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).
Awesome, thanks for the info! Pinning so more folks can see this. And definitely interested in that book recommendation! Mea culpa, I opted for cable/line because I didn't want to figure out how to mechanically secure thin spring steel ribbons. 😅 But after building these I can definitely see what you mean regarding unwanted motion in the perpendicular direction. Will do some reading and see how to incorporate that in a small package (probably just some M1.5 screws holding them down or something)
@@BreakingTaps The book is called "Exact Constraint: Machine Design Using Kinematic Principles" by Douglas Blanding. Sounds like a tough pill, but especially the first few chapters (the most important ones) are very well written and totally readable without a mathematical background. It specifically addresses how to constrain bodies together, to get certain desired motions. Warning: Once you have learned the knowledge in this book, you will start to see poorly designed mechanisms everywhere you go ;) The book might be hard to find, but I heard that some pirates might have some copies lying around as well, although I'd never advocate for such purposes ;) As further reading if you want to dive a bit deeper into flexure design specifically (which is very closely related to exact constraint design, and builds upon those principles), Johnathan Hopkins has a series here on youtube titled 'Compliant Mechanism Lecture Series'. A warning for some people, there's some undergraduate math involved for a few lectures, but you can quite safely skip those without missing too much. A bit more background for those interested: There's only a couple of research groups in the world who are renowned for flexure designs, and his 'flexible research group' at UCLA is one of them. He is most well known for coming up with the 'FACT' framework, which is a convenient way to envision/design compliant mechanisms using a visual system (the FACT chart).
My new headcanon for Terminator is the T-900 model got put on injury reserve due to a torn ACL and couldn't go back to 1987 to kill John Connor as a toddler.
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'd love to see a video that is a marriage of mat sci + biology, to bridge the gap between tissue level architecture of bone, tendon, ligament, and muscle and the structure of the musculoskeletal system.
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!
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
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"
@@truthhunterhawk3932 define "is not designed"? we have biologic records dating back millions of years for how animal joints first came to be and slowly transformed into what we see today over many different iterations. rolling joints didnt just pop into exitance 6,000 years ago.
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.
Doubt that nylon would do anything. Those are rolling joints, NOT sliding joints. since there's no surface to surface sliding, having a low friction material is irrelevant.
@@ytrew9717 Yes, but the friction is intended to PREVENT sliding. The idea to use nylon because of "lower friction" is akin to saying that we should use nylon for car tires because of "lower friction" and it would be even better if we slathered those nylon tires with grease to lower the friction even more.
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.
@@Cssfiend Ah, right, the Jacob's Ladder! I think I was a bit too young to be fascinated/confused by that when I first experienced it, plus the Magic implemented the joint in two dimenstions, not just one. But yes, certainly an earlier example in toy form.
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.
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 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.
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.
Have you seen how small they can get the retro encabulators now? I know it's more a vanity project to even have one now since they just invert the gram-meters duo-planially now, but it's nice to see.
Personally I prefer lotusoid delta-type spurving bearings for this type of application, but it is hard to find an ambivascient lunar waneshaft this small. Always out of stock on McMaster Carr.
@@jazzdirtDyneema has a problem with losing strength due to heat/UV exposure, the friction from knots will significantly weaken dyneema more than other materials which is a pain since it's hard to attach stuff to it otherwise. I think that's where spliced and woven dyneema comes in though
@@jazzdirt not cable and not steel, but thin shims (< .1mm) and stainless (316). And since the shims are constrained (wedged between the surfaces) they have a lot of sideways strength, so it improved the sideways stability. Not saying "this is the way", just mentioning another design I've seen.
@@brynyard Yeah, when I studied Material science engineering that's what they were going for... Eventually it turns out to be more useful in uses where you would otherwise use Kevlar... But the thing they set out to do was to make a strand that was stronger then steel... To make lighter cables.. but it's not suited for that as @cheyannei5983 also pointed out.... I never finished the Material science engineering study... I just know the faculty was working on Dyneema when I was studying there... Studying engineering was trying to do the sensible thing.. I always knew I wanted to make music and I always have.. so that's where I eventually ended up...
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.
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.
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
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.
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 😊
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
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
Plain bearings are always an option. small Bronze bushing bearings. Consider that heavy equipment like excavators, Bulldozers, Use plain bearings for maximum strength.
