This mechanism definitely needs a free wheeling second sun gear to prevent exactly this kind of failure. There is an argument for also needing a planet carrier to take up the side to side tilting forces on the planets.
Yeah pretty much what OP said. I saw the failure mode coming way before he even finished assembling it. Though someone sugested brass gears, i dare you fabricate 5 different gears in brass that are not straight lines like normal gears. These gears have the same manufacturing problems double heiringbone gears have. You need to cnc them tooth by tooth on a 4 axis precision cnc mill with a really fine end mill.
lagynas Pffft. La Dee Dah. Conversions are a fact of life, no getting around it by moving decimal points. There’s this really neat technology now that makes miles equal kilometers and cent da grades equal fair-in-hights, it’s a major pain in the neck and requires you to speak out to your google assistant or fav smartphone “convert 6 millimeters to yards!” Baaaam! Get a pen and paper it’s gonna spit that badboy out with no mercy.
"Why are harmonic drives more popular" - because they have no backlash (0,0°). If a robot wiggles, it is not good. If robot does not wiggle, it is accurate. Anyway thanks for your videos and the very interesting content each time. Best Regards
@@OmegaF77 it's funny because my coworker designed a robotic worm that appeared on a hackaday article and the comments were golden along those lines of "sure, robotic worm, that's what it was for", haha!
What differentiates harmonic drives from this gear system that would make them have any less backlash? The harmonic drive constructed here admittedly has some backlash (at 6:57): ruclips.net/video/Emvo3bLT-Z4/видео.html
Harmonic drives can have backlash. Maybe you meant they can't be back-driven? Which depending on the robot, maybe you want a degree of back-drivability
@@bj_ backlash < 0,0°, of course microarcs are always there. back-drivability can work on higher reductions or larger assemplys (or any other) with distortion detection of the flexspline. with load cells.
I stumbled onto something similar few month ago, but their design was backdrivable. The paper is called "Bilateral Drive Gear-A Highly Backdrivable Reduction Gearbox for Robotic Actuators". (commented this already with a DOI link, but comment is gone, I don't think youtube likes me :)
The planets are indeed loaded in torsion in this GBox, but a carrier does not help in reducing that twist, in my opinion. Although there are many carrierless designs for this GBox, I agree with you: you need a carrier to support the overturning torque produced by the two tangential forces at the meshing contacts with both annular wheels. A sun gearwheel won't solve the problem: it improves radial support, but not overturning, tangential torque. The carrier solves both... but it is heavier! 🤷♂️
The reduction on these is essentially unlimited. The formula is "one minus the ratio of the ratios". Basically, the closer the planet/ring ratio of the top half is to the planet/ring ratio of the bottom half, the higher reduction you'll get... all the way to infinity if they're perfectly matched (i.e. the output won't move at all). Another interesting thing is that if you add a planet carrier, you can drive the carrier directly and eliminate the sun gear. However it does result in very high RPM of the planet gears. Maybe ok with metal, but for 3D printed the sun engagement is usually worth its added efficiency loss.
Fujimoto's Bilateral Drive, indeed one of the most advanced implementations of the 3K/Wolfrom planetary. And the gear ratio was higher, around 100:1 if I recall that correctly!
Please I'm trying to work out how to calculate reduction for this setup. Could you please point me in the right direction? A textbook maybe or a website? I've been trying to figure this out for weeks
@@boluwarin do you still need it? I've just finished making spreadsheet on determining teeth configurations (teeth number, pitch diameter, and gear ratio) for this type of planetary gear train (split-ring compound)
I'm using one of these in a robot actuator, quite impressive performance if you can stop the planets from tilting inward. I added an "idler sun" on top that helps with this. It still skips teeth before stalling the motor, but is surprisingly debris and damage tolerant, even in 3D printed PETG!
I would definitely put a planet carrier, with your design the planets can move every which way they want, which puts weird stresses on all the teeth. That would be a big step forward, and I think much better results can be obtained, even with 3d printed parts.
Maybe I am missing something buy couldn't you put a sun gear on the top set isolated from the drive with a bearing. That should force those planets out on the top.
That is one idea, though I might have to get clever with the ratios to get this to work. I forgot to mention in the video, but the top gearset has a really weird fractional module, so a sun might not fit.
or even a planet carrier on the top reduction would hold the planet axial centers in place no? You'd have the extra friction of the planet gears against the carrier axles to worry about but given that you're not taking a drive force off of the carrier not sure how impacting that might be? you might even be able to build a cage structure if you use a carrier plate on the top and bottom?
One of the remixes of Gear-down-for-what uses a top "sun" gear that has a round hole (not D shape) so that it just floats on the motor shaft, but serves to keep all the planet gears engaged with the top ring gear. It will solve your torque issue with only one part!
Helical gears do not always contribute to higher torque ceiling. They disadvantage to helical gears is that they cause non parallel/perpendicular force on the surrounding components. Helical gears require a stronger housing and provisions outside of the gear itself. While the gear itself maybe stronger do to the increased surface area for the teeth. It can cause misalignment and premature failure during over torque conditions
That's the thing about this channel, it's extremely armature. Nothing more than experiments, sometimes unrealistic designs, and poorly educated guesses. There's been issues with past projects, there's issues with this project as well, especially when it comes to design; a lot of these designs also seem to be initial prototypes with no real refinement. These same designs are also unrealistic, such as this design having gears of eight different profiles, which would extend production time and drastically increase cost _if_ this were to become a production product, with a refined design of course. Then there's the issue brought up in this comment, falsely equivalating two different gearboxes based on the idea that they have a 'similar operation,' which is nothing more than an uneducated guess, which leads to poorly informed claims. Then things like questioning why harmonic drives are favored over a dual stage planetary gearbox, as if the host has forgotten that backlash exists, and every implementation of harmonic drives specifically uses them to minimize backlash while also having a deep gear ratio; while stacked gearboxes have a multiplication of backlash, I think the lack of backlash here comes down to the printer's tolerances, a properly machined set of gears more than likely would not have this this tight of a fit, _plus_ printed gear mechanisms _do_ need to be broken in before they're tested, something that isn't really seen on this channel at all. I like this channel for it's interesting concepts, but there really needs to be another channel hosted by someone with an actual engineering background that would analyze these designs from a proper prospective. Like the last video, the differential drive, it had numerous flaws that an actual engineer can fully improve the design of, the idea has potential but the implementation was subpar. Then there's designs from a couple videos ago, the compliant harmonic drive, which still does have it's flaws but was an actual educated guess that could actually lead to improvements in harmonic drives, both the idea and implementation were good but it needs refinement. Then there's videos like this, that're DOA, as the concept itself already exists and has already been refined throughout it's existence, for example this exact mechanism was in use in WWII planes for driving propellers, where this mechanism itself is just one of many dual-stage planetary gearboxes; the poor design here, uneducated guesses, and falsely equivalating the mechanism to other mechanisms is 100% the fault of the host, and there's not fixing that unless they better educate themselves, or at least do better research, and the video is almost entirely a misrepresentation of the mechanism. There's similar issues with other channels, notably when mechanisms are either entirely or almost entirely 3D printed. Herringbone gears, for example, are simple to 3D print, yet machining one is an absolute pipe dream. That's not even the entire issue, every time a herringbone gearbox is assembled from all of these 3D printed parts, especially planetary sets, the housing either has to be split or the housing has to be flexed, and this doesn't work with real-world machined parts. It's a disconnection between what rapid prototyping can provide and how a long-lasting real-world part can be machined, something seen with almost every channel that primarily uses 3D printing for designs. A similar issue can be seen with every one-off project, where the design may work fine for a singular production, but doesn't make sense if production is scaled to anything larger.
