[HN Gopher] CARA - High precision robot dog using rope
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CARA - High precision robot dog using rope
https://www.youtube.com/watch?v=8s9TjRz01fo
Author : hakonjdjohnsen
Score : 279 points
Date : 2025-07-23 17:38 UTC (5 hours ago)
(HTM) web link (www.aaedmusa.com)
(TXT) w3m dump (www.aaedmusa.com)
| hakonjdjohnsen wrote:
| See also the youtube video about the project:
| https://youtu.be/8s9TjRz01fo
| PaulDavisThe1st wrote:
| The linked page has that video embedded.
| btbuildem wrote:
| I've watched and re-watched Aaed's videos on the capstan drive,
| it's great stuff. High speed, high torque, compliance,
| effectively no backlash. It's fascinating to watch a legit
| engineering mind at work.
| DeepSeaTortoise wrote:
| He's easily one of my favorite content creators. Ofc, there are
| much better engineers, domain experts or more entertaining
| people on youtube, but he strikes a very enjoyable balance.
|
| I wanted to start writing a list of other tech related, pop-sci
| and industrial-design Youtubers I kinda enjoy, but noticed just
| how many channels I'm subscribed to... If there's any interest,
| I'll drop it, just tell me. Meanwhile I have some filtering and
| sorting to do.
| Lerc wrote:
| I recently found his videos also. It's one of those things that
| gets my mind bubbling with ideas for things I want to make,
| never enough time to do them all though (and this breadboard
| beside me is asking for attention)
|
| It does make me wonder about the algorithm, Quite a lot of
| things I find on Youtube turn up on HN a week or two later. I'm
| not sure if this is an indicator of the effectiveness or
| failure of the algorithm. It is definitely succeeding in
| finding videos popular with some people and showing it to more
| who might share that interest. The question is, are the things
| I (and consequently many others of similar interests) see the
| best of all there is, or a subset of the excellent videos out
| there that happen to get noticed.
|
| I sometimes find channels that are years old with a goldmine of
| good information. That suggests that there is more good stuff
| out there than what I see. Were they just unlucky that I didn't
| see them before? Am I lucky to be seeing them now? It also
| might be that it is not luck but the algorithm has arbitrarily
| decided that the video has some special factor that requires
| promotion or that I have passed some arbitrary threshold of
| perceived character development that makes me supposedly now
| interested in such things.
| adolph wrote:
| I haven't watched the one about the dog, but the one with the
| initial explication of capstan drives [0] was excellent. I've
| been dreaming about it for the last year, especially since
| about the same time another person started working with the da
| Vinci robot actuators which use cables to generate find motion.
|
| 0. High Precision Speed Reducer Using Rope:
| https://www.youtube.com/watch?v=MwIBTbumd1Q
|
| 1. Building a DIY Surgical Robot
| https://www.youtube.com/watch?v=d_8rHKrwr-Q
| oc1 wrote:
| Ai, robots, where are we heading? Not far until ai + robot will
| replace humans
| A4ET8a8uTh0_v2 wrote:
| I don't think it is fair to downvote this comment. It is a
| genuine concern and should be addressed. Amusingly, given that
| the thought has entered mass consciousness by means of question
| on 'whether all this is a simulation', matrix ( the animated
| series ) explored this question a little and it is interesting
| in how the timeline aligns with what the movie presented.
| asoneth wrote:
| > It is a genuine concern and should be addressed.
|
| No disagreement, but does the comment meaningfully contribute
| to the discussion about this particular project?
| falcor84 wrote:
| That's an interesting reference, but do our timelines really
| align with what was presented in (ani)matrix? Their timelines
| are quite murky, but it seems that in their universe things
| only started getting problematic between humans and AIs
| around 2090 and The First Machine War started in 2139 [0].
| With how fast things are progressing, it's not clear to me
| that we have so much time.
|
| [0] https://screenrant.com/matrix-timeline-year-future-when-
| sett...
| zuminator wrote:
| It's absolutely a legitimate concern but since this robot
| project has no chance of replacing humanity, it seems like a
| derail in terms of the subject matter of the video. It's as
| if someone posted a link to an incremental advancement in
| graphene aluminum-ion battery tech and a person chimed in
| with a general lament about heavy metal battery toxic waste
| disposal.
| nawgz wrote:
| Definitely.
|
| It's intellectually exciting.
|
| On the flip side, capitalistic / private / special interests
| both controlling the progress and having the most ability to
| utilize it to further centralize power and wealth is deeply
| concerning. We can already see more controversial figures
| involved in AI using it to spread their personal viewpoints.
|
| It feels really easy to see how our jobs/labor and therefore
| our capital and therefore our value in the modern system are
| being directly attacked by these capabilities and deeply
| concerning to imagine how further centralization of power could
| be good for the masses.
| A4ET8a8uTh0_v2 wrote:
| There is a weird mixture of hope and dread in me as I watch this.