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
As others have mentioned, you have ligaments, self-correction, etc involved in biology. It will be difficult to get this 'tight'. Ball bearings are 'loose' when small, and overkill for a small, slow joint. Sleeve and pin type bearings especially with bronze may get you a much better, more precise joint. When you go small scale like this, you quickly want to start studying watches, almost every consideration you can possibly come up with has already been done in that field. Or you could make the leg about 4x longer, probably still doable and that would get the same error and play down to a more reasonable percentage of the over overall motion. Not knocking it if you want to try it at all, but off hand it's just very hard to reduce the inherent play in something like this, vs instant high precision with a sleeve bearing type system.
was looking for this comment, a simple bushing is the correct thing for this application, cheaper, more precise and more durable than any of the other options
it reminds how nanoscopic insect have lashes looking wings because at this scale air is to thick to be navigated with "paddles" It's basically the same here, you adapted your technology to the scale, with something not expected in the robotic field, that's awesome, you can be absolutly proud of yourself, keep up the good work !
Holy grail of mechanical joints! As many (if not all) biological beings with joints, we have proprioception and there's a constant feedback of tentioning and loosing stabilizators (in our case muscles) without being aware. This is looking extremely similar to knee joint (with missing couple stabilizing tendons) but with the right tention sensing feedback and a good enough processor, we might see this everywhere as it looks cheap and clever. World loves cheap and clever! Thanks for sharing!
You could also make it so that it reacts to changes instantly , one good example is "Birdbot" , it uses cables as tendons and they react to changes instantly , also is way less bulkier than other designs and is scalable
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!
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?
Another advantage I can think of is that the r-c joints are pretty much immune to failing from (in plane?) compressive impacts. The force (in the case of a bird) would travel down the leg and through the joint. For a ball bearing this could ruin the surface finish in the inner races and potentially jam it, this is because the force is concentrated basically at several points (spheres contact a surface at a point). R-c joints contact along lines, therefore forces are spread over a lot more surface area. Bearings have the advantage that forces applied in planes are treated equally in every direction, whereas a r-c joint is going to perform much worse in tension than in compression.
Judging by 2:43 it's as simple (cough) as moving the axles closer or further apart. The string will want to keep the hinge in the least tensioned position. Moving the leg will either abrubtly tension the cord, creating an "end stop' or when turned the other way will gradually increase tension. That would mean that the neutral "strength" can also be adjusted by varying the amount of rope ever so slightly.
I plan on making full size self powered anatomically functional digi legs once I have the money to invest in materials and this video is immediately inspiring some new things for my eventual prototyping
The makers of the Rubik's cube made a couple puzzles they called the Rubik's magic and master magic(I think). They used a rolling compliant mechanism like these in a way. The regular one consisted of 8 square tiles in a 4x2 arrangement. The goal was to fold and flip the puzzle in various ways to change their shape into more of a v shape while rearranging the tiles so the photo on the back turned into three linked rings. They usually got turned into a tangled mess of fishing wire and tossed into the garbage. I have a few of them!
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
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?
Definitely an option! I have a design for the smallest oil bushings McMaster sells somewhere in my CAD folder and it probably would work well, although I spent more of the "design volume" then dealing with limiting range of motion. But very viable, and I probably should have mentioned bushings!
Yeah, it was a revolution for me when I realized that using ball bearings for low-speed joints is stupid. Teflon is a wonder material. The overall structure ends up so much smaller and lighter weight for the same strength, and you can buy meters of tube for a few bucks and 3D print jigs to hold it and guide a razor blade to slice off precise lengths effortlessly. For larger bearings I use teflon sheet, and cut flat circles for the thrust surface, and strips to wrap around into radial bearings. Strips are easy to cut, but flat circles are pretty fiddly. But it is nice that you only need to buy one sheet to make any diameter bearings you want.
@@BreakingTapsanother really fancy option is iglidur z; I’m working on my uni’s student formula and we’ve been using them for a lot of brushings because theyre basically self lubricating teflon bushings with better mechanical properties (around 0.05 to 0.14 u w/ steel iirc) Though we had a bit of issue with them being too low friction and slippage was happening in other places the company were super helpful though and they made a lot of different sizes and could be another lot to check out you end up looking for polymer bushings
Also worth noting is that McMaster often isn't a great supplier for tiny things on that scale. A better option for tiny bushings would be Northwest Short Line, who do parts for model trains. Along those lines, the "needlepoint bearings" that are often used for model traincar wheels can also work well down to quite small sizes. Those are a simple mechanism where the ends of the axles are pointed to sharp points, and they snap into small conical recesses that have a bit larger angle than the axle points. Typically the axles are steel, and the sockets are a delrin-like plastic, though I've also seen this in brass.
