I cannot un-see these left border hints, it's driving me crazy.

Its completely impossible to trust an article when half the diagrams have serious issues and headlines are worst slop indicators. I am sure the author is knowledgeable and spend some time on this. But please please, with butter, please, either spend the last 10% to get rid of these issues or just don't publish it! Keep it in your ai research gallery or if you want to publish that gallery as ai research?

AI was clearly heavily used in the making of this article, and I almost dismissed it as slop. But after reading it I think there's enough correct information here for it to be useful as a general overview of the problems in the space.

AI that drew the diagram couldn't get it's neurons around how planetary screws in linear actuator should work.

Here's an actual schematic: https://ae-pic-a1.aliexpress-media.com/kf/Sd3fe9841e4ed4871b...

Why these screws are used instead of just threads? Because rolling friction is lower than sliding friction. You can use less or more of them trading friction for shock resistance.

Do they run Doom?

I really like the idea of using two series elastic actuators in parallel on the same joint. This way motors acting in opposite direction can pre-tension the springs making the leg stiffer or softer. And if a lot of strength is needed they can act in the same direction summing their forces.

It should be fairly straightforward to control dynamically so you can use pretty much any motor and gearbox.

Except we don't need 100% bipedal robots. Wheels are perfectly ok for majority of city work and factory floor.

Put the robot on rollerskates break the wheels for the occasional stair.

TLDR: we don't have the actuators required to make humanoid locomotion work reliably.

Also: something every human actually kind of knows. You need to take impacts on muscles, not on mechanical connections. Even if we had the actuators required, you also need perfect control. The only way actuators can work this well is if they properly predict the impacts so that the power of the motor ("the magnetic field") can absorb nearly all the impact. If you try to take the impacts even on human bones (that are very solid and self-repairing) they will break surprisingly quickly.

My opinion is that the need for high reduction is only because we can't have high voltage on the motors. If we either had very small distances between the magnets and electrical wires (think micrometers), or we have voltages in the 100s to 1000s of volts, we don't have to make this poisoned choice. (in a way, VERY small distances between magnets and wires is how human and animal muscles do it. But they go all the way down to sub-10 nanometers)

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