Planetary roller screw actuator · serves as: Actuator, Transmission.
Which group Kepler KEPLERGEAR belongs to and how it is built
Linear actuators using a planetary roller screw (PRS) for power transfer with line contact instead of point contact.
Linear actuator with a planetary roller screw. High load capacity thanks to line contact.
Vendor claim
Vendor claim
KEPLERGEAR is a proprietary linear actuator developed by Kepler Robotics that uses a planetary roller screw transmission instead of a conventional ball screw. It is deployed in the main load-bearing joints of the Forerunner K2 humanoid — thighs, calves and arms — where high axial stiffness, large force density and precise position control are required.
A planetary roller screw replaces the recirculating balls of a ball screw with multiple threaded rollers orbiting a central screw shaft. The larger continuous contact area carries the load, yielding higher force density, greater axial stiffness and longer service life than a comparable ball screw of the same diameter. In KEPLERGEAR the mechanism is coupled with an electric motor that drives the screw, converting rotary motion into precise linear motion.
KEPLERGEAR is part of the hybrid drivetrain of the Forerunner series — Kepler uses planetary roller screw linear actuators in high-load areas (thighs, calves, arms) and rotary actuators in joints such as shoulders and waist. According to the manufacturer, this layout enables the K2 robot to carry 15 kg per arm (30 kg total) and walk at up to 4 km/h; in July 2025 the K2 completed an 8-hour continuous livestream at WAIC 2025, demonstrating runtime comparable to a full industrial shift.
The component is part of Kepler's closed platform — it is not offered as a standalone catalogue product and no public datasheet PDF is available.
