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

Xiangyu Li, Mingwei Lai, Mengke Zhang, Junxiao Lin, Tiancheng Lai, Junping Zhi, Chao Xu, Fei Gao, Yanjun Cao

TL;DR

This work addresses the need for a true triphibious platform that can operate seamlessly across air, ground, and water. It introduces TriphiBot, a minimalist quadcopter-based design with two passive wheels and an eccentric CoG to align thrust with ground motion, paired with a unified Field-Oriented Control propulsion system and a Hybrid Nonlinear Model Predictive Control framework for cross-domain transitions. The authors provide differential flatness analyses for aerial and terrestrial modes and validate their approach through aerial, terrestrial, underwater, and cross-domain experiments, demonstrating improved efficiency, responsive torque control, and smooth mode switching. The resulting platform offers a lightweight, low-complexity solution for hazardous environment tasks with rapid multi-domain mobility and robust cross-domain transitions, though future work should address water flow disturbances and more robust cross-domain positioning.

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.

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

TL;DR

This work addresses the need for a true triphibious platform that can operate seamlessly across air, ground, and water. It introduces TriphiBot, a minimalist quadcopter-based design with two passive wheels and an eccentric CoG to align thrust with ground motion, paired with a unified Field-Oriented Control propulsion system and a Hybrid Nonlinear Model Predictive Control framework for cross-domain transitions. The authors provide differential flatness analyses for aerial and terrestrial modes and validate their approach through aerial, terrestrial, underwater, and cross-domain experiments, demonstrating improved efficiency, responsive torque control, and smooth mode switching. The resulting platform offers a lightweight, low-complexity solution for hazardous environment tasks with rapid multi-domain mobility and robust cross-domain transitions, though future work should address water flow disturbances and more robust cross-domain positioning.

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.
Paper Structure (21 sections, 20 equations, 14 figures, 1 table)

This paper contains 21 sections, 20 equations, 14 figures, 1 table.

Table of Contents

  1. Introduction
  2. Hardware Design
  3. Structure Overview
  4. FOC based Unified Propulsion System
  5. System Electronic Design
  6. Dynamic Model
  7. Triphibious Motion Mode Dynamics
  8. Flight Mode
  9. Ground Mode
  10. Differential Flatness
  11. Control Architecture and Motor Control
  12. Hybrid Control Architecture
  13. Motor Control
  14. Experiment
  15. Experiments Setup
  16. ...and 6 more sections

Figures (14)

  • Figure 1: A depiction of the mission profile of TriphiBot, a triphibious robot that has the capability of flying in the air, swimming in water, and moving on land or the seabed, with smooth cross-domain, cross-mode transitions.
  • Figure 2: Illustration of the TriphiBot's hardware layout. It can be devided into the control system, propulsion system and power system.
  • Figure 3: (a) The coordinate frames of the dynamics model of TriphiBot. (b) Attitude transition of TriphiBot (side view).
  • Figure 4: The electronic equipment of the TriphiBot. The propulsion system consists of four FOC propulsion units.
  • Figure 5: Conceptual diagram of cross-domain transitions. (a) After changing the body's attitude, robot takes off, flies and lands, including crossing obstacles by changing the attitude. (b) From the seabed to the air.
  • ...and 9 more figures