10 ms·
Active ball joint mechanism with 3 DoF based on spherical gear meshings (2021)
- luma 4y agoHere’s a video of this linkage in action: https://youtu.be/AHUv9Zda_48 https://youtu.be/AHUv9Zda_48
- jcims 4y agoSome incredible explanatory animations.
- etrautmann 4y agoAnyone know what CAD software was used to make these animations?
- hwillis 4y agoProbably 90% chance its either fusion 360 or solidworks
- luma 4y agoTogether Autodesk and Dassault account for less than 40% of the market: https://www.cadalyst.com/cad/pandemic-transforms-cad-industry-2020-and-beyond-76189 https://www.cadalyst.com/cad/pandemic-transforms-cad-industr... That number also includes CATIA from Dassault and Inventor and AutoCAD and all the other stuff from AutoDesk. Solidworks and F360 themselves are likely less than 20% of the overall market. f360 and Solidworks are common in the maker communities/youtube/etc as they both offer free/cheap licenses to get started, so that's what you're mostly likely to encounter unless you actually work in the field.
- johnwalkr 4y agoThis project is out of universities which in my experience usually have Solidworks licenses, plus some students using F360 because they were already using it before joining the university. I went to one of the author's universities (Tohoku) and indeed Solidworks was generally used there. The animations look too good to me to come from such software though. Maybe they used blender.
- etrautmann 4y agoexactly - I couldn't get this video out of Fusion 360. I think it's missing basic features like section / cutaway views in renderings.
- londons_explore 4y agoI think that data is deceptive... When people think CAD, they think "making a 3D model of a teapot". Whereas most of the dollars in that pie chart are spent on super specialist software that does things like modelling the electron flow through a 3 nanometer transistor... Or modelling people flows in an evacuation of a tunnel...
- luma 4y agoThat data is the market reality. Nobody in business cares about 3d models of teapots, they're trying to build physical products and there's a lot more that goes into that process than the mechanical drawing of the end product. There are some users who need to do things like electron flow, but the overwhelming use case is in fact product engineering and development. The other 80% of the people not using Solidworks are not doing anything weird, they just aren't using Solidworks for whatever reason. When mechanical engineering teams think "CAD", they aren't thinking "CAD", but rather Product Lifecycle Management ("PLM"). The drawing tool is one part of a much larger system. Think the difference between Quickbooks and SAP. Siemens NX is the big entry in this market. You don't hear about it because 3D printer users aren't making YouTubes about it, and because you probably don't work in the field.
- luma 4y agoI'm curious as well, the "flat" shader being used is gorgeous.
- ge96 4y agoat 2:01 that differential pinion... trying to figure out how that would work... it looks like it's locked in place yet it spins. edit: oh maybe it's some kind of worm gear/helical gear to translate 90 deg or maybe weird bevel gear
- henearkr 4y agoEdited. Thought the name in the linked article ("ABENICS") was a reference to the former PM (yikes), but instead it is probably a reference to the author of the article himself. Still weird to call a technology by one own's name... usually we let other people do it for us. Especially in Japan, where humbleness is valued. Thus I am still a bit suspicious. I would still welcome an alternative name, more descriptive. Edit: "spherical gear" is the name used elsewhere, and it fits nicely!
- jabbany 4y agoUmm, you do realize that the first author's surname is also Abe? And that in general it's a common-ish surname...
- henearkr 4y agoOk. I edited my comment accordingly. Thanks.
- HPsquared 4y agoPerhaps someone else in the group coined the name?
- henearkr 4y agoDoesn't make sense if the Abe person is part of the group who developped it (at least, according to the way Japanese people think of groups of persons). Unless he's dead.
- RobotToaster 4y agoThe fact that it's in capitals makes me think it's an acronym of some kind? Active Ball Effector? Or since it's always written next to "active ball mechanism" it could be Active Ball mEchaNICS?
- formerly_proven 4y agoMight be a pun on both one of the author's name and abenomics.
- calvinmorrison 4y ago[flagged]
- jacquesm 4y agoTrivial??
- deleted 4y ago[deleted]
- samwillis 4y agoThis is far from trivial, there is significant control needed to keep the gears in sync and track the relative position of the main spherical gear.
- calvinmorrison 4y agoSignificant like more than someone can do with a 3d printer and two stepper motors? I don't know... I just feel like this would have been solved. Looks like an old mouse, except it has a motor instead of a sensor
- calvinmorrison 4y agoand here's a very similar article from 2008.. "A new kind of spherical gear and its application in a robot's wrist joint"
- carabiner 4y agoPreviously: https://news.ycombinator.com/item?id=28556208 https://news.ycombinator.com/item?id=28556208
- henearkr 4y agoHere we are! "spherical gear" (used in your link) is a waaayy better name than "abenics" (used in the link of the present HN submission)...
- TEP_Kim_Il_Sung 4y agoNamed after Old Abe, the Japanese scientist.