Some of the slots are not completely populated with a cord and can be tapered to aid in assembly- once you start threading, each path will be obvious. Likewise, the transverse routes from side to side can have grooves the depth of the cord to guide the cord, and where the cord is wrapped around the outside of the bones grooves can recess the cord to protect it from abrasion. If each cord is independent, a single damaged cord will not destroy the integrity of the joint. A smaller hole for a stopknot, or a hook or peg for the end to be attached to can help. A compact means for tensioning the cords can tighten up the joint, too. This can be as simple as a screw and a washer- loosen the screw, wrap the cord around, tighten the screw, just like the rudder adjust on my Hobie kayak.
I also think a flat profile ribbon would be the way to go as the connector... Adds even more lateral stability for "free" and won't chew into the underlying surface as quickly.
Dyneema is also used in climbing ropes. If you haven't found them yet, the HowNot2 channel has all kinds of neat break tests on all kinds of climbing gear, and a lot depends on the ropes used. I would think the slipperiness of the dyneema would end up causing some issues, and it seems to be hard to get tension on it in your flexures. They will most likely fail over time as the dyneema cord stretches and deforms over time, it isn't very stable and will stretch over sustained load. Cool project!
The weight savings for a bird leg seen like a substantial benefit. I would imagine you want the foot to be the heaviest part for stability. Eliminating metal bearings mid leg will allow it to pop and spring nicely
I wonder if small bird legs are semi-sprung flexural components (the lengths of the legs, not just non-linear joints) That could be a way to generate a lot of hop.
I turned myself into a pickle, Morty! Boom! Big reveal: I'm a pickle. What do you think about that? I turned myself into a pickle! W-what are you just staring at me for, bro? I turned myself into a pickle, Morty! Morty: And? Pickle Rick: "And"? What more do you want tacked on to this? I turned myself into a pickle, and 9/11 was an inside job? Morty: Was it? Pickle Rick: Who cares, Morty? Global acts of terrorism happen every day. Uh, here's something that's never happened before: I'm a pickle. I'M PICKLE RIIIICK!!
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 !
Actually, you need the highest amount of friction for the rolling joint to work properly. Otherwise, the whole assembly will slip and the contact surfaces will stay still. Thank you for the shearing and you did a great design, to be honest.
I am a trained machinist and in our classes the teacher showed us a ball bearing for a 0.5mm shaft but sadly he couldnt tell us what sucha bearing would cost as it was a gift from another trainee that was at that school. So regarding just the bearing size it would be possible to get small enough bearings but as you pointed out theres other reasons than just the size to not use ball bearings.
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!
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'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.
This is really clever solution! Though when it comes to more traditional bearing types, it might be worth considering ruby watch bearings. I assume they’re likely cost prohibitive, but in terms of using more traditional construction techniques for the joints they might be worth looking into
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.
I feel like you could make a soft close cabinet hinge with this method. I really want to see that done now actually. Good soft close hinges at a fraction of the price would be great haha
I'll be honest, I read the first and last words of the thumbnail and thought this was a much different video about robots rolling joints. Quite intriguing nonetheless!
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"
Our knee is a.Rolling and Sliding contact joint. But so complicated, with ligaments and meniscus providing tension at specific "points" during motion. Make one with plastic.
I just realized that these things can be incredibly flat and still work as designed. This could make for an excellent human friendly wearable mechanism, since you can also tune its breaking point by choosing the right cable.
A Jacob’s ladder toy works similarly. It had 5 blocks with woven ribbons between each block and as you folded one block into a lower block it would Cascade to the bottom block. Similarly to how the rolling joints are woven together.
oh i didn't realize you were the one who made that homemade CCD. That was awesome! Great channel 🤙 You must have a fascinating career or just an awesome set of hobbies!
ooh this also makes me think of those old jacob's ladder toys with the rounded wooden blocks and ribbons-- perhaps if steel ribbon is difficult, hdpe ribbon or tape would provide benefits too. anyway super cool video i think it really helped my intuition for biological joints!
