Design and Analysis of a Bi-directional Transformable Wheel Robot Trimode

This article presents a novel transformable wheeled robot with three motion modes. Based on the four-bar mechanism design, the transformable wheel can transform into CW (clockwise) legged wheel mode and CCW (counterclock-wise) legged wheel mode from the circular wheel. Both legged wheel modes achieve good obstacle-climbing performance when the robot overcomes obstacles such as steps in the forward and backward directions. Mathematical expression of shape of the transformable wheel is established for design variables selection of the wheel to improve the obstacle-overcoming ability of the legged wheel modes. Dynamics model of the robot in the step-overcoming scene is analyzed to determine and reduce the torque load of the motor. Finally, two prototypes of the robot are developed. The early-stage prototype made by 3D printing verifies the step-overcoming ability of the transformable wheel. Then, structural strength of the robot chassis and the robustness of the hardware are improved in the second prototype, which can play a role in SAR and indoor service tasks. In general, the prototype can overcome steps with the height of more than 2 times the radius of the wheel in CW/CCW legged wheel mode and move at a maximum speed of 3.15 m/s in circular wheel mode (about 5.83 times the length of the robot per second).