I've only seen one example of such a double ring compound harmonic drive is Oskar Puzzle's "Harmonic Hyperdrive", which is a 300:1 gear ratio and extremely small (and delicate).
@@FeignJurai Oskar has some amazing designs, but it's a shame that he's only really into puzzles. So many of his designs and concepts could have actual real-world applications if they were refined, improved upon, made of proper materials and had proper construction (e.g. using bearings on the various mechanisms that have rotating pieces, proper housings, etc.), and tested under real-world conditions. Oskar also has some interesting concepts that I don't think would have any real-world applications outside of puzzles. For example, he had a spherical gear design years ago, Spherigear I think it was called, that could've worked in two rotational axes, but the housing only hinged in one axis, and the tooth profile on the spherical gear is not optimal. This eventually evolved into his Flip Gear, which better suits the singular hinged axis design. Then the Flip Gear eventually evolved, by request, into a design that has the coaxial configuration decoupled, called Flip Gear Disconnect, where the original Flip Gears were coupled in that orientation. Real world use of all three of these would require a CV joint boot around the gears and housing, and of course bearings between the gears' shafts and the hinge housing; then of course a way to actuate the hinge, but that's on a per- use case basis, not something that's inherent to the core design of the mechanism. The Sphereigear would also need a bi-axis hinge mechanism of it's own to operate correctly, which has yet to be designed to my knowledge. I've also noticed that the Spherigear has some variations, five total that I know of, four can be found by searching 'Spherigear' on his page, and the fifth is in the form of his Tracker Ball 3D; though spherical gear designs go past this, such as the ABENICS Active ball Joint Mechanism, or theoretical designs that use a stellated (positive and negative stellations as a gear pair) geodesic or Goldberg (dual of a geodesic) polyhedron, I believe there's also a peg-based design that uses dimples and nubs, and there's a few other designs floating around out there. Biggest downfall is that spherical gears would ideally need teeth separated by equidistant points along the sphere's surface, something that's a concept that, as far as I know, has not been mathematically been proven to exist outside of using the vertices of the platonic solids; and even then, there's no telling if we can make spherical gears have the same performance as 2D involute helical gears once we do find optimal tooth placement. Another example would be Oskar's Magic Gears, the bi-lobed friction gears, and his Illegal Gears, the tri-lobed friction gears, though not his original design, I believe these lobed friction gears largely originate from Jacques Maurel in the form of 'paradoxical gear.'' Jacques made a publication(s) in '04-'05, though some of his papers on relevant topics go back to '02, but I don't know if Jacques _invented_ the type of 'gear' or not, it's just the oldest publication of the gear that I've come across so far. I also don't believe they've been tested outside of proof-of-concept scenarios, I'd imagine the best real-world use of them would be in the form of a modified traction drive. Oskar's variations seems to be the most popular source for these types of gears, though. But again, efficiency is a concern with this kind of 'gear,' though further research into it, and further improvements, should be far easier than the spherical gear issue. Unfortunately, his Grinder Gears and Harmonic Hyperdrive are victims of the same shortcomings, designs and concepts that could have real-world uses, or at least potential of being more than just a toy, yet nobody has really taken the ideas and put them into real-world scenarios with actual engineering behind them.
yeah, totally. drop a ring on top with 5x bearings that support the centers of each planet gear. easy, and will remove that failure mode. the next failure mode would be the teeth shearing off.
Idler gear at the center shat for the top part of the planetary gears and a carrier/cage for them all. I think that would suffice. Although I'm not an engineer.
If you do a bit of research this gear design is credited to Ulrich Wolfrom more than a century ago. It is often referred to as a Wolfrom drive. The publication is Wolfrom, U.: Der Wirkungsgrad von Planetenrädergetrieben. Werkstattstechnik, Vol. VI, 1912
If you put a sun gear between the planet gears that doesn't interface with the shaft, on the second ring layer, it will help support the planet gears. Oh, and now you're talking about that exact thing... :P
The mechanical nerd in me says you need carrier/holder plates for the planet gears, and have bosses coming out of the ends of the gears. Very cool design, and I learned something new today, thanks for the video!!
This looks pretty cool. Have you heard about Archimedes drive? The design is based on a planetary gear system but it uses friction (toothless gears aka cylinders) instead of gears. I'm not sure if you can 3d print it but you could definitely give it a shot.
Look into hydraulic torque hubs made by Fairfield Mfg Company. Used quite a lot in mobile and industrial hydraulic applications. The one I worked on used in a recycling plant, driving a large crusher/shredder. The torque hub was driven by a very small displacement Charlynn-Eaton geroler type hydraulic motor. It was a pain getting the planet gear timing set correctly
Make secondary sun gear which wont bind with motor axis or make star that will connect centers of planetary gears . If you prevent slip its way harder to brake tooths!
@@nemoskull2262 What would be the benefit of that approach? Do you think you can vacuum cast gears with a higher yield strength than what you could cut using EDM? How are you going to produce the molds?
Using the same gear tooth numbers in the same volume you can get yet another order of magnitude by allowing the planet tooth count to differ on each layer. The highest ratio is when the product of opposite planet and ring teeth differs by only 1 (ie. P1R2=P2R1+1). Such high ratios are of limited use, but it does give you much more flexibility when choosing other constraints.
With stepper motors, it may seem like they have a low max speed, but if you slowly accelerate them you can go faster. If you're starting from a stop and you just try a high speed it will just stall because there is no momentum, but if you slowly increase the speed in code to match the momentum you can make them go much faster.
If you add an idle gear in the middle of the output section, it will stop the flex and increase the output torque. Also, check out Geardownforwhat RUclips channel :-)
1. Watch "gear down for what", it is possible to get reduction ratio of 1000:1 and more with one stage of this gear, if you are not restricted with gears of one module. 2. You need another sun gear to support the planet gears. 3. This abrupt motion at 4:44 is annoying. The fact it continues such motion until 7:44 renders this video unwatchable for 3 minutes straight. You could easily overcome this effect by choosing looping time according to your planets' period (if you can not continue true animation for the whole 3 minutes).
Many Cycloidal ( Strain Wave / Harmonic ) designs have essentially *Zero* Backlash. And that is extremely important for precise positioning. Your Split-Ring Epicyclic design has an *unacceptable* amount of backlash.
Gear Down For What made a planetary gear that didn't have a sun gear. Somehow. Since you have access to 3D printers, you might be able to ditch spur gears in your designs in favor of herringbone gears. Much more efficient!
