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.
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!
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 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"
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.
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.
@@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.
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.
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.
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
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.
@@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...
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 tend to ablate 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.
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.
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.
Fascinating rolling joint the way you weaved fishing line to make flexible..do you 3d print these joints? If you do would you sell the smaller versions for about bird type joints? I would like to experiment with that rolling joint..Thanks for sharing!😎🗝✝️🙏🏼🇺🇸
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 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.
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
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 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.
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.
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
Loved the vid! Looks like an interesting project! As for tiny joints; `IGUS Plastics` sells very tiny high performance polymer bearings and bushings. Thurst, flange, sleeve, etc. We buy a lot of their stuff for small robotics. Options.
Plain bearings are always an option. small Bronze bushing bearings. Consider that heavy equipment like excavators, Bulldozers, Use plain bearings for maximum strength.
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.
@Breaking Tap0s , Why didn't you just make the joint and interlocking hing? Giving the leg more strength and durrability thus allowing it to have evenly spaced coils for weight distrabution.
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!!
Looking at that joint, I wonder if you could print-in-place your ligaments. I suspect it would take too high an elastic modulus at that scale, unless you multi-material it.
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 somehow expected those surfaces to interlock into each other and rolling on the "inside bottom" not "inside wall" (that would cause huge friction) like.. imagine rolling one fist over the knuckles of your other fist. would that be possible as well? also this would give more stiffness to sideway rotation (one downside: instead of a "dislocation" you would now have a risk of breaking but this would come with more stiffness/resistance towards unwanted sideway rotation)
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'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
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
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
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 😊
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
Might it not be a good idea to attach one end of the connective "tendon" to a very small (e.g. 1.5mm dia. x 6mm lg) extension spring preloaded to around 50% of maximum extension to compensate for wear, cord stretch and to prevent joint/tendon damage due to accidents?
Definitely! There are a few designs out there that use that idea to not only allow compliance, but also attach it to an actuator so that compliance can be dynamically altered (helpful for some highly dynamic motions like jumping and landing)
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!
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.
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.
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 ^_^
Super cool concept. Have you considered making the contacting parts concave+convex and giving them gear-like teeth? It seems like they might help support the joint against any kind of slippage in the wrong directions
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"
That is really cool. I haven't done much robotics so never run across this kind of joint but it really is ingenious. I do wonder if you had printed them sideways if you could get away with a purely printed joint (assuming two types of filaments one rigid for the joint itself and one to replace the wire)
When I was a kid in Tx,in the 70s,I was using these to replicate human structure and movement in some early robot stuff I did. I was influenced by Gray's Anatomy,and some Med school students in Baylor, n Rice.I did it with mostly R.C. parts ,n stuff I scavenged from stuff around my hood( bikes,old pumpz ,etc. I did it cause it was cheap,,minimum parts, and strong,..I worked on it a coulpa summers,got it good, made a working full sized model,,then I got into skateboards n music,and it got shelved,until now,,n its even more fun now,cause Ive the time ,resources,and the internet,..Its nice to know my thinking wasnt off by much back then,And its good 2 know other folks think like I have for most of my life.. CREATE,! LIVE LEARN, STAY CURIOS!! Dont be afraid to fail, this is where we get some of our most valuable lessons...Peace Out!!
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 !
How will the leg stay “up-right” (or stand on its own) since you are holding it up @10:19… Also, the ball at top will only add complications since it’s adding more DOF. Simply put, the physics isn’t there yet!
I think this is cool... But I am lazy :D When it comes to my 3d printing, I might try to think of a way to stick a single elastic band in there, hopefully in a one-shot deal. This looks like too much effort, albeit probably worth it if you want a actual working bird robot.. As opposed to me, just something cool that moves to impress my nephew :D
I like the idea but I don't trust the wire/string after thousands of cycles it will wear out. There is a mechanical way to make a single part flexible joint in a big scale model or using rubber for 3D printing for that specific joint, I didn't try yet myself but planning in the future a small demonstration as I'm working on small parts as well with small scale 10~5mm bearings.
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 !
Bionic is the best Blueprint for Robotics! (i mean, nature works....right?!) sadly its oftentimes an overlooked area, compared to math/computer simulations!
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
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
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
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"
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
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.
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 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.
We all know you’re secretly making a robot for barnaby Dixon.
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!
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 been rolling some joints myself and these are really cool!
I see what you did there ;)
amen
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!
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'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...
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 tend to ablate 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.
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 ?
Im in a hospital bed looking at getting 2 new knees.
You don't know how topical this is!
This solves a 3d printing problem I had for a long time, thanks!
9:27 thats the sound my knee made when i got hit from the side by a scooter.
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.
You're on to something.
So excited for this video after seeing your community post!
Fascinating rolling joint the way you weaved fishing line to make flexible..do you 3d print these joints? If you do would you sell the smaller versions for about bird type joints? I would like to experiment with that rolling joint..Thanks for sharing!😎🗝✝️🙏🏼🇺🇸
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 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.
Im so glad you uploaded, I desperately needed something epic to watch
What happened to this project? This looks too neat, you need to show us the working robot!
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
Fun fact: god would have used ball bearings when creating all animals, but the hardware store was closed that day.
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?
You take on the coolest projects, and actually mostly succeed, love it
But can it roll a joint?
Hey try Plain Bearings : )
+ Thanks for this Video : )
1:52 I wasn't ready for this
Nah me neither I thought I was having a stroke or something 😆
Nice work.
Would a pin & bushing (plain bearing) have too much friction or was this more about doing something different & unique?
can't make a 12 minute video about a simple bushing
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!
