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

翻译：本文介绍了一款链式驱动夹层腿式中型四足机器人，其设计目标是为学界提供一个易于使用的研究平台。该设计重点提升了运动性能、驱动可靠性及安全性，并采用简化且成本效益高的制造方案。通过夹层式腿部结构与双电机配置降低了腿部惯量，从而实现了更敏捷的运动能力。可靠性及安全性方面，采用坚固的线缆应力消除结构、用于热管理的电机散热片以及限制腿部运动的机械限位装置。设计融合了准直驱执行器与低成本制造工艺（如激光切割和3D打印），支持快速原型制作。该机器人重$25\,\mathrm{kg}$，制造成本低于8000美元，为四足机器人研究提供了经济实用的平台。实验展示了机器人在平坦地面及斜坡上的小跑与爬行步态。我们同时开源了机械设计文件。视频：https://youtu.be/ygSMCPcFnP8?feature=shared CAD文件：https://github.com/singhaman1750/stoch3-design.git