This paper reports on the design, integration, and performance evaluation of a novel four-leg/four-wheel transformable mobile robot, Quattroped. In contrast to most hybrid platforms that have separate mechanisms and actuators for wheels and legs, this robot is implemented with a unique transformation mechanism that directly switches the morphology of the driving mechanism between the wheels (i.e., a full circle) and 2 degrees of freedom leg (i.e., combining two half circles as a leg), so that the same system of actuation power can be efficiently utilized in both wheeled and legged modes. The design process, mechatronics, software infrastructure, behavioral development, and leg-wheel dynamic characteristics are described. The performance of the robot is evaluated in various scenarios, including driving and turning in wheeled mode, driving, step and bar crossing, irregular terrain passing, and stair climbing in legged mode. Taking advantage of the leg-wheel combination on a single platform, the comparison of the wheeled and legged locomotion is also discussed.

We report a new dry adhesive structure using a rippled poly(dimethylsiloxane) (PDMS) elastomer bilayer film, whose surface roughness and adhesion can be reversibly regulated by applying mechanical strain. It has a set of advantages not offered by other techniques for regulation of adhesion, including real-time tunability, no requirement of specific surface chemistry, operability under ambient conditions, and relative ease of control. To understand the mechanism for adhesion regulation quantitatively, we have modeled the mechanics of adhesion in the limits of small- and large-amplitude ripples, and show good agreement with indentation experiments. We demonstrate the real-time tunability of the new adhesive structure by repeatedly picking and releasing a glass ball simply by modulating the mechanical stretch of the rippled PDMS film.

The authors report the formation of various submicron wrinkle patterns and their transition from one-dimensional (1D) ripples to two-dimensional (2D) herringbone structures on poly(dimethylsiloxane) films. Using mechanical force they can separately control the amount and timing of strain applied to the substrate on both planar directions (either simultaneously or sequentially), which appears to be critical to maneuver the pattern formation in real time. They demonstrate reversible transitions from flat to 1D ripple, to ripple with bifurcation, to ripple/herringbone mixed features, and to well-controlled formation of a highly ordered zigzag-based 2D herringbone structures.

Terrestrial arthropods negotiate demanding terrain more effectively than any search-and-rescue robot. Slow, precise stepping using distributed neural feedback is one strategy for dealing with challenging terrain. Alternatively, arthropods could simplify control on demanding surfaces by rapid running that uses kinetic energy to bridge gaps between footholds. We demonstrate that this is achieved using distributed mechanical feedback, resulting from passive contacts along legs positioned by pre-programmed trajectories favorable to their attachment mechanisms. We used wire-mesh experimental surfaces to determine how a decrease in foothold probability affects speed and stability. Spiders and insects attained high running speeds on simulated terrain with 90% of the surface contact area removed. Cockroaches maintained high speeds even with their tarsi ablated, by generating horizontally oriented leg trajectories. Spiders with more vertically directed leg placement used leg spines, which resulted in more effective distributed contact by interlocking with asperities during leg extension, but collapsing during flexion, preventing entanglement. Ghost crabs, which naturally lack leg spines, showed increased mobility on wire mesh after the addition of artificial, collapsible spines. A bioinspired robot, RHex, was redesigned to maximize effective distributed leg contact, by changing leg orientation and adding directional spines. These changes improved RHex's agility on challenging surfaces without adding sensors or changing the control system.

We report the fabrication of a new superhydrophobic surface with dual-scale roughness by coating silica nanoparticles on a poly(dimethylsiloxane) (PDMS) elastomer bilayer film with micro-scaled ripples. The wetting behavior of the surface can be reversibly tuned by applying a mechanical strain, which induces the change in micro-scale roughness determined by the ripples. The dual-scale roughness promotes the wetting transition of the final dual-structure surface from Wenzel region into the Cassie region, thus, reducing the sliding angle at least three times in comparison to that from the surfaces with single-scale roughness (either from the nanoparticle film or the wrinkled PDMS film). In addition, three-times and fast-response tunability of the sliding angle by applying mechanical strain on this dual-roughness surface is demonstrated.