The proble, is not that the gear can not take the torq but that the motor is too strong for it, with small motor this would be realy smal and provide 6nm torq. if you would put a bit more effort supporting the gears it could handle much more torq, anyway, interesting, thanks.
16:52 - That's a "no load current". A stall torque is when your motor transitions from full-load (still dynamic) to stall (output shaft no movey-movey). The phrase you're looking for is "idle current draw". 17:09 - That 2 lb water bottle drew 290 mA, as you transitioned from 270 degrees, static and proceeded to decrease from there. (Which makes sense, since you've overcome the static friction and also abs(sin(270)) =1, w/r/t gravity. Which is why if you're reefing on a bolt with a ratchet and cheater bar it's always easiest around perpendicular+the amount of downwards angular momentum you can develop). Then it reverts back to an idle current of 110mA. (Which is a lot. Was the motor still drawing that much current after you removed the assembly?) Your failure analysis is spot on re: folding itself in. It's typically bad form to say you "designed it", even if you cite the Wikipedia page. Even more so when you say "of anything I've designed", implying this is the result of multiple iteration cycles of you and/or your team. If you want to see real power density, take a look at The Torque Test channel. Handheld impact hammer drills are putting out > 1,000Nm running on stock Samsung battery packs in messy environments (ever seen a contractor work in a class 100 ISO Clean Room? Yeah me neither.) The general technique is 3 stages of planetary gearsets, each stage sequentially moving slower/made out of a denser material. By the time you hit stage 3, everything is forged steel and the lost kinetic energy (those BLDCs get up to around 22k or so) is made up for by the mass. Their setup is pretty good, but not AvE good, sadly. Developing 1,000Nm of torque is impressive, but we've been able to do that for ages with diesel generators and airlines (railroads, oil rigs, etc all operated with Ingersoll compressors). The issue is those setups have literally < 5% output efficiency. It blows my mind that these *handheld drills* can drive exploratory drill string with comparatively no losses
why robotics don't use this type of output is also for the backlash , harmonic drive have 0 backlash , imagine a medical robot with backlash when doing dissection
The pcd's of tye outer gear set does not allign properly. For 50T ring gear, the radius is 50T*module which is equal to (20T/2+15T)*module=25*module. For the 2nd ring gear the radius is only 24.5*module. The appropreite planet gear is 24.5-20T/2=14.5T. This means that standard gear will not mesh properly. You may get awsy with this by increasing backlash which is done by scaling down the gear
I am a bit confused with your setup since you want to operate at 1.4 A (or the left of a performance curve), which is around 500 RMP (for this motor). Yet, for your demo you start at “No-load” RMP and then jack it up to what exactly. Aside from failure, you want to know where you are on the performance curve… But yeah, with my rough calculations this should be able to produce a CW-torque of apx 120 lbf*ft (you mentioned 150 lbf*ft), which is way more than 10 lbf but I did neglect the weight of the arm (but I don’t think its heavy enough to cause the failure). Lastly, what is securing your “drive-gear” to the motor shaft (nothing really), and if the teeth were steel they would most likely not fail.
you could simply put a star shaped cap connecting all of the planetary gears together on the 2nd stage that holds them at a fixed distance. doing this would also cap off the exposed planetary gears for saftety
... I was watching the video peacefully until I heard "foot pounds"... Damn, why the hell you're not using the metric system, and more in general, the International System Units?!
There was a 5 part article in Elektor Magazine in 2001 that used this mechanism for a Polar co-ordinate PCB drilling machine. Links aren't working in comments so search - Elektor Magazine PCB Drilling Machine March 2001
Most definitely need a bushing/alignment pins for the gear sets to prevent deflection, this would increase the torque it can handle immensely up until the shear strength of the gear teeth I bet it still would be nothing to sneeze at for this thing to handle crazy amounts of torque, but like you said...nowhere near mathematically "calculated" torque just imagine the angular accuracy it could attain however! Ah...disregard...you already did :) ruclips.net/video/66MlWxoQE1s/видео.html
As far as this gear set goes you add more planets to a planetary gear set and the torque goes up there's a reason why cars and semi trucks use these in their automatic transmissions. I would like to see you print another sun gear to go in the center of that second planetary without a keyed input to the shaft and then see what your torque limits are. But I will agree that the backlash would be relatively unacceptable for robotics though
Put small bearings at the top of each red gear, and one around the shaft that they engage with. That way they push outward always and maybe get higher weight/torque?
top layer planetary doesn't need to be the same module as the bottom layer. And the difference in teeth number not necessarily be one. A lot degree of freedom for such designs. Some of them allow a secondary free spinning sungear.
I spent many years running a gear cutting company. I cut from 10 teeth on a 1MM (.040") diameter to 10 inches 1/4" circular pitch, not DP or Mod but circumferential, used in the printing trade on roller presses. My design experience rases concerns that the unit is using approach side drive, that is thedriving teeth are acting like a wedge plunging into the gap in the driven gear. For long life and quiet operation receding drive is better, the driving tooth slides outward and "flips" the driven tooth away. As to the spring away issue, a planet is not the answer, gears are not suitable as load rollers. Studs on the gears and a 5 hole bearing ring would be better.
It is impossible to install a second sun gear (it should have 19 teeth, but it is not divisible by 5), just install the axes of the planetary gears on the carrier in the form of a ring. If the planets have 15 teeth, and the ring gears are different, then the planets cannot be on common axes, with the same module. The module of one half of the gearbox needs to be slightly changed so that everything engages correctly and the module becomes non-standard.
How can the top and bottom be aligned if one has 1 tooth less? If the top and bottom outer gears have the same reference circle but different number of teeth then they by definition have a different modulus, so how can the teeth mesh? Oh, you're explaining the mechanism later, at 13:00, rather than at the beginning when you claim to explain it. Gosh! I watched the purported explanation countless times until giving up...only to find out that the real explanation comes later...
Torque and ratio are decoupled in a compound planetary. I found this when I compared a 48:1 to a 705:1 (same size) and found the torque to be about the same.
If that is enough torque for your application, then you can use a weaker motor. When the torque is limited by the output gears, then the only way to increase the torque is to improve those output gears. The pessimist, optimist, and engineer see the same partially full glass. The engineer sees a glass that is twice as big as it needs to be, assuming no safety margin. The engineer then takes into account that the liquid is red wine and there is a white carpet. The engineer then realizes the amount of fluid isn't the issue. They are simply at the wrong kind of party. They make an excuse about a problem at work. Then leave the pessimist behind and go off to a backyard party hosted by another engineer.
@@hamjudo I didn't have enough torque, he motor stalled and nothing broke. The torque was good, just not what I expected. I had to change the geometry not the ratio.
Torque Ratio is Speed Ratio multiplied by efficiency in a planetary. You efficiency in the 705:1 GBox must have been around 15x lower than for the 48:1. It sounds like a lot, but it is actually possible if your planet wheels were large enough, compared to the sun gearwheel...
The motor controller isn't increasing the amps that's just what motors do when they are impeded they draw more amps. The motor controller will limit the maximum amps it can draw so it doesn't go above the motors rating i.e. it does the opposite of what you are saying.
