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43.3:1 Compound Planetary Gearbox For Robotic Arm Project!

by Gear_Down_For_What, published

43.3:1 Compound Planetary Gearbox For Robotic Arm Project! by Gear_Down_For_What Feb 11, 2017
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Summary

Updates!

4/27/17-Made another version of this with a higher gear ratio.
https://youtu.be/8H3fbxzmF9w

Where's Everything Else???

  • This gearbox has an newer, nearly identical twin, with the same form factor and different gear ratio, it can be found in the collection
    https://www.thingiverse.com/Gear_Down_For_What/collections/robotic-arm
    In This Collection you will find:
    • All other related parts for this project
    • Future Updates to this Project
    • All User Submitted Remix's
    • Click that watch button to get notifications on future uploads!

Assembly

Align the planet gears in order as shown in the main picture, insert a sun gear, Snap Ring Gear #1 on, Inset all sun Gears, snap the other 2 or 3 ring gears on, also, you will need to close the gap in the rings before you spin this gear set or else it could skip teeth and get out of alignment, for this i have included the ring closures, that fits over all the rings

Compatibility

  • This Gearbox is 100% compatible with the Robotic Arm Project!
  • This Gearbox can be used in any application that the 66:1 Gearbox is used in, because the outside of the rings gears, and the width of the ring gears are identical.
  • Do not mix and match gears between this Gearbox and the 66:1.

How it works

  • When you rotate the one piece sun gear, The Planet gears orbit that gear, when the Planet Gears make a full 360 Degree rotation around the Sun Gears, Ring Gear #2 and Ring Gear #4 will move 27.7 Degrees, ( 2 Teeth)

  • The other important thing to realize here is that Ring Gears #1 & #3 will be at the same potential and Ring Gear #2 & Ring Gear #4 will be at the same potential

  • The use of Ring Gear #4, the 4 Module Planet Gears, and Sun Gear #4 is optional and used to increase the amount of torque this gearbox can transfer, as well as to decrease the amount of load on each gear, think of it like a door hinge.

Other Important Info:

CAD Files??

The most recent version of this project can be downloaded in lots of different formats from this link: http://a360.co/2wW8PDX

Show Your Work!
  • Make a "make" and show everyone what you made! (make? :0) Everyone will thank you for it!

For More Cool Projects and Upgrades, Don't forget to Follow Me on Thingiverse and Subscribe to my Youtube Channel

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Great work.
I like to see gear-bearings in practical use.

I thought about designing conical gear-bearings with "soft sinusodial herringbone" design preventing roller slide-out (and with cycloid teeth).
I think with such a design it should be possible to reduced clearance down to zero by just tensioning the bearing axially.

Btw:
I think the bad shaking seen visible in the video (maximal vibration amplitudes I guess ~5mm)
seems to come from some issues with the motor control plus amplification by mechanical resonance.
There's the reprap morgan 3D-printer. A scara robot with remotely similar design. It has parallel mechanics though.
It archives incredible accuracies I guess somewhere in the 10um range or even below.
That difference can't be just the different mechanics.
So I think if you focus on motor control improvement there should be orders of magnitude to gain in performance.

3D printer firmware (e.g. marlin) is already quite advanced.
I don't know if it could be adopted for controlling such a pick and place robot.

Regarding the super time consuming programming.
If I ever come about to making a pick and place robot (This one: http://reprap.org/wiki/RepRec_Pick_%26_Place_Robots)
I'd like to try making a library for it in a ridiculous high level language like Haskell.
Tying all the required software plumbing together sounds like a major nightmare though.

Sorry my first response was a little rushed.
I really like your ideas for the conical gear bearing, I'm wondering if it could be possible to accomplish that with a differential planetary. With a differential planetary being as complex and confusing as it is, I'm sure it would be a hard thing to model. If I understand you right, your basically talking about making into more of a tapered roller bearing style? It would be awesome to easily adjust backlash.

A big problem with my program is the amount of calculations that it has to do per second. I'm probably doing it in the worst way possible, especially because I only started learning Arduino code a year ago. Like you mentioned if you can do it in a better programming language or on faster hardware It would much more fluid movements.

