High Reduction Ratio Planetary Drive

by mkeveney, published

High Reduction Ratio Planetary Drive by mkeveney Sep 17, 2012

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This model illustrates an interesting planetary drive variation that produces a very low gear ratio.

Click the video link to see it in action:


Recent Comments

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this is a very interesting mechanism. i would like to try it. can u just tell me that how u calculated that second speed reduction, i.e. 16:1 . Em not getting it. Please help me out. Thank you!!!

 thx a bunch... will let you know GMT

Okay. Profiles.dxf has the same info as the drawing illustrating hole sizes.  I think that ought to get you off to a good start
Let us know what you come up with!

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The video shows how it works and includes some construction tips.

You'll probably want to make the Tube cutting tool as well:


I started designing this in metric units, but was only able to find brass tubing in imperial sizes, so I simply used both measurement systems. If you live in a metric part of the world, you should be able to adapt to locally available materials by drilling out the bearing holes as necessary


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pranitm4u on Feb 25, 2014 said:

this is a very interesting mechanism. i would like to try it. can u just tell me that how u calculated that second speed reduction, i.e. 16:1 . Em not getting it. Please help me out. Thank you!!!

Greymantalker on Oct 3, 2012 said:

Any chance of also posting DXF file output from the stl program for us poor laser cutter folks?   I believe this could also be fab'd using acrylic or even wood...  thx, GMT   Great video on utube BTW !!!

mkeveney on Oct 5, 2012 said:

I used a few different tools to develop the models.  I think I can get the gear profiles and perhaps a few basic outlines exported to DXF, but you'll have to take it from there.

I'll try to get something posted this weekend.

CodeCreations on Sep 28, 2012 said:

I thought I'd add my comments and video here, too. The mechanism runs pretty smoothly. I had to do a bit of filing to get it to fit together, and despite your warning I ended up snapping one of the dovetails trying to remove it after a too-tight test fit. I used a bit of superglue to fix the break, and also to secure the handle. I found it easier to line up and insert the little bushings by sticking them on a small round detail file to get them started straight.

Here's my video: http://youtu.be/0i59XkmR7y8 Thanks for the great design! I think the kids' classmates will have a good time figuring this out!

mkeveney on Sep 28, 2012 said:

Thanks for the update.  Love the video!

CodeCreations on Sep 21, 2012 said:

Well, I printed one. It turns out that the last hobby shop in the area (that doesn't just deal in RC stuff) closed down a couple years ago, and no one else seems to have the brass tube. :/ So I ordered them online. Hopefully by next weekend I'll be able to assemble it, and I'll post a picture when I do... 

mkeveney on Sep 21, 2012 said:

Ah, sorry you had to resort to that.  If anyone else has the same problem, be sure to call the hobby shops, craft stores and hardware stores... the RC hobby shops used to be your best bet, but I guess now it's all prefab.  Ask if they have a "K&S Metal Center" rack.  It's not terribly hard to find at least in the US:

emmett on Sep 18, 2012 said:

I've heard of this being called a differential planetary gear set. You can find my parametric version from last year here: http://www.thingiverse.com/thi.... It was just a proof of concept; making a desktop model is a good idea.

mkeveney on Sep 18, 2012 said:

Very nice! I decided to make mine in part because I hadn't found an example on Thingiverse. Thanks for pointing yours out!

CodeCreations on Sep 18, 2012 said:

Awesome! I'm going to try it -- seems like it would be a great model to bring into the kids' school, too. Thanks for the design and the very informative video!

danielpublic on Sep 17, 2012 said:

Very Nice, especially the documentation! Keep up the good work!

chaleg on Sep 17, 2012 said:

very impressive. I am starting to print it NOW.

aubenc on Sep 17, 2012 said:

Beautiful !!!

I like the way the things are put together (and choice of colors) and I do love the dial !!

mkeveney on Sep 17, 2012 said:

Ah, good to hear from you aubenc. Your 'tiny planetary gear' set is one of the things that inspired me to make this one!

fma on Sep 17, 2012 said:

Interesting concept. But this means that the module of the second ring does not exactly match the sun module, does it? It guess it works fine with plastic gears, but it would not work as well with metal gears (ar at least with a lot of friction)... In fact, this is a mix between a standard planetary gears and harmonic drive ;o)

mkeveney on Sep 17, 2012 said:

Yes, strictly speaking, the planet gears should have a step in the middle, with a slightly different diameter where they intersect the driven ring, and the sun gear should only intersect the half that meshes with the stationary ring. In this model, the difference is well below the manufacturing tolerance of the gears.

Yes, it does function much like the harmonic drive. I'm not sure whether this drive has a proper name, but it's been around a long time. I first discovered it in a hobby-motor reduction drive when I was a kid.