Mobility Improvement on the Two-Wheeled Dynamically Balanced Robot – $\mathrm{J}4.\beta$

Abstract

Dynamically self-balancing wheeled robots possess the characteristics of having a small footprint, low base-to-height ratios, high accelerations and speeds, and low costs. They are suitable for working in human-centric environments. As part of our ongoing effort in creating self-balancing wheeled robots, in this article, we reported the development of our latest model – $\mathrm{J}4.\beta$. In contrast to the previous model – $\mathrm{J}4.\alpha$, the new model has a greater dynamic mass-to-total ratio; thus, the acceleration and the ultimate speed are both increased. Here, the maximum speed of 4.4 m/s of the motion platform is achievable by $\mathrm{J}4.\beta$. We analyzed the system dynamics and had confirmations from measurements; a speed servo system was developed based on PID control. To simplify the dynamics of the mobile robot, a stepper motor instead of a DC motor was adopted for the actuation of the dynamic mass; the overall controlled plant could be approximated as a second-order system. To acquire the PID coefficients, a series of road tests were performed in a common office building. A set of suitable PID coefficients was obtained and verified by three speeds: 0.5 m/s, 1 m/s, and 2 m/s. The speed curves exhibited fast ramp-up, low overshoot, setpoint matching, and low oscillation. For regulation testing, a zero speed was set and external disturbance was applied. The robot was witnessed to slow down rapidly and remain stationary without intensive oscillation. While constructing the autonomous navigation and remote control systems for the mobile robot, the sampling rate of the control system was largely upgraded to 4k Hz to achieve a better tracking and regulation ability.