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 ^_^
Your work is a breath of fresh air in the cloud of farts youtube became... I am surprised you did not put string in both directions. I mean, you sew it interchanging under-over, but when we did our plane model control surface hinges (way before RC became a hobby for mortals) we put under-and-over in each "hole" or groove. You get way more rigidity all around that way. Also, just more than one strand and a ton of tension is beneficial. Sorry if this is obvious and you did that just for visual simplicity...
Just didn't think about it to be honest! The small model is pretty space-constrained so it was a struggle to get one pass sewn, although I could tweak the design to allow for a bit more space for the reverse. It's a good idea!
I love how the algo works, i was just thinking last night if I could use a rolling or sliding joint for the 3 z-axis that could be entirely 3d printed. The goal is to allow the bed to tilt but not slide and lifted out without removing hw
You're reproducing a knee joint/articulation very nicely here :D For the lateral movement, you can also just tense a cable on each side, it should help to stabilize... like in your knees, you have 2 tendons on the sides :) good luck to do it in such a small scale :D Nice project
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
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).
how abt u just give me the book
Awesome, thanks for the info! Pinning so more folks can see this. And definitely interested in that book recommendation!
Mea culpa, I opted for cable/line because I didn't want to figure out how to mechanically secure thin spring steel ribbons. 😅 But after building these I can definitely see what you mean regarding unwanted motion in the perpendicular direction. Will do some reading and see how to incorporate that in a small package (probably just some M1.5 screws holding them down or something)
@@BreakingTaps The book is called "Exact Constraint: Machine Design Using Kinematic Principles" by Douglas Blanding. Sounds like a tough pill, but especially the first few chapters (the most important ones) are very well written and totally readable without a mathematical background. It specifically addresses how to constrain bodies together, to get certain desired motions. Warning: Once you have learned the knowledge in this book, you will start to see poorly designed mechanisms everywhere you go ;)
The book might be hard to find, but I heard that some pirates might have some copies lying around as well, although I'd never advocate for such purposes ;)
As further reading if you want to dive a bit deeper into flexure design specifically (which is very closely related to exact constraint design, and builds upon those principles), Johnathan Hopkins has a series here on youtube titled 'Compliant Mechanism Lecture Series'. A warning for some people, there's some undergraduate math involved for a few lectures, but you can quite safely skip those without missing too much.
A bit more background for those interested: There's only a couple of research groups in the world who are renowned for flexure designs, and his 'flexible research group' at UCLA is one of them. He is most well known for coming up with the 'FACT' framework, which is a convenient way to envision/design compliant mechanisms using a visual system (the FACT chart).
@@tHaH4x0r thank you for sharing!
@@tHaH4x0r Your comments here are exactly the sort of insights I've been itching for thanks a ton. Can't wait to dive into that book.
Finally robots can also have bad knees.
Hahahaha nice 👏🏻. I've been waiting for when robots can finally replace humans in the personal injury category as well
The hate is real. We already put them through hell and now we're going to make them feel pain for it?! Man that's evil.
My new headcanon for Terminator is the T-900 model got put on injury reserve due to a torn ACL and couldn't go back to 1987 to kill John Connor as a toddler.
Almost as bad as mine.
They're gonna be so mad
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'd love to see a video that is a marriage of mat sci + biology, to bridge the gap between tissue level architecture of bone, tendon, ligament, and muscle and the structure of the musculoskeletal system.
@@ZeroG_Bandit carbon fibre wrapping might be the key?
RF85 for the cams
@@BongoWongoOGlike kernmantle ropes? Sheath braid and core fibers?
@@Dan-gs3kg pretty much, max strength and low weight
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!
I too am an expert in the art of rolling joints
You can see an example of such joints in bow cams
Suddenly dislocating joints make a lot more sense seeing this.
I can see this rolling geometry allowing for some cool variable strength grippers
Now only for some form of synthetic synovial fluid...
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
Can you share the name of that paper?
@@5eurosenelsuelo “Tape-spring rolling hinges” watt and pellegrino 2002
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"
I am impressed that not only have you recapitulated the human knee joint, but also the cruciate ligaments which support it.
