8 ms·
Spherical Gear [video]
- warrenm 5y agoI think my brain just broke watching that Very cool!
- addaon 5y agoApologies for the content-light comment, but this is awesome. Interesting mechanism, well illustrated, and taken through completion with integration into a module, not just a single mechanism.
- Dig1t 5y agoI think illustrating how everything fits together with an animated 3D model is extremely underrated. I wish there were more videos explaining all kinds of concepts using this approach. So much information is conveyed so quickly with this spacial representation, though it's probably a lot of work to produce videos like this.
- adamrezich 5y agototally, I played the video without sound so I don't even know if there was any verbal explanation but if there was it was unnecessary, the visuals conveyed everything perfectly.
- trevcanhuman 5y agoI watched the video and there wasn’t any sound. Definitely a step by step graphical explanation helps a lot.
- eco 5y agoI came across the YouTube channel of Jared Owens[1] recently which is basically just that. 1. https://www.youtube.com/channel/UCbsfyGlrjrKQC0gbzK0-EiA https://www.youtube.com/channel/UCbsfyGlrjrKQC0gbzK0-EiA
- Dig1t 5y agoWow, this guy is amazing, thank you for sharing this!
- colordrops 5y agoI was about to reply with this guy. There's no comparison, he's light years ahead. He can make any complex system comprehensible on first pass. Watch his video on bowling pin setters, it's amazing.
- quakeguy 5y agoYou may find this channel interesting, all animations are selfmade by him: https://youtube.com/user/thang010146 https://youtube.com/user/thang010146
- sfteus 5y agoWhile the animated breakdown itself is phenomenal and certainly makes the video, one of the other key aspects is the progressive explanation of _why_ this mechanism is designed the way it is. You can watch the video without sound, and probably without the text as well, and see exactly how the "spikey ball" was designed, how the driver gears were created, how to get two types of movement from the drivers from linear inputs, and how those movements translate to moving the ball joint. It reminds me of the old Chevy videos, such as the one on differentials[1]. It was created in 1937, and through some live demonstrations and clever use of stop motion the film shows how to separate wheel movement, fix gear slippage, attach a drive shaft, then optimize for space. Different visual technology, but same type of presentation. There's similar videos for transmissions, suspensions, etc, all incredibly enlightening. [1]: https://youtu.be/yYAw79386WI?t=202 https://youtu.be/yYAw79386WI?t=202
- convolvatron 5y agodoes anyone understand why we have 4 drive motors for 3 degrees of freedom? it didn't seem that way from the presentation but maybe the motor axes aren't aligned with the drive axes?
- jbay808 5y agoTwo of the motors have to be synchronized together, because there are certain angles where either one or the other lose any torque transmission.
- zardo 5y agoIt eliminates gimbal lock
- Animats 5y agoNo, it doesn't. Watch the video out to the end, and you'll see what happens as you go through a pole. This isn't a homogeneous system; there's a moment when the gear flips.
- jbay808 5y agoThat's an accident of the trajectory chosen for the animation. The system doesn't have a kinematic singularity from input to output, just from output to input. Instead it has a zero from input to output, which is why it needs an otherwise redundant motor. To elaborate, there's one point where spinning an input motor doesn't rotate the output. When they reverse-generated the input trajectory from the output trajectory, that point has no unique solution; spinning the input motor has no effect on the output so the input can do whatever it wants. The animator let the input do a sudden backflip, but it didn't have to; that motion was not required and had no effect. It was probably just the output of a matlab script or something.
- gfodor 5y agoThis makes me wonder if ML could be used to explore the space of threadings to optimize torque or reduce risk of disengagement. Maybe even drop a motor.
- antegamisou 5y agoBecause ML (and NNs ofc) is definitely a one-size-fits-all solution to interdisciplinary problems..
- gfodor 5y agoWhat happened to you that you decided replying to this with a emotional strawman was worth your time and energy? It's a particularly dumb strawman too because we already know AI can generate solutions to mechanical engineering problems that humans normally would not. https://medium.com/intuitionmachine/the-alien-look-of-deep-learning-generative-design-5c5f871f7d10 https://medium.com/intuitionmachine/the-alien-look-of-deep-l...
