CARA – High precision robot dog using rope
175 comments
·July 23, 2025btbuildem
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.
monuszero
So, Aaed was our intern last summer - and he’s the real deal. I got to work with him on some really cool bespoke robotic end-effectors and the guy has great design instincts. Picked up mechatronics skills like a sponge, grokked hamming codes in like 30sec from a whiteboard doodle. Super hard worker too, he would stay late in the electronics lab to work on the motor design for what turned out to be CARA - we had fun testing the backlash one evening and ever since I’ve been trying to shoehorn one of those actuators into a project.
Potential and active founders here should consider reaching out (i think a startup setting would suit him better than corporate research), though he’s obviously got his own stuff going on and a degree to finish!
Lerc
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.
imtringued
I get absurdly niche videos with 33 views in my feed about robotics but most of them have views in the low thousands. The algorithm isn't holding you back.
mrheosuper
i noticed recently YT has been suggesting micro-small channel(<1000 subscriber) to me, not sure if this is good thing.
godelski
> It does make me wonder about the algorithm
If I'm misremembering or missed something please correct me. I'm out now but I'll try to find the video of him talking about gating when I'm back if someone hasn't already linked it.
Also, I love how YouTube has all these "small" creators doing extremely impressive stuff. It's a real shame the algorithms make discovery challenging. The beauty of something like YouTube is not about just getting something to watch, it's by being able to get access to any content. Search is always a difficult problem to solve but I'm afraid it's currently over optimizing for views rather than intent. Which, to be fair, is much harder to measure. But I say over optimized because frequently I can search the title with 90% accuracy and fail to find the video. Something minor like missing an "s" or something effectively non meaningful. It's extremely frustrating...
8note
the algorithm in question is youtube's for how its getting to all the HN users at about the same time. i was also suggested this same video a few days back
DeepSeaTortoise
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.
patatman
I'm interested as well! I never can get enough of these builders and engineers.
DeepSeaTortoise
Hey, I'll reply later to noman-land's comment below, but progress is kinda slow. It takes more time than expected to categorize this many channels and I stopped yesterday after having sorted a bit over 500 and have barely reached the letter "H" (most not tech related ofc, so no worries about getting a monstrous list).
I got a bit more time today, so maybe today evening (German time), elsewise I'll have to skip Friday, so likely Saturday afternoon.
noman-land
I am interested. I love these builder channels.
Keyframe
"back in the day", we used capstans to drive film (movie) rolls around the scanning aparatus. Both high speed and precise without backlash. Great stuff. Somehow I always thought maybe lack of high torque is the issue more people aren't using them or wear and tear.. but, apparently not?
mlhpdx
Dynema makes a huge difference, a true game changer in many ways. I came across it rigging sailboats where is started out replacing ropes and now replaces steel cables as well. Spectra is another brand with different, equally amazing properties.
Keyframe
Interesting you've mentioned sailboats. I've encountered dyneema for the first time in spearfishing!
darksaints
Spectra and Dyneema are both UHMWPE. They're different brand names (from Honeywell and DSM respectively) but chemically and mechanically the same, possibly with some small and insignificant differences due to manufacturing processes.
foobarian
These drives sound amazing, so why are they not used everywhere? What are the disadvantages?
adolph
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
ACCount36
The "DIY Surgical Robot" vid is so good. And it's also posted over a year ago with no follow-up. Damn.
dyauspitr
How is there no backlash? I can’t imagine a rope drive without backlash.
Animats
Improved materials. Kevlar and Dyneema.[1] Dyneema is about 15x stronger than steel per unit weight. Kevlar toothed belts have been available for many years, and can be used for many of the same applications as this capstan setup. Neither material has much elasticity.
The advantage over gears is that overloads are distributed over much more material. You don't snap gear teeth. This is good for leg landing shocks.
[1] https://www.impact-fibers.com/info/unveiling-the-strength-ke...
kragen
The relevant feature of Dyneema is specifically that its Young's modulus is much higher than most other organic fibers, about half that of steel, which is probably what you mean by "neither material has much elasticity".
Steel cables would work just as well if weight isn't a consideration, but I think Dyneema is likely to be more resistant to abrasion. However, heat produced by any significant dynamic friction will ruin it immediately, as I found to my sorrow. Kevlar is much more heat-resistant, and of course steel is more heat-resistant than Kevlar.
scotty79
It's very non-stretchy rope material. I imagine with enough force you can bend it away from the set position a little bit but it comes back when you remove the force. Nothing like traditional backlash with gears where you can move it with very little force between two adjacent gear teeth.
mikewarot
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.
