TriphiBot: A Triphibious Robot Combining FOC-based Propulsion with Eccentric Design

TL;DR

TriphiBot is a minimalist triphibious robot that seamlessly transitions across air, land, and water using a novel eccentric CoG design and a unified FOC-based propulsion system, validated through experiments.

Contribution

The paper introduces a triphibious robot with a passive wheel design, eccentric CoG for efficiency, and a unified FOC propulsion system for multi-medium motion, addressing limitations of prior dual-mode robots.

Findings

Successful multi-domain motion demonstrated in experiments

Enhanced propulsion efficiency through eccentric CoG design

Effective control system enabling seamless mode transitions

Abstract

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.