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Comment by clairity | Hacker News Reader

human-like gaits mainly require the correct structural elements (rather than machine learning), like locking knees (as noted in the article) and slightly elastic legs and joints (for energy storage/release as well shock absorbtion).

most robots are energetically inefficient and require extraneous computational power because they don't take advantage of passive dynamics (https://en.wikipedia.org/wiki/Passive_dynamics). it's disappointing to realize that we still haven't caught up to fundamental biological systems yet, even though the research is 2+ decades old.

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Related to "passive dynamics," see "preflexes" https://en.wikipedia.org/wiki/Preflexes

"Preflexes are the latent capacities in the musculoskeletal system that auto-stabilize movements through the use of the nonlinear visco-elastic properties of muscles when they contract.[1][2] The term "preflex" for such a zero-delay, intrinsic feedback loop was coined by Loeb. [3] Unlike stabilization methods using neurons such as reflexes and higher brain control, it happens with minimal time delay. Its chief disadvantage is that it works only to stabilize the main movements of the musculoskeletal system."

neat!

somewhat related to that, our tendons are tuned to our gait dynamics to return the optimal energy back to us as we locomote (more accurately, our strides optimize around tendon elasticity and leg length).

Roboticists have built passive walking robots like the one from Cornell, it walked 5.6 miles without power. https://www.youtube.com/watch?v=LDljbN7eJ5Y Japanese roboticists have built passive walking robot with locking knees: https://www.youtube.com/watch?v=rhu2xNIpgDE

Exactly. The thing that hasn't been figured out yet is how to combine the energy efficiency and aesthetics of passive walking with the versatility needed to have the robot do useful work, especially in a principled way.

nice! i had seen an earlier prototype of the cornell walker but it’s really great to see this record-setting video!

it's disappointing to realize that we still haven't caught up to fundamental biological systems yet, even though the research is 2+ decades old.

Given that we're the result of billions of years of natural selection, shouldn't we expect that?

in general, yes (natural selection is amazing), but the knowledge in this case has been readily available for literally decades but not applied appropriately.

organisms have evolved over billions of years to take advantage of passive dynamics, which is basically the application of newtonian physics to what is mostly a mechanical design problem. we've known for a long time that passive dynamic elements are not only energetically more efficient, but also makes computations simpler.

by contrast, active dynamic locomotion is akin to putting a joint between the front fork of a bike and the shaft, and installing a hand pump that you have to constantly actuate to keep the bike stable while you're riding it. you could do it, but it's not the best solution.

The trick is in the application. Most of our "industrial lego" is for making mostly rigid things with some spinny parts and a few, mostly passive sproingy/squishy bits. However, we ourselves are mostly sproingy/squishy and a lot of that is dynamic.

By the same token, most of the tooling and parts for building airplanes isn't all that useful for building orinthopters.

So it's not just knowledge. It's knowledge expressed in the form of industrial infrastructure and products.

yes, legged robots at scale requires such industrial infrastructure, but at the current r&d stage, they can still apply these learnings.

> but the knowledge in this case has been readily available for literally decades but not applied appropriately.

This isn’t a kinematics homework where you can draw the links and joints and get full marks. You have to actuate them. For a human gait, you need to generate the same torque, at the same velocities, and the mass of the actuator needs to distribute across the linkages in the same proportion. Guess what? Actuators like that are hard to find.

the proper kinematics makes both the mechanical design and the control systems simpler, including leeway in choosing the actuators. you’re right in that we don’t have muscle-like fast-acting axial actuators with pliable multi-insertion endpoints, but you don’t need to exactly mimic a human leg (which is effectively impossible right now) to apply these principles.

This isn’t a kinematics homework where you can draw the links and joints and get full marks. You have to actuate them.

I should paraphrase that for interviews. "This isn't a CS homework where you can cite Big-O and get full marks. We have to be able to implement code that uses them."

And by that, I don't mean that you have to write all of the actual code. But one needs to be able to specify it exactly so someone could implement it and know enough about that to tell someone of the pitfalls in the current problem context/framework.

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