Cool stuff. I work a lot with flexures, didn't expect you to make a video on a compliant mechanism. These kinds of joints are indeed quite common in low friction robotics and mechanisms (such as tele-operation with haptic feedback). Your joint has very low sideways support stiffness, as the compliant elements you used are essentially wire flexures (at least as long as you keep the wire in tension). They are compliant in the bending mode about the knee axis of rotation (which you obviously want), but also a similar bending mode in the rotation axis perpendicular to the knee rotation axis and perpendicular to the length of the constraint. Pure rotations in your design are somewhat compensated for due to the spacing of the wires, but pure translations sideways I expect the joint to have nearly zero support stiffness as well. If you want to improve this, use blade flexures of some kind. You can perhaps just use thin metal sheets to fabricate these out of, I believe they are common in hobby stores for scale models. Considering the scale of the joint, the metal sheet you need to use is likely so thin you could cut it with a razor blade. Alternatively you could add a supporting flexure in parallel with the joint you already have (for example a folded leaf), but to do that properly is likely too hard without experience in flexural design. If you want, I can give you a book recommendation that would significantly help you with such joint design (and mechanical constraint design in general).

Finally robots can also have bad knees.

These are also considerably lighter than metal ball bearings. The main problem with these is strength. Biology has incredible designs for ligaments, bones, etc that are very difficult to match with traditional materials. Fun stuff!

I've seen rolling contact joints used for telescope pointing and some 3d-printed flexures, but never considered non-circular profiles. Can't wait to see the teeny-tiny birdbot in action!

Suddenly dislocating joints make a lot more sense seeing this. I can see this rolling geometry allowing for some cool variable strength grippers

I love how in picking up the rolling-contact leg it instantly is recognizable as something more biological and light, as opposed to the bigger clunkier mechanical bearing-based design These rolling contact joints are something I became interested in recently while trying to find a compliant but weight-bearing hinge, and came across a paper from the 2000s where they used it to make satellite solar panel deployment mechanisms

I first learned of this joint as a kid, with the Rubik's Magic puzzle. That thing fascinated me, not for the puzzle, but for the compound folding joints it used.

I've been rolling some joints myself and these are really cool!

Something to think about if you are not already would be to use nylon for the joints, nylon is self lubricating so it should reduce friction. It may not have a huge impact as friction is already low but it may be worthwhile to test.

That rolling contact point joint version looks eerily like a real leg. I was listening to what you were saying, but my brain immediately went "oh, thats a bird leg"

10:08 That's how my last digit of my ring finger dangles if I stretch my other fingers and contract the ring finger entirely. Try it. Probably works because it's the same type of mechanism lol. 9:27 And I felt that in my knee.

I am impressed that not only have you recapitulated the human knee joint, but also the cruciate ligaments which support it.

Did we just see the start of Mecha-Dabchick ?

I too am fascinated by rolling joints 🔥

I usually do a makeshift rolling contact joint to explain why training the opposite of a muscle is just as important. Also helps with teaching correct deadlift form and anterior pelvic tilt.

2:14 That undesired movement is called "Side Fumbling", and what you have created there are some rudimentary marzlevanes.

I started my version of this back in 05. Here's what I learned. You can make them cams to increase torque advantage to position ratio. The "ligament" cables tent to abrate on each other and the groves. I was able to mitigate this some by Drafting the groves by 5°. That's as far as I got. Good luck.

Thats pretty cool, thank you for sharing! Point about the bearings: Ball bearings are generally meant for high speed, low dynamic load, rotating applications. For small, low speed and impact loads such as those joints, I think you'd be better off using bushes/sleeve bearings instead. That being said, rolling contact joints are awesome!

I've seen those with stainless steel bands, they provide a bit of stability/stiffness to the joint as well. Nice design :)

It's like these glasses cases! With the three stripes, if you know what I'm talking about. Edit: I think they're called "magic cases". They were all the rage back in the late 00's

We all know you’re secretly making a robot for barnaby Dixon.

I used on a previous project, related to hands and fingers, neodymium magnet and steel balls to form a joint. The Magnet was sort of inverse cone shaped to give a pan for the ball to sit in. Added some 'guards' on the side as your joint has to prevent the lateral displacement. Worked really well, rolled like nothing, but was compliant enough for a joint to dislocate when stressed to far.

Any references on how to design the curves in the joints?

never heard of rolling contact joints before, but it makes total sense. you never dissapoint with your videos, thanks for all the work you put in to share knowledge with us all

You take on the coolest projects, and actually mostly succeed, love it

So hyped! I said yes when you asked whether people would be interested in a standalone video on these types of joints. Glad to see you decided to make one 😊

Im so glad you uploaded, I desperately needed something epic to watch

So excited for this video after seeing your community post!

Im in a hospital bed looking at getting 2 new knees. You don't know how topical this is!

