll post a link to your 'ible in my applicable 'ible!