Shishir N. Y. Kolathaya

arXiv2026

A Chain-Driven, Sandwich-Legged Quadruped Robot: Design and Experimental Analysis

This paper introduces a chain-driven, sandwich-legged mid-size quadruped robot designed as an accessible research platform. The design prioritizes enhanced locomotion, improved actuation reliability and safety, and simplified, cost-effective manufacturing. Locomotion performance is improved through a sandwiched leg architecture and dual-motor configuration, reducing leg inertia for agile motion. Reliability and safety are enhanced using robust cable strain reliefs, motor heat sinks for thermal management, and mechanical limits to restrict leg motion. The design incorporates quasi-direct-drive (QDD) actuators and low-cost fabrication methods such as laser cutting and 3D printing for rapid prototyping. The $25\,\mathrm{kg}$ robot is built under \$8000, providing an affordable quadruped research platform. Experiments demonstrate trot and crawl gaits on flat terrain and slopes. We also open-source the mechanical designs. VIDEO: https://youtu.be/ygSMCPcFnP8?feature=shared CADs: https://github.com/singhaman1750/stoch3-design.git

cs.RO↗

arXiv2025

Comparison between External and Internal Single Stage Planetary gearbox actuators for legged robots

Legged robots, such as quadrupeds and humanoids, require high-performance actuators for efficient locomotion. Quasi-Direct-Drive (QDD) actuators with single-stage planetary gearboxes offer low inertia, high efficiency, and transparency. Among planetary gearbox architectures, Internal (ISSPG) and External Single-Stage Planetary Gearbox (ESSPG) are the two predominant designs. While ISSPG is often preferred for its compactness and high torque density at certain gear ratios, no objective comparison between the two architectures exists. Additionally, existing designs rely on heuristics rather than systematic optimization. This paper presents a design framework for optimally selecting actuator parameters based on given performance requirements and motor specifications. Using this framework, we generate and analyze various optimized gearbox designs for both architectures. Our results demonstrate that for the T-motor U12, ISSPG is the superior choice within the lower gear ratio range of 5:1 to 7:1, offering a lighter design. However, for gear ratios exceeding 7:1, ISSPG becomes infeasible, making ESSPG the better option in the 7:1 to 11:1 range. To validate our approach, we designed and optimized two actuators for manufacturing: an ISSPG with a 6.0:1 gear ratio and an ESSPG with a 7.2:1 gear ratio. Their respective masses closely align with our optimization model predictions, confirming the effectiveness of our methodology.

cs.RO↗