1X NEO Robot Hand: Deep Dive into the Mechanism & Design

[00:00:00]So, recently OneHandX released some videos showing how their robotic hand moves. And in this video, I'm going to be going into a deep dive on exactly how I think the different parts work. So, let's first talk about the degrees of freedom, also called DOF. So, if we take a look at the fingers, let's start with the pinky. You can see right here we have one, two, and when I draw these lines, it means it rotates about the joint axis. So, we have one, two, three.

[00:00:30]So, there's three axes, and then there's another one that's coming in like this.

[00:00:35]So, that gives us four. We have one, two, three, four, five fingers, right?

[00:00:41]So, each of them, up to some point where the knuckles are, it has four degrees of freedom. So, we have 5 * 4 is 20. Now, you can see there's a bit of a cut here.

[00:00:54]So, this part assumes that the pinky has additional degree of freedom that allows it to pivot in and out. So, I think that's what this part is. So, we're going to give it additional degree of freedom here.

[00:01:09]And same with the thumb, you can see this mechanism, which we'll talk about later on. But, this part is basically cable-driven mechanism that allows it to have rotation at the base of the thumb.

[00:01:21]So, this whole thing is allowed to pivot about this axis here. So, that gives us additional degree of freedom here that gives us a total of 22 DOF for their hand.

[00:01:35]But, this total hand has degree of freedom of 25 based on what their website said, right? So, this additional three degree of freedom, this plus three here, this three is coming from the wrist. So, this wrist has a special mechanism.

[00:01:53]So, this is three DOF here.

[00:01:56]It's basically a cable driven differential. And you can see these are some examples of how differentials are and it's a MIMO system. Basically, you might see it as this, which is multi-input multi-output. But the idea is they really derive from a lot of the car designs with car differentials where you have a bevel gear. So, you you'll have like one axis of rotation here, another axis of rotation here.

[00:02:24]So, there's only two motors that control this. All right, in this example, there's some timing belts. Probably have some motors down here that's rotating it.

[00:02:35]It's just not shown.

[00:02:36]But you can see that it's driven by belts and when these two things rotate simultaneously, you could have control over how the end of this works. And then when the two is rotating in opposite directions, you could rotate the end. So, looking at the mechanism here, it's possible that they've implemented a differential. I'm not quite sure entirely. This is just my guess. So, you can see the two axes here. They could be driven both of them independently to allow the base here to rotate. But then you can also see there's another pivot here, which means that they probably added additional rotation that allows it to also flex this other way. So, it might be a combination of a differential and additional axes that allows it to do all three degrees of freedom.

[00:03:29]Uh that's one guess. Another guess is that um if these two axes are directly driven, then the roll might be somewhere in the back of the hand. But what makes the mechanism really nice is that you can see the center of the design is hollow.

[00:03:46]So, that allows all the Bowden cables to pass through here, which is really nice.

[00:03:52]Uh but you can see here, this is some close-up of their Bowden cable. And you know it's a Bowden cable because you can see this part is a black part, which is the inner cable, and then you have the outside That part is going to be the sheath that allows it to have something to push against. So, we take it down here, you can see this is the general anatomy of a Bowden cable, right? So, you're going to have termination ends on both sides. Uh, but one part that they don't show is that usually the outside conduit or casing, like the blue part, usually some of this part needs to be grounded somewhere because otherwise, if you're pushing the cable, you need to be holding it against something to push and exert the force. So, because they don't show it uh, down here, it looks like the sheath is floating, right? So, that tells me that if we look at the top part, it's most likely the sheath is being held somewhere near the end of the hand where the palm is, which is probably covered with some of the casing.

[00:04:58]So, you can see here in their finger, you can't quite see, but um, either the Bowden cable, the inner cable is flexible enough to, you know, bend through these grooves here, or they might have it attached to a secondary material that can be more flexible, but I'm not quite sure how how flexible the material is, but just by looking at the finger here, this bend radius has to be pretty tight.

[00:05:30]Uh, it could be, you know, like Nitinol can bend pretty well in a tight radius and still exert a lot of force, so I'm not quite sure how they implemented this, but um, that's kind of my guess.

[00:05:42]But you can see that the mechanism here, there's You can see there's two that comes in. So, this one is passing to the back and is not being actively controlled, but you can see up here there's being two, right? So, when this motor right here is rotating back and forth, it's going to be either pushing one or pulling one. So, if we take a look at the finger down here, you can see that there's going to be two parts of this, right?

[00:06:16]So, it's supported on either side. And my guess is that if you have a finger mechanism like that where, you know, it's supported on both ends, then it's possible that these Bowden cables go all the way up to the finger to each of the joints. And possibly one is attached on one side and then another's is like attached on the back end so that it's pulling in opposite directions. So, that's kind of my guess of how it works. And again, I could imagine if the Bowden cable is not able to have such a tight bend radius, then it's also possible that they might have like the Bowden cable and then attach to some more flexible cable to allow, you know, that full range of motion and tight radius. As for the thumb, you can see that back then we saw that the base is rotating, but here's a close-up. If you look closely, you can see these cables are routed a few wraps. And the reason for that is because usually when you have uh cable designs, you want to have it wrap couple times because the wrapping creates tension and this tension creates additional friction. The friction is actually the main part because when you have these several wraps, the friction allows it to um let's say like the end of the cable has some termination, right? And you do some wraps. It doesn't rely solely on the termination to hold the load of the cable. So, this will allow the design to last longer and also exert more strength up to the limit of the cable, of course.

[00:08:00]So, that's basically how this is designed and you can see they have some clever ways to redirect the direction by using some idler pulleys in between.

[00:08:10]But, ultimately this gives the thumb that additional rotation and gives it more dexterity.

[00:08:16]And one thing I want to point out, too, is some notes about the actuators. So, uh two things. One is the configuration of the actuators and the second is the gear ratio. So, they mentioned most of their gear ratios are pretty low. I think it mentioned like somewhere around 5 to 15 is their main gear ratio. And this is a core concept of QDD actuators, quasi-direct drive actuators. And these low actuators really allow for good uh current sensing just because of how transparent the transmission is. So, this current sensing allows it to do additional uh force control techniques that, you know, higher gear ratios would otherwise not be able to uh unless they have additional sensors like output encoders or force torque sensors at the end of the hand. So, I think that's really why they went down with this choice of actuators with low gear ratios. And also a cool thing, too, is if you look at the layout of the actuators, right? So, you can see um pretty sure if you were to look like through the hand, the top view, like the cross section of the hand, I'm pretty sure most of these motors are, you know, somehow going through like passing through each other but stacked at different levels. So, it's a pretty compact spacing that they've got here because if you're staggered at different levels, then you could either cross past it or they happen to be on the same level then they just have to make sure their motor is no longer than the radius of the hand. So, I can't quite see the backside of the hand here.

[00:10:01]So, these are just my guess but uh based on their layout, it looks like they have plenty of space to have a stick pop probably to the other side of the hand.

[00:10:12]So, you know, that makes me feel like they're probably not limited to the center and if they're staggered enough, they could have one that crosses over all the way and then another one that crosses all the way over and so on and so forth. Now, if you're new here, my name is Kevin. I've been doing robotics and AI for 10 plus years and have lots of resources on my channel. If you want to see more deep dive videos on exactly how I build my projects, you could come up here, join. It's going to be the robotics builders. Join the community and learn more about my behind-the-scene videos. I also have additional resources like my master's robotics and AI bundle as well as my robotics projects bundle.

[00:10:53]You could check it out. Link in the video description.