Control of two-wheeled humanoid robots poses several challenges due to the unstable dynamics of their mobile base and the coupling between upper and lower body dynamics. The problem is often faced in the literature with methods based on linearized or simplified models that fail in exploiting the whole body dynamic capabilities of the platform in use. In this work we tackle the problem of whole-body dynamic control for a mobile wheeled unstable humanoid robot. Compared to existing approaches based on on-line optimization to guarantee respect of the constraints, we propose a control method that takes into account the nominal constrained dynamics of the robot in the quasi-velocities through an internal model, thus reducing the computational burden. A computed-torque control law in the quasi-velocities is used to stabilize the robot around the upper position. We report on preliminary experimental results and on the method effectiveness in rejecting unknown external disturbances.

Robots face the eventuality of falling. Unplanned events, external disturbances and technical failures may lead a robot to a condition where even an effective dynamic stabilization is not sufficient to maintain the equilibrium. Therefore, it is essential to equip robotic platforms with both active and passive fall protection means to minimize damages, and enable the recovery and restart without physical human intervention. This work introduces a method to design an integrated safety system for two-wheeled humanoids. As a case study, the method is applied to a robot and experimentally tested under several conditions corresponding to different causes of robot instability, such as motor jamming, external disturbances, and sudden shutdown .

To enable the design of planning and control strategies in simulated environments before their direct application to the real robot, exploiting the Sim2Real practice, powerful and realistic dynamic simulation tools have been proposed, e.g., the ROS-Gazebo framework. However, the majority of such simulators do not account for some of the properties of recently developed advanced systems, e.g., dynamic elastic behaviors shown by all those robots that purposely incorporate compliant elements into their actuators, the so-called Articulated Soft Robots ASRs. This paper presents an open-source ROS-Gazebo toolbox for simulating ASRs equipped with the aforementioned types of compliant actuators. To achieve this result, the toolbox consists of two ROS-Gazebo modules: a plugin that implements the custom compliant characteristics of a given actuator and simulates the internal motor dynamics, and a Robotic Operation System (ROS) manager node used to organize and simplify the overall toolbox usage. The toolbox can implement different compliant joint structures to perform realistic and representative simulations of ASRs, also when they interact with the environment. The simulated ASRs can be also used to retrieve information about the physical behavior of the real system from its simulation, and to develop control policies that can be transferred back to the real world, leveraging the Sim2Real practice. To assess the versatility of the proposed plugin, we report simulations of different compliant actuators. Then, to show the reliability of the simulated results, we present experiments executed on two ASRs and compare the performance of the real hardware with the simulations. Finally, to validate the toolbox effectiveness for Sim2Real control design, we learn a control policy in simulation, then feed it to the real system in feed-forward comparing the results.