This study presents the electromechanical design, the control approach, and the results of a field test campaign with the hybrid wheeled‐leg rover SherpaTT. The rover ranges in the 150 kg class and features an actively articulated suspension system comprising four legs with actively driven and steered wheels at each leg’s end. Five active degrees of freedom are present in each of the legs, resulting in 20 active degrees of freedom for the complete locomotion system. The control approach is based on force measurements at each wheel mounting point and roll–pitch measurements of the rover’s main body, allowing active adaption to sloping terrain, active shifting of the center of gravity within the rover’s support polygon, active roll–pitch influencing, and body‐ground clearance control. Exteroceptive sensors such as camera or laser range finder are not required for ground adaption. A purely reactive approach is used, rendering a planning algorithm for stability control or force distribution unnecessary and thus simplifying the control efforts. The control approach was tested within a 4‐week field deployment in the desert of Utah. The results presented in this paper substantiate the feasibility of the chosen approach: The main power requirement for locomotion is from the drive system, active adaption only plays a minor role in power consumption. Active force distribution between the wheels is successful in different footprints and terrain types and is not influenced by controlling the body’s roll–pitch angle in parallel to the force control. Slope‐climbing capabilities of the system were successfully tested in slopes of up to 28° inclination, covered with loose soil and duricrust. The main contribution of this study is the experimental validation of the actively articulated suspension of SherpaTT in conjunction with a reactive control approach. Consequently, hardware and software design as well as experimentation are part of this study.

This paper presents the multirobot team RIMRES (Reconfigurable Integrated Multirobot Exploration System), which is comprised of a wheeled rover, a legged scout, and several immobile payload items. The heterogeneous systems are employed to demonstrate the feasibility of reconfigurable and modular systems for lunar polar crater exploration missions. All systems have been designed with a common electromechanical interface, allowing to tightly interconnect all these systems to a single system and also to form new electromechanical units. With the different strengths of the respective subsystems, a robust and flexible overall multirobot system is built up to tackle the, to some extent, contradictory requirements for an exploration mission in a crater environment. In RIMRES, the capability for reconfiguration is explicitly taken into account in the design phase of the system, leading to a high degree of flexibility for restructuring the overall multirobot system. To enable the systems' capabilities, the same distributed control software architecture is applied to rover, scout, and payload items, allowing for semiautonomous cooperative actions as well as full manual control by a mission operator. For validation purposes, the authors present the results of two critical parts of the aspired mission, the deployment of a payload and the autonomous docking procedure between the legged scout robot and the wheeled rover. This allows us to illustrate the feasibility of complex, cooperative, and autonomous reconfiguration maneuvers with the developed reconfigurable team of robots.

This paper introduces locomotion modes for the planetary rover Sherpa 1 . The rover's locomotion system consists of four wheeled-legs, each providing a total of six degrees of freedom. The design of the active suspension system allows a wide range of posture and drive modes for the rover. Selflocking gears in the suspension system allow to maintain the body height without the need of actively driving the actuators. Thus, energy-efficient wheeled locomotion and at the same time high flexibility in ground adaption and obstacle negotiation are possible, as well as high payload capabilities. Furthermore, the rover will be equipped with a manipulator arm explicitly designed to be used for locomotion support. Thus, all degrees of freedom of the system can be used to enhance the locomotive capabilities. This paper gives an overview of the mechanical design of the rover, kinematic considerations for movement constraints on the wheel contact points are presented. Based on these constraints, the wheel motions due to the commanded velocities of the platform can be calculated, taking into account the flexible posture of the rover. A first set of possible locomotion modes for the rover is presented in this paper as well.

The LUNARES (Lunar Crater Exploration Scenario) project emulates the retrieval of a scientific sample from within a permanently shadowed lunar crater by means of a heterogeneous robotic system. For the accomplished earth demonstration scenario, the Shakelton crater at the lunar south pole is taken as reference. In the areas of permanent darkness within this crater, samples of scientific interest are expected. For accomplishment of such kind of mission, an approach of a heterogeneous robotic team consisting of a wheeled rover, a legged scout as well as a robotic arm mounted on the landing unit was chosen. All robots act as a team to reach the mission goal. To prove the feasibility of the chosen approach, an artificial lunar crater environment has been established to test and demonstrate the capabilities of the robotic systems. Figure 1 depicts the systems in the artificial crater environment. For LUNARES, preexisting robots were used and modified were needed in order to integrate all subsystems into a common system control. A ground control station has been developed considering conditions of a real mission, requiring information of autonomous task execution and remote controlled operations to be displayed for human operators. The project successfully finished at the end of 2009. This paper reviews the achievements and lessons learned during the project.

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