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High Reduction Ratio Planetary Drive

by mkeveney, published

High Reduction Ratio Planetary Drive by mkeveney Sep 17, 2012

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Description

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

Click the video link to see it in action:

youtu.be/P-Obt-9tZVo

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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Instructions

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

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

thingiverse.com/thing:30619

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
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!!!
Hi,
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 !!!
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.
 That would be terrific... I do know that it can't be exact but with enough of the basic gearing done to dxf.. then others can re-create the "extra stuff" thx
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!
 thx a bunch... will let you know GMT
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!
Thanks for the update.  Love the video!
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... 
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:
http://www.ksmetals.com/retail.html
I've heard of this being called a differential planetary gear set. You can find my parametric version from last year here: thingiverse.com/thing:7390. It was just a proof of concept; making a desktop model is a good idea.
Very nice! I decided to make mine in part because I hadn't found an example on Thingiverse. Thanks for pointing yours out!
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!
Very Nice, especially the documentation! Keep up the good work!
very impressive. I am starting to print it NOW.
Beautiful !!!

I like the way the things are put together (and choice of colors) and I do love the dial !!
Ah, good to hear from you aubenc. Your 'tiny planetary gear' set is one of the things that inspired me to make this one!
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)
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.
Very nice :)

I think "Split annulus, compound planet, epicyclic gears" might be correct: en.wikipedia.org/wiki/Epicyclic_gearing#Gallery
(Although your planets aren't actually compound due to the tolerance as you mentioned)
Ah, yes that does look like it. I missed it on my first read of that page. Thanks for pointing it out!
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