I don’t know, I feel like complexity is another mark against drives like this. I like the idea of a harmonic drive in some ways, but I would expect less wear in a system like yours.
Like the article. The planetary gears do not have a cage holding them. This was not pointed out. The only issue is that their is a torque force with the axis between the two gears with one tooth difference of the planets thus there is also a torque in each gear keeping it from typing and for the gears without a sun there is a thrust also towards the center that need a matching torque on the sun gear. I do not know if you can make a floating sun gear for the top planetary. My Atlas lathe has a 14.5 degree gear tooth pitch angle. The most common is 20 deg, however; special gear have higher angles that will be stiffer and carry more torque at the expense of higher thrust towards the axis of the gears. Which means that the ring gear needs to be beefed up. Same thing happens for cyclonic gear because the physics or geometry is the same at the line of contract angle. It will produce the same forces independent of the type. Friction drive can use the same approach. Also there is not cage, but without teeth slippage will cause a problem. So at least two sets of rollers are needed to set an even spacing. Then there needs to be a free wheeling sun for the second. Now at least one of the roller could be an elastic item such as a tube. This will reduce the tight tolerance at the cost of the peak torque.
Gears sets, when properly produced, only have rolling friction. The involute profiles for the teeth are such that when the teeth touch, there is no sliding friction. Did you change the pitch diameter for the top teeth so that the reduction from 50 teeth to 49 teeth did not result in sliding friction on the top gear sets? It’s basically a differential gear set at that point.
If you think youre the first to invent something that resembles a type of simple machine, you are probably wrong...someomes made it and patented it before...
I think they're all out of phase with each other. Considering that the bottom half of the planets mesh with the sun, and the top halves are all offset by fractions of a tooth, it doesn't seem possible to mesh with all of them at the same time. Maybe adding a third segment to the planets with the original phase, and meshing with another sun gear, you could solve the cantilevered planet issue and counteract the twisting moment the planets are undergoing. I'm curious what the planets look like after the destruction; I suspect the teeth are deformed in a twisted manner.
@@ericcmcgraw That's what I thought initially, so I openScad it and there is no geometric problem. You can find my design here : www.thingiverse.com/thing:4889174
The top ring gear has one less tooth than the bottom ring gear. Doesn't that mean the upper pitch circle is smaller than the lower pitch circle? If the planet gear axes are parallel to the outer ring gear axes, then the upper planet pitch circles would have to be a little smaller than the lower planet pitch circles. That can be done, by having one less tooth in the upper planet pitch circle, but you didn't do that. Since your module on the upper and lower planet gears is the same, the upper and lower planet pitch circles are the same. As a result, your lower ring gear pitch circle has to be a little bit bigger than what would be tangent to the planet pitch circles. This means the pitch circles of the planet and lower ring gears are not tangent, there's a little extra space in there. That's okay, involute gears can handle that extra space... but they do it with extra sliding. Your lower gear has extra sliding and extra drag for this reason.
You would not be able to insert a gear in the center of the planetary because you will not be able to make it coincide with all the planetary gears. But I believe that you perfectly identified that. In order to limit the flex of the planetary gears, you could instead either insert a cylinder with the right diameter eventually soft or make a system with axis for the planetary gears.
I don't understand why the bottom planetary gears are all different. I made something similar with them all the same size. I also had a free spinning sun gear on the top, which you discovered helps things.
Insert a exta gear in the middle on top which is loose to prevent skipping. Also integrate a Ballbearing made out of airsoft bbs. I got mine up to 50Nm
does the same problem of structural stability apply to planetary gears as well or is it just to this type of gearbox which has the problem of just one tooth engageing?
All you needed to add was a star with bearing to go in the outboard end of the planet gears. That should about double the usable torque, or will at least reach the strength of the material. I don't think a free second sun gear would match the offset teeth of the planets.
This mechanism definitely needs a free wheeling second sun gear to prevent exactly this kind of failure. There is an argument for also needing a planet carrier to take up the side to side tilting forces on the planets.
An end plate with axle-pins and brass pinions... 🤔
This was my thought as he was showing off the top of the design.
Or do it symmetrical, input-output-input
@@flipschwipp6572 Yes, this works, but does not allow an undisturbed 360° output as you need to connect the two input ring gears somehow.
Yeah pretty much what OP said. I saw the failure mode coming way before he even finished assembling it.
Though someone sugested brass gears, i dare you fabricate 5 different gears in brass that are not straight lines like normal gears. These gears have the same manufacturing problems double heiringbone gears have. You need to cnc them tooth by tooth on a 4 axis precision cnc mill with a really fine end mill.
I'll become patron when you start using metric as main system.
I do
@@LeviJanssen what are foot chooch'rs then? ;)
lagynas
Pffft.
La Dee Dah.
Conversions are a fact of life, no getting around it by moving decimal points.
There’s this really neat technology now that makes miles equal kilometers and cent da grades equal fair-in-hights, it’s a major pain in the neck and requires you to speak out to your google assistant or fav smartphone “convert 6 millimeters to yards!”
Baaaam! Get a pen and paper it’s gonna spit that badboy out with no mercy.
Why, whats wrong withmeasuring in banana's?
😭 wah
"Why are harmonic drives more popular" - because they have no backlash (0,0°). If a robot wiggles, it is not good. If robot does not wiggle, it is accurate. Anyway thanks for your videos and the very interesting content each time. Best Regards
Bute if I want a robot worm, I need the wiggle. Wiggle Wiggle
@@OmegaF77 it's funny because my coworker designed a robotic worm that appeared on a hackaday article and the comments were golden along those lines of "sure, robotic worm, that's what it was for", haha!
What differentiates harmonic drives from this gear system that would make them have any less backlash? The harmonic drive constructed here admittedly has some backlash (at 6:57): ruclips.net/video/Emvo3bLT-Z4/видео.html
Harmonic drives can have backlash. Maybe you meant they can't be back-driven? Which depending on the robot, maybe you want a degree of back-drivability
@@bj_ backlash < 0,0°, of course microarcs are always there. back-drivability can work on higher reductions or larger assemplys (or any other) with distortion detection of the flexspline. with load cells.
I stumbled onto something similar few month ago, but their design was backdrivable. The paper is called "Bilateral Drive Gear-A Highly Backdrivable
Reduction Gearbox for Robotic Actuators".
(commented this already with a DOI link, but comment is gone, I don't think youtube likes me :)
Industrial robots are taught by taking their "hand" and moving them through the motions you want them to do. This backdrives the reduction gears.
