AirCrab: A Hybrid Aerial-Ground Manipulator with An Active Wheel

TL;DR

AirCrab introduces a hybrid aerial-ground manipulator with a single active wheel to achieve stable ground contact and enhanced manipulation accuracy while maintaining aerial performance. The work provides a comprehensive dynamics model that accounts for wheel-ground interaction and develops a PCA-based control allocation to prioritize attitude maintenance and minimize thrust in ground mode. Attitude control and ground-mode allocation are validated experimentally, showing improved pitch stability and notable reductions in end-effector tracking error compared with aerial-only operation, along with energy-efficient ground assistance. Hybrid missions, including forming the letters 'NTU', demonstrate practical capabilities for precise manipulation on narrow surfaces and transitions between air and ground modes. This approach offers a path toward robust, energy-efficient autonomous hybrid manipulation for constrained terrains.

Abstract

Inspired by the behavior of birds, we present AirCrab, a hybrid aerial ground manipulator (HAGM) with a single active wheel and a 3-degree of freedom (3-DoF) manipulator. AirCrab leverages a single point of contact with the ground to reduce position drift and improve manipulation accuracy. The single active wheel enables locomotion on narrow surfaces without adding significant weight to the robot. To realize accurate attitude maintenance using propellers on the ground, we design a control allocation method for AirCrab that prioritizes attitude control and dynamically adjusts the thrust input to reduce energy consumption. Experiments verify the effectiveness of the proposed control method and the gain in manipulation accuracy with ground contact. A series of operations to complete the letters 'NTU' demonstrates the capability of the robot to perform challenging hybrid aerial-ground manipulation missions.

Figures (8)

• Figure 1: The AirCrab mimics the nesting behavior of egrets, standing on a single active wheel, maintaining attitude with propellers, and performing precise operation.
• Figure 2: Coordinate frames for AirCrab. The inertial frame is labeled with a subscript $I$ and the body frame is labeled with a subscript $b$.
• Figure 3: The response of proposed method with ${T_\text{ground}}/{T_\text{max}} = 7.5\%$, the settling time $t_s = 0.9195s$. In this figure, $0^{\circ}$ is the desired state and the region of $\pm3^{\circ}$ error is colored in green.
• Figure 4: Pitch angle error and power consumption under various throttle levels.
• Figure 5: The time-lapse photos of the manipulation experiment. The yellow points and red arrows illustrate the movement of the end effector.