I'm wondering if it could be possible to accomplish that with a differential planetary.<<

Yes, right after posting I realized that you've actually need planetary gearboxes.
That is what this "thing" is about after all.
I think I once started to ponder about this a bit but came to no conclusion.
I'm not sure if this is possible. (... parallel force path tensioning issue ... mumble mumble ...)
Conical gears are better suitable for differential gear-boxes which are
basically highly deformed planetary gearboxes.
But this geometry does not fit your robot.

If I understand you right, your basically talking about making into more of a tapered roller bearing style?<<

Exactly. Just with gear teeth.

In roller bearings some part of the force is always converted to in roller axis slide-out force.
Conventional roller bearings capture this force with cages or insets.
For insets see here: https://de.wikipedia.org/wiki/Datei:Schema_Roller_bearing,_tapered.svg
But when toothed rollers are used they can be made in a herringbone shape which can catch this load instead.
I think when gear-bearings that have sharp herringbone kinks in tooth-extrusion-direction are loaded
with forces running along the roller axes this might not be a too good idea.
The load concentrates too punctually near the kinks.
Therefore I think a soft (sine?) shaped extrusion curve should be much better.

Here's some info about conventional non-geared tapered roller bearings:
They come in X, O and thrust configuration:
X: https://commons.wikimedia.org/wiki/File:Montage_x_techno.png
O: https://commons.wikimedia.org/wiki/File:Montage_o_techno.png
thrust: http://www.deinabearing.com/Tapered-Roller-Thrust-Bearing.html
-- found no freely reusable images for this last one :(
The nomenclature refers to the lines of force not the
shape / roller orientation. (I Just figured that finally out right now. Yay!)
These kind of bearings can be found in motorcycle wheels.

It would be awesome to easily adjust backlash.<<

I think free movement backlash could literally be reduced down to zero.
Depending on the tension force the unavoidably remaining flex-backlash
could be reduced at cost of increased friction and wear. A trade-off.

About generating the needed conical gears:
The cone angles must meet certain geometry constrains
such that speeds match and there is pure rolling and no sliding.

I found that hyperbolic gears are the highest form gears could be abstracted to.
Given any two oblique angled axes and a gearing ratio a pair of matching gears can be generated.
I found some papers describing the math.
(This is made manageable with the very useful Plücker screw vectors -- https://en.wikipedia.org/wiki/Pl%C3%BCcker_coordinates)
But when modelling this in OpenSCAD IIRC I hit some roadblocks with non matching signs.
So I've not yet published this work yet.
There seems to be someone else trying something similar:
https://www.thingiverse.com/thing:881568
But I think this model doesn't draw from the theory of the papers I've read.

Turns out only cycloid gears are easily and straightforwardly generalizable to the hyperbolic case.
Evolvent teeth are an open research problem.

That's not a problem tough.
Cycloid gears are usually avoided since they
A) are hard to manufacture with conventional means.
But we do 3D-Printing for which soft curves are ideal. And
B) because they need zero lash (they have non adjustable inter-axis-distance).
But zero lash is what's targeted here anyway. And
C) because their varying attack angle can cause vibrations when high forces are transmitted.
But these are no steel gears so really high forces are not present.


Regarding the micro-controller programming:

I think I can give a bit of history of the 3D printer firmware marlin:
https://github.com/MarlinFirmware/Marlin
The developers really worked miracles there.
I have an Ultimaker Original 3D-printer from the very first generation.

The first firmware (I think it was sprinter back then) sounded like a machine gun.
The more "corners" a circle had (the better triangulated) the worse the issue.
As I understand this was an issue with missing look-ahead.
At every line segment endpoint there was a full stop.

With one really groundbreaking firmware update (look-ahead) this was solved.
It works somehow like that:
If the next (few) line segments have almost the same direction as previous one => keep speed.
If there's a sharp kink a few segments ahead => slowly reduce speed in advance.