Very hyped to see you take on this project! A potential source of inspiration to look for might be IRIM Koreatech's LIMS-Ambidex system- they hve a very effective implementation of a rolling contact joint for the elbows of their bot. Their pulley system is one of a kind.

Thank you very much for sharing this. I found the video very interesting, and appreciate that you put the time and effort into printing a scaled-up model to show us how it works and how to thread it.

THANK YOU! I was one of the people who commented on the post because it might help my research with finger prosthetics! Thank you so much!

I have tried to do that basically all my life, so I'm very hyped to see your full version of this tiny robot with motors etc

i love how diverse all your projects are! And i always learn something new. great video as usual

It’s a great joint solution for sure, very effective. But not like animal joints, the bones of which do not roll against each other but have a cartilage pad between that allows the bones to slide against each other, which prevents bone wear. Would be interesting to see a design worked up using nylon or graphite cartilage to slide two ‘bones’ against each other

Ah, compliant rolling contact joints. Nicholas J. Seward designed an elbow driven delta 3d printer based on the concept, though it was only a concept prototype (the Reprap Gus Simpson). He used herringbone gears to keep the parts aligned through the rolling motion,. maybe it would scale sufficiently well down with plain gears?

I've had a glasses case that used the same principle. Beyond the flexure joint itself you just had it operate like hinges, but you could flip it all the way around to change the color! The bands holding it together has different colors on the two surfaces. It was a pretty cool mechanism and I liked fidgeting with it.

Never seen this mechanism before, I can see a huge range of applications for this, especially as the fastennings and 'ligaments' can be designed to attach to the housing. Very nice, wish my mechano when I was a kid had these joints !

Thank you, I'm definitely going to integrate this joint into one of my future projects :) so cool!

I had JUST gone on a Breaking Taps binge this weekend because I realized I missed this kind of content. Just went to the channel, sorted by oldest, and clicked play. It was great, I highly recommend it especially for people who might be new to the channel! The style is different but the quality is the same and the themes are still interesting and useful

Fascinating project, and joint mechanism. Look forward to seeing more videos as you work to build up the mechanism into a working robotic limb. Neat idea to make a scaled up version for demo, it really helped show details.

Neat! This is the same joint that was commonly used on early aircraft to attach control surfaces and is still used on models today.

Extremely cool and innovative! I love small complex parts just like this, especially ones that solve a problem cleverly! Good Stuff!!!

I am not any sort of actuall mechanical engineer, but as an artist who loves realism and sci fi, i absolutely adore seeing different variations of mechanical joint systems, and am definitely going to draw something inspired by this design

This solves a 3d printing problem I had for a long time, thanks!

This is so amazing, ive had this exact kind of robot in mind for a long time, using ligaments and natural bone structure, mimicking nature, im going to have to copy the motor attachment method because I haven't figured out how to power the ligaments but this is like the coolest thing ever, I literally have a 5+ year old playlist on youtube for "tiny robots"

Amazing video man. Looking forward to seeing the finished project.

This is really great! Awesome work so far, I was thinking of designing something far different than your avian concepts, I'm aiming more rudimentary/simple in nature and would love for you to keep posting this kind of content. I truly appreciate what you have covered so far. I'm not big on STEM, never did good in school, I just love to tinker.

Very nice to see a video about this. That 'Open Hand' thing had a video come out a month or two ago and I was surprised to see ball bearings instead of this.

0:58 i get a ton of micro bearings from old odometers. Whenever i go shopping for replacement parts i made it a purpose to get at least 10 of those, because inside there are sub mm shaft ball bearings that are pretty high quality. Not only are they bearings in the regular sense, but at least one of them is also a side load one (usually the one that's on the main shaft from where the spedo cable would pop in). But we're talking pre-90's odometers. Most modern ones (if they even have mechanical ones) have plastics inside, teflon revolution.

it WAS interesting indeed. Really thank you for spreading awareness, it's so cooool and inspiring

this is so cool! thanks for making such a clear and simple demo :D

This had nothing to do with what I was trying to find on YT, but I was fascinated by it and had to watch it anyway! That is so cool man!!!

Cool neat to see other versions and innovations of this. I worked on and off last year on a simpler banded version of complient rolling joints. Tricky but rewarding . Interesting you use of fishing line

When I first saw this on Twitter, I was like- This can be used in micro scale Models! Use this as a Steering Hinge in a Hotwheels car or a Model Kit!

Really nice! I have used this kind of braided fishing line to change the angle of rotation, when gears were too small to work reliabily. I hope to see this project advancing, it's very cool!

Impressive. Can’t fathom how much time and effort it took to think it up and design it. Way to go!

First time seing this joint! Thanks from France for spreading some awarness!

Very satisfying joint movement, and it does look cool!

Dude from the intro setup alone i can tell you must be a legend within your maker community. Awesomw video!

