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Comment by chris_va | Hacker News Reader

I am not a robotics expert, and I've always wanted to ask one...

Why do these designs always have the actuators mounted directly at the joints?

Why not have some high modulus yarn transfer the joint loads (ala a bike brake cable, say with high modulus aramid?)? One could keep the actuators near the center of mass (or a trolley that follows it around), and keep the suit fairly minimal.

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> bike brake cable

Funny you mention that, this guy [1] made an actuator/arm recently doing that technique. Does work but accuracy/flex can be a problem.

[1] https://www.youtube.com/watch?v=ahSS5HUylT8

Curious, could one apply fancy control theory and modern computing at the problem and fix most of the accuracy and flex problem? Position feedback with integrated sensors can be very compact and highly accurate, and human muscle seem to also use feedback control for holding position..

The human system doesn't use single-muscle feedback for holding position though; it requires flexing both the push and pull muscles and coordinating the strength between them; positional information is relayed not just from the muscles, but the surrounding skin as well.

The constant muscle tone is largely to help bones stay in ball-and-socket joints. Presumably, such tone wouldn't be necessary with other kinds of joints.

Rather than control theory you can use geometry to reduce the problems with cable driven robots. There are more but I like the Ambidex: https://youtu.be/aLaqMreVj9o

Hey ! I am not a robotics expert, but I work at this company (Wandercraft) as software dev, so I know some of the reasons :) First of all I'd say that's because it simpler: we have so much to do that simplicity is a strong decision factor. That way you also reduce the number of moving parts, so maintenance is easier. On the software side you also get the marginal benefit that you keep a 1:1 mapping between joints and actuator (an example with coupled actuators: Cassie, from the Oregon State University). That way you can have different control strategies for the different joints.

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