Tilt-Ropter: A Novel Hybrid Aerial and Terrestrial Vehicle with Tilt Rotors and Passive Wheels

TL;DR

The paper tackles the limited endurance of micro aerial vehicles by introducing Tilt-Ropter, a fully actuated hybrid aerial-terrestrial platform that uses tilt rotors and passive wheels to enable energy-efficient air and ground locomotion. A unified wrench-based nonlinear model predictive controller (NMPC) tracks trajectories while incorporating ground contact and actuator constraints, complemented by an external wrench estimation module for robustness during terrestrial interaction. Key contributions include the novel mechanical design with centralized tilting, a comprehensive dynamic model and a wrench-based control allocation, and a robust wrench estimator that accounts for servo dynamics. validated through Gazebo and hardware experiments, the system achieves precise aerial and ground tracking, seamless mode transitions, and substantial energy savings, notably a $92.8\%$ reduction in ground-power consumption during terrestrial operation, enabling long-duration missions in energy-constrained environments.

Abstract

In this work, we present Tilt-Ropter, a novel hybrid aerial-terrestrial vehicle (HATV) that combines tilt rotors with passive wheels to achieve energy-efficient multi-mode locomotion. Unlike existing under-actuated HATVs, the fully actuated design of Tilt-Ropter enables decoupled force and torque control, greatly enhancing its mobility and environmental adaptability. A nonlinear model predictive controller (NMPC) is developed to track reference trajectories and handle contact constraints across locomotion modes, while a dedicated control allocation module exploits actuation redundancy to achieve energy-efficient control of actuators. Additionally, to enhance robustness during ground contact, we introduce an external wrench estimation algorithm that estimates environmental interaction forces and torques in real time. The system is validated through both simulation and real-world experiments, including seamless air-ground transitions and trajectory tracking. Results show low tracking errors in both modes and highlight a 92.8% reduction in power consumption during ground locomotion, demonstrating the system's potential for long-duration missions across large-scale and energy-constrained environments.

Figures (10)

• Figure 1: Tilt-Ropter: a novel hybrid aerial-terrestrial vehicle.
• Figure 2: Exploded view of Tilt-Ropter key components.
• Figure 3: Illustration of the design of the tilt arm.
• Figure 4: Definition of coordinate frames.
• Figure 5: Control architecture of Tilt-Ropter. $\bm{p}_m$ and $\bm{q}_m$ are the measured position and quaternion of the robot from motion capture system. $\bm{\Omega}_m$ is the measured rotor speeds from ESC.