I still don't see why people think that the body is not designed. Very good joint design
Recapitulated..? I'm sure you mean recreated haha
@@aone9050 No, he means recapitulated -- to repeat in concise form.
@@truthhunterhawk3932 define "is not designed"? we have biologic records dating back millions of years for how animal joints first came to be and slowly transformed into what we see today over many different iterations. rolling joints didnt just pop into exitance 6,000 years ago.
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.
Doubt that nylon would do anything. Those are rolling joints, NOT sliding joints. since there's no surface to surface sliding, having a low friction material is irrelevant.
@@johncochran8497 irrelevant, or even make things worse by introducing unwanted sliding.
@@johncochran8497 but aren't rolling joint contacting each other and thus creating friction on surface to surface rolling?
@@ytrew9717 Yes, but the friction is intended to PREVENT sliding. The idea to use nylon because of "lower friction" is akin to saying that we should use nylon for car tires because of "lower friction" and it would be even better if we slathered those nylon tires with grease to lower the friction even more.
@@johncochran8497 thank you, but why would it bad if it slides instead of rolling (stupid question but ...)?
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 also thought of a toy immediately, but a jacob's ladder instead
@@Cssfiend Ah, right, the Jacob's Ladder! I think I was a bit too young to be fascinated/confused by that when I first experienced it, plus the Magic implemented the joint in two dimenstions, not just one. But yes, certainly an earlier example in toy form.
@@Cssfiend same here i was looking for a comment about it. i had no idea it was so biological!
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.
wow that ring finger trick looks so bizarre
...I regret learning what this comment taught me.
Interesting! Works with other fingers too, but maybe my ring finger is the floppiest.
That's awfully cursed. Thank you
I too am fascinated by rolling joints 🔥
They let u play wit matches?
And are good for making contact.
I've been rolling some joints myself and these are really cool!
I see what you did there ;)
amen
Did we just see the start of Mecha-Dabchick ?
my first thought at seeing the thumbnail too
Had the same idea haha
I would actually love to hear Barnaby's opinion on the subject from a puppeteer standpoint
Can you imagine an animatronic Dabchick?
fuck yeah
I was literally thinking on how this could be used for puppets! Lol
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 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.
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.
2:14 That undesired movement is called "Side Fumbling", and what you have created there are some rudimentary marzlevanes.
Have you seen how small they can get the retro encabulators now? I know it's more a vanity project to even have one now since they just invert the gram-meters duo-planially now, but it's nice to see.
@@shanevonknuth it’s like engineers making fun of doctors 😂
Personally I prefer lotusoid delta-type spurving bearings for this type of application, but it is hard to find an ambivascient lunar waneshaft this small. Always out of stock on McMaster Carr.
Goddamnit you actually got me with this lol
I've seen those with stainless steel bands, they provide a bit of stability/stiffness to the joint as well.
Nice design :)
Dyneema was engineered to replace steel cables.. It's lighter and non corrosive and way stronger..
@@jazzdirtDyneema has a problem with losing strength due to heat/UV exposure, the friction from knots will significantly weaken dyneema more than other materials which is a pain since it's hard to attach stuff to it otherwise. I think that's where spliced and woven dyneema comes in though
@@jazzdirt not cable and not steel, but thin shims (< .1mm) and stainless (316). And since the shims are constrained (wedged between the surfaces) they have a lot of sideways strength, so it improved the sideways stability.
Not saying "this is the way", just mentioning another design I've seen.
@@brynyard Yeah, when I studied Material science engineering that's what they were going for... Eventually it turns out to be more useful in uses where you would otherwise use Kevlar... But the thing they set out to do was to make a strand that was stronger then steel... To make lighter cables.. but it's not suited for that as @cheyannei5983 also pointed out.... I never finished the Material science engineering study... I just know the faculty was working on Dyneema when I was studying there...
Studying engineering was trying to do the sensible thing.. I always knew I wanted to make music and I always have.. so that's where I eventually ended up...
We all know you’re secretly making a robot for barnaby Dixon.
This solves a 3d printing problem I had for a long time, thanks!
1:52 I wasn't ready for this
Nah me neither I thought I was having a stroke or something 😆
9:27 thats the sound my knee made when i got hit from the side by a scooter.
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.
Im in a hospital bed looking at getting 2 new knees.
You don't know how topical this is!
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!
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.
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
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.
