Author Topic: Planetary gearbox - an attempt to make sense of how it works  (Read 6522 times)

Offline sorveltaja

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #15 on: April 15, 2019, 10:44:29 PM »
MJM460, I think you are right!

I Drilled right through the gear A to make the M3 thread for the grub screw, which goes through the brass tube input axle:


Here is the first version assembled. I was able to distinguish three or four gear ratios, while operating it manually. It is rather noisy and is stiff to rotate, and has numerous not so well thought quick-fixes:


While spinning it slowly with a power drill device, braking gears one by one, there was an anomalous 'unwinding' -thing happening, which locked almost the whole thing to solid lump.
So I spinned it backwards, and that locking situation was gone. I did it few times, and always the same results. 

Once again, I dismantled it, and couldn't find reason for that. All the possible suspects, like planet gears, that were fastened with screws, had also brass sleeves,
long enough to allow the gears to rotate freely, even when the screws were tightened.

Next suspect was the carrier D on the output side:

And the actual carrier, that was still tightly fastened:


But enough of that buggy first version.
---------------------------------------

Mike, thanks for the pictures, and yes, it would be greatly appreciated, if you could provide the DXF-files of that transmission. I'd like to make a 3d-model of it, and print the parts, to test it.
I have no idea though, of how the DXF-files could be transferred through this forum. Anyone?

Hugh, I also have troubles calculating planetary gear ratios, as there isn't that many sources, that explain it as clearly as you have done. Big thanks for that.



« Last Edit: April 15, 2019, 10:48:05 PM by sorveltaja »

Offline Vixen

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #16 on: April 15, 2019, 10:55:47 PM »
Hi sorveltaja

Jo or one of the administrators or Ade, should be able to tell us how to send a DXF file to each other.

Mike
It is the journey that matters, not the destination

Offline crueby

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #17 on: April 15, 2019, 11:00:20 PM »
As long as they are not too large, cannot dxf files just be attached to a post through the 'attachments and other options' feature?

Offline Vixen

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #18 on: April 15, 2019, 11:09:57 PM »
Hi sorveltaja

This is an attempt to attach two DFX files to this message using Attachments and other options.

The attachments don't show up on the Preview, which threw me, but are attached to the post

Actually, I sent two AutoCAD DWG files by mistake. I will do the DXF's in the morning.

Mike
« Last Edit: April 15, 2019, 11:21:55 PM by Vixen »
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Offline sorveltaja

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #19 on: April 15, 2019, 11:39:32 PM »
Mike, thanks. I imported those DWG-files to Rhino with no problem, just for a test. Take your time with DFX's. No hurry at all.

Offline Vixen

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #20 on: April 16, 2019, 11:05:35 AM »
Good morning sorveltaja.

Here is the DXF file for my 4 speed and reverse Merritt-Wilson transmission. Unfortunately the overall assembly DXF drawing was too big to send as an attachment, you will have to make do with the DWG file

Mike
« Last Edit: April 16, 2019, 11:09:29 AM by Vixen »
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Offline Roger B

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #21 on: April 16, 2019, 05:49:10 PM »
Thank you for posting those Wilson drawings Mike  :ThumbsUp:  :ThumbsUp:  :wine1:
Best regards

Roger

Offline Vixen

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #22 on: April 16, 2019, 06:04:36 PM »
My Merritt-Wilson 4 speed and reverse transmission was based on the gearset from Sturmey-Archer push bike gear hubs. You will need three hubs. I chose them because used ones are still available in the UK. They are tough, robust and almost indestructible. I still have a few spare S-A hubs in store. Of course other gear sets could be used, but they would give different gear ratios and their own set of design compromises.

Mike :noidea:
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Offline sorveltaja

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #23 on: April 16, 2019, 09:09:54 PM »
Thanks for the drawings, Mike :)

This is the progress so far:


After I get the modelling done, I think I'll replace the ball bearings with simple brass bushings. On the other hand, they seem to be in metric sizes, so it shouldn't be that hard to source them.

The brake spools are somewhat challenging, what comes to 3d-printing. To prepare them for printing, some of them might need to be splitted, but that's just a part of the thing, that I want to learn also.

Offline dieselpilot

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #24 on: April 16, 2019, 09:21:04 PM »
Did you catch this image in their photo gallery? http://project38.net/wp-content/uploads/IMG_0202.jpg

Offline Vixen

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #25 on: April 16, 2019, 11:06:22 PM »
Hi sorveltaja,

Some quick 3D drawing work there. 4th gear is a direct drive ie. no gear reduction. It is engaged by a dog clutch in my version. You may wish to make it a simpler 3 speed plus reverse gearbox by discarding the red dog clutch disc.

The bearings shown are all metric and readily available on e-bay. there is no need for high quality bearings at the prototype stage, so go for the cheapest available.

If you print the brake spools oversize or split,  do you have lathe facilities to turn them to the correct size and perfectly round and concentric?

The Sturmey-Archer gears have plenty of clearance, so print your prototype gears slightly undersized, so they don't bind.

Mike
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Offline sorveltaja

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #26 on: April 16, 2019, 11:13:22 PM »
Dieselpilot, yes I have seen that image. But as it is just a sketch, it is somewhat difficult to interpret, as there are no exact dimensions of the most important parts, like gears, mentioned.

I tried to model it using their only cad-drawing, that is available on the site: http://project38.net/wp-content/uploads/A001-Transmission-Full2013-BSize.jpg

Maybe I'm missing something crucial, but to me, that drawing is quite sparse, or lacking. I just can't figure out, how the gear sets are linked together

In the meantime, I'll stick with Mike's drawings, which I can understand.

Offline sorveltaja

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #27 on: April 16, 2019, 11:39:02 PM »
Mike, thanks for the tips. Yes I have the lathe ready to go. When ready for printing, I'll do some test samples first, to see, and set the tolerances. Better bit loose than too tight.

Those ball bearings, I might get them from a local supplier. Have to check the required sizes availability, though. If not suitable sizes available, I'll go to ebay.


Offline sorveltaja

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #28 on: April 17, 2019, 11:08:06 PM »
Getting there piece by piece:


While going through my junk boxes, I managed to find two ball bearings, that are exactly same size as the ones, that are on both ends(10x26x8). Haven't done the search for the real ones yet, but in the meantime, I printed 'mock-up' -bearings, which don't have any moving parts in them. They need to be turned to proper sizes, though:


Today I got seriously distracted by 3d-printed ball and roller bearings. But no matter what form they have, there seems to be always problems with tolerances.

Either whole object is frozen to one lump, or is too loose. There are some, that try steel balls, but it gets very complicated, as there needs to be cage(s) to keep the balls or rollers in certain positions,
like the real ball or roller bearings have.


Offline ddmckee54

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Re: Planetary gearbox - an attempt to make sense of how it works
« Reply #29 on: April 18, 2019, 05:49:51 PM »
Silly question, but have you tuned the steps/mm on your printer so that when you tell it to print a 20mm cube, you get a 20mm cube?

Before I fixed my first printer it was WAY off, a printed circle was visibly an ellipse.  My second printer was not so bad, but it still needed to be tweaked a little.  If you haven't been printing mating parts you might not have noticed any issues.

Don
« Last Edit: April 18, 2019, 06:27:17 PM by ddmckee54 »