DIGbot: Complex Climbing Maneuvers in a Hexapod RobotEric D. Diller, Luther R. Palmer, Roger D. Quinn

Dept. of Mechanical & Aerospace Engineering, Case Western Reserve UniversityAdvanced locomotion maneuvers such as climbing over

obstacles, making sharp turns on a vertical surface, and making vertical-to-horizontal wall transitions require novel leg trajectories and force generation. These motions are further complicated by available adhesive strategies. Directional adhesive materials, which mimic gecko feet, adhere to the surface when leg forces are applied in a single direction, but deactivate when forces are applied in the opposite direction. Current robots use their own weight to apply forces on attachment pads, and hence can only climb vertically. A robot expected to walk up, down, and sideways on a vertical surface must overcome this limitation.

These aspects of climbing are investigated on a cockroach-like legged vehicle in an attempt to mimic the cockroach's ability to quickly maneuver over a variety of surfaces, as well as climb up and over objects. We have constructed DIGbot, a 6-legged robot with 19 degrees of freedom, to investigate the low-energy and robust adhesion strategy of Distributed Inward Gripping (DIG). Rather than relying on the body's weight to activate the directional adhesion, the DIG strategy creates the necessary force by pulling opposing legs inward. The feet rely on cockroach-like spines to achieve the directional adhesion, which allows DIGbot to climb inverted on ceilings and on walls in any orientation with respect to gravity. In the future, intelligent control strategies such as fuzzy rule bases and genetic algorithms will be implemented to achieve more complex maneuvers.

Abstract

20 µm

Drosophila

Adapted from S. Gorb, Attachment devices of insect cuticle, 2001.

DIGbot: Complex ManeuversBiological Inspiration

Climbing with SpinesPerformance on Wire Mesh

References

Syrphid fly

Courtesy of S. Gorb

Future Work

Some of the anticipated maneuvers are shown in simulation (right.) Also, further work is being done to understand the role that sensing at the end effectors play on robust locomotion on unprepared natural surfaces.

K. A. Daltorio et al. “A robot that climbs walls using micro-structured polymer feet.” in Proc. of CLAWAR ’05, London, UK, September, 2005.

G. D. Wile et al. “Screenbot: Walking Inverted Using Distributed Inward Gripping.” 2008.

Passive Foot Design; Climbing Inverted

Beetle clinging to glass ceiling

Cockroaches employ a flexible body to reduce high centering when making a transition. Mimicking this body architecture would add immense complexity to a robot system, so a singular axis of rotation will be implemented on DIGbot.

Gecko: Dry Adhesive

Insect Attachment Mechanisms

Cockroach: Claw / Spines

Experiments of Chrysolina fastuosa beetles on glass ceilings show that the beetles generally attempt to distribute their contacting feet around the center of mass, with a tensile force pulling inwards. We will call this principle of opposing tension of the legs as “distributed inward gripping” (DIG).

Geckos and cockroaches are two of the most studied climbing animals. Research labs are beginning to mimic the dry adhesives (left) that geckos use to achieve a high degree of mobility. Cockroaches, instead, often rely on spines (right) to grab onto small asperities in the surface, or to dig into softer terrains. Both animals use Distributed Inward Gripping (DIG) during high-speed locomotion.

Screenbot: Proof of Concept

Periplaneta, Courtesy of S. ZillCourtesy of Kellar Autumn

The images to the left are from analysis to compute the optimal body-joint location for transitioning between orthogonal surfaces. Only the body is shown in the above figures, and required leg lengths to execute the transitions are computed from the distance from each hip to the surface. Forward body-joint locations result in larger hip-to-wall separations and would require legs to have longer available strokes. The optimal body joint location is at the center hip position in the center (lengthwise) of the body.

Given the body trajectories during a transition, optimized foot locations for the transition can be computed.

DIGbot climbs vertically and under inverted mesh ceilings. DIGbot has 19 actuated degrees of freedom, servo controlled through serial communication from a PC while the algorithms are still in development. Ultimately, all processing will be done onboard through high-performance microprocessors and power autonomy will be achieved through onboard batteries.

Using DIG, ScreenBot climbs in any orientation to gravity, including inverted ceilings. A single motor and drive system propels all 6 ScreenBot legs.

Distributed Inward Gripping

Mesh screens mimic natural terrains such as tree bark or rocky surfaces by forcing the robot to search for suitable footholds.

Compliant angle designs allow the feet to approach the screen from any angle and still achieve attachment.