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 😊
You take on the coolest projects, and actually mostly succeed, love it
Im so glad you uploaded, I desperately needed something epic to watch
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
Was just about to comment that! They also come as calculators, pen cases, manicure sets and probably a lot more.
yesss those and jacob's ladders
And Rubik's Magic, if anyone else here recalls those!
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
Plain bearings are always an option. small Bronze bushing bearings. Consider that heavy equipment like excavators, Bulldozers, Use plain bearings for maximum strength.
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
As others have mentioned, you have ligaments, self-correction, etc involved in biology. It will be difficult to get this 'tight'. Ball bearings are 'loose' when small, and overkill for a small, slow joint. Sleeve and pin type bearings especially with bronze may get you a much better, more precise joint.
When you go small scale like this, you quickly want to start studying watches, almost every consideration you can possibly come up with has already been done in that field.
Or you could make the leg about 4x longer, probably still doable and that would get the same error and play down to a more reasonable percentage of the over overall motion.
Not knocking it if you want to try it at all, but off hand it's just very hard to reduce the inherent play in something like this, vs instant high precision with a sleeve bearing type system.
was looking for this comment, a simple bushing is the correct thing for this application, cheaper, more precise and more durable than any of the other options
Neat! This is the same joint that was commonly used on early aircraft to attach control surfaces and is still used on models today.
I thought I've seen these before in Lego sets from the 90s. 3612 part # from the aqua zone kits
So excited for this video after seeing your community post!
This could revolutionize prosthesis engineering! I can only imagine the many applications
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!
it reminds how nanoscopic insect have lashes looking wings because at this scale air is to thick to be navigated with "paddles"
It's basically the same here, you adapted your technology to the scale, with something not expected in the robotic field, that's awesome, you can be absolutly proud of yourself, keep up the good work !
Holy grail of mechanical joints!
As many (if not all) biological beings with joints, we have proprioception and there's a constant feedback of tentioning and loosing stabilizators (in our case muscles) without being aware.
This is looking extremely similar to knee joint (with missing couple stabilizing tendons) but with the right tention sensing feedback and a good enough processor, we might see this everywhere as it looks cheap and clever. World loves cheap and clever! Thanks for sharing!
You could also make it so that it reacts to changes instantly , one good example is "Birdbot" , it uses cables as tendons and they react to changes instantly , also is way less bulkier than other designs and is scalable
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!
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?
Another advantage I can think of is that the r-c joints are pretty much immune to failing from (in plane?) compressive impacts. The force (in the case of a bird) would travel down the leg and through the joint. For a ball bearing this could ruin the surface finish in the inner races and potentially jam it, this is because the force is concentrated basically at several points (spheres contact a surface at a point). R-c joints contact along lines, therefore forces are spread over a lot more surface area.
Bearings have the advantage that forces applied in planes are treated equally in every direction, whereas a r-c joint is going to perform much worse in tension than in compression.
Any references on how to design the curves in the joints?
Judging by 2:43 it's as simple (cough) as moving the axles closer or further apart. The string will want to keep the hinge in the least tensioned position. Moving the leg will either abrubtly tension the cord, creating an "end stop' or when turned the other way will gradually increase tension.
That would mean that the neutral "strength" can also be adjusted by varying the amount of rope ever so slightly.
I plan on making full size self powered anatomically functional digi legs once I have the money to invest in materials and this video is immediately inspiring some new things for my eventual prototyping
The makers of the Rubik's cube made a couple puzzles they called the Rubik's magic and master magic(I think). They used a rolling compliant mechanism like these in a way. The regular one consisted of 8 square tiles in a 4x2 arrangement. The goal was to fold and flip the puzzle in various ways to change their shape into more of a v shape while rearranging the tiles so the photo on the back turned into three linked rings. They usually got turned into a tangled mess of fishing wire and tossed into the garbage. I have a few of them!
There's a much older "folk toy" called a Jacob's ladder that is basically the precursor to those.
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
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?
Definitely an option! I have a design for the smallest oil bushings McMaster sells somewhere in my CAD folder and it probably would work well, although I spent more of the "design volume" then dealing with limiting range of motion. But very viable, and I probably should have mentioned bushings!
Yeah, it was a revolution for me when I realized that using ball bearings for low-speed joints is stupid. Teflon is a wonder material. The overall structure ends up so much smaller and lighter weight for the same strength, and you can buy meters of tube for a few bucks and 3D print jigs to hold it and guide a razor blade to slice off precise lengths effortlessly.
