RM-Act 2.0: A Modular Harmonic Actuator Towards Improved Torque Density

In modern robotics, actuator performance is fundamental to achieving efficient and durable motion, with compactness and torque density being especially critical. Compact actuators enable integration in space-constrained systems without compromising functionality, while high torque density ensures powerful output relative to size, enhancing efficiency and versatility. Harmonic gearboxes embody these qualities, offering lightweight design, zero backlash, and excellent torque density, which have made them a standard choice in robotics. However, their widespread adoption is limited by high manufacturing costs due to the precision machining required. To address this challenge, the authors previously introduced RM-Act, a Radial Modular Actuator employing two synchronous belts as harmonic speed reducers. Building on this concept, RM-Act 2.0 is introduced as an improved version that employs a single synchronous belt. This design reduces transmission slippage, improves torque density, and offers greater modularity with a wider range of reduction ratios. The work details the development and validation of RM-Act 2.0 through a functional prototype and performance model, highlighting its advancements over the original RM-Act in compactness and torque density.