@@lawrenceoatman4464 ”hmm, yes! Let me just teach the move-set to this Kuka Titan by pushing it”
I think you mean cobots :P
No planet carrier? Those compound planets are trying to twist under load. A carrier would resist that and make it a lot stronger
The planets are indeed loaded in torsion in this GBox, but a carrier does not help in reducing that twist, in my opinion. Although there are many carrierless designs for this GBox, I agree with you: you need a carrier to support the overturning torque produced by the two tangential forces at the meshing contacts with both annular wheels. A sun gearwheel won't solve the problem: it improves radial support, but not overturning, tangential torque. The carrier solves both... but it is heavier! 🤷♂️
The reduction on these is essentially unlimited. The formula is "one minus the ratio of the ratios". Basically, the closer the planet/ring ratio of the top half is to the planet/ring ratio of the bottom half, the higher reduction you'll get... all the way to infinity if they're perfectly matched (i.e. the output won't move at all). Another interesting thing is that if you add a planet carrier, you can drive the carrier directly and eliminate the sun gear. However it does result in very high RPM of the planet gears. Maybe ok with metal, but for 3D printed the sun engagement is usually worth its added efficiency loss.
Fujimoto's Bilateral Drive, indeed one of the most advanced implementations of the 3K/Wolfrom planetary. And the gear ratio was higher, around 100:1 if I recall that correctly!
Please I'm trying to work out how to calculate reduction for this setup. Could you please point me in the right direction? A textbook maybe or a website? I've been trying to figure this out for weeks
@@boluwarin do you still need it? I've just finished making spreadsheet on determining teeth configurations (teeth number, pitch diameter, and gear ratio) for this type of planetary gear train (split-ring compound)
No, the reduction is certainly not unlimited. It's high, yes but not unlimited. There are some geometrical constraints
@@josetjaw8161 True. From trial and error with my calculator, the max ratio seems to be always less than ring teeth x planet teeth.
I'm using one of these in a robot actuator, quite impressive performance if you can stop the planets from tilting inward. I added an "idler sun" on top that helps with this. It still skips teeth before stalling the motor, but is surprisingly debris and damage tolerant, even in 3D printed PETG!
if you need a part made over the summer, just send over the CAD and I'll send the part your way....
cool vijeo btw
Could you please include metric too?
At least put it on screen.
Holding my Milwaukee M12 stubby tiny little impact wrench with 160+ ft/lbs of torque like a gun while watching this.
It reminds me a lot of a differential screw, just in gear form!
I would definitely put a planet carrier, with your design the planets can move every which way they want, which puts weird stresses on all the teeth. That would be a big step forward, and I think much better results can be obtained, even with 3d printed parts.
Is 1300:1 possible with this?
Maybe I am missing something buy couldn't you put a sun gear on the top set isolated from the drive with a bearing. That should force those planets out on the top.
That is one idea, though I might have to get clever with the ratios to get this to work. I forgot to mention in the video, but the top gearset has a really weird fractional module, so a sun might not fit.
or even a planet carrier on the top reduction would hold the planet axial centers in place no? You'd have the extra friction of the planet gears against the carrier axles to worry about but given that you're not taking a drive force off of the carrier not sure how impacting that might be? you might even be able to build a cage structure if you use a carrier plate on the top and bottom?
This is a very common gear reduction. Check gear down for what and you after watching some his movies you get a ton of recommendations to make them.
One of the remixes of Gear-down-for-what uses a top "sun" gear that has a round hole (not D shape) so that it just floats on the motor shaft, but serves to keep all the planet gears engaged with the top ring gear. It will solve your torque issue with only one part!
Need to move that 3d printer camera to the other end of the bed (you'll be able to see the print even better
Try redesigning the gears to be double helical. Helical gears can carry more torque.
Helical gears do not always contribute to higher torque ceiling. They disadvantage to helical gears is that they cause non parallel/perpendicular force on the surrounding components. Helical gears require a stronger housing and provisions outside of the gear itself.
While the gear itself maybe stronger do to the increased surface area for the teeth. It can cause misalignment and premature failure during over torque conditions
Adding sun gear to top that isn't connected to axile is obvious next step.
This is a “double deck” planetary set, shouldn’t it be compared to a “double deck” harmonic drive ?
Yep. Also compared to a 2 stage planetary gearbox
That's the thing about this channel, it's extremely armature. Nothing more than experiments, sometimes unrealistic designs, and poorly educated guesses. There's been issues with past projects, there's issues with this project as well, especially when it comes to design; a lot of these designs also seem to be initial prototypes with no real refinement. These same designs are also unrealistic, such as this design having gears of eight different profiles, which would extend production time and drastically increase cost _if_ this were to become a production product, with a refined design of course. Then there's the issue brought up in this comment, falsely equivalating two different gearboxes based on the idea that they have a 'similar operation,' which is nothing more than an uneducated guess, which leads to poorly informed claims. Then things like questioning why harmonic drives are favored over a dual stage planetary gearbox, as if the host has forgotten that backlash exists, and every implementation of harmonic drives specifically uses them to minimize backlash while also having a deep gear ratio; while stacked gearboxes have a multiplication of backlash, I think the lack of backlash here comes down to the printer's tolerances, a properly machined set of gears more than likely would not have this this tight of a fit, _plus_ printed gear mechanisms _do_ need to be broken in before they're tested, something that isn't really seen on this channel at all.
I like this channel for it's interesting concepts, but there really needs to be another channel hosted by someone with an actual engineering background that would analyze these designs from a proper prospective. Like the last video, the differential drive, it had numerous flaws that an actual engineer can fully improve the design of, the idea has potential but the implementation was subpar. Then there's designs from a couple videos ago, the compliant harmonic drive, which still does have it's flaws but was an actual educated guess that could actually lead to improvements in harmonic drives, both the idea and implementation were good but it needs refinement. Then there's videos like this, that're DOA, as the concept itself already exists and has already been refined throughout it's existence, for example this exact mechanism was in use in WWII planes for driving propellers, where this mechanism itself is just one of many dual-stage planetary gearboxes; the poor design here, uneducated guesses, and falsely equivalating the mechanism to other mechanisms is 100% the fault of the host, and there's not fixing that unless they better educate themselves, or at least do better research, and the video is almost entirely a misrepresentation of the mechanism.
There's similar issues with other channels, notably when mechanisms are either entirely or almost entirely 3D printed. Herringbone gears, for example, are simple to 3D print, yet machining one is an absolute pipe dream. That's not even the entire issue, every time a herringbone gearbox is assembled from all of these 3D printed parts, especially planetary sets, the housing either has to be split or the housing has to be flexed, and this doesn't work with real-world machined parts. It's a disconnection between what rapid prototyping can provide and how a long-lasting real-world part can be machined, something seen with almost every channel that primarily uses 3D printing for designs. A similar issue can be seen with every one-off project, where the design may work fine for a singular production, but doesn't make sense if production is scaled to anything larger.
I've only seen one example of such a double ring compound harmonic drive is Oskar Puzzle's "Harmonic Hyperdrive", which is a 300:1 gear ratio and extremely small (and delicate).
@@FeignJurai Oskar has some amazing designs, but it's a shame that he's only really into puzzles. So many of his designs and concepts could have actual real-world applications if they were refined, improved upon, made of proper materials and had proper construction (e.g. using bearings on the various mechanisms that have rotating pieces, proper housings, etc.), and tested under real-world conditions. Oskar also has some interesting concepts that I don't think would have any real-world applications outside of puzzles.