I did that once when I was trying to achieve basically the same thing. Was amazed at how well it worked actually. Very well suited to 3d printing and I can't imagine a more cost effective solution. Actually amazing low friction and durable too. I didn't know it was a thing though. Mine were more bone shaped with grooves like small gear teeth to stop the 2 ends sliding/slipping. With the elasticity of the fishing line it makes not only a very strong joint, but just like bones it would dislocate if you applied too much force in the wrong direction, which meant you could just push it back together for an easy fix (so I didn't bother with the side bits or vertical grooves, as just 2 gear like ends and enough tension in the line would make it hard enough to dislocate and virtually indestructible). Had almost forgotten about it until I saw this. Leg looks awesome, I'm looking forward to seeing how it turns out!

I wondered why you didn’t do the figure-8 in all 4 slots, then realized that keeping them separate is necessary to prevent the cable from wearing against itself. Very nice joint and explainer!

I've seen that in some toys but they used a band instead of a string. They were fun to fiddle with

I mean, to be perfectly honest with you ive got bearings with a 1mm id and 3mm od, and ive seen smaller ones, but these will be SUPER useful for a few ideas i had a while back so thank you for teaching it anyway ^_^

Great video. Now I will wait patiently and later enjoy your video about that Dyneema tendons that do not stretch too much, actually stretch enough to make control really, really hard. Bu man, your robot looks so cool in CAD, cannot wait to see it materialize.

Very nice work - congratulations. Those components out of aluminium with a very thin stainless steel cable for no stretch could become a joint that is suitable for a bipedal or quadrupedal robot. The kinematic and inverse kinematic calculations would be much more accurate with a very stable joint. Also, actuating the joint with an actuator in the "body" and driving "lines" that run down to the joint keeps the weight and therefor the inertia way down - whats not to like? Try to find a build buddy at the show that lives near to you that has a small 5 axis mill capable of cutting aluminium properly and I can see this bird strutting and jumping around.

I didn't know that I needed this in my life - but now I do.

Fantastic little demonstration of the rolling joint!

Very interesting,I look forward to seeing how you control the actuation👍🏻

Very cool. I make these for boat stuff. They are how they make rudders on wharram designs. They work great, very low friction. I didnt know what to call them but now i do! For me they work a lot better with a bit of glue in the holes, to stop the side to side motion.

First time seeing your channel ! Love it !

Would love more on this project!

Its a very cool mechanism that suits this project really well but since its a low load, slow moving joint, woulnt a bronze/oilite or teflon bushing be a suitable alternative to miniature ball bearings?

This joint is very cool. Thanks for sharing!

Cool idea and build. Watches and other small devices do use small bearings, but the way they're are used is different.

This is fascinating, thanks for the explanation!

Wow cool project! Can't wait to see more about it.

Fascinating! Thanks for uploading.

I've designed a rolling joint like that couple years ago. Adding some meshing teeths like gears to prevent slipping improves stiffness and accuracy of the movements very well. Not sure you can add with the sizes you are working with tho

This is brilliant, love these joints, reminds me of the wood block and ribbons puzzles. Or sewing model airplane control surfaces in figure 8 pattern.

Really cool project! You're right that this type of joints is rarely spotted in hobby projects

These are also used, I think, in old hard disk mechanisms for the stepper motor to move the heads. It was a little metal strip that wrapped around the output shaft.

This could revolutionize prosthesis engineering! I can only imagine the many applications

Really amazing design.

Wonderful joint! Thanks for sharing!

nice video, if you want very small pivot assemblies there are also some very, veeery small bronze bushings that due to their size and low friction have extremely small resistant torque, they're not very interesting to show but it gets the job done

Awesome! Definitely going to play with this hinge type.

Very interesting. Looking forward to the follow up. This is what makes youtube great.

Cool idea, thanks for sharing! Much inspiring! 👍

Very interesting rolliong mechanism design and knotting technique.

very impressive, thanks for spreading the knowledge

Another interesting thing to consider is how hopping insects joints work, they have some very simple and clever mechanical ways to get the stored potential energy power for a good hop.

Really neat stuff! If you want to prevent rotation, you could impose a gear teeth row on the outer 'bearing surfaces' so that the movement is not only constrained by the (flexible) rope.

This is amazing work! Looking forward to your builds :D May I suggest making small indentations on the sides of the lower part of the hinge so that the cable can be kept more secure and flush against the plane of the joint?

I highly recommend getting into knots, a solid knot makes a huge difference.

This is a lovely technique. The smallest commercially available ball bearings I'm aware of are those for model trains. Past that it gets into jewells for clockwork.

This is just like the old cable rocking chair, not just in robotics. Cool!

Thats so sick, thanks for sharing!

Awesome. This gives me many ideas for new designs...

I dont know why youtube decided to show me this but i'm glad it did. this is so cool! i learned something new today! thanks.