Andrew D. Horchler

A small wall-walking robot with compliant, adhesive feet

The ability to walk on surfaces regardless of the presence or direction of gravity can significantly increase the mobility of a robot for both terrestrial and space applications. Insects and geckos can provide inspiration for both novel adhesive technology and for the locomotory mechanisms employed during climbing. For this work, Mini-Whegs/spl trade/, a small quadruped robot that uses wheel-legs for locomotion, was altered to explore the feasibility of scaling vertical surfaces using compliant, adhesive feet. Modifications were made to reduce its weight, and its legs were redesigned to enable its feet to better attach and detach from the substrate, mimicking homologous actions observed in animals. The resulting vehicle is self-contained, power-autonomous, and weighs only 87 grams. Using pressure-sensitive tape, it is capable of walking up a vertical surface, walking upside-down along an inverted surface, and transitioning between orthogonal surfaces.

A Small, Insect-Inspired Robot that Runs and Jumps

This paper describes the latest additions to the Mini-Whegs™ series of small robots. These new robots are fully enclosed, measure 9 to 10 cm long, and range in weight from 90 g to 190 g. Mini-Whegs™ 7 weighs less than 90 g, but can run at over three body-lengths per second and surmount 3.8 cm high obstacles. The most recent iteration, Mini-Whegs™ 9J, incorporates fully independent running and jumping modes of locomotion. The controllable jumping mechanism allows it to leap as high as 18 cm.

A Robot that Climbs Walls using Micro-structured Polymer Feet

Insect-inspired foot materials can enable robots to walk on surfaces regardless of the direction of gravity, which significantly increases the functional workspace of a compact robot. Previously, Mini-Whegs™, a small robot that uses four wheel-legs for locomotion, was converted to a wall-walking robot with compliant, conventional-adhesive feet. In this work, the feet were replaced with a novel, reusable insect-inspired adhesive. The reusable structured polymer adhesive has less tenacity than the previous adhesive, resulting in less climbing capability. However, after the addition of a tail, changing to off-board power, and widening the feet, the robot is capable of ascending vertical surfaces using the novel adhesive.

Mini-Whegs TM Climbs Steep Surfaces Using Insect-inspired Attachment Mechanisms

When climbing vertical or inclined surfaces, insects utilize claws, tibial spines, and tarsal pads to create attachment forces. These devices allow them to climb on a variety of substrates, including those that are smooth, soft, or porous. Recent advances in materials may make long-lasting dry adhesives and arrays of sharp hooks feasible attachment mechanisms for small robots. Mini-WhegsTM are a series of robots that use rotating wheel-legs driven by a single motor for locomotion. By testing specially designed wheel-legs with office tape, pairs of spines, and Velcro®, this work demonstrates the feasibility of applying novel adhesives and frictional materials passively on simple rotating legs. The resulting robot climbs vertical fabric surfaces with Velcro®, crosses ceilings with Scotch® tape, and climbs steep concrete inclines with sharp spines and provides a test-platform for future adhesive materials such as dry adhesive tape.

Robot phonotaxis in the wild : a biologically inspired approach to outdoor sound localization

Cricket phonotaxis (sound localization behavior) was implemented on an autonomous outdoor robot platform inspired by cockroach locomotion. This required the integration of a novel robot morphology (Whegs) with a biologically based auditory processing circuit and neural control system, as well as interfacing this to a new tracking device and software architecture for running robot experiments. In repeated tests, the robot is shown to be capable of tracking towards a simulated male cricket song over natural terrain. Range fractionation and gain control were added to the auditory control circuit in order to deal with the substantial change in amplitude of the signal as the robot approached the outdoor sound stimulus. We also discuss issues related to acoustic interference from motor noise, the need for a motor feedback mechanism to better regulate the drive signal and plans for future work incorporating additional sensory systems on this platform.

New technologies for testing a model of cricket phonotaxis on an outdoor robot

If biological inspiration can be used to build robots that deal robustly with complex environments, it should be possible to demonstrate that ‘biorobots’ can function in natural environments. We report on initial outdoor experiments with a robot designed to emulate cricket behaviour. The work integrates a detailed neural model of auditory localisation in the cricket with a robot morphology that incorporates principles of six-legged locomotion. We demonstrate that it can successfully track a cricket calling song over natural terrain. Limitations