Adaptive Flexible Wheels for Planetary Exploration

Abstract :

The exploration of planetary surfaces is a major focus of international space research activities. Mobility of exploration platforms is a key to examine a wide area, focus on interesting sites and thereby maximise the output of scientific data. The compromise of a reliable, compact, lightweight system with maximal mobility in rough terrain, leads to very specialized vehicle designs and a high degree of optimization in each individual subsystem of the overall locomotion system. All robotic planetary rovers, having been in the field (Moon / Mars), have been designed with rigid wheels. These wheels are reliable and have a wide heritage from terrestrial applications; in addition to that, their design is very simple and fail safe. Their main disadvantage is the relative high ground pressure, soil sinkage and compaction resistance. As a result of that, the trafficability is reduced and areas with loose soil have to be avoided. An alternative way to overcome the disadvantages of traditional rover wheels was already chosen with the introduction of flexible wheels in the ESA ExoMars rover design. Flexibility of wheels leads to flattened footprints. Thus lower ground pressure and sinkage into the soil appears. The tractive performance increases with flexible wheels, so smaller wheel diameter can be chosen. In the final design, this leads to lower volume and power requirements at a higher degree of mobility due to better trafficability in loose soil. The next step in wheel optimization shall provide the optimal wheel for each individual underground. This can be realized by developing a smart, flexible wheel with adjustable stiffness. A smart, adaptive, flexible wheel is currently under development at DLR Bremen in the department of Exploration Systems and is related to the German RIMRES robotics project. In this project, a flexible metallic wheel for extraterrestrial use is re-designed with sensors, analysis capabilities, control electronics and a stiffening system. This mechanism allows to vary the wheel stiffness from soft to hard and to minimize the sinkage in loose soil, as well as to minimize the hysteresis losses on hard ground. The therefor required sensor system and control circuit of the wheel stiffness is part of this investigation as well. First tests with breadboard models have shown the feasibility of the chosen concepts and a prototype is in the process of hardware realization.

Keywords :

Planetary rover, flexible wheel, intelligent wheel, instrumented wheel, adaptronic, trafficability