- antegamisou 5y agoIt's generally a bad idea to invest too much in ML methods for physical world problems, especially considering it a panacea when their mathematical foundations are still poorly understood. The cost may be only computational when it comes to areas like Image Processing/NLP, however it's nowhere near the same for things like AVs (safety), Engineering Design problems (materials) etc. And this is because real world imposes real hard constraints, to the point that it'd be unfair to expect similar success to CS-related disciplines here from ML methods. This is no different for manufacturing problems. Excluding the absurd PoCs/artworks, most of the actual structures in the article you've linked are impossible to mass-manufacture without 3D printing, which is still limited to precisely printings parts with unsuitable materials for their target application. Keep in my mind that I was mainly referring to applying emerging trendy methods for which mathematical guarantees have not yet been established. Genetic Algorithms, for example, have been able to come up with successful antenna design optimizations like the one in the article for almost three decades.
- _Adam 5y agoThis is super cool and the video explanation is very intuitive. Robotic manipulators seems like the obvious application; I wonder how the torque transmission compares to a more traditional arm design.
- baybal2 5y agoPTZ cameras
- everyone 5y agoAwsum!
- Animats 5y agoOh, that's clever. They have to coordinate four motors to get three degrees of freedom. Not clear what the invariant is, but it may be something like a normalized quaternion. Mechanically, all the load is on maybe two tiny teeth at a time. This isn't going to be an industrial robot leg joint. Or, probably, even an arm joint. Too easy to strip the teeth off the sphere.
- gugagore 5y agoI don't think the constraint is like normalization. Consider a platform with https://en.wikipedia.org/wiki/Omni_wheel https://en.wikipedia.org/wiki/Omni_wheel There are 3 degrees of freedom for rigid bodies in the plane. If you have four wheels, then there is a constraint. Associate with each wheel a unit vector along the direction it can impart force, perpendicular to the direction that it imparts no force. Now take a vector indicating the velocity you want to travel in (ignore rotation for simplicity). To figure out how the velocity of each wheel, take the dot product of that wheel's unit vector with the target vector. To see that normalization doesn't play in the constraint in the omniwheel case, note that any valid assignment of wheel velocities is still valid if you scale it up or down. I think the case here is more complicated because it's not a euclidean space. There are poles. I believe underlyingly my analogy holds, though, if you think about manifolds and tangent spaces.
- Animats 5y agoI don't think the constraint is like normalization. Yes, this is different. I was thinking of a 3DOF trackball setup. There are 3DOF trackballs (you can both roll and twist) where a big trackball rests on three small ball-bearing balls. Two of those balls each have 2 axes of rotation sensing; one is just an idler. It's all friction-based; no gear teeth. So you have four incremental data signals coming out, which resolve to the three motions a sphere can do. That approach is homogeneous; no position of the trackball is special.
- chrisBob 5y agoThis looks amazing, but it isn't 3 full degrees of freedom is it? I feel like there are some orientations that wouldn't be possible with this, but I am really not sure.
- chrisBob 5y agoThe paper (Open Access!!!) https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=9415699 https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=941... Says that I am wrong, and I am willing to trust their analysis.
- aj7 5y agoHere: https://www.researchgate.net/publication/351357682_ABENICS_Active_Ball_Joint_Mechanism_With_Three-DoF_Based_on_Spherical_Gear_Meshings/fulltext/60afd69492851c168e47ed2b/ABENICS-Active-Ball-Joint-Mechanism-With-Three-DoF-Based-on-Spherical-Gear-Meshings.pdf?origin=publication_detail https://www.researchgate.net/publication/351357682_ABENICS_A...
- R0b0t1 5y agoThe retaining cusp does impose some restrictions.
- rtkwe 5y agoThose aren't usually counted in enumerating the degrees of freedom of a robot arm unless it's a significant restriction.
- baybal2 5y agoYou can make a spherical induction motor
- dialogbox 5y agoThis is very cool. However I'm not sure how much torque the ball can endure. All gears have to be really strong and very precise. Is it really practical?