For larger bearings I use teflon sheet, and cut flat circles for the thrust surface, and strips to wrap around into radial bearings. Strips are easy to cut, but flat circles are pretty fiddly. But it is nice that you only need to buy one sheet to make any diameter bearings you want.
@@BreakingTapsanother really fancy option is iglidur z; I’m working on my uni’s student formula and we’ve been using them for a lot of brushings because theyre basically self lubricating teflon bushings with better mechanical properties (around 0.05 to 0.14 u w/ steel iirc)
Though we had a bit of issue with them being too low friction and slippage was happening in other places
the company were super helpful though and they made a lot of different sizes and could be another lot to check out you end up looking for polymer bushings
Also worth noting is that McMaster often isn't a great supplier for tiny things on that scale. A better option for tiny bushings would be Northwest Short Line, who do parts for model trains.
Along those lines, the "needlepoint bearings" that are often used for model traincar wheels can also work well down to quite small sizes. Those are a simple mechanism where the ends of the axles are pointed to sharp points, and they snap into small conical recesses that have a bit larger angle than the axle points. Typically the axles are steel, and the sockets are a delrin-like plastic, though I've also seen this in brass.
@@BreakingTaps Yeap -- gonna keep asking
What happened to the Space Shuttle / spaceX ceramic heat tiles ?
Some of the slots are not completely populated with a cord and can be tapered to aid in assembly- once you start threading, each path will be obvious. Likewise, the transverse routes from side to side can have grooves the depth of the cord to guide the cord, and where the cord is wrapped around the outside of the bones grooves can recess the cord to protect it from abrasion.
If each cord is independent, a single damaged cord will not destroy the integrity of the joint. A smaller hole for a stopknot, or a hook or peg for the end to be attached to can help. A compact means for tensioning the cords can tighten up the joint, too. This can be as simple as a screw and a washer- loosen the screw, wrap the cord around, tighten the screw, just like the rudder adjust on my Hobie kayak.
I've seen that in some toys but they used a band instead of a string. They were fun to fiddle with
I also think a flat profile ribbon would be the way to go as the connector... Adds even more lateral stability for "free" and won't chew into the underlying surface as quickly.
Dude from the intro setup alone i can tell you must be a legend within your maker community.
Awesomw video!
That 0:32 looks more like the Robo Cop, than a bird lol
Please put down your banana, you have 20 seconds to comply.
Dyneema is also used in climbing ropes. If you haven't found them yet, the HowNot2 channel has all kinds of neat break tests on all kinds of climbing gear, and a lot depends on the ropes used.
I would think the slipperiness of the dyneema would end up causing some issues, and it seems to be hard to get tension on it in your flexures. They will most likely fail over time as the dyneema cord stretches and deforms over time, it isn't very stable and will stretch over sustained load.
Cool project!
But can it roll a joint?
The weight savings for a bird leg seen like a substantial benefit.
I would imagine you want the foot to be the heaviest part for stability. Eliminating metal bearings mid leg will allow it to pop and spring nicely
I wonder if small bird legs are semi-sprung flexural components (the lengths of the legs, not just non-linear joints)
That could be a way to generate a lot of hop.
Pickle Rick vibes
I turned myself into a pickle, Morty! Boom! Big reveal: I'm a pickle. What do you think about that? I turned myself into a pickle! W-what are you just staring at me for, bro? I turned myself into a pickle, Morty!
Morty: And?
Pickle Rick: "And"? What more do you want tacked on to this? I turned myself into a pickle, and 9/11 was an inside job?
Morty: Was it?
Pickle Rick: Who cares, Morty? Global acts of terrorism happen every day. Uh, here's something that's never happened before: I'm a pickle. I'M PICKLE RIIIICK!!
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 !
Only 1 view in 29 seconds? Breaking taps fell off smh
Bro has gained the irrelevant achievement!
thank you
Someone should make a browser addon that hides these comments
Actually, you need the highest amount of friction for the rolling joint to work properly. Otherwise, the whole assembly will slip and the contact surfaces will stay still. Thank you for the shearing and you did a great design, to be honest.
Thank you so much for taking the time to make, edit and publish this video! A very clever design, indeed.
