Locomotion modes for a hybrid wheeled-leg planetary rover

Future planetary rovers are expected to probe across steep sandy slopes such as crater rims where wheel slippage can be a critical problem. One possible solution is to equip locomotion mechanisms with redundant actuators so that the rovers are able to actively reconfigure themselves to adapt to the target terrain. This study modeled a reconfigurable rover to analyze the effects of posture change on rover slippage over sandy slopes. The study also investigated control strategies for a reconfigurable rover to reduce slippage. The proposed mechanical model consists of two models: a complete rover model representing the relationship between the attitude of the rover and the forces acting on each wheel, and a wheel‐soil contact force model expressed as a function of slip parameters. By combining these two models, the proposed joint model relates the configuration of the rover to its slippage. The reliability of the proposed model is discussed based on a comparison of slope‐traversing experiments and numerical simulations. The results of the simulations show trends similar to those of the experiments and thus the validity of the proposed model. Following the results, a configuration control strategy for a reconfigurable rover was introduced accompanied by orientation control. These controls were implemented on a four‐wheeled rover, and their effectiveness was tested on a natural sand dune. The results of the field experiments show the usefulness of the proposed control strategies.

Section: Introductionmentioning

confidence: 99%

Modeling, Analysis, and Control of an Actively Reconfigurable Planetary Rover for Traversing Slopes Covered with Loose Soil

Inotsume

Sutoh

Nagaoka

et al. 2013

“…SherpaTT is the successor of the system Sherpa (Cordes, Dettmann, & Kirchner, ) improving the workspace of the legs while having a reduced number of active DoF (Cordes et al, ). Both Sherpa‐versions are designed to work together with other robots in unstructured terrain; while Sherpa has to transport a highly mobile six‐legged walking robot (Roehr et al, ), SherpaTT has to transport immobile payloads requiring higher flexibility in the rover’s body pose control for deployment and pick‐up.…”

Section: Sherpatt: System Overviewmentioning

confidence: 99%

“…An ICR in infinity of the y ‐axis of the SCS corresponds to a pure forward movement, while positioning the ICR at the origin of the SCS results in a pure point turn of the robot. In Cordes et al (), an explicit calculation of the wheel orientation and wheel velocity for a rover with variable footprint is presented for the system Sherpa. The calculation assumes quasi‐static states and neglects the current movement of the suspension system.…”

Section: Control System Designmentioning

confidence: 99%

“…Details on the modularity and the multirobot scenario can be found in Roehr, Cordes, and Kirchner (2014), Sonsalla et al (2014Sonsalla et al ( , 2017, Wenzel, Cordes, and Kirchner (2015). SherpaTT is the successor of the system Sherpa (Cordes, Dettmann, & Kirchner, 2011) improving the workspace of the legs while having a reduced number of active DoF .…”

Section: Sherpatt: System Overviewmentioning

confidence: 99%

See 1 more Smart Citation

Design and field testing of a rover with an actively articulated suspension system in a Mars analog terrain

Cordes¹,

Kirchner

Babu³

2018

Self Cite

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.

“…Sherpa makes use of an active suspension system that allows to select from a set of locomotion modes depending on the current terrain situation. These modes range from various postures to enhance the relationship between the center of gravity and the center of the support polygon to substantially different drive modes, for example planar omnidirectional movements or inchworming modes (Cordes et al., ). Figure displays the final state of the integration of Sherpa.…”

Section: Rimres – a System Of Systemsmentioning

confidence: 99%

Reconfigurable Integrated Multirobot Exploration System (RIMRES): Heterogeneous Modular Reconfigurable Robots for Space Exploration

Roehr¹,

Cordes²,

Kirchner

2013

Self Cite

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.