Nema 17 Stepper 5:1 Planetary Reducer
Description
Warning! There be overhangs here!
I have yet to see what sort of torque this can handle but it seems like it will handle quite a bit. I'm able to stop it if I grab two of the screws sticking out of the planet carrier. Hopefully I'll measure the torque soon.
This is intended to be used with another bearing somewhere on the output shaft. I can't imagine that it would handle any load with only one bearing on there. A different cover could easily be made with a spot for another bearing.
The current design adds 38.5mm in length to your stepper, it could be less but the makerbot supplied stepper that I have has long shaft so I had to make it longer to stop it from interfering with the bolt for the output.
It could probably be 5mm or so shorter pretty easily with a shorter stepper shaft.
Change Log
5/11/2011 Initial Upload
5/12/2011 Switched to 2x 683ZZ bearings for planets, shortened planets a bit, increased backlash and clearance, added list of some possible ratios
5/13/2011 Added addendum/dedendum adjustment to gear library for internal gear.
Removed most of the constants at the top and switched to arguments with defaults
Added multi-stage capability, now you can stack multiple stages in one case
5/20/2011 Added a way to get a screw in to bolt to the stepper and nuts in so that you can bolt it to something (I didn't think it would be too easy to find screws to go through the whole thing into the stepper)
Added a relief on the underside of the cover to clear the screws in the carrier.
5/25/2011 Uploaded separate STLs and modified involute_gears library
Instructions
Warning! There be overhangs here!
Print all the parts (either separately or all at once, be sure to print 3 planet gears).
Clean them up as necessary.
Press the bearings into either side of the planets. (2 683ZZ per planet, 6 total).
Insert a 6mm bolt in the carrier to use as an output shaft.
Screw the bearings/planets to the carrier with 3mm screws, nuts and loctite (don't overtighten)
Insert the carrier assembly into the case
Insert a bearing into the cover (606)
Insert nuts in either side of the sun gear in the pockets and thread in set screws.
Attach the sun to your stepper, tighten both set screws and insert it into the case.
Screw it all together (and to whatever you are attaching it to).
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Here's a video of the one I made. Almost no backlash, less than a step. Really great job on the design.
Your scad file doesn't work properly with the new version of OpenSCAD. I don't know what is wrong but the sun gear no longer renders with teeth. I had to revert to an older version of OpenSCAD (2010.05), probably the version you had when you built this.
I don't know where you bought your 683ZZ bearings, but I found that many places were charging a lot more than I wanted to pay. I found that the 683ZZ are found on a t-rex 600 model helicopter and can be purchased at your local hobby store 4 for $6.
Wonder what it would take to modify the scad to work with nema 23 steppers... :)
Have you considered rotating the motor mount by 45 degrees to make accessing the fastening screws for both motor and gearbox easier to access?
Have you considered adding a mounting flange to the gearbox? That way the stepper could be attached to the gearbox, the gearbox to a level surface, and two problems are solved at once.
it remind me the 4 speed tamiya remote control truck in the 70's :-D
Currently printing, so more feedback to come.
Working with the STL provided.
The planets seem to be upside-down, they have a serious overhang as a result.
The planet carrier seems to have a geometry error, with the inset for the head of the center bolt returning to a 6mm hole for the last 1mm or so. Again, creating a nasty overhang.
Looks w
onderful though ;)
Pics of it in silver PLA to follow. And if the print looks workable I'll order some 683 bearings!
New version uploaded.
The holes for the bolts/nuts cut into the internal gear a bit but I don't really think it is a problem. I could make the gears a bit smaller but to maintain the 5:1 ratio the sun gear might get too small to have the shaft protruding through it. This wouldn't be a problem with a stepper with a shorter shaft but with the makerbot steppers, the shaft has to go all the way through (unless the hole assembly was made about 11 mm taller.
It seems to be able to handle the torque. I could get the stepper to miss steps by grabbing on to two of the screws protruding from the carrier. There was no way I was going to stop it grabbing the 6mm bolt though. Maybe tomorrow I'll actually test the torque with a scale.
Here is a movie of it in it's current state:
http://www.flickr.com/photos/5...
