Ubiquitous Field Transportation Robots with Robust Wheel-Leg Transformable Modules

Abstract

This paper introduces two field transportation robots. Both robots are equipped with transformable wheel-leg modules, which can smoothly switch between operation modes and can work in various challenging terrains. SWhegPro, with six S-shaped legs, enables transporting loads in challenging uneven outdoor terrains. SWhegPro3, featuring four three-impeller wheels, has surprising stair-climbing performance in indoor scenarios. Different from ordinary gear-driven transformable mechanisms, the modular wheels we designed driven by self-locking electric push rods can switch modes accurately and stably with high loads, significantly improving the load capacity of the robot in leg mode. This study analyzes the robot's wheel-leg module operation when the terrain parameters change. Through the derivation of mathematical models and calculations based on simplified kinematic models, a method for optimizing the robot parameters and wheel-leg structure parameters is finally proposed.The design and control strategy are then verified through simulations and field experiments in various complex terrains, and the working performance of the two field transportation robots is calculated and analyzed by recording sensor data and proposing evaluation methods.

Figures (17)

• Figure 1: The two hybrid wheel-leg transformable robots developed in this paper, with schematic diagram of the wheel-leg module operational mode shown in the top left corner of each sub-figure. Top row: the SWhegPro robot has 6 wheel-leg transformable modules, which can be switched between wheel mode (a) and S-shaped leg mode (b). Bottom row: the SWhegPro3 robot has 4 wheel-leg transformable modules, which can be switched between wheel mode (c) and three-impeller leg mode (d). The mode switching of each wheel-leg transformable module is achieved by the self-locking electric push rods, which can significantly improve the robot's robustness and load capacity.
• Figure 2: Detailed mechanism design of wheel-leg transformable modules, where the upper column is the module in SWhegPro and the lower column shows the module in SWhegPro3. The configuration of the module in legged modes (a). The section view of the transformation mechanism (b), showing the electric slip rings and the synchronous pulley. The wire-frame drawing (c) and the transformation between wheel mode and leg mode (d).
• Figure 3: Situations should be considered to determine the wheel parameters. The contact position between the wheel and the standard stair is shown in (a). The limitation while meeting inappropriate stairs, e.g., the length of the rim is too long as (b) shown.
• Figure 4: Comparison of cost when robots equipped with different number of wheels. The cost curves of SWhegPro runs on flat ground which equipped with 4 wheels (a) and 6 wheels (b). The cost curve of SWhegPro3 equipped with six wheels while climbing the stairs (c) and its schematic diagram in Webots simulation environment (d).
• Figure 5: Assumptions and the flow diagram of optimal wheelbase calculation while designing SWhegPro3.