I am a trained machinist and in our classes the teacher showed us a ball bearing for a 0.5mm shaft but sadly he couldnt tell us what sucha bearing would cost as it was a gift from another trainee that was at that school.
So regarding just the bearing size it would be possible to get small enough bearings but as you pointed out theres other reasons than just the size to not use ball bearings.
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!
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'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.
This is really clever solution! Though when it comes to more traditional bearing types, it might be worth considering ruby watch bearings. I assume they’re likely cost prohibitive, but in terms of using more traditional construction techniques for the joints they might be worth looking into
Impressive. Can’t fathom how much time and effort it took to think it up and design it. Way to go!
A useful thing to have highlighted, I think; I'd've never thought to try and replicate a biological joint in this way.
It’s so cool! Its very reflective of bones and muscles which I love
I recommend adding a thin film of Teflon (plumbing tape)between the rolling joint. This is biomimicry and the Teflon would be the cartilage
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.
I feel like you could make a soft close cabinet hinge with this method. I really want to see that done now actually. Good soft close hinges at a fraction of the price would be great haha
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.
Thank you so much for making this video. This is perfect for a project of mine. You rock!
I'll be honest, I read the first and last words of the thumbnail and thought this was a much different video about robots rolling joints. Quite intriguing nonetheless!
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"
I did not know that human joints followed this principle. I assumed they were more of the ball & socket variety. I learned something today.
Cool idea and build. Watches and other small devices do use small bearings, but the way they're are used is different.
Thank you, I'm definitely going to integrate this joint into one of my future projects :) so cool!
Our knee is a.Rolling and Sliding contact joint. But so complicated, with ligaments and meniscus providing tension at specific "points" during motion.
Make one with plastic.
I just realized that these things can be incredibly flat and still work as designed. This could make for an excellent human friendly wearable mechanism, since you can also tune its breaking point by choosing the right cable.
A Jacob’s ladder toy works similarly. It had 5 blocks with woven ribbons between each block and as you folded one block into a lower block it would Cascade to the bottom block. Similarly to how the rolling joints are woven together.
oh i didn't realize you were the one who made that homemade CCD. That was awesome! Great channel 🤙 You must have a fascinating career or just an awesome set of hobbies!
Salto 1-P uses bushings for this very reason - but these joints are SUPER COOL! (also very sensible for a biomimetic robot)
Very tiny, but I love it. 3D printing has been a big help for it.
ooh this also makes me think of those old jacob's ladder toys with the rounded wooden blocks and ribbons-- perhaps if steel ribbon is difficult, hdpe ribbon or tape would provide benefits too. anyway super cool video i think it really helped my intuition for biological joints!
Using metals like stainless with bronze as a bearing surface for both joints is not a bad idea! It would sure add to the life cycle.
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 ^_^
This would be incredibly useful for animatronics. It's both robust and lifelife!
Really cool project! You're right that this type of joints is rarely spotted in hobby projects
Your work is a breath of fresh air in the cloud of farts youtube became...
I am surprised you did not put string in both directions. I mean, you sew it interchanging under-over, but when we did our plane model control surface hinges (way before RC became a hobby for mortals) we put under-and-over in each "hole" or groove. You get way more rigidity all around that way. Also, just more than one strand and a ton of tension is beneficial.
Sorry if this is obvious and you did that just for visual simplicity...
Just didn't think about it to be honest! The small model is pretty space-constrained so it was a struggle to get one pass sewn, although I could tweak the design to allow for a bit more space for the reverse. It's a good idea!
If you do have to go the bearing route, the smallest I know of are 681 bearings. 1mm thick, 3mm diameter, 1mm centre hole.
I recently had an epiphany (maybe last week or so) about this kind of joint, but in my model, it was with rubber bands. I'm glad to find its name.
I love how the algo works, i was just thinking last night if I could use a rolling or sliding joint for the 3 z-axis that could be entirely 3d printed. The goal is to allow the bed to tilt but not slide and lifted out without removing hw
You're reproducing a knee joint/articulation very nicely here :D
For the lateral movement, you can also just tense a cable on each side, it should help to stabilize... like in your knees, you have 2 tendons on the sides :)
good luck to do it in such a small scale :D
Nice project
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!!!
When I saw this thumbnail I thought, wow, if this is what rolling joints looks like these days then stoners have really embraced the future.
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