K'nex Piston

Introduction: K'nex Piston

About: I have an Associates Degree in Electrical Engineering Technology and I am currently working as a manufacturing Engineer. I have many interests which are ever expanding, but one of the things which I love doin…

Welcome to my instructable on how to build a k'nex piston!

Be sure to check out my k'nex piston version 2 also!

This k'nex piston converts rotational motion to linear motion. (or vice versa). This piston is able to retract/extend 65 mm (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: Parts List

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

4 - white circle connectors

20 - blue 3D connectors

3 - brown clips

11 - grey clips

1 - red connector

11 - black clips

12 - grey spacers

18 - blue spacers

8 - white rods

26 - blue rods

5 - yellow rods

2 - red rods

2 - grey rods

Step 2: The Track

The track will be what guides the rack gear and piston.

  • Pic 1:
    • Build two of these (one will be set aside for the next step)
  • Pic 2:
    • Snap a grey rod onto the white connector
    • Then snap a red connector on the grey rod so the hole on the red connector lines up with the hole on the white connector
  • Pic 3:
    • Snap the other grey rod onto the red and white connector
  • Pic 4:
    • Slide the connectors to the end of the grey rods so that the red connector is at the end.

Step 3: The Rack Gear

  • Pic 1:
    • This is the rack gear. Build exactly as shown on a yellow rod.
  • Pic 2-3:
    • Slide the rack gear onto the track as shown. Make sure that the side with only 3 grey connectors is on the track. Make sure that the yellow rod is lined up with the hole on the white connector.
  • Pic 4:
    • Clip the white connector from the previous step onto the grey rods as shown.

Step 4: The Structure

The structure holds everything together.

  • Pic 1:
    • Build 2 of these. (again, one will be set aside to be used later)
  • Pic 2:
    • Add 5 blue rods as shown.
  • Pic 3-4:
    • Attach the track and rack gear.

Step 5: Attaching the Piston Shaft

Now we will attach the piston shaft to the rack gear. The piston shaft used in the instruction will be a red rod. However a yellow or grey rod may also be used.

  • Slide the red rod through the red and white connectors. Slide it down until it is flush against the yellow rod of the rack gear.
  • Clip a black clip on the rods where they meet. This will secure them together.

Step 6: The Rotational Gear

Now we will build the rotational gear which will drive the rack gear and piston.

  • Pic 1:
    • Build 2 of these.
  • Pic 2-3:
    • Slide two grey and two blue spacers onto a red rod.
    • Slide the two parts we built from the first picture on both sides of the spacers.
    • Clip two grey clips on both sides of the rod and slide everything together in the center of the rod.
    • Make sure the black clips on the white connectors are aligned.
  • Pic 4:
    • Clip a blue rod on the white connectors.
  • pic 5:
    • Build 5 of these.
  • pic 6-7:
    • `clip the parts built in pic 5 to the black clips.

Step 7: Mounting the Rotational Gear

  • Slide 3 spacers on both sides of the gear axle
  • Mount the gear axle on the yellow connector of the structure and secure it with a grey clip
  • note the alignment between the gear and rack gear shown in picture 4 and make sure your gears are aligned properly.

Step 8: Completion

Now add the last part of the structure you built earlier.

Congratulations you have just built a piston out of k'nex!

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

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    3 years ago

    I've been working on assembling a fully functional claw machine and this was exactly what I was looking for to control the vertical movement of the claw.


    4 years ago

    Pretty neat! A little on the large side, unfortunately :(


    5 years ago

    this is very Impressive! there are hundreds of situations in which this could be used. Great job ;D


    Reply 5 years ago

    Thanks! :) I'm currently working on one which uses actual gears, but it will be longer. I'm hoping using gears will make it a little bit smoother.


    Reply 5 years ago

    sounds great! looking forward to what you come up with ;D


    5 years ago