Triphibious robots capable of multi-domain motion and cross-domain transitions are promising to handle complex tasks across diverse environments. However, existing designs primarily focus on dual-mode platforms, and some designs suffer from high mechanical complexity or low propulsion efficiency, which limits their application. In this paper, we propose a novel triphibious robot capable of aerial, terrestrial, and aquatic motion, by a minimalist design combining a quadcopter structure with two passive wheels, without extra actuators. To address inefficiency of ground-support motion (moving on land/seabed) for quadcopter based designs, we introduce an eccentric Center of Gravity (CoG) design that inherently aligns thrust with motion, enhancing efficiency without specialized mechanical transformation designs. Furthermore, to address the drastic differences in motion control caused by different fluids (air and water), we develop a unified propulsion system based on Field-Oriented Control (FOC). This method resolves torque matching issues and enables precise, rapid bidirectional thrust across different mediums. Grounded in the perspective of living condition and ground support, we analyse the robot's dynamics and propose a Hybrid Nonlinear Model Predictive Control (HNMPC)-PID control system to ensure stable multi-domain motion and seamless transitions. Experimental results validate the robot's multi-domain motion and cross-mode transition capability, along with the efficiency and adaptability of the proposed propulsion system.

翻译：能够进行多域运动及跨域转换的三栖机器人有望应对不同环境下的复杂任务。然而，现有设计主要集中于双模式平台，且部分设计存在机械复杂度高或推进效率低的问题，限制了其应用。本文提出一种新型三栖机器人，通过将四旋翼结构与两个被动轮结合的最小化设计，无需额外执行器即可实现空中、陆地与水中运动。针对基于四旋翼的设计在地面支撑运动（陆地/海底移动）效率低下的问题，我们引入了一种偏心重心设计，使推力与运动方向自然对齐，在无需专门机械变形设计的情况下提升了效率。此外，为应对不同流体（空气与水）导致的运动控制剧烈差异，我们开发了基于磁场定向控制的统一推进系统。该方法解决了扭矩匹配问题，实现了跨介质精确、快速的双向推力生成。基于生存条件与地面支撑的视角，我们分析了机器人的动力学特性，并提出一种混合非线性模型预测控制-PID控制系统，以确保稳定的多域运动与无缝模式转换。实验结果验证了机器人的多域运动与跨模式转换能力，以及所提出推进系统的高效性与适应性。