- mhb 4y agoAmong others: https://hn.algolia.com/?q=spherical+gear https://hn.algolia.com/?q=spherical+gear
- jacquesm 4y agoThat's a beautiful write-up. At the end under 'media' there are two videos linked.
- Ord3rChaos 4y agoI saw this last year, really cool demo. Stronger materials are needed to make this useful and that looks like a nightmare to manufacture at scale. Also mechanical advantage seems to be a major tradeoff. There is a reason biology tugs on ropes and lets reaction surfaces slide around instead.
- miketery 4y agoWhat is meant by "reaction surfaces slide"? Is this referring to joints?
- busyant 4y ago> Also mechanical advantage seems to be a major tradeoff. There is a reason biology tugs on ropes and lets reaction surfaces slide around instead. I'm not sure I understand. Do you think that there's a biological benefit to ropes and sliding (compared to this)? Or is it simply that ropes/sliding are easier to evolve? You probably know this, but (in case others are unaware) there are rotary "engines" in biology (e.g., bacterial flagellum and F0F1 ATPase), but, obviously, they are not quite like this spherical gear.
- irjustin 4y agoI believe the parent comment is talking about scale at human sized.
- busyant 4y agoThank you. I wasn't catching that.
- scotty79 4y agoImagine two sliding surfaces held agains each other and pulled by ropes. You can shape the surfaces the way you want for the movement you need. Make them as big or small depending on how much compressive load you need to transfer. You can place as many ropes, controlled ropes or just stretch ropes to have as much flexibily, control and ability to survive tension as you need. You can do all of this with pretty crappy materials and high tolerances. When compared to that, gears that transfer all of the load through individual small teeth that must be made from incredible materials and struggle if you need multiple degrees of freedom there's really no competition. Unless you need to deal with fast spinning things or simple 1dof fixed axis rotations gears are terrible technology and they rarely ever evolved not because they are hard but because they have huge weeknesses and barely any advantages. The only gears that ever evolved that I know of are used for syncing movement.
- lizardactivist 4y agoJust looking through the paper makes my head spin. The Japanese are undoubtedly the most skilled engineers in the world.
- williadc 4y ago[flagged]
- lizardactivist 4y agoNo.
- jacquesm 4y ago[flagged]
- xpe 4y ago> If you're only going to post once a month or so make it count. I agree in a sense. Life is short. Our online comments probably will last longer than us. What do we want to put out into the world? We can use comments to learn, or we can respond uncharitably. The former is more worthwhile in most cases. [1] inclusive-or
- deleted 4y ago[deleted]
- xpe 4y ago>> Just looking through the paper makes my head spin. The Japanese are undoubtedly the most skilled engineers in the world. > May I have your permission to use this as an example of a logical fallacy? _If_ the comment was "Just looking through the paper makes my head spin; therefore, the Japanese are undoubtedly the most skilled engineers in the world." then it would be a logical fallacy. As written, one has to make an _uncharitable_ assumption in order to classify it as a fallacy. A _charitable_ reading is that the author has other experience suggesting the ascendancy of Japanese engineers. Such a mindset would open the door to interesting conversation, such as "What else have you seen that impresses you about Japanese engineering?" That might lead to everyone learning more, and, heck, even being inspired. Try this next time, please?
- hinkley 4y agoThis solution seems to have a lot of “gimbal lock” positions so I’m not sure 3 degrees is really accurate. The gears are so large that you lose 120° of rotation along one axis. 2.6 DoF is probably more accurate.
- xpe 4y agoWhat are some ways the robotics field / industry quantifies degrees of freedom?
- hinkley 4y agoThe six degrees I’m aware of are translation through three dimensions and rotation along each axis. Assembling a car takes a lot of those for some fiddly bits for the interior and under the car. Some configurations of this device can rotate 180° on one and about 240° on another. One configuration, the one that gets the most screen time, is worse than that, which is what got me wondering in the first place.
- ajb 4y agoNot sure - the controllers have 4 degrees of freedom, so maybe they managed to arrange only to lose at most one at any given time, so that they always have three?
- hinkley 4y agoI’ve been noodling on this while doing shores today. I think the main thing is not degrees of freedom here, but degrees of freedom around a fixed point. There are four servos in this thing, and about nine gears. You can rotate a probe through a full three degrees of freedom with three servos and six gears, but you also need the X Y and Z coordinates if you want to spin an object without moving it. I think one more motor would give you full 3 degrees of freedom by allowing you to move the braces out of the path of movement. But I also suspect that one more of these motor assemblies would get you close to five degrees, and four of them total would get you six, with some wiring troubles to deal with. In the end you’d have an arm with just a “shoulder” and a wrist, which could be pretty interesting. I aLso wonder if you could invert the gear and the cog, with motors inside the sphere.
- leeoniya 4y agoreminds me of the Triple Gear: https://www.youtube.com/watch?v=I9IBQVHFeQs https://www.youtube.com/watch?v=I9IBQVHFeQs
- _a_a_a_ 4y agoCan't see teh video but I think I've seen this before - very neat but there seems to be a couple of conditions where a kind of lock up (gimbal lock?) could occur.
