4 ms·

That may be but if you want an equivalent robot arm driven by an ordinary motor you still need the torque. Otherwise you would need a completely different syst

That may be but if you want an equivalent robot arm driven by an ordinary motor you still need the torque. Otherwise you would need a completely different system of actuation. I've heard of "artificial muscle" systems but I'm not sure if they're sufficiently developed yet.

candiodari 6y ago
It's difficult to see, but the arm and hand are as strong as they are because the "motors" are one step up. The motors for the hand are (predominantly) in the lower arm. The motors for the lower arm are in the upper arm, pulling on ropes connected to the lower arm (and significantly bigger than the lower arm). And the muscles doing the full arm are what's covering the front and back of your upper torso. This means that the force of your fingers is generated by a muscle roughly the size of a cola bottle, the force of your lower arm is generated by between 2 and 3 stacked cans of cola, and the force of your entire arm is generated by a muscle the size of a decent shoebox. So while muscles are pretty good, they're worse than our best motors. Or at least, if you can provide them with the power they need they are. And you think this is not the case because your body hides pretty sizeable muscles in your torso where everybody thinks you have almost only organs and fat, when in fact about half is muscle.
- tgflynn 6y ago
  So are you saying that using cables and motor driven pulleys is a better solution ? Most robotic arms I've seen appear to have a motor located at the elbow joint that drives the equivalent of the lower arm either directly or through a gear box. If cables and pulleys give better torque without loss of speed why aren't they in more widespread use in robotic arms ?
  - candiodari 6y ago
    > If cables and pulleys give better torque without loss of speed why aren't they in more widespread use in robotic arms ? Because it requires more parts, so there's more to break, it's more complex, it loses accuracy, and it fundamentally limits range of motion.

candiodari 6y ago

It's difficult to see, but the arm and hand are as strong as they are because the "motors" are one step up. The motors for the hand are (predominantly) in the lower arm. The motors for the lower arm are in the upper arm, pulling on ropes connected to the lower arm (and significantly bigger than the lower arm). And the muscles doing the full arm are what's covering the front and back of your upper torso. This means that the force of your fingers is generated by a muscle roughly the size of a cola bottle, the force of your lower arm is generated by between 2 and 3 stacked cans of cola, and the force of your entire arm is generated by a muscle the size of a decent shoebox. So while muscles are pretty good, they're worse than our best motors. Or at least, if you can provide them with the power they need they are. And you think this is not the case because your body hides pretty sizeable muscles in your torso where everybody thinks you have almost only organs and fat, when in fact about half is muscle.

tgflynn 6y ago
So are you saying that using cables and motor driven pulleys is a better solution ? Most robotic arms I've seen appear to have a motor located at the elbow joint that drives the equivalent of the lower arm either directly or through a gear box. If cables and pulleys give better torque without loss of speed why aren't they in more widespread use in robotic arms ?
- candiodari 6y ago
  > If cables and pulleys give better torque without loss of speed why aren't they in more widespread use in robotic arms ? Because it requires more parts, so there's more to break, it's more complex, it loses accuracy, and it fundamentally limits range of motion.