Thought this video was going to teach me something very different from that thumbnail
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.
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.
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
Loved the vid! Looks like an interesting project! As for tiny joints; `IGUS Plastics` sells very tiny high performance polymer bearings and bushings. Thurst, flange, sleeve, etc. We buy a lot of their stuff for small robotics. Options.
Plain bearings are always an option. small Bronze bushing bearings. Consider that heavy equipment like excavators, Bulldozers, Use plain bearings for maximum strength.
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.
That 0:32 looks more like the Robo Cop, than a bird lol
Please put down your banana, you have 20 seconds to comply.
@Breaking Tap0s , Why didn't you just make the joint and interlocking hing? Giving the leg more strength and durrability thus allowing it to have evenly spaced coils for weight distrabution.
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!!
Looking at that joint, I wonder if you could print-in-place your ligaments. I suspect it would take too high an elastic modulus at that scale, unless you multi-material it.
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 somehow expected those surfaces to interlock into each other and rolling on the "inside bottom" not "inside wall" (that would cause huge friction) like.. imagine rolling one fist over the knuckles of your other fist. would that be possible as well?
also this would give more stiffness to sideway rotation (one downside: instead of a "dislocation" you would now have a risk of breaking but this would come with more stiffness/resistance towards unwanted sideway rotation)
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
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!
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!
Hey, have you considered plastic bushings? Igus got some nice ones, not sure if that small
6:22 could you use a 2 material printer to print the joint on its side with print-in-place TPU ligaments?
Ther is a toy called "jacobs ladder" that is based on this string connection: ua-cam.com/video/ADXvQtk3bSI/v-deo.html
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
I did not know that human joints followed this principle. I assumed they were more of the ball & socket variety. I learned something today.
Why not stagger the channels and have the two sides mesh together. That would eleminate lateral movement and lend extra strength.
I thought this was a video about weed. Should have read the description better.
00:21 ... that better not be a cybernetic velociraptor, just sayin, we've all seen Jurassic Park!
(Hmm, birds are still dinosaurs, not cool man, not cool (well, cool, but not cool!))
seems like a bushing would be simpler, stronger, and less wear-prone
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
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
Bro you casually dropped a 3d printed knee with fiber meniscus.
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 😊
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
Might it not be a good idea to attach one end of the connective "tendon" to a very small (e.g. 1.5mm dia. x 6mm lg) extension spring preloaded to around 50% of maximum extension to compensate for wear, cord stretch and to prevent joint/tendon damage due to accidents?
Definitely! There are a few designs out there that use that idea to not only allow compliance, but also attach it to an actuator so that compliance can be dynamically altered (helpful for some highly dynamic motions like jumping and landing)
Cool idea and build. Watches and other small devices do use small bearings, but the way they're are used is different.
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
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!
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.
I was thinking it gonna be for that puppetier guy, with the cool birb puppets
So, your building a bird because birds aren't real
duuude this. this is sick. I will be looking for you at opensauce!
For a minute there I thought you were about to make that banana walk!
Thank you, I'm definitely going to integrate this joint into one of my future projects :) so cool!
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.
Bearings are a design constraint.
Me: use graphite coated bushings 😎
Breaking taps: use a non constant geometry rolling joint.
Me: 😵💫
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 ^_^
Super cool concept. Have you considered making the contacting parts concave+convex and giving them gear-like teeth? It seems like they might help support the joint against any kind of slippage in the wrong directions
*you could 3d print this joint in 1 piece*
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"
Love this new project!!
That is really cool. I haven't done much robotics so never run across this kind of joint but it really is ingenious.
I do wonder if you had printed them sideways if you could get away with a purely printed joint (assuming two types of filaments one rigid for the joint itself and one to replace the wire)
When I was a kid in Tx,in the 70s,I was using these to replicate human structure and movement in some early robot stuff I did. I was influenced by Gray's Anatomy,and some Med school students in Baylor, n Rice.I did it with mostly R.C. parts ,n stuff I scavenged from stuff around my hood( bikes,old pumpz ,etc. I did it cause it was cheap,,minimum parts, and strong,..I worked on it a coulpa summers,got it good, made a working full sized model,,then I got into skateboards n music,and it got shelved,until now,,n its even more fun now,cause Ive the time ,resources,and the internet,..Its nice to know my thinking wasnt off by much back then,And its good 2 know other folks think like I have for most of my life.. CREATE,! LIVE LEARN, STAY CURIOS!! Dont be afraid to fail, this is where we get some of our most valuable lessons...Peace Out!!
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 !
How will the leg stay “up-right” (or stand on its own) since you are holding it up @10:19… Also, the ball at top will only add complications since it’s adding more DOF. Simply put, the physics isn’t there yet!
I think this is cool... But I am lazy :D
When it comes to my 3d printing, I might try to think of a way to stick a single elastic band in there, hopefully in a one-shot deal.
This looks like too much effort, albeit probably worth it if you want a actual working bird robot.. As opposed to me, just something cool that moves to impress my nephew :D
i love how diverse all your projects are! And i always learn something new. great video as usual
I like the idea but I don't trust the wire/string after thousands of cycles it will wear out.
There is a mechanical way to make a single part flexible joint in a big scale model or using rubber for 3D printing for that specific joint, I didn't try yet myself
but planning in the future a small demonstration as I'm working on small parts as well with small scale 10~5mm bearings.
Very interesting solution! But why not just use bushings?
Friction
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 !
Bionic is the best Blueprint for Robotics! (i mean, nature works....right?!)
sadly its oftentimes an overlooked area, compared to math/computer simulations!