The processor of the UM Original (early days) is not the strongest one:
https://www.arduino.cc/en/Main/ArduinoBoardMega2560
(goes with this: http://reprap.org/wiki/Ultimaker%27s_v1.5.3_PCB)

Also there where problems printing directly from via USB cable connection.
since there is no dedicated USB decoding hardware this is done in software.
Excessive load frequently caused fatal hiccups.
Printing from SD solved that 100%.


I like your ideas, if you can figure out how to model them. haha. <<

I realize what I've gotten myself into there.
So I've identified and split of a more manageable sub-problem that would be useful standing on its own.
This one: http://reprap.org/wiki/ReChain_Frame_System
I already have some 3D-models revolving around that one.
But nothing fits together yet. (I'm still way below the percolation limit where the pieces star to fall in place naturally)
One aspect are friction-avoiding tensioning mechanisms.
I literally now have a dozen detailed out ways how they do not work.
I really need to publish all that stuff in a coherent way.

ONE GEAR FOR ALL
by dlajoie

I'm sorry I didn't see your latest post, but better late than never right?

on the roller bearings, it there any reason that the rotational axis of both sides cannot be parallel? otherwise the gear needs to be flexible haha

I like your ideas, if you can figure out how to model them. haha.

And yes the robot does have a resonance issue that I haven't managed to solve yet

how much to print me the Planet_Gears i have tried like 3 time get half and get move off by head

hello the best king about planetary gear i fiind this
perhaps you can design and mixt exactly the same with your planetary gears
that is soo nice to have that
look
best
http://www.yoycart.com/Product/17760448145/

When using One_Piece_Sun this replace Sun Gear 1,2 and 3. is this correct and do you forfeit torque.I don't see Sun Gear 2 in the one piece

Yes the one piece sun replaces Sun gears 1,2 & 3.

No the one piece Sun does not cause any additional friction, it actually helps keep the planet gears straight and probably reduces friction.

The One Piece sun does not contact the Planets in Module #2 because there isn't enough room to have a gear there, and i don't believe its necessary to have a gear there because the planets are supported from both ends, though it would be better to have a gear there, if there was room.

if your talking about the independent #2 Sun missing from the "thing" files, I re uploaded it yesterday, I don't know why it disappeared.

Thank you, Using the one piece sun do you get less torque.

I dont understand the question. Less output Torque? probably not.

Have you test the max load it can lift with Nema 17

No, not very scientifically.

I am trying to use the 4 module version, but Sun Gear 1 and Sun Gear 3 are both too big to fit in the 4th slot on the Optional 4 Module Planet Gear. It seems like slot 1 and slot 3 on the 4 module planet gears are narrower than slots 2 and 4?
Also, the instructions reference a Sun Gear 2 that should be used in slot 4, yet the files list does not include anything by that name.

Sun gear #2 is uploaded. I figured out how to do it from my phone :)

I'm really sorry about this. I will upload the #2 sun gear as soon as I get home, and reply to this so you know it's done. I don't know where it went, sorry!
I'm surprised that nobody else mentioned this.

I finally had a chance to print out the #2 Sun Gear, works perfectly, thank you!

Glad you like it! Haha I'm also going to release a one piece sun gear with slightly more clearance tonight too!

Great news on the sun gear with more clearance! My biggest issue has been the tight tolerances, It takes a lot of force to get the EZ Print ring holders to fit around the ring gears once all the gears are inserted. Managed to break an entire set of planet gears and a one piece sun gear by using too much force (hammer).... I would rather have just a little bit more slop in the system if it meant an easier time swapping parts around.

Great job, I'm also building a robot using the InMoov design, I'm not a mechanical engineer. Can you remix to be 50:1 for me leg joints

Are you asking for the exact same thing accept to change the gear ratio to 50:1?

I'm no engineer myself, to be honest. If it is something that lots of people request i could spend some time figuring out how to backwards calculate the gear ratio but for now I'm just going by "well that outta be a large enough gear ratio"

I'm only really able to guess what the gear ratio outcome is on these gearboxes at this point.

I found this 50:1 http://www.thingiverse.com/thing:2071318. which is also your.

Compound Planetary Gearbox (38.75:1 or 50.4) No Bearings, No Hardware!
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