A direct-drive air-ground reconfigurable robot for high-agility tri-modal locomotion and payload transport

To address the limitations of existing air-ground robots regarding environmental adaptability and structural efficiency, this paper proposes a novel direct-drive reconfigurable robot capable of switching between Unmanned Ground Vehicle (UGV), Unmanned Aerial Vehicle (UAV), and Mobile Inverted Pendulum (MIP) modes. In terms of mechanical design, the system features hollow-shaft direct-drive joints coupled with symmetrically arranged gear-link mechanisms, ensuring a compact layout with high payload capacity. By adopting direct-drive actuation for propulsion, this design eliminates transmission backlash in the driving and balancing loops, while the gear linkages are strictly reserved for quasi-static reconfiguration, which enhances structural rigidity. A hierarchical control architecture is proposed, featuring centroidal MPC planning, unified dynamics feedforward, and a second-order reference model for smooth mode transitions. Experimental validation confirms a rapid mode switching time of within 4 s. The system demonstrates exceptional versatility: high-speed ground mobility (3 m/s) with millimeter-level positioning accuracy, stable aerial payload transport (1.5 kg), and agile near-zero-radius turning in MIP mode. This system effectively resolves structural and adaptability bottlenecks, offering an efficient solution for complex cross-domain operations.