Thomas Thueer

Mobility evaluation of wheeled all-terrain robots

Standardized performance evaluation is uncommon in mobile robotics. Therefore, it is difficult to compare published results and estimate their value. This work aims at providing a basis for the evaluation and comparison of the mobility performance of wheeled, all-terrain robots with respect to terrainability. Precisely defined existing and novel metrics are proposed for this purpose. The utility of these metrics is shown by applying them in a comparison to a selection of rover suspension systems known from the literature. Appropriate models for evaluation of the performance are described as well as the validation of the metrics by means of experimental testing. The simulations reveal significant differences in performance between the rovers which is confirmed by the test results. The correlation of the performance in simulation and reality is highly satisfying and supports the applicability of the proposed metrics.

Performance comparison of rough-terrain robots—simulation and hardware

The design of a rover for a specific environment is a complex procedure which requires modeling a chassis and evaluating it with specific criteria. This is the aim of the performance optimization tool (POT) presented in this paper. The POT enables the comparison and optimization of a rover chassis in a quick and efficient way. The tool is based on a static approach including optimization of the wheel torques in order to maximize traction. Tests with real hardware were performed to validate the POT. Two different rovers, CRAB and RCL-E, were assessed in simulation and hardware with respect to specific, well defined metrics. In simulation, their performances were compared to the rocker-bogie-type rover MER. CRAB and MER showed similar performance, while RCL-E had significant problems with the benchmark obstacle. A very good match between simulation results and real measurements was achieved.

Rover control based on an optimal torque distribution - Application to 6 motorized wheels passive rover

The capability to overcome terrain irregularities or obstacles, named terrainability, is mostly dependant on the suspension mechanism of the rover and its control. For a given wheeled robot, the terrainability can be improved by using a sophisticated control, and is somewhat related to minimizing wheel slip. The proposed control method, named torque control, improves the rover terrainability by taking into account the whole mechanical structure. The rover model is based on the Newton-Euler equations and knowing the complete state of the mechanical structures allows us to compute the force distribution in the structure, and especially between the wheels and the ground. Thus, a set of torques maximizing the traction can be used to drive the rover. The torque control algorithm is presented in this paper, as well as tests showing its impact and improvement in terms of terrainability. Using the CRAB rover platform, we show that the torque control not only increases the climbing performance but also limits odometric errors and reduces the overall power consumption.

Performance Optimization of All-Terrain Robots: A 2D Quasi-Static Tool

The creation of a rover for a specific task requires designing and selecting the mechanical structure specifically for its mission. This can be done by modelling a chassis and evaluating it with specific criteria, which is the aim of the performance optimization tool presented here. This software makes it possible to compare and improve existing and new designs in a quick and efficient way. The tool presented in this paper is based on a quasi-static approach including optimization of the friction coefficients to model and evaluate the rover

Antarctica Rover design and optimization for limited power consumption

Abstract The design process of the new locomotion platform called K11 aims at obtaining a rover capable of traveling thousands of kilometers at 1 m/s in the harsh environment of Antarctica during summer and carrying a 100 kg payload. A model including the drive-train power consumption and masses is used to optimize the parameters of the rover in order to minimize the power consumption. The obtained configuration consumes theoretically only 58W on flat ground and has limited power consumption while climbing a slope. The prototype built based on the optimization results is used to confirm the model.

Planetary Vehicle Suspension Options

A study of locomotion performance of different suspension types was conducted in order to find the rover that matches best any given mission requirements. Two modeling approaches were chosen to evaluate the performance on hard ground and obstacles, as well as on loose soil and inclined planes. A number of metrics were defined which precisely specify what qualifies as good or bad performance. The simulations revealed significant differences between the various configurations for important metrics like torque, power or velocity. These results were used to characterize the performance of each rover and put it in relation to the weighted mission requirements. The sum of the performances multiplied by the weight factors of the requirements was taken as the measure for how good a rover fits the mission needs. This study has shown that a four wheeled rover can be a valuable alternative to the rocker bogie but only in very specific missions.

Characterization and Comparison of Rover Locomotion Performance Based on Kinematic Aspects

Evaluation and comparison of locomotion performance of rovers is a difficult, though very important issue. The performance is influenced by a large number of parameters. In this work, three different rovers were analyzed from a kinematic point of view. Based on a kinematic model, the optimal velocities at the actual position were calculated for all wheels and used for characterization of the suspension of the different rovers. Simulation results show significant differences between the rovers and thus, the utility of the chosen metric. It is shown that a substantial reduction of slip can be achieved by integrating kinematics in a model-based velocity controller.