Why Hands Are a Handful for Tesla's Humanoid Robots

On Friday, we reported on Tesla’s Optimus humanoid robot program, which may fall well short of Elon Musk’s ambitious goal to pump out 5,000 robots by the end of the year. 

It turns out the robots’ hands are among the big factors holding up production. In fact, some Optimus robots that are mostly complete have been sitting unused at a Tesla facility because they don’t have hands or lower forearms, we reported. Musk deserves some sympathy. Five-fingered hands are notoriously difficult for roboticists to get right, and many robotics companies steer clear of them, settling for simple pinchers instead.

To see why, consider the number of joints in a human hand. A hand and wrist can perform about 27 different movements (in robotics-speak, that’s 27 “degrees of freedom”). To put that in perspective, a robotic arm is considered pretty agile even if it has as few as seven degrees of freedom.

All those degrees of freedom add up to trouble for the roboticists designing the hands. More joints require separate motors to move them, and the motors need to be powerful enough to enable the robot to do useful work. For example, the humanoid robots of 1-year-old startup Foundation can carry up to 45 pounds using their hands and arms. Still, like many other robot hands, Foundation’s are not strong enough to pinch and unscrew a bottle cap, according to someone familiar with the company.