Inspired by the fifth-year anniversary celebration of the homonymous symposium at the International Mechanical Engineering Congress & Exposition (IMECE), this Special Section with ten articles shares the latest research efforts in design, theory, development, and applications for mobile robots and unmanned ground vehicles.

The adoption of field robotics has rapidly increased with many notable examples that have been developed and validated for operations in overground (terrestrial or extraterrestrial), underground, underwater, and in air or space settings.

Applications range from agriculture, mining, surveillance, and environmental monitoring, to search and rescue and disaster relief, planetary exploration, and nuclear power plant and industrial operations. According to the International Federation of Robotics (IFR), professional service robotic solutions have seen a tremendous increase in recent years, and the market has a potential development that in 2023 will reach 537,000 units, with +31% compound annual growth rate. In this Special Section, an example of mobile robot for agricultural automation is presented by Galati et al. who discuss the design, construction, and testing of a tracked service robot that is able to increase the overall bulk density of the flax raw material moving inside a truck container and rolling over it. Experimental results—in emulated and real settings—demonstrate the effectiveness of the proposed robotic solution.

To effectively operate in their working environment, many challenges need to be tackled and addressed. For example, when operations on uncharted highly irregular terrain are required, an appropriate choice and functional design of the locomotion system is critical, and many options have been investigated including passive/active articulated suspension systems for wheeled robots, articulated tracked vehicles, legged robots, and hybrid solutions.

Within this topic, Carbonari et al. discuss a class of articulated multiwheel robots designed for improved mobility over rough terrain. The locomotion performance has been evaluated via dynamic model-based simulations. Data obtained in real experiments were used to identify the model parameters. Cardenas et al. propose a vision-based control approach for mobile manipulators to traverse uneven terrain, so that the loading platform is kept close to the horizontal configuration. An innovative suspension system is designed to compensate for irregularities in the terrain by using a crank-slider mechanism that facilitates the control of the platform using a vision-based approach.

The adoption of hybrid locomotion systems is extensively discussed in the study by Atay et al. who describe the dynamic modeling and the trajectory tracking control system of a bi-modal, multirotor vehicle that is capable of omnidirectional terrestrial rolling and multirotor flight. The proposed robot may roll along the ground to preserve energy and extend autonomy, but it may also fly to provide high mobility and maneuverability when necessary. In a second work, the same authors present and validate a robust method for controlling the terrestrial motion of the same bi-modal, multirotor vehicle. A nonlinear, multi-input–multi-output, sliding mode controller is proposed, and constrained optimization techniques are used for developing a control allocation strategy, which minimizes power consumption while rolling. Finally, Tyler et al. propose a design optimization framework for a rolling-flying vehicle using a multi-objective genetic algorithm to optimize a parameterized multi-physics model. The research represents an interesting contribution for the whole multirotor community.

Robots are also required to interact with the surrounding environment via mobile manipulators that bring dedicated tools or sensors for proximity measurements. As an example, Kim et al. introduce a new robot system that uses its manipulator to switch between wheeled and legged locomotion. Wheels are ideal for energy efficiency, but they can suffer from limitations in the presence of obstacles or complex ground. Rotating legs can help traverse obstacles but at the cost of a lower energy efficiency. The system described uses the manipulator to attach/detach the so-called propulsor, and transform the wheels in rotating legs.

A service/field robot operates with a high degree of autonomy based on an inbuilt control system. Lee et al. present a whole-body controller for a quadrupedal robot by using the actual joint torque measured from a torque sensor and using the robot's dynamics, which enables the robot both to demonstrate dynamic locomotion and react to external disturbances. Using the computed center of mass moment, a moment-based impedance controller distributes a feed-forward force to stabilize the robot's balance.

Navigation strategies are also important especially when long-distance and long-duration missions are involved. Environment-aware planners can help to develop safe and energy efficient paths toward the intended goal. Yandun et al. explore a novel approach to model and predict the vehicle–terrain interaction that is treated as a statistical random process via particle Markov chains to get approximations of the posterior parameter distributions. The proposed approach is supported by an extensive set of simulations using a kinematic vehicle model and real data using an experimental earthmoving vehicle.

For a systematic and comparative analysis of field and service robots, it is important to provide quantitative measures of their performance in the field in terms of traction, climbing and traversability, safety and stability, power consumption, autonomy, and reliance on human supervision. This aspect also calls for the investigation of physics-based multibody models that capture with high fidelity the dynamic response of robots considering the interaction with the operating environment and that can be useful during the design and development stages before field validation of the system. Herrera-Cordero et al. present an example of msc adams/matlab co-simulation for the dynamics study and control of a single-wheel pendulum robot with inertial locomotion actuation to characterize design solutions based on the validation of analytical results.

We hope that this Special Section contributes to the increasing interest in research and applications for service and field mobile robots.