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The force an impulse generates on a contact depends on the speed of deceleration. It's just F=m*a

Slow deceleration leads to low forces. If you have a contact event with a hard substance, like a rigid metal for accurate kinematics, the deceleration to zero upon a contact has to happen instantly. Meaning the deceleration is incredibly high, resulting in extremely high forces for a few milliseconds.

Human bodies are made out of a flexible and impact resistant material: water. When a contact event happens, your body deforms, which means that the deceleration happens over a longer time frame with less force. Not just that, your muscles also have a certain amount of flexibility in them and basically zero internal inertia. All the inertia is in the limb as a whole, whereas for a robot there is a spinning motor and gearbox that needs to slow down as well.

You could solve this as a control problem by adding series elastic actuators, which means you need to change your mechanical design.

by hwntw3 hours ago|

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The human body goes further than that too, when you're out jogging - as your foot approaches the ground for a stride, you slow the velocity of your foot downwards towards the ground so there's less of a sudden deceleration.

Imagine when you throw a tennis ball high in the sky, and then you catch it on your racket without bouncing by matching it's velocity, your feet do the same thing with the ground on a smaller scale.

by nixon_why6950 minutes ago|

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Then you have several hinges absorbing/dissipating that energy if you're using good form: foot flexes with a pivot in the arch of your foot, calf/achilles stretches with a pivot in your ankle and quad with a pivot in your knee. It should look like an angled, backwards Z at strike with nothing just straightened and tanking the impact.

Nobody actually runs perfectly enough to take 100% of the impact out of your joints but good form routes as much as possible into the muscles/ligaments around the joints instead of straight through them. It's a lot of little bitty unconscious nerve endings and muscles so one could expect it will take a while to iron out for robots.

Thinking about it more, maybe the issue here is that there's no self-healing stretchy ligaments involved in robots to begin with, even before the control issue.