[HN Gopher] Spherical Gear [video] ___________________________________________________________________ Spherical Gear [video] Author : carabiner Score : 109 points Date : 2021-09-16 19:29 UTC (1 days ago) (HTM) web link (www.youtube.com) (TXT) w3m dump (www.youtube.com) | chrisBob wrote: | This 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 wrote: | The paper (Open Access!!!) | https://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=941... | Says that I am wrong, and I am willing to trust their analysis. | addaon wrote: | Apologies 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. | dialogbox wrote: | This 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 wrote: | It 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 wrote: | I guess this would make a fast, precise, and optically | centered pan-tilt mount for a camera. | theelous3 wrote: | I 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 wrote: | Awesome! Can you recommend some intro resources to help someone | get started? What worked for you? What didn't? | rfrey wrote: | The youtube channel "blondiehacks" is excellent for the | machining-curious. | aj7 wrote: | Yes that's where to start. | rfrey wrote: | The other appealing (to me) thing about machining is that one | simultaneously: (1) is forced to realize that perfection is | completely illusory: everything is made of rubber, there's no | such thing as an exact dimension (2) gets as close as any human | endeavor to actual perfection. An amateur can, with care, skill | and some money, work to microns. | _Adam wrote: | This 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. | everyone wrote: | Awsum! | Dig1t wrote: | I 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. | eco wrote: | I came across the YouTube channel of Jared Owens[1] recently | which is basically just that. | | 1. https://www.youtube.com/channel/UCbsfyGlrjrKQC0gbzK0-EiA | Dig1t wrote: | Wow, this guy is amazing, thank you for sharing this! | adamrezich wrote: | totally, 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 wrote: | I watched the video and there wasn't any sound. Definitely a | step by step graphical explanation helps a lot. | sfteus wrote: | While 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 | quakeguy wrote: | You may find this channel interesting, all animations are | selfmade by him: https://youtube.com/user/thang010146 | tejtm wrote: | Very 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 wrote: | Slightly 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. | convolvatron wrote: | does 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 wrote: | Two of the motors have to be synchronized together, because | there are certain angles where either one or the other lose any | torque transmission. | zardo wrote: | It eliminates gimbal lock | Animats wrote: | No, 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. | warrenm wrote: | I think my brain just broke watching that | | Very cool! | gfodor wrote: | This 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 wrote: | Because ML (and NNs ofc) is definitely a one-size-fits-all | solution to interdisciplinary problems.. | gfodor wrote: | What 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-l... | antegamisou wrote: | It'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. | Animats wrote: | Oh, 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 wrote: | I don't think the constraint is like normalization. | | Consider a platform with | 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. | holoduke wrote: | Wonder 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 ___________________________________________________________________ (page generated 2021-09-17 23:00 UTC)