[HN Gopher] Spherical Gear [video]
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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
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