[vova_hn2]

Probably a dumb question, because I know nothing about robotics, but:

> The "Zero RPM" Problem

> When a robot bends its knees to stand, the motor must constantly fight gravity. There is no skeletal structure to lock against. To an electric motor, holding a static load—known as stall torque—is the most punishing state possible.

Why not just add some kind of brake that can fully or partially lock the joint?

[blueblisters]

Brakes are being added to actuators but they're more useful for static holds / locking than dynamic balancing. Standing even in humans is a dynamic balancing activity.

[regularfry]

It is, but you don't have to do it at every joint all the time. If you lock your knees your front and back thigh muscles don't have to work on balancing in that axis at all.

[thrownthatway]

Complexity, weight, failure modes, wear, maintenance, support burden of legacy parts.

Also the brake components are never in the same plane as the drive components, so now you have additional forces to engineer for.

[korse]

It's just weight. If you remove the human scale constraint, you can use hydraulics and easily lock out all your joints with reasonable complexity and maintenance demands. If you're unfamiliar, just look up the history of electrohydrostatic actuators and see where they're at now.

https://www.moog.com/products/actuators-servoactuators/actua...

[AntiUSAbah]

You need to keep balancing fast enough. I don't think a break would give you this agility.