| I am ridiculously excited over a person like me being able to
| mess around with something that, until recently, was gated
| behind, well, a lot of hard problems to overcome ( I am only now
| slowly getting through old Peter Scott's robotics to get some
| perspective ). By comparison, it should be so much easier to
| explore aspects of robotics that may go beyond strict math and
| engineering.
| bmau5 wrote:
| Why dread?
| fusionadvocate wrote:
| Why spend so much effort to achieve an "exact" gear ratio? Having
| more zeros does not equal to being more "precise".
|
| Also, I wonder how resistant this mechanism is to wear and
| fatigue.
| skeeter2020 wrote:
| >> Having more zeros does not equal to being more "precise"
|
| Isn't having more decimal places the exact definition of
| precision (vs accuracy)?
| munchler wrote:
| The point is that those decimal places don't have to be
| zeros. 7.893 is just as precise as 8.001.
| a3w wrote:
| Yet for some reason unknown to me, people get annoyed when
| you tell them ,,let us meet at 13:37. that is no more
| accurate than let us meet at 14:00 hours"
| sabareesh wrote:
| That was confusing part of this video . May be there are some
| limitation on the tools he uses to tune
| dvt wrote:
| I don't think the _number_ of the gear ratio really matters,
| what matters is that you know what it actually _is_ (since
| every IK calc depends on said ratio); 8:1 is probably
| arbitrary and /or looks nice & might simplify some stuff.
| eichin wrote:
| It might be a lot easier to _check_ the ratio "by hand"
| (by counting rotations etc) if it's numerically simple.
| (IIRC in some earlier videos he noticed that the pulley
| size ratio wasn't producing the expected movement ratio,
| _because_ they were built as an obvious 8:1 or 10:1 or
| something, and didn 't match - which led to him figuring
| out the subtleties of the design - I can easily imagine
| wanting to preserve that aspect just for debugging, at that
| point, even if you _now_ have correct math.)
| michaelt wrote:
| Well, it probably wasn't _that_ much effort. When you 're 3D
| printing you're going to end up printing everything 2-3 times
| _anyway_ , so why not dial in the ratio while you're at it?
|
| And you can't really declare your design is "high precision"
| and present yourself as someone others should take transmission
| design advice from if you aimed for a gear ratio of 8 and
| achieved "somewhere around 7.9 to 8.2"
| LeifCarrotson wrote:
| It probably doesn't matter so much whether it's 7.913 or
| 8.186, but it would be important to know the exact value for
| kinematics. One way to do that is to build an object very
| accurately, the other is to build inaccurately and then
| measure the result after the fact.
|
| It's also interesting because competing actuators with
| strain-wave, cycloidal, or planetary gearboxes will state
| _exactly_ what the ratio is. The actual gear teeth may not be
| spaced out perfectly around the circumference, but the number
| of teeth is an integer with an infinite number of zeros.
| tonyarkles wrote:
| Yeah, I think one of the nice things about making it a
| "clean" number (either an integer or a rational with a
| small integer denominator) is that you can easily validate
| it without needing high-precision measurement equipment:
| put a mark on both gears (maybe even embedded in the 3D
| print), line up the marks, rotate the large gear 1 full
| rotation, and count the number of rotations the smaller
| gear makes. Check to see if the marks line up perfectly
| after those rotations.
| throwawayffffas wrote:
| I think it's about kinematics, the more precise your gears the
| better the model fits the real world.
|
| That's why pro crews don't use gears and ropes. At high
| impulses deformations and elasticity throw the kinematics off
| what's actually happening. Modeling the deformations and the
| elasticity is a computational no no. Instead what you see is
| the motors right on the joints.
|
| At least that was the case last time I had a look at robotics.
| PaulDavisThe1st wrote:
| more than 30 years ago I was writing code for a "robotic"
| device that used motors, directly on the joints.
|
| the motors were so sloppy the company wasted a ton of money
| [0] having me write heuristics to tackle the errors they
| accumulated over several hours.
|
| one of his whole points is that by using dyneema (rope),
| there's almost no elasticity at all in the capstans.
|
| [0] relative to the cost of better motors
| michaelt wrote:
| _> That 's why pro crews don't use gears and ropes. [...]
| Instead what you see is the motors right on the joints._
|
| The answer here, as with so many things in robotics, is: It
| Depends.
|
| UR10e robot arm that can lift a 4kg object with a reach of 1m
| and has sub-1mm repeatability? Strain wave gears in the base
| and shoulder joints, 100:1 ratio.
|
| MIT Mini Cheetah robot dog that can do backflips? 6:1
| planetary gearbox.
|
| Shadow Hand with 20 degrees of freedom? Tendon driven, with
| the 20 motors in the forearm to keep the fingers slim.
|
| Little dinky Huggingface SO-101? Servo motors, integrating
| 1:345 gearing with a series of 6 tiny brass gears.
|
| Mid-price CNC milling machine, if you call that a robot?
| Really long ballscrews, driven by stepper motors.