For example, he had a spherical gear design years ago, Spherigear I think it was called, that could've worked in two rotational axes, but the housing only hinged in one axis, and the tooth profile on the spherical gear is not optimal. This eventually evolved into his Flip Gear, which better suits the singular hinged axis design. Then the Flip Gear eventually evolved, by request, into a design that has the coaxial configuration decoupled, called Flip Gear Disconnect, where the original Flip Gears were coupled in that orientation. Real world use of all three of these would require a CV joint boot around the gears and housing, and of course bearings between the gears' shafts and the hinge housing; then of course a way to actuate the hinge, but that's on a per- use case basis, not something that's inherent to the core design of the mechanism. The Sphereigear would also need a bi-axis hinge mechanism of it's own to operate correctly, which has yet to be designed to my knowledge. I've also noticed that the Spherigear has some variations, five total that I know of, four can be found by searching 'Spherigear' on his page, and the fifth is in the form of his Tracker Ball 3D; though spherical gear designs go past this, such as the ABENICS Active ball Joint Mechanism, or theoretical designs that use a stellated (positive and negative stellations as a gear pair) geodesic or Goldberg (dual of a geodesic) polyhedron, I believe there's also a peg-based design that uses dimples and nubs, and there's a few other designs floating around out there. Biggest downfall is that spherical gears would ideally need teeth separated by equidistant points along the sphere's surface, something that's a concept that, as far as I know, has not been mathematically been proven to exist outside of using the vertices of the platonic solids; and even then, there's no telling if we can make spherical gears have the same performance as 2D involute helical gears once we do find optimal tooth placement.
Another example would be Oskar's Magic Gears, the bi-lobed friction gears, and his Illegal Gears, the tri-lobed friction gears, though not his original design, I believe these lobed friction gears largely originate from Jacques Maurel in the form of 'paradoxical gear.'' Jacques made a publication(s) in '04-'05, though some of his papers on relevant topics go back to '02, but I don't know if Jacques _invented_ the type of 'gear' or not, it's just the oldest publication of the gear that I've come across so far. I also don't believe they've been tested outside of proof-of-concept scenarios, I'd imagine the best real-world use of them would be in the form of a modified traction drive. Oskar's variations seems to be the most popular source for these types of gears, though. But again, efficiency is a concern with this kind of 'gear,' though further research into it, and further improvements, should be far easier than the spherical gear issue.
Unfortunately, his Grinder Gears and Harmonic Hyperdrive are victims of the same shortcomings, designs and concepts that could have real-world uses, or at least potential of being more than just a toy, yet nobody has really taken the ideas and put them into real-world scenarios with actual engineering behind them.
You missed an edit around 18:30 if you're concerned about such things.
Whoops, thanks, I’m trying to fix it
I guess fixing bending gears issue should be quite easy. You can just connect them all together on top with bearings, right?
via a common carrier?
yeah, totally. drop a ring on top with 5x bearings that support the centers of each planet gear.
easy, and will remove that failure mode. the next failure mode would be the teeth shearing off.
or just add a top sun.
@@steamcastle true, needs to be disconnected from the lower sun though.
Idler gear at the center shat for the top part of the planetary gears and a carrier/cage for them all.
I think that would suffice. Although I'm not an engineer.
Great stuff! Have you thought about using herringbone gears with this system? Will help to achieve higher torque output
Have you tried pushing herringbone gears into a planetary gearsystem before? =D
When will we see an update on the Coilgun Project!? Those lithium batteries were insaneee.
If you do a bit of research this gear design is credited to Ulrich Wolfrom more than a century ago. It is often referred to as a Wolfrom drive. The publication is Wolfrom, U.: Der Wirkungsgrad von Planetenrädergetrieben. Werkstattstechnik, Vol. VI, 1912
If you know someone with an EDM machine, it would be fascinating to see what could be achieved with precisely cut steel gears.
Great video dude, I don't think I would never have found this type of gear if it wasn't for you. You just gained a new subscriber
Ditto!
Maybe this would work well for a gravity powered light.
It's not back drivable
Brick experimentation channel made this out of legos already
If you put a sun gear between the planet gears that doesn't interface with the shaft, on the second ring layer, it will help support the planet gears. Oh, and now you're talking about that exact thing... :P
Exactly!
In the 1970s, there was a "visible V8" model engine that had a starter motor that contained a split ring planetary drive to turn the engine.
The mechanical nerd in me says you need carrier/holder plates for the planet gears, and have bosses coming out of the ends of the gears. Very cool design, and I learned something new today, thanks for the video!!
Sponsored by a Chinese company.
Very cool concept, but if I may, I would really like a post failure tear down to see the actual damage ! (But I am sure there will be a V2 😄)
This looks pretty cool. Have you heard about Archimedes drive? The design is based on a planetary gear system but it uses friction (toothless gears aka cylinders) instead of gears. I'm not sure if you can 3d print it but you could definitely give it a shot.
Well thats no 20-30mA - thats 200-300mA. And make SIM wheel out of that motor -I wanna se how quiet it will be !
Look into hydraulic torque hubs made by Fairfield Mfg Company. Used quite a lot in mobile and industrial hydraulic applications. The one I worked on used in a recycling plant, driving a large crusher/shredder. The torque hub was driven by a very small displacement Charlynn-Eaton geroler type hydraulic motor. It was a pain getting the planet gear timing set correctly
Make secondary sun gear which wont bind with motor axis or make star that will connect centers of planetary gears . If you prevent slip its way harder to brake tooths!
He could probobly get away with a blank cylinder because there will be virtuelly no torque on it
@@matsv201 ring like geer, just to prevent rubbing and friction with inner diameter lager than shaft
Maybe build a wire EDM machine next to cut your own gears out of steel or other metals?
better off vaccum casting.
@@nemoskull2262 What would be the benefit of that approach? Do you think you can vacuum cast gears with a higher yield strength than what you could cut using EDM? How are you going to produce the molds?
Using the same gear tooth numbers in the same volume you can get yet another order of magnitude by allowing the planet tooth count to differ on each layer. The highest ratio is when the product of opposite planet and ring teeth differs by only 1 (ie. P1R2=P2R1+1). Such high ratios are of limited use, but it does give you much more flexibility when choosing other constraints.
This reminds me of the Split Ring Compound Planet Epicyclic Gear - ruclips.net/video/-VtbSvVxaFA/видео.html
With stepper motors, it may seem like they have a low max speed, but if you slowly accelerate them you can go faster. If you're starting from a stop and you just try a high speed it will just stall because there is no momentum, but if you slowly increase the speed in code to match the momentum you can make them go much faster.
Hello from a fellow Texan here. Love your videos. I wish I could design something that looks half as good as your designs in cad.
If you add an idle gear in the middle of the output section, it will stop the flex and increase the output torque.
Also, check out Geardownforwhat RUclips channel :-)
Who noticed the typo on field at 8:12?
Hello! I think, that you can place one more sun gear on the stepper shaft, with no connection. It will prevent bending the satellites inwards.
1. Watch "gear down for what", it is possible to get reduction ratio of 1000:1 and more with one stage of this gear, if you are not restricted with gears of one module.
