Cycloids and Hypocycloids

Thu, 21 Mar 2013

Okay, back to the gear zine. I'm not sure whether this will work but I've been experimenting with cycloid gears. They are looking promising so far. The cycloid is the shape traced by a point on a circle as the circle rolls.


In this case, I've wrapped seven cycloids round the outside of a circle generating this hypocycloid internal gear.

The six lobed gear uses lobes the same size as the circle used to create the cycloid. These fit neatly into the seven segment hypocycloid.

The inner piece rotates in a sort of eccentric way within the outer advancing one tooth at a time as it does so.

I'll see if I can put together a stop motion or a flash animation of the mechanism shortly to more clearly explain what is going on.

It is certainly looking like a promising mechanism. If I can get it working smoothly it will make an interesting project with some interesting uses. A single gear like this reduces speed by a ratio of 1:7 adding a second gear back to back with the first should reduce the ratio a further 1:7 making a total reduction of 1:49 with only three moving parts!

Fingers crossed.

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Comments (2)

  • Smelter March 22, 2013 at 7:32 am

    And a practical use for this

    And a practical use for this gear, for anyone who doesn't know is…

    a fuel pump!

    • umehta March 22, 2013 at 5:55 pm

      Find us the


      Find us the animation showing how does it look when it rotates. 

      I’m just working on one now… – RI

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