- knodi123 5y agoIt can handle a pre-determined amount. Just like all gearings. :-) There's definitely a tradeoff here, but I imagine there are plenty of applications where it makes complete sense.
- Aspos 5y agoI guess this would make a fast, precise, and optically centered pan-tilt mount for a camera.
- amelius 5y ago> Is it really practical? Not sure. One application would be the last stage of a robotic manipulator (at the end of an arm), but I suspect it's really too big for that.
- bserge 5y agoTbf, gearbox shafts and gears can handle a lot of torque and power for their size.
- theelous3 5y agoI got in to machining at the start of the pandemic, I suppose just short of two years ago. Absolutely brilliant hobby. I remember a comment here a while ago about a lad who was interested broadly in systems and diagnostics, and had initially aimed to be a doctor. They then discovered they wanted to work on systems designed by logical first principles, and pivoted to comp sci and programming - only to find they'd discovered a whole new kind of almost random organic system. I think machining is about as close as it gets, in terms of the physical. The depth to the subject is off th charts. It all logically follows from first principles ;everything is rubber ;D It has an incredibly satisfying balance between the theoretical and the applied. Physical mechanics is a truly beautiful thing. Doing it yourself is equally fascinating and fun. Can't recommend it enough.
- diego898 5y agoAwesome! Can you recommend some intro resources to help someone get started? What worked for you? What didn’t?
- rfrey 5y agoThe youtube channel "blondiehacks" is excellent for the machining-curious.
- theelous3 5y agoFor learning to love it in an approachable way, this old tony https://youtube.com/c/ThisOldTony https://youtube.com/c/ThisOldTony For more practical stuff, joe pie https://youtube.com/channel/UCpp6lgdc_XO_FZYJppaFa5w https://youtube.com/channel/UCpp6lgdc_XO_FZYJppaFa5w For the very precise, robrenz. https://youtube.com/c/ROBRENZ https://youtube.com/c/ROBRENZ But my favorite - stefan gottswinter https://youtube.com/c/StefanGotteswinter https://youtube.com/c/StefanGotteswinter Take a shop tour with stefan and nycnc: https://youtu.be/H-Sf7Nvkwzg https://youtu.be/H-Sf7Nvkwzg
- tejtm 5y agoVery nice. One perhaps counterintuitive thing about threads and gears is the optimal "tooth" size is a function of the material strength, not the geometry of the object the tooth is on. Another is that when regular involute gears mesh, they press but do not rub, no sliding friction. Here I am not seeing how to avoid sliding friction which is a small price to pay for the extra degrees of freedom but one to factor in.
- rfrey 5y agoSlightly know-it-all, but in fact involute gears do rub against each other - they experience pure rolling motion where they contact at the pitch circle. That's the only point where the circumferential speed of the gears is the same. The purpose of the involute shape is to maintain constant torque transmission during tooth contact.
- jerome-jh 5y agoI believed like OP involute gears had true rolling motion with no slide however quoting Wikipedia (https://en.wikipedia.org/wiki/Involute_gear https://en.wikipedia.org/wiki/Involute_gear): "Where the line of action crosses the line between the two centres, it is called the pitch point of the gears, where there is no sliding contact." So I learnt something :) I also believed torque varied slightly because the point of contact between teeth was not at a constant distance of the gears centers. Illustration: https://en.wikipedia.org/wiki/Involute_gear#/media/File:Involute_wheel.gif https://en.wikipedia.org/wiki/Involute_gear#/media/File:Invo... Would you have sources for the affirmation "constant torque transmission during tooth contact"? BR
- rfrey 5y agoI overspoke when I said "constant" - like everything, involute shape is a compromise, in this case (I think) between constant torque and manufacturability. I should have said "the shape is intended to minimize torque transmission ripple". I'll pull out my old textbook and see if I can figure out where I picked that up from.
- holoduke 5y agoWonder whether the non driving gear needs to be aligned with the sphere. Or does the force push the driving gear into a gear alignment? Or is it done in software. I noticed some jerkiness in some movements. Seems that in some cases gear play is definitely there. Not good for precision. A very cool design though. Makes me want to 3d print it
- nope96 5y agowouldn't this need some sort of lubricant, or it would wear down over time?