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I have some technical questions about feet. Human feet have metatarsophalangeal joints connecting the toes to the rest of the foot. But humanoid robots don't h

• codekansas 1y ago
  So, most humanoids you see that are relatively cost-effective are just "humanoid" in that they look like humans, but there are significant mechanical differences between them and real humans. It's almost always driven by the cost of manufacturing different components. A good example is the lead screw you see in the knee and ankle on Optimus - while it is more human-centric to have tendon-like actuation, it drives the price up quite a bit. Put differently, humans have a lot of specialization which is not great if you want to mass manufacture something. For walking, the most important thing is that the robot can be simulated well, so in our case, we tried to model the foot contact with the ground in simulation quite accurately. In fact, we found that force sensors in the foot probably help but they're not necessary in simulation, and we wanted to shave off anything that wasn't necessary. I am not sure how close we will get to human mobility - it's definitely a learning process - but you can get much further in simulation than you'd expect.
• cpgxiii 1y ago
  Feet/ankles on humanoids are really hard mechanically. In many ways the kinematic requirements for the ankle are similar to a wrist, but while the wrist of a robot arm is the least-heavily-loaded, the ankle area can be the most heavily loaded. Humans get away with it by having most of the highly-stressed actuators in the lower leg, not the ankle itself, whereas many humanoid robots end up putting more of the actuators in the ankle assembly itself. In general, I think the best way to think about the differences between human muscles and robot actuators is that human muscles are simultaneously incredible in terms of strength and power density, and also incredibly fragile. Robot actuators are fairly robust, but comparatively poor. Humans are essentially falling apart at all times, but the repair mechanisms in the body do a good enough job that it doesn't matter (although you probably know someone with a "career-disruptive/ending" sports-related injury that shows these mechanisms have limits). Robotics is a long way away from making actuators that can be fixed online in such a process. Even cable stretching in cable-driven mechanisms remains hard to handle effectively, and that's one of the simplest types of mechanism wear.
  • bbertelsen 1y ago
    These are the kinds of comments that make comments worth reading. Thank you!
  • codekansas 1y ago
    This is a much better answer than mine
• tlb 1y ago
  There are certainly things a robot can't do with rigid feet, like climbing a tree or rock face. But anything a human can do with rigid shoes like wooden clogs should be possible. Whatever happens inside the clog stays inside.
  • chrsw 1y ago
    That sounds plausible but it is actually true? When I'm walking in the woods the ground is very uneven, has different friction between the ground and my feet, is sometimes soft, sometimes hard. Yes I have flat shoes or boots on. But they're just normally flat, not rigid. And my feet can still feel the ground beneath me, through the shoes. That helps me balance, know where to put my weight, etc. Mostly subconsciously. I almost never fall over, too. My concern is all the sophistication of the human anatomy isn't just useful, it's essential for something that's going to be less trouble than its worth.