246 research outputs found
Keep Rollin' - Whole-Body Motion Control and Planning for Wheeled Quadrupedal Robots
We show dynamic locomotion strategies for wheeled quadrupedal robots, which
combine the advantages of both walking and driving. The developed optimization
framework tightly integrates the additional degrees of freedom introduced by
the wheels. Our approach relies on a zero-moment point based motion
optimization which continuously updates reference trajectories. The reference
motions are tracked by a hierarchical whole-body controller which computes
optimal generalized accelerations and contact forces by solving a sequence of
prioritized tasks including the nonholonomic rolling constraints. Our approach
has been tested on ANYmal, a quadrupedal robot that is fully torque-controlled
including the non-steerable wheels attached to its legs. We conducted
experiments on flat and inclined terrains as well as over steps, whereby we
show that integrating the wheels into the motion control and planning framework
results in intuitive motion trajectories, which enable more robust and dynamic
locomotion compared to other wheeled-legged robots. Moreover, with a speed of 4
m/s and a reduction of the cost of transport by 83 % we prove the superiority
of wheeled-legged robots compared to their legged counterparts.Comment: IEEE Robotics and Automation Letter
System Design, Motion Modelling and Planning for a Recon figurable Wheeled Mobile Robot
Over the past ve decades the use of mobile robotic rovers to perform in-situ scienti c investigations on the surfaces of the Moon and Mars has been tremendously in uential in shaping our understanding of these extraterrestrial environments. As robotic missions have evolved there has been a greater desire to explore more unstructured terrain. This has exposed mobility limitations with conventional rover designs such as getting stuck in soft soil or simply not being able to access rugged terrain. Increased mobility and terrain traversability are key requirements when considering designs for next generation planetary rovers. Coupled with these requirements is the need to autonomously navigate unstructured terrain by taking full advantage of increased mobility. To address these issues, a high degree-of-freedom recon gurable platform that is capable of energy intensive legged locomotion in obstacle-rich terrain as well as wheeled locomotion in benign terrain is proposed. The complexities of the planning task that considers the high degree-of-freedom state space of this platform are considerable. A variant of asymptotically optimal sampling-based planners that exploits the presence of dominant sub-spaces within a recon gurable mobile robot's kinematic structure is proposed to increase path quality and ensure platform safety. The contributions of this thesis include: the design and implementation of a highly mobile planetary analogue rover; motion modelling of the platform to enable novel locomotion modes, along with experimental validation of each of these capabilities; the sampling-based HBFMT* planner that hierarchically considers sub-spaces to better guide search of the complete state space; and experimental validation of the planner with the physical platform that demonstrates how the planner exploits the robot's capabilities to uidly transition between various physical geometric con gurations and wheeled/legged locomotion modes
Enabling Faster Locomotion of Planetary Rovers with a Mechanically-Hybrid Suspension
The exploration of the lunar poles and the collection of samples from the
martian surface are characterized by shorter time windows demanding increased
autonomy and speeds. Autonomous mobile robots must intrinsically cope with a
wider range of disturbances. Faster off-road navigation has been explored for
terrestrial applications but the combined effects of increased speeds and
reduced gravity fields are yet to be fully studied. In this paper, we design
and demonstrate a novel fully passive suspension design for wheeled planetary
robots, which couples a high-range passive rocker with elastic in-wheel
coil-over shock absorbers. The design was initially conceived and verified in a
reduced-gravity (1.625 m/s) simulated environment, where three different
passive suspension configurations were evaluated against a set of
challenges--climbing steep slopes and surmounting unexpected obstacles like
rocks and outcrops--and later prototyped and validated in a series of field
tests. The proposed mechanically-hybrid suspension proves to mitigate more
effectively the negative effects (high-frequency/high-amplitude vibrations and
impact loads) of faster locomotion (>1 m/s) over unstructured terrains under
varied gravity fields. This lowers the demand on navigation and control
systems, impacting the efficiency of exploration missions in the years to come.Comment: 8 pages, 13 figure
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