- keepquestioning 4y agoCan this be used in 3d printing?
- xpe 4y agoTo clarify: you are wondering if this has applications to make better 3D printers?
- keepquestioning 4y agoyes
- jwagenet 4y agoI could see this being used for a 5 axis fdm printer to replace a traditional 2 axis gimbal. I’m not sure where the value would be except for highly specialized applications where you are ok with fdm, but want to avoid traditional layer building (think making a sphere ‘smooth’)
- Animats 4y agoThat's very clever. I've seen videos of this before. It's a robotic actuator. Notice that it's overconstrained. The ball has 3 degrees of freedom, but is driven by 4 motors, which must maintain some invariant relationship. It's kind of like a mechanical implementation of a quaternion.
- dtgriscom 4y agoGood point. I wonder how they manage the inevitable mis-match of the motor positions? Seems like it would be easy to get the system into a high-tension state, with motors fighting each other.
- xg15 4y agoEven moreso as the "pitch" of each monopole gear is controlled by a worm gear. So I think if you don't implement the controller very carefully, you could get situations where both worm gears work against each other.
- jacquesm 4y agoThere appears to be an improved version that they have in the works: https://link.springer.com/chapter/10.1007/978-3-031-08140-8_35 https://link.springer.com/chapter/10.1007/978-3-031-08140-8_...
- hinkley 4y ago> the main disadvantage of Abe et al.’s design is that it is an over-actuated mechanism: it requires four instead of only three actuators. In this paper, we propose a variation on this mechanism which requires three actuators, thus simplifying its control and its potential cost. That’s sort of the problem. Four motors and nine gears, versus three motors and six gears. I suspect their solution here may be as simple as having two rolling motors at angles, and only one motor for twisting.
- jacquesm 4y agoI once designed a mirror array to track the sun and reflect the image on a solar panel to get more concentrated power (solars cells = expensive, mirrors = cheap). Obviously there are all kinds of limits to that but the interesting part in the current context was the drive: it started off with two motors per mirror and in successive iterations that went to one motor per row of mirrors and one motor per column to one for all the rows and one for all the columns and finally a single motor for all of the mirrors. It was mostly my lack of understanding about the way the sun and the earth interact over time at the beginning of the project that caused me to choose the most naive solution, but as understanding increased I saw more and more ways to optimize the whole thing ending up with a set of gears that resemble the relationship between the two bodies pretty much in the same way that a planetarium would do, with the angles of the mirrors as the function of the time of day and the position of the earth in its orbit around the sun as well as the axis of tilt. That whole process took about a year and it looks to me as though this project is on a similar path of optimization, though it likely won't go much further than 3 motors, 4 gears assuming they can find a way to put the twist motor inside the spherical gear, which would come with its own challenges (supplying power, feedback).
- 4y ago
- xg15 4y agoI buy everything up to the point where they present a second prototype with the motors opposite to each other, i.e. right in the gimbal lock position you'd usually be careful to avoid. (3:55 in the video) How does that even work?
- philsnow 4y agoI thought the same thing at around 1:17 in the video; if they stopped the pitch axis movement 90 degrees earlier (so that the poles were aligned), it wouldn't be able to do the roll axis movement because it'd be in a gimbal lock position, right? At https://www.youtube.com/watch?v=AHUv9Zda_48#t=5m20s https://www.youtube.com/watch?v=AHUv9Zda_48#t=5m20s they show its behavior around the poles, but the motion it's doing right then is pitch, not roll.
- sacnoradhq 4y agoOskarPuzzle 1D passive linkage in the recommendations, different than a U-joint that has much less 2D of freedom: https://youtu.be/7Tv-aUC6lpM https://youtu.be/7Tv-aUC6lpM
- sacnoradhq 4y agoPDF thesis about another design for a 3DOF active joint (2009 IEEE/RSJ) from different authors and different universities, coincidentally mostly from Japan: https://vigir.missouri.edu/~gdesouza/Research/Conference_CDs/IEEE_IROS_2009/papers/1367.pdf https://vigir.missouri.edu/~gdesouza/Research/Conference_CDs... Also interesting OMNIA wheels: https://www.omniawheel.com/omnia-wheels https://www.omniawheel.com/omnia-wheels
- CamperBob2 4y agoVery cool design (and analysis, and animation) -- this is one case where I'm glad the authors paid up to make the paper available to the public. (And equally annoyed that they had to.) I will say that I don't really get the problem being solved here, though. There are any number of ways to do this if you don't need to rotate the output arm around its own axis. If you do, simply adding another motor to the output arm seems like the most straightforward way to solve the problem, and with fewer compromises elsewhere. Can any robotics gurus comment on the relative advantages of the all-in-one approach using a single spherical gear?
- o-o- 4y agoHonorable mention: Not a gear, however 4(!) DoF with a locking mechanism (the spherical bushing expands both inward and outward: https://www.youtube.com/watch?v=6qnYgE-qNHU https://www.youtube.com/watch?v=6qnYgE-qNHU