As part of a student-led (See Andrew Daetz’s excellent overview) collaboration, we developed a modular robotics kit designed around lightweight, high-precision revolute joints for rapid prototyping and physical human-robot interaction research. Each joint integrates precision ball bearings and a 14-bit capacitive encoder housed within a custom 3D-printed carbon fiber structure, enabling smooth, cog-free motion with exceptional velocity resolution. The joints connect via angled mesh carbon fiber tubing for high stiffness under bending loads, using a combined press-fit and through-hole strategy to minimize stress concentrations.

Power is transmitted using a remote capstan cable system—based on tensioned sailing rope and secured with knots—to eliminate backlash and decouple structural alignment from actuation. A two-stage tensioning mechanism allows both gross and fine adjustment, with compact brushless DC motors mounted at a distance for improved balance and responsiveness. The platform was successfully demonstrated with a five-bar planar linkage, showcasing its ultra-lightweight, stiff, and precision-controlled motion capabilities.

This design is intended to allow students or hobbyists to easily and quickly configure their own robot designs in open or closed kinematic chain configurations with grounded or floating motors. Future plans could explore extensions to allow a twisting degree of freedom to complement our current revolute joint motion. This update would then enable robot configurations for 3D motion.