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I think electric motors are just barely suitable for mobile / humanoid robots. Compared to human muscles, they're heavy and they overheat quickly. Current human

by Geee 7mo ago

I think electric motors are just barely suitable for mobile / humanoid robots. Compared to human muscles, they're heavy and they overheat quickly. Current humanoid robots are spending most of their energy in carrying around just themselves, which is a huge amount of dead weight, while being unsafe for anyone to be around. If someone invents a new type of 'artificial muscle' which has low inertia, high force/torque density, and can work without overheating, that would instantly kill all other robotics companies.

adrian_b 7mo ago
Electric motors are heavy, but they have better energy efficiency than muscles. The reason why muscles do not overheat as much as electric motors, despite lower efficiency, is because they have good liquid cooling, by blood. The cooling system of animals has outstanding reliability, due to self repair. Liquid cooling is also possible for electric motors, but it is usually avoided due to high cost and low reliability. The weight problem of the electric motors is solved by keeping them in the body of the robot and transmitting the movement towards the moving parts that need low inertia by various means (ropes, cables, levers, hydraulic/pneumatic fluids). This is also done with muscles, which frequently are far away from the bone that they are moving and the movement is transmitted by long thin tendons, to reduce the inertia of the moving limb.
- Geee 7mo ago
  Electric motors can have quite a low efficiency in slow speed / high torque regime, where robots operate, because torque scales linearly with current, and power loss (resistance -> heat) scales quadratically to current (P=UI, U=RI -> P=RI^2). In addition, when the motor is statically loaded, when it's just holding a position, it wastes a lot of power (depending on the torque) with zero efficiency, if it doesn't have mechanical brakes. I think only 1X is using tendon drives for all (?) joints in their robots, but most robots use them just for hands. 1X uses tendons just for moving the motor one link upwards the chain, not through multiple joints to the body (elbow motor is in shoulder etc.). Transmitting power from the body to remote joints with tendons is quite hard problem, and I'm not aware of anyone doing it this way. One problem is that there is no obvious way to decouple the motion of tendons when they go through a joint, e.g. if the elbow joint moves then it affects all tendons which go through the elbow. Also, it's rather complex and there is friction, stretching and vibration and so on, which might be hard to model / simulate. Hydraulics might work, but Boston Dynamics gave up on it, so I think it's probably not worth it. Hydraulics could in theory be very good because it needs just one motor for the pump and the fluid can distribute the power to many actuators. Moving the motors to the body is a good way to solve the mass / inertia problem, but no one has really figured out how to do it. Whatever 1X is doing might be the sweet spot.

by Geee 7mo ago

adrian_b 7mo ago

Electric motors are heavy, but they have better energy efficiency than muscles. The reason why muscles do not overheat as much as electric motors, despite lower efficiency, is because they have good liquid cooling, by blood. The cooling system of animals has outstanding reliability, due to self repair. Liquid cooling is also possible for electric motors, but it is usually avoided due to high cost and low reliability. The weight problem of the electric motors is solved by keeping them in the body of the robot and transmitting the movement towards the moving parts that need low inertia by various means (ropes, cables, levers, hydraulic/pneumatic fluids). This is also done with muscles, which frequently are far away from the bone that they are moving and the movement is transmitted by long thin tendons, to reduce the inertia of the moving limb.

Geee 7mo ago
Electric motors can have quite a low efficiency in slow speed / high torque regime, where robots operate, because torque scales linearly with current, and power loss (resistance -> heat) scales quadratically to current (P=UI, U=RI -> P=RI^2). In addition, when the motor is statically loaded, when it's just holding a position, it wastes a lot of power (depending on the torque) with zero efficiency, if it doesn't have mechanical brakes. I think only 1X is using tendon drives for all (?) joints in their robots, but most robots use them just for hands. 1X uses tendons just for moving the motor one link upwards the chain, not through multiple joints to the body (elbow motor is in shoulder etc.). Transmitting power from the body to remote joints with tendons is quite hard problem, and I'm not aware of anyone doing it this way. One problem is that there is no obvious way to decouple the motion of tendons when they go through a joint, e.g. if the elbow joint moves then it affects all tendons which go through the elbow. Also, it's rather complex and there is friction, stretching and vibration and so on, which might be hard to model / simulate. Hydraulics might work, but Boston Dynamics gave up on it, so I think it's probably not worth it. Hydraulics could in theory be very good because it needs just one motor for the pump and the fluid can distribute the power to many actuators. Moving the motors to the body is a good way to solve the mass / inertia problem, but no one has really figured out how to do it. Whatever 1X is doing might be the sweet spot.