From what I can tell, difficulties in dexterous manipulation are partly a hardware problem and partly a software problem. On the hardware side, current robotic manipulators are very far from being as capable as a human hand. Human hands are very strong while being capable of complex and precise motions, and it’s difficult to match this with a robot hand. Robot hands are often surprisingly weak. An
average man has enough grip strength to lift 40 kg or more off the ground (20 kg in each hand), and a strong man can lift upwards of 100 kg. By contrast, NASA’s
Robonaut 2 hand had a payload capacity of 9 kilograms, and the
Shadow dexterous hand (billed as the “most advanced 5-fingered robotic hand in the world”) has a payload capacity of just 4 kilograms.
More importantly, human hands are extremely sensitive, and capable of providing a lot of tactile feedback to help guide our actions. A human hand has around
17,000 touch receptors, and is sensitive enough to discriminate between textures that differ by
mere nanometers. Robot hands
are getting better, but still don’t appear to be close to what a human hand can do.
This robot hand, for instance, boasts “17 tactile sensors,” and
this one from Unitree has 94.
Dexterous robot hands also tend to be extremely expensive. The Robonaut 2 hand apparently cost on the order of
$250,000 dollars apiece, and the Shadow dexterous hand
costs around $100,000. Unitree’s G1 humanoid
starts at just $16,000, but that price doesn’t include any hands at all. Add a pair of hands to that and you’re looking at
another $16,000, and those will be less capable 3-fingered hands with limited sensor capabilities. (If I’m
reading the specs right, the 3-fingered Unitree hands only have a payload capacity of 0.5 kilograms.)