There is a little bit of runout in it. I think this might be from some little blobbies on the ends of the planet's teeth. It should go away when it's bolted together. I need to get a longer 6mm bolt for the output shaft....
I'm going to change it so you can bolt the housing to the motor and th
en insert nuts in the housing so you can then use screws through the cover to attach it to something else (an extruder maybe?).
This is getting there! I just did another print. The mesh is great. It's not to tight. Without the stepper installed I can turn the gearbox just with the friction of my finger against the bottom of the sun gear.
I need to adjust the depth of the bearing pockets in the planets, when it's tightened down, the gear is rubbing against the carrier instead of just the bearing. I haven't installed it on a stepper yet though.
Late to the party but, this is fantastic. Hope it really works under load. What a boon. Next, print a stepper motor? Too bad they get so hot....
Thanks! My printer has been giving me a little trouble lately so I haven't been able to test it lately. I just got the bearings in yesterday so hopefully I can test it out soon.
I figured I could maybe put an arm of a known length on it and use my kitchen scale to test the torque output.
I just uploaded a new version, I haven't printed it yet. I will soon.
It should now leave enough room for the internal gears now that I have modified the involute gears library.
It also has support for multistage gearboxes now. We'll see how that works after I try out a single stage one.
So, now you should be able to get 625:1 reduction in about 89 mm of length (plus the stepper).
Does anyone who has fooled around with the involute gears modules know how I would go about increasing the clearance at the tip of the gear?
If you subtract a gear from a something with no backlash and clearance and then nest inside it the same gear but with a backlash and clearance value, you can see that the tips of the teeth are touching the outer gear in all but the most extreme settings. If you crank the backlash up really high, it starts to eat away at the tip a bit but that doesn't happen until you get pretty high. I could just clip the ends of the teeth off the gear but that seems kind of like a hack. Any ideas?
dont know if this is what you were asking about... but copy/pasted this involute code into my code:
http://www.thingiverse.com/thi...
i am no expert but when i change 'clearance' the tooth seems to get shorter....
Not sure, but isn't there a provision for negative clearance and/or backlash for what you are trying to do?
Beautiful! Curious, do you print with 3mm MK6? I'm not loving my 1.75mm right now. Strings etc...
Thanks! It is with 1.75mm filament and a stepper extruder. It's my filament drive though.
I have the reversal speed set at 45 and the times at 70
&
amp; 75
It's pushing back a little too early and there is a little blob before it is supposed to start extruding but its not too bad. I would rather that than have voids in the gears.
I just did a test with it actually attached to a stepper. The gear mesh is a little too tight and causes some binding in spots which makes the stepper miss steps. I think I also need to reduce the height of the planets a bit so they aren't rubbing on the bottom and sink the bolt head in a little further so it isn't hitting the planets.
Wow you totally read my mind, I'm working on a turntable for 3D scanning and last night I was thinking of making a planetary gear attachment like this to make a very slow turning bed. It would be great if you made your scad script configurable to allow for higher reduction. (at the expense of widening the housing to fit it in)
It's configurable right now, you just have to mess around with the teeth on the sun and the annular gear. I haven't really played with it much other than getting 5:1 working.
I could try making a wider version. I was kind of working on getting it working at all and then I figured I'd neaten it up and make it more configurable. There are a few hard coded values scattered in there but most of it is configurable at the top.
You just have to look at the output and make sure it isn't trying to make a gear with a half tooth. There is no error checking.
Great! :) :) :)
Is it possible to use for Extruder?
I'm wondering strength of gears.
I'm changing the design to use 2 3mm x 7mm x 3mm bearings in the planets.
That way they can hold onto the planet gears and glue won't be necessary. I also might try to fit in some sort of frame supporting the other side of the planets to help them stay in position.
looks good. :)
Can't wait to see how much it handles and what the backlash is. :)
More from jag
What bearings do I need to get to build this?
You mentioned 2x 683ZZ in the updates but there's no mention of any bearings in the assembly instructions and no parts list.
I really want to build one of these. :)
(Need the 1:5 reduction to have more torque on a NEMA17 project)
6 683zz bearings (2 for each planet)
1 606 bearing for the output shaft