2. You need another sun gear to support the planet gears.
3. This abrupt motion at 4:44 is annoying. The fact it continues such motion until 7:44 renders this video unwatchable for 3 minutes straight. You could easily overcome this effect by choosing looping time according to your planets' period (if you can not continue true animation for the whole 3 minutes).
Im new to the whole scene. There is one thing I learned watching instructional videos on RUclips. PcBwAY iS a CircutBoaRd ManUfActUrer thAt...
Many Cycloidal ( Strain Wave / Harmonic ) designs have essentially *Zero* Backlash. And that is extremely important for precise positioning. Your Split-Ring Epicyclic design has an *unacceptable* amount of backlash.
Gear Down For What made a planetary gear that didn't have a sun gear. Somehow.
Since you have access to 3D printers, you might be able to ditch spur gears in your designs in favor of herringbone gears. Much more efficient!
Gear down for what made a nice version of this few years ago. It had a secondary sun to avoid planets bending inwards.
That guy makes some cool stuff
The proble, is not that the gear can not take the torq but that the motor is too strong for it, with small motor this would be realy smal and provide 6nm torq. if you would put a bit more effort supporting the gears it could handle much more torq, anyway, interesting, thanks.
16:52 - That's a "no load current". A stall torque is when your motor transitions from full-load (still dynamic) to stall (output shaft no movey-movey). The phrase you're looking for is "idle current draw".
17:09 - That 2 lb water bottle drew 290 mA, as you transitioned from 270 degrees, static and proceeded to decrease from there. (Which makes sense, since you've overcome the static friction and also abs(sin(270)) =1, w/r/t gravity. Which is why if you're reefing on a bolt with a ratchet and cheater bar it's always easiest around perpendicular+the amount of downwards angular momentum you can develop). Then it reverts back to an idle current of 110mA. (Which is a lot. Was the motor still drawing that much current after you removed the assembly?)
Your failure analysis is spot on re: folding itself in. It's typically bad form to say you "designed it", even if you cite the Wikipedia page. Even more so when you say "of anything I've designed", implying this is the result of multiple iteration cycles of you and/or your team.
If you want to see real power density, take a look at The Torque Test channel. Handheld impact hammer drills are putting out > 1,000Nm running on stock Samsung battery packs in messy environments (ever seen a contractor work in a class 100 ISO Clean Room? Yeah me neither.) The general technique is 3 stages of planetary gearsets, each stage sequentially moving slower/made out of a denser material. By the time you hit stage 3, everything is forged steel and the lost kinetic energy (those BLDCs get up to around 22k or so) is made up for by the mass. Their setup is pretty good, but not AvE good, sadly. Developing 1,000Nm of torque is impressive, but we've been able to do that for ages with diesel generators and airlines (railroads, oil rigs, etc all operated with Ingersoll compressors). The issue is those setups have literally < 5% output efficiency. It blows my mind that these *handheld drills* can drive exploratory drill string with comparatively no losses
why robotics don't use this type of output is also for the backlash , harmonic drive have 0 backlash , imagine a medical robot with backlash when doing dissection
The pcd's of tye outer gear set does not allign properly. For 50T ring gear, the radius is 50T*module which is equal to (20T/2+15T)*module=25*module. For the 2nd ring gear the radius is only 24.5*module. The appropreite planet gear is 24.5-20T/2=14.5T. This means that standard gear will not mesh properly. You may get awsy with this by increasing backlash which is done by scaling down the gear
I am a bit confused with your setup since you want to operate at 1.4 A (or the left of a performance curve), which is around 500 RMP (for this motor). Yet, for your demo you start at “No-load” RMP and then jack it up to what exactly. Aside from failure, you want to know where you are on the performance curve… But yeah, with my rough calculations this should be able to produce a CW-torque of apx 120 lbf*ft (you mentioned 150 lbf*ft), which is way more than 10 lbf but I did neglect the weight of the arm (but I don’t think its heavy enough to cause the failure). Lastly, what is securing your “drive-gear” to the motor shaft (nothing really), and if the teeth were steel they would most likely not fail.
Another reason they arent used is because they are extremely complicated, and have a substantial amount of backlash. Harmonic gears have 0 backlash.
@8:23 - "Hmm. This scientific explanation just spelled 'Field' wrong..."
you could simply put a star shaped cap connecting all of the planetary gears together on the 2nd stage that holds them at a fixed distance.
doing this would also cap off the exposed planetary gears for saftety
... I was watching the video peacefully until I heard "foot pounds"... Damn, why the hell you're not using the metric system, and more in general, the International System Units?!
There was a 5 part article in Elektor Magazine in 2001 that used this mechanism for a Polar co-ordinate PCB drilling machine. Links aren't working in comments so search - Elektor Magazine PCB Drilling Machine March 2001
Most definitely need a bushing/alignment pins for the gear sets to prevent deflection, this would increase the torque it can handle immensely up until the shear strength of the gear teeth
I bet it still would be nothing to sneeze at for this thing to handle crazy amounts of torque, but like you said...nowhere near mathematically "calculated" torque just imagine the angular accuracy it could attain however!
Ah...disregard...you already did :)
ruclips.net/video/66MlWxoQE1s/видео.html
Muscatine, Iowa, first time viewer. I'm definitely going to have to build one of these! Great video!
Iowa! You got this
As far as this gear set goes you add more planets to a planetary gear set and the torque goes up there's a reason why cars and semi trucks use these in their automatic transmissions.
I would like to see you print another sun gear to go in the center of that second planetary without a keyed input to the shaft and then see what your torque limits are.
But I will agree that the backlash would be relatively unacceptable for robotics though
Put small bearings at the top of each red gear, and one around the shaft that they engage with. That way they push outward always and maybe get higher weight/torque?
top layer planetary doesn't need to be the same module as the bottom layer. And the difference in teeth number not necessarily be one. A lot degree of freedom for such designs. Some of them allow a secondary free spinning sungear.
I spent many years running a gear cutting company. I cut from 10 teeth on a 1MM (.040") diameter to 10 inches 1/4" circular pitch, not DP or Mod but circumferential, used in the printing trade on roller presses. My design experience rases concerns that the unit is using approach side drive, that is thedriving teeth are acting like a wedge plunging into the gap in the driven gear. For long life and quiet operation receding drive is better, the driving tooth slides outward and "flips" the driven tooth away. As to the spring away issue, a planet is not the answer, gears are not suitable as load rollers. Studs on the gears and a 5 hole bearing ring would be better.
It is impossible to install a second sun gear (it should have 19 teeth, but it is not divisible by 5), just install the axes of the planetary gears on the carrier in the form of a ring. If the planets have 15 teeth, and the ring gears are different, then the planets cannot be on common axes, with the same module. The module of one half of the gearbox needs to be slightly changed so that everything engages correctly and the module becomes non-standard.
How can the top and bottom be aligned if one has 1 tooth less? If the top and bottom outer gears have the same reference circle but different number of teeth then they by definition have a different modulus, so how can the teeth mesh? Oh, you're explaining the mechanism later, at 13:00, rather than at the beginning when you claim to explain it. Gosh! I watched the purported explanation countless times until giving up...only to find out that the real explanation comes later...
