Abstract
The paper discusses the redesign of the second version of the Mantis hybrid leg-wheel mobile robot, conceived for surveillance and inspection tasks in unstructured indoor and outdoor environments. This small-scale ground mobile robot is characterized by a main body equipped with two front actuated wheels, a passive rear axle and two rotating legs. Motion on flat and even ground is purely wheeled in order to obtain high speed, high energetic efficiency and stable camera vision; only in case of obstacles or ground irregularities the front legs realize a mixed leg-wheel locomotion to increase the robot climbing ability; in particular, the outer profile of the legs, inspired by the praying mantis, is specially designed to climb square steps. The multibody simulations and the experimental tests on the first prototype have shown the effectiveness of the mixed leg-wheel locomotion not only for step climbing, but also on uneven and yielding terrains. Nevertheless, extensive experimental tests have shown that the front wheels may slip in the last phase of step climbing in case of contact with some materials. In order to overcome this problem, the leg design has been modified with the introduction of auxiliary passive wheels, which reduce friction between legs and step upper surface; these wheels are connected to the legs by one-way bearings, in order to rotate only when they are pulled by the front wheels, and remaining locked when they have to push forward the robot. The influence of the auxiliary wheels on the front wheels slippage is investigated by means of theoretical analysis and multibody simulations.
Highlights
In the last years, the scientific and industrial research interest about ground mobile robots is continuously growing
In the research and industrial scenarios there is a wide variety of proposed locomotion systems, and it is not easy to perform a complete and synthetic classification and comparison; if we exclude robots with locomotion principles oriented to specialpurpose applications, it is possible to identify three main categories of ground mobile robots: wheeled (W), tracked (T), and legged (L); four hybrid categories can be derived by combination
In order to maximize the operative flexibility of ground mobile robots, the main difficulty is to design a locomotion system which fulfils conflicting requirements, such as high speed and efficiency on flat terrains and obstacle climbing ability
Summary
The scientific and industrial research interest about ground mobile robots is continuously growing. If we consider small-scale robots, the inertial forces related to trajectory discontinuities are usually not critical, and this allows to adopt simpler locomotion mechanisms; there is a wide variety of locomotion architectures with simplified mechanics, which are not suitable for heavy robots but that provide an excellent compromise between performance and cost for lightweight robots Examples of this design approach for small-scale robots are RHex [10], Whegs [11] and Loper [12]; these robots are characterized by a locomotion principle based on one-degree-of-freedom rotating legs which perform differential steering; their mechanical design and their control are quite simple; thanks to the design of their flexible legs, their speed and obstacle climbing ability are rather good. The influence of the auxiliary wheels on the front wheels slippage and robot motion is analysed by means of theoretical analysis and multibody simulations
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