ErigmolCt
Feels like the golden age of DIY engineering
sneak
I agree 1000%, which is why I find the whole “the internet sucks now” movement really disheartening. There are huge upsides to a network this large.
zelphirkalt
DIY and "the Internet" (the web?) have fairly little overlap, aside from learning resources existing. Those learning resources could just as well exist, and probably better or more, in a healthier web. I don't think contrasting the 2 things is making much sense.
aldousd666
I watched this last week and my jaw was on the floor. He's both a great technician, and he has the personality to make it interesting. He walked through his testing strategy far enough that you could understand his methodology and the thought process behind it, but didn't belabor it by making us watch it all. Banger!
AIorNot
Amazing presentation! - somebody hire this kid asap
abraae
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."
abtinf
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.
salomonk_mur
Why would you put someone with clear talent at building stuff in charge of running a startup? He'll get bogged down in lawyers, day to day operations and growth strategies.
Hire him and put him in R&D in some robotics company.
robotresearcher
Y’know, sometimes smart, dedicated, curious, self-directed people are that way with a lot of things.
I was a professor for a long time. My observation was that often a top researcher was also a top teacher and even a top administrator. There are exceptions of course. But if someone is smart and effective at using their attention, those skills transfer to many things.
It’s a pain in the ass when allocating university roles. I want that person to do EVERYTHING ‘cos they always deliver.
ppaattrriicckk
... what tf?
On top of studying engineering at uni, his "side-gig" is being creative, empathetic, and fantastic at communication - and your prime recommendation is to "hire" him to be a specialist hidden away in the back office? Which interwebz forum are you on?
EDIT: My last question is clearly an echo-chamber statement. But that doesn't subtract from the fact that, yeah, should he found a business, yes, he'll deal with certain "BS". That is the weight we'll all carry. But he's quite likely capable of moving civilization forwards, so... :shrug:
wraptile
Yes but also the robotics industry notoriously has an extremely low shipping rate. So choose your bog I guess?
otikik
Eugh. No. Let him create stuff and let someone else take care of the taxes and payroll and the sales and all that other stuff.
andrewstuart
He might be perfectly happy doing projects and YouTube.
dvt
Likely makes more money, too!
geerlingguy
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).
busymom0
His current Patreon has 57 paid members. Unless he has another revenue stream, I think he'd need more paid members.
smohare
[dead]
dev0p
Very impressive. Commenting to be able to find this later because I need to keep tabs on this guy. The CD launcher is incredibly cool.
lhmiles
Nobody hire him!
throwaway2037
Another cool project from this person's blog: "Wrist Mounted CD Launcher" -> https://www.aaedmusa.com/projects/wrist-mounted-cd-launcher
It definitely gives off Elysium (film) vibes.
tgtweak
I think he'll have success with youtube/vlogging more than getting into the corporate world honestly - especially with some healthy sponsorships and great projects like this.
einrealist
What is the power consumption of these robots? I often wonder how limited and viable autonomous robots really are. When I look at Tesla's Optimus or Boston Dynamics' spectacular robots, how quickly do they need to be recharged?
hinkley
My understanding is that those motors he uses are pretty special. And I would expect “efficient” to be part of that special. You’re optimizing for torque and accuracy per unit of mass and energy in this sort of space. I know he talked about them in earlier videos but I no longer recall the details.
einrealist
Aside from the onboard computing required to power the AI model controlling the robot, which also consumes energy, it is important to be as efficient as possible. However, if an Optimus is intended to replace human labour, such as lifting objects and wander around with it, the energy efficiency of the platform becomes negligible.
The platform in the video and the robot dogs from Boston Dynamics are ideal for tasks where they are only limited by their own weight and the amount of computing power required to navigate, such as exploration.
I suppose that's why we mostly see autonomous delivery robots on wheels.
Or maybe I am being too pessimistic about other platforms...
mnurzia
Wow! I actually met Aead last week while he was printing parts for this project (we both work at the same place). Surreal to see it at the top of HN.
pillars
Some resources related capstan drive: https://www.osti.gov/servlets/purl/1340266 https://fab.cba.mit.edu/classes/865.21/topics/mechanical_des...
syarb
This project is so cool! Congrats Aaed.
Breaking Taps on YouTube did a really awesome video on a somewhat similar mechanism (I'm no mechanical engineer haha, it was new to me!), rolling contact joints. I love the idea of using string/ropes. Worth checking out as well if this kind of stuff interests you! https://www.youtube.com/watch?v=TQiLLcumqDw
ErigmolCt
This is an absolute masterclass in DIY robotics. With a proper battery and a tougher foot material, this thing could really stomp.
amelius
Speaking about battery, how much current does it draw while at rest?
ezekiel68
I had never seen a rope use a robot dog before so I clicked immediately. It wasn't what I expected from the headline, but very cool nonetheless.
https://www.youtube.com/watch?v=8s9TjRz01fo