Torque and ratio are decoupled in a compound planetary. I found this when I compared a 48:1 to a 705:1 (same size) and found the torque to be about the same.
If that is enough torque for your application, then you can use a weaker motor. When the torque is limited by the output gears, then the only way to increase the torque is to improve those output gears.
The pessimist, optimist, and engineer see the same partially full glass. The engineer sees a glass that is twice as big as it needs to be, assuming no safety margin.
The engineer then takes into account that the liquid is red wine and there is a white carpet.
The engineer then realizes the amount of fluid isn't the issue. They are simply at the wrong kind of party.
They make an excuse about a problem at work. Then leave the pessimist behind and go off to a backyard party hosted by another engineer.
@@hamjudo I didn't have enough torque, he motor stalled and nothing broke. The torque was good, just not what I expected. I had to change the geometry not the ratio.
Torque Ratio is Speed Ratio multiplied by efficiency in a planetary. You efficiency in the 705:1 GBox must have been around 15x lower than for the 48:1. It sounds like a lot, but it is actually possible if your planet wheels were large enough, compared to the sun gearwheel...
@@pablolopez-garcia853 I used to think that. It's wrong, the math is more complex than that. Look at it as a connected lever.
Why don you make helicoidal gears? It should improve resistance isn't it?
The world of bicycling loves ratios this extreme. Allowing 20k+ rpm electric motors yet still allow 120 rpm pedal cadence.
The motor controller isn't increasing the amps that's just what motors do when they are impeded they draw more amps. The motor controller will limit the maximum amps it can draw so it doesn't go above the motors rating i.e. it does the opposite of what you are saying.
You can't get arbitrary precise positions with FOC, it's limited by the resolution of the sensor/encoder used. Am I missing something?
I don’t know, I feel like complexity is another mark against drives like this. I like the idea of a harmonic drive in some ways, but I would expect less wear in a system like yours.
Epicyclic gearing, used in the Antikythera Mechanism? If so, it's been around for a LONG time.
Like the article. The planetary gears do not have a cage holding them. This was not pointed out. The only issue is that their is a torque force with the axis between the two gears with one tooth difference of the planets thus there is also a torque in each gear keeping it from typing and for the gears without a sun there is a thrust also towards the center that need a matching torque on the sun gear.
I do not know if you can make a floating sun gear for the top planetary. My Atlas lathe has a 14.5 degree gear tooth pitch angle. The most common is 20 deg, however; special gear have higher angles that will be stiffer and carry more torque at the expense of higher thrust towards the axis of the gears. Which means that the ring gear needs to be beefed up. Same thing happens for cyclonic gear because the physics or geometry is the same at the line of contract angle. It will produce the same forces independent of the type.
Friction drive can use the same approach. Also there is not cage, but without teeth slippage will cause a problem. So at least two sets of rollers are needed to set an even spacing. Then there needs to be a free wheeling sun for the second. Now at least one of the roller could be an elastic item such as a tube. This will reduce the tight tolerance at the cost of the peak torque.
Gears sets, when properly produced, only have rolling friction. The involute profiles for the teeth are such that when the teeth touch, there is no sliding friction. Did you change the pitch diameter for the top teeth so that the reduction from 50 teeth to 49 teeth did not result in sliding friction on the top gear sets? It’s basically a differential gear set at that point.
If you think youre the first to invent something that resembles a type of simple machine, you are probably wrong...someomes made it and patented it before...
Is there a reason you didn't put a freewheeling sun gear for the top stage to support the planet gear ?
I think they're all out of phase with each other. Considering that the bottom half of the planets mesh with the sun, and the top halves are all offset by fractions of a tooth, it doesn't seem possible to mesh with all of them at the same time. Maybe adding a third segment to the planets with the original phase, and meshing with another sun gear, you could solve the cantilevered planet issue and counteract the twisting moment the planets are undergoing. I'm curious what the planets look like after the destruction; I suspect the teeth are deformed in a twisted manner.
@@ericcmcgraw That's what I thought initially, so I openScad it and there is no geometric problem. You can find my design here : www.thingiverse.com/thing:4889174
This is the gear setup in a winch, using a small 3600 rpm motor to pull a car up a ramp..slowly.
The top ring gear has one less tooth than the bottom ring gear. Doesn't that mean the upper pitch circle is smaller than the lower pitch circle?
If the planet gear axes are parallel to the outer ring gear axes, then the upper planet pitch circles would have to be a little smaller than the lower planet pitch circles. That can be done, by having one less tooth in the upper planet pitch circle, but you didn't do that. Since your module on the upper and lower planet gears is the same, the upper and lower planet pitch circles are the same.
As a result, your lower ring gear pitch circle has to be a little bit bigger than what would be tangent to the planet pitch circles. This means the pitch circles of the planet and lower ring gears are not tangent, there's a little extra space in there. That's okay, involute gears can handle that extra space... but they do it with extra sliding. Your lower gear has extra sliding and extra drag for this reason.
You would not be able to insert a gear in the center of the planetary because you will not be able to make it coincide with all the planetary gears. But I believe that you perfectly identified that.
In order to limit the flex of the planetary gears, you could instead either insert a cylinder with the right diameter eventually soft or make a system with axis for the planetary gears.
I don't understand why the bottom planetary gears are all different. I made something similar with them all the same size. I also had a free spinning sun gear on the top, which you discovered helps things.
Insert a exta gear in the middle on top which is loose to prevent skipping. Also integrate a Ballbearing made out of airsoft bbs. I got mine up to 50Nm
Skyentific made a 3d printed gearbox like this about 2 months ago: ruclips.net/video/2dG_F9rR-jM/видео.html
I guess I'm officially stupid, but I did not at all understand how that works. I would love a better explanation.
Nice. I think i just invented (or reinvented) the split ring harmonic drive just by whatching this video :D
does the same problem of structural stability apply to planetary gears as well or is it just to this type of gearbox which has the problem of just one tooth engageing?
All you needed to add was a star with bearing to go in the outboard end of the planet gears. That should about double the usable torque, or will at least reach the strength of the material. I don't think a free second sun gear would match the offset teeth of the planets.
The only weakness I can see is misregistration of the assembly will cause an escalating "bolts in a coffee grinder" failure mode.
my god man so much talk just show it already so i can skip if im not interested. wtf 😡
Thanks, interesting. But since when do you use pounds? Please stay with the metric system like all sane people.
As far as I know this kind of mechanism is not about torque at all. It is all about precision. It is like angular micrometer.
Great work Levi!
Have you considered live-streaming some of your CAD work?
Any way to make this but with the motor driving the outside and the center gear being the output?
This the same gear train as used in the driver hub of excavators. Rebuilt l helped rebuild one a few months ago.
I will be contacting your sponsor pcbway ,and I will mention I heard of them threw you
Herringbone tooth may be stronger, but could probably not be assembled.
Have you had any problems for your ender 3 v2 bed carriage? Mine wobbles as it moves
Planetary gears are dime a dozen on YT.
What happened to your cycloidal drive ideas?
How do you calculate? I mean size of gears vs its influence on torque, etc.