| Joel_Mckay wrote:
| In general, for some platforms each gear mechanism adds
| backlash precision loss, lower energy efficiency, and might
| not be back driven.
|
| >Mid-price CNC milling machine
|
| A ball-screw is mostly decorative on small machines... =3
| AIorNot wrote:
| Amazing presentation! - somebody hire this kid asap
|
| https://www.aaedmusa.com/
| abraae wrote:
| I'm going to tell my 12 year old that when he leaves education
| he wants something like this on his personal web site:
|
| "CARA (Capstans Are Really Awesome) is my latest quadrupedal
| robot, following ZEUS, ARES, and TOPS. Built over the course of
| a year, CARA is easily my most dynamic and well-designed
| quadruped yet."
| andrewstuart wrote:
| He might be perfectly happy doing projects and YouTube.
| dvt wrote:
| Likely makes more money, too!
| geerlingguy wrote:
| For many, no; taking on lots of sponsorships, you can make
| a good amount of money (especially the ones where you agree
| to do X posts across Y social media accounts for Z period
| of time, essentially being fully sponsored across a large
| swath of life).
|
| But for a lot of tech/engineering channels, it'd be
| immensely difficult to make the same salary as you could
| working at a FAANG or the like. (I'm making about half what
| I made when I had a W-2, but it's enough).
| sitkack wrote:
| You just need to start selling supplements, anti-aging
| creams and time shares.
| abtinf wrote:
| Do fun projects of your choosing vs the grind of
| corporate life.
|
| The former has a rather large non-pecuniary component of
| total compensation.
| busymom0 wrote:
| His current Patreon has 57 paid members. Unless he has
| another revenue stream, I think he'd need more paid
| members.
| abtinf wrote:
| That would be a terrible path for someone with this extreme
| level of _demonstrated_ talent, motivation, and follow-through.
|
| Much better for someone to fund a startup run by him.
| TheBozzCL wrote:
| Thanks for sharing this! What a treat of a video. It's a fun
| project, and it's presented very well. This guy has a talent for
| communication - the video was super clear and well explained. I
| really admire that ability and I want to get better at it.
| mikewarot wrote:
| It's amazing what he's done in terms of the robotics, and the
| presentation of it to the viewer. I'm amazed at the quality of
| cinematography on the internet these days.
|
| The implications of the tools we now make available for use in
| our own personal workshops are still being discovered, and will
| be for some time.
| csours wrote:
| Professor of Upstairs Neighboring.
| https://youtu.be/8s9TjRz01fo?t=1128
| micromacrofoot wrote:
| I'm so excited for a smaller open source version of this, I'd
| love to make one. What a great project.
| andrewstuart wrote:
| He's got the magic combination of tech skill plus ability to make
| and edit entertaining videos.
| heap_perms wrote:
| Fascinating! I want to get into this type of stuff. But I have no
| idea where to start, I just have just a CS degree and 3 years
| experience as a developer.
| taneq wrote:
| Arduinos and hobby servos. No, neither of them are "industrial
| grade" and yeah, you'll reach their limits pretty quickly, but
| building a physical thing that does stuff is (in my experience)
| a huge motivator.
|
| Or if you're already all over the basics, figure out what kind
| of stuff you want to build and then try and build it. :)
| Paddywack wrote:
| Can you recommend where to find beginners projects that "do
| stuff".
| Retr0id wrote:
| Just like the article, there's a huge amount of hobbyist-
| accessible projects on youtube, you can click around the
| recommended videos.
| sitkack wrote:
| Grab a servo and start playing with it.
| adolph wrote:
| I recommend a Brachiograph build. It will introduce you to some
| fundamentals of PWM and inverse kinematics. It is well
| documented but not cookie-cutter. Using a Raspberry Pi will
| give you more direct access to running the servos than the
| microcontroller experience. All the parts are infinitely
| reusable afterward if you don't want to keep it around.
|
| https://www.youtube.com/watch?v=u4Jh1daCl60
|
| https://www.brachiograph.art/
|
| https://github.com/evildmp/BrachioGraph Sample
| Supply List for $80 budget: Pi Zero with header $20:
| https://www.adafruit.com/product/6008 Power supply $9:
| https://www.adafruit.com/product/1995 SD Card $10:
| https://www.adafruit.com/product/1294 Three hobby servos
| $18: https://www.adafruit.com/product/169 Breadboard
| wires $5: https://www.adafruit.com/product/153 Breadboard
| $5: https://www.adafruit.com/product/64 Glue, popsicle
| sticks, pen and paper $10
| ZeWaka wrote:
| Just saw this at Open Sauce last weekend! Super cool project,
| looking at all the gearing was fascinating.
| s_dev wrote:
| Cara is the Irish word for 'friend'. Not sure if thats what was
| intended or is just a coincidence.
| srameshc wrote:
| I remember a post previously related to him here on HN but I am
| surprised at how I forgot about him and how cool he is to build
| all these incredible stuff and also teaches in his videos. I am
| subscribing so that I never miss anything from him again.
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