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RomanHujer

Modular planetary gearbox 1024:1

by RomanHujer Oct 15, 2017
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you are a fucking genius :)

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I tried printing one of these and din't have any luck either. I measured all my parts and they are within the tolerance that my printer promises. After some pondering, I can came to the conclusions that it's the planetary gears. They too tight of a fit. I put the stl files into cad program and it looks to me the design is too tight (attached an image). What is the radius of the pitch circle supposed to be on these ? if its 6mm, then I'd need 36 mm on the outer gear (right ?), which I'm only measuring at 32mm.

I did not notice any problem with my Anet A8 printer, model is OK too. The printed parts can be easily set up. time. (Planet wheels first place in the wreath then deploy the rider and end deploy sun). 32mm is the correct hole dimension in the wreath cover.

Thanks for the reply ! Would you mind sharing some of the other dimensions ? To be honest, this is the first time since middle school I’ve bothered to calculate gear pitch and ratio…

If 32 mm is the correct dimension on the outer gear ring, then I get:

2pir = 100.53 / 27 teeth = 3.72 mm per tooth

This seems to be different from what I measure the planetary gears. From my print of your model I measure at pitch circle with a diameter of 11mm. thus:

2pi5.5 = 34.56 mm / 9 teeth = 3.84 mm per tooth

Thanks for the help !

Moudule is 1.2mm outer gear ring dimesion is (27+2) x 1.2. = 34.8mm --- 32mm is only hole in gearbox cover.

For calculation of pitch circle:
Sun and Planet gear have a pitch circle: 9 x 1,2 = 10,8 mm (tooth x module)
The outer pitch circle is 27 x 1.2 = 32.4 mm is the same as 2 x (10.8 + 10.8 / 2) The proposal is therefore right :-)

Thanks ! I guess, I just learned what a gear module is ;)

If the outer pitch circle has a radius of 16.2 (32.4/2), then the outer pitch circle is 2xpixR = 101.8 mm.
Divide this by 27 teeth, that gives me a pitch of 3.77 mm per tooth.

If the sun gear has a pitch circle of 10.8, then 2xpixR = 33.93 mm
Divide that by 9 teeth gives me 3.76 mm per tooth.

It must be that my printer is printing on the large side of the tolerance. I guess, on a 10.8mm gear 0.1 mm is about a 1% error, which might be just too much to make my gears fit properly.

I wonder if I could print the sun and planetary gears at 99.5% of scale….?

I made a simple models (desing in FreeCAD) and printed on my printer (scale 1:1), assembled and used for more than a year in my telescope. Print error about is 0.05 to 0.1 mm, can be corrected eg by needle file.
If my model does not suit you, you can try another one, such as https://www.thingiverse.com/thing:2114390 or design your own.
It is only plastic 3D printed parts, can not be wait miracles :-)
Roman

Compact planetary gearbox

actually, its what you did with your telescope that I really like. I'm trying to make something similar, though not for a telescope.

Got it to work -- key for me was to print the planetary gears at 98% size and everything else at 100%. Thanks for the feedback !

Struggling to get this to print. Getting closer now. 4th attempt.
My printer is bang on, e.g. the Outer is 41.02mm square.
The trick seems to be minimum temps so that the teeth form exatly as they should rthare than flow a little.
Using a Pruisa i3. 0.3 nozzle. Slic3r.
Printing at 205 now. 55 Bed.
2 shells. 30% infill.

Hello,
I printed your first group of gear and enclosure and I am having trouble getting them to fit together. I am wondering if I had a printer setting different than your... can you tell me what your's were. I had a 1.2mm shell. .1mm Layer thickness, cooling on.
Thanks.

Printer: ANET A8
Filament: PLA 1.75mm
Setting:
Nozzle Diamater 0.4 mm
Extrusion 0,9
Layer Height 0,2 mm
Infill 50%
Temperatures 50/200 °C
Cooling on. 2nd layers