This paper presents the software framework established to facilitate cloud-hosted robot simulation. The framework addresses the challenges associated with conducting a task-oriented and real-time robot competition, the Defense Advanced Research Projects Agency (DARPA) Virtual Robotics Challenge (VRC), designed to mimic reality. The core of the framework is the Gazebo simulator, a platform to simulate robots, objects, and environments, as well as the enhancements made for the VRC to maintain a high fidelity simulation using a high degree of freedom and multisensor robot. The other major component used is the CloudSim tool, designed to enhance the automation of robotics simulation using existing cloud technologies. The results from the VRC and a discussion are also detailed in this work.

A trajectory tracking controller based on differential flatness is presented for a nonlinear bicycle model. This controller maps the bicycle dynamics into a point mass located at a center of oscillation with an additional degree of freedom of yaw dynamics. A state transformation is performed that reveals structure in the yaw dynamics resembling a Lie¿nard system. A candidate Lyapunov function inspired by this structure is used to assess the stability of the yaw dynamics while tracking straight-line trajectories and steady turns. The basin of attraction of the controller is limited by actuator constraints and the presence of unstable equilibrium points during turns with high lateral acceleration. The controller properties and the stability of yaw dynamics are demonstrated in simulation.

An analogy between the dynamics of a cart-pole system and vehicle rollover dynamics is used to derive a controller for tipping up and stabilizing a planar model of a passenger vehicle near rollover by controlling lateral tire friction forces. The controller is based on a previously published controller for stabilizing a cart-pole using partial feedback linearization and energy shaping. A necessary condition for tip-up is given based on the surface friction coefficient and the location of the vehicle center of gravity (c.g.). A multi-body vehicle model with suspension is presented in the form of the robotic manipulator equations. Simulation results are presented demonstrating the effect of friction and suspension properties on the tip-up problem.

In this video, a novel tracked mechanism for sideways motion is presented. The tracked mechanism is of circular cross-section and has active rolling axes at the center of the circles. Conventional tracked mechanisms can support massive loads, but cannot produce sideways motion. Additionally, previous crawler edges sink undesirably on soft ground, particularly when the vehicle body is subject to a sideways tilt. The proposed design solves these drawbacks by adopting a circular cross-section crawler. A prototype has been developed to illustrate the concept. Motion experiments confirm the novel properties of this mechanism: sideways motion and robustness against edge-sink. Motion experiments, with a test vehicle are also presented.

This paper describes the design of unified active safety framework that combines trajectory planning, threat assessment, and semi-autonomous control of passenger vehicles into a single constrained-optimal-control-based system. This framework allows for multiple actuation modes, diverse trajectory-planning objectives, and varying levels of autonomy. The vehicle navigation problem is formulated as a constrained optimal control problem with constraints bounding a navigable region of the road surface. A model predictive controller iteratively plans the best-case vehicle trajectory through this constrained corridor. The framework then uses this trajectory to assess the threat posed to the vehicle and intervenes in proportion to this threat. This approach minimizes controller intervention while ensuring that the vehicle does not depart from a navigable corridor of travel. Simulated results are presented here to demonstrate the framework's ability to incorporate multiple threat thresholds and configurable intervention laws while sharing control with a human driver.

Path tracking control on non-flat terrain is an important capability of mobile robots operating in outdoor environments. A path tracking controller based on the model predictive control (MPC) framework is presented that explicitly considers terrain geometry and actuator limitations. The controller performance is studied with three vehicle dynamic models in a high-fidelity ADAMS simulation. The effect of model order on path tracking performance on flat terrain and sloped terrain is evaluated. It is shown that improved performance can be obtained by explicitly considering terrain effects.

In this paper, a novel crawler mechanism for sideways motion is presented. The crawler mechanism is of circular cross-section and has active rolling axes at the center of the circles. Conventional crawler mechanisms can support massive loads, but cannot produce sideways motion. Additionally, previous crawler edges sink undesirably on soft ground, particularly when the vehicle body is subject to a sideways tilt. The proposed design solves these drawbacks by adopting a circular cross-section crawler. A prototype has been developed to illustrate the concept. Motion experiments confirm the novel properties of this mechanism: sideways motion and robustness against edge-sink. Motion experiments, with a test vehicle are also presented.

Mobile robots and passenger vehicles are frequently required to operate at high speeds, on terrain that is sloped or uneven. These systems can be susceptible to rollover, particularly during severe maneuvers. This paper presents an analysis of rollover stability measurement for mobile robots operating at high speeds. The analysis examines the accuracy of a commonly accepted rollover stability metric during operation on sloped and rough terrain. The effects of sensor placement, center-of-gravity position estimation error, and wheel dynamics are examined. It is shown that these effects can have a significant impact on stability measurement during high speed operation