CapsuleBot: A Novel Hybrid Aerial-Ground Bi-Copter Robot With Two Actuated-Wheel-Rotors

TL;DR

CapsuleBot addresses the challenge of achieving long-endurance, low-noise operation in a hybrid aerial-ground robot by introducing the actuated-wheel-rotor, which reuses tilting motors as wheel actuators to enable ground propulsion with only four motors. The design couples a bi-copter aerial model with a two-wheel self-balancing terrestrial model and adds a transitional state to reorient rotors for takeoff, backed by comprehensive dynamics and cascaded control for both modes. Experimental results demonstrate high energy efficiency ($\eta \approx 98.9\%$), low wheel-mode noise approaching ambient levels, and robust capability to climb inclines, fly over cliffs, and traverse rough terrain, positioning CapsuleBot as a viable covert and persistent ISR platform. The work also provides benchmark comparisons showing advantages over existing bi-copter designs in motor count, efficiency, and decoupled air-ground control, with future plans for autonomous multimodal path planning.

Abstract

This paper presents the design, modeling, and experimental validation of CapsuleBot, a novel hybrid aerial-ground bi-copter robot designed for long-endurance and low-noise operations. CapsuleBot combines the maneuverability of a bi-copter in the air with the low power consumption and low noise of a two-wheel self-balancing robot on the ground. To achieve this, we design an innovative mechanical structure named the actuated-wheel-rotor, which uses a servo motor and a brushless motor to function as both a tilting rotor in the air and an actuated wheel on the ground. CapsuleBot is equipped with two actuated-wheel-rotors, enabling it to achieve hybrid aerial-ground propulsion using only four motors, with no additional motors required compared to a bi-copter. Additionally, we develop comprehensive dynamics and control systems for both air and wheel mode, based on the bi-copter model and the two-wheel self-balancing robot model. A prototype of CapsuleBot is constructed, and its performance in terms of low power consumption and low noise is validated through experiments. Challenging tasks demonstrate CapsuleBot's capability to climb steep, fly over cliffs, and traverse rough terrains.

Figures (13)

• Figure 1: Our CapsuleBot prototype.
• Figure 2: An envisioned application scenario for CapsuleBot involves deploying the robot into a concealed reconnaissance area using either aerial or wheel modes. The aerial mode is utilized not only for air dropping and flying over obstacles that are difficult for ground mode to traverse but also for maneuvering through pipes and narrow spaces. Besides, ground mode is prioritized for tasks requiring low dust generation, low noise, and long endurance.
• Figure 3: The composition of CapsuleBot is detailed below. (a) The comprehensive structural diagram of the robot. (b) Details of gear transmission structures. (c) Details of a slip ring. The serial numbers on (a) correspond to specific components: (1) actuated-wheel-rotor, (2) flight controller and electronic speed controller (ESC), (3) slip ring, (4) servo motor, (5) gear, (6) carbon fiber wheel, (7) bearing, (8) carbon fiber frame, (9) battery.
• Figure 4: Electrical architecture of CapsuleBot, where the yellow lines represent logic circuits, and the red lines denote power circuits.
• Figure 5: Dynamic model.