Duawlfin: A Drone with Unified Actuation for Wheeled Locomotion and Flight Operation

TL;DR

Duawlfin proposes a unified-actuation hybrid UAV that uses one-way bearings and a differential drivetrain to enable bidirectional ground mobility without extra actuators or propeller-based propulsion. The system reuses the four quadrotor motors for both flight and ground driving, with a mode-switch control framework that preserves standard quadrotor flight characteristics while enabling efficient terrestrial locomotion. Experimental validation shows substantial energy savings and agility in ground mode, up to 30° slope climbing, and smooth aerial-ground transitions, with only modest penalties to flight performance. The approach offers a simple, lightweight, and safe solution for urban logistics and indoor navigation, with open-source design assets to facilitate adoption and further development.

Abstract

This paper presents Duawlfin, a drone with unified actuation for wheeled locomotion and flight operation that achieves efficient, bidirectional ground mobility. Unlike existing hybrid designs, Duawlfin eliminates the need for additional actuators or propeller-driven ground propulsion by leveraging only its standard quadrotor motors and introducing a differential drivetrain with one-way bearings. This innovation simplifies the mechanical system, significantly reduces energy usage, and prevents the disturbance caused by propellers spinning near the ground, such as dust interference with sensors. Besides, the one-way bearings minimize the power transfer from motors to propellers in the ground mode, which enables the vehicle to operate safely near humans. We provide a detailed mechanical design, present control strategies for rapid and smooth mode transitions, and validate the concept through extensive experimental testing. Flight-mode tests confirm stable aerial performance comparable to conventional quadcopters, while ground-mode experiments demonstrate efficient slope climbing (up to 30°) and agile turning maneuvers approaching 1g lateral acceleration. The seamless transitions between aerial and ground modes further underscore the practicality and effectiveness of our approach for applications like urban logistics and indoor navigation. All the materials including 3-D model files, demonstration video and other assets are open-sourced at https://sites.google.com/view/Duawlfin.

Figures (8)

• Figure 1: Top: Duawlfin is in aerial mode. Bottom: Duawlfin is runing on the sidewalk in ground mode. The propellers are still turning at low speed since the friction in the one-way bearings' free mode.
• Figure 2: (a): Top-side view of Duawlfin. It shows its aerial propulsion system. The vehicle features four A2212 1400 kv motors driving 8-inch (8045) propellers. Each propeller is mounted via a one-way bearing and secured by a shaft collar, ensuring that in flight mode the bearings lock to generate thrust, while in ground mode the propellers freewheel. (b): Bottom-side view. It shows the ground drivetrain arrangement. Each motor shaft is equipped with a small pulley that drives a belt connected to a larger pulley on one of the differential’s input shafts. Two opposing motors feed their respective differentials, whose output shafts are directly connected to integrated wheels. Universal ball casters at the front and rear provide stable ground support.
• Figure 3: Motor directions for drive and flight modes. In the flight mode, the propellers are engaged with the one-way bearings that allow torques to be transmitted to generate thrust. In the drive mode, the motors reverse and decouple the propellers. The motor speed differences are manipulated to provide full bidirectional ground mobility through the differentials.
• Figure 4: The diagram of the two-mode control framework. In aerial mode, a closed-loop cascaded controller manages acceleration, with inputs coming from either manual controls (for outdoor FPV flights) or an outer-loop position controller (for indoor Motion Capture flight). In ground mode, desired linear and rotational speeds are directly mapped to motor speed commands using factors such as gear ratio and wheel radius.
• Figure 5: Motor speed profiles for a complete square-path maneuver in the ground mode. The vehicle departs waypoint 1 and reaches waypoint 2 at $t = 1.5$ s, then performs a $90^\circ$ in-place rotation from $t = 1.5$ s to $2.5$ s. It travels to waypoint 3, arriving at $t = 4.0$ s, executes a second $90^\circ$ turn from $t = 4.0$ s to $5.0$ s, then moves to waypoint 4, arriving at $t = 6.5$ s. At waypoint 4 it performs a third $90^\circ$ rotation between $t = 6.5$ s and $7.5$ s before returning toward waypoint 1 to complete the square.