Tesla’s Robot Hand Patent Reveals the Clever Engineering Inside Optimus’s Fingers

Tesla appears to have filed a patent for a new robotic hand, offering the clearest look yet at how the company plans to engineer the fingers and wrist of its Optimus humanoid robot.

The international patent, published today and titled “Mechanically Actuated Robotic Hand,” describes a five-fingered hand controlled by a network of cables running from the forearm through the wrist and into each finger, similar in concept to how tendons work in a human hand. This design brings 22 degrees of freedom, which is double that of the previous generation design.

The Fingers

Each finger has four segments connected by rolling joints, the same way human knuckles work, where the contact surfaces roll against each other rather than rotating around a fixed pin. This gives a more natural bending motion and lets the pivot point shift slightly as the finger curls, which more closely mimics real finger movement.

Every finger except the thumb has four segments. The thumb has three. Each finger is controlled by three cables. One cable runs all the way to the fingertip and handles the curling of the upper two segments. The other two cables attach to the middle of the finger and handle spreading the fingers apart and together, what you’d call abduction and adduction.

The cables are routed deliberately, some running along the back of a joint, some along the front, depending on which direction they need to pull to create the right movement. Small grooves carved into each finger segment keep the cables in line as they travel toward their anchor points, preventing them from drifting sideways and accidentally pulling the finger in the wrong direction. Springs inside the finger return it to a fully open position whenever the cables are released, so the hand defaults to open rather than closed.

The Wrist

The wrist can move in two directions, tilting up and down and rotating side to side, using only two motors instead of four. That’s made possible by a specific arrangement of joints where moving both motors together tilts the wrist, and moving them in opposite directions rotates it. It’s a mechanical trick that cuts weight and part count without sacrificing range of motion.

The bigger engineering challenge is getting all the finger control cables through the wrist without the wrist’s own movement accidentally pulling on them. Tesla’s solution is to rotate the cable bundle as it passes through the wrist joint, going from a flat horizontal arrangement on the forearm side to a vertical stack on the hand side. That transition is carefully positioned to sit right at the center of the wrist’s rotation axes, which means the cables barely change length when the wrist moves. Less length change means less unintended finger movement, which is the crosstalk problem that would otherwise make the hand twitch every time the wrist bends.

The cables themselves can be made from braided polymer for flexibility and durability, and can run inside low-friction lined tubes that can be lubricated to reduce heat and force loss over time.

The Bigger Picture

The patent traces back to a US provisional application filed in October 2024, suggesting Tesla has been developing this design for over a year. The level of detail in the filing, covering cable routing, joint geometry, termination methods and friction management, points to a design that is well past the concept stage.

Dexterous robotic hands have long been one of the hardest problems in humanoid robotics. Most current robots either use simple grippers or hands so complex and expensive they aren’t practical for real-world use. Tesla’s cable-driven approach borrows from established robotics research but is clearly being engineered with manufacturing scale in mind, keeping part counts low and using materials and methods that could be produced in volume.

Earlier this month, Elon Musk said Optimus 3 is almost ready and delayed the unveil. “Optimus 3 is walking around, but needs some finishing touches before it’s ready to be shown.” We were supposed to see Optimus 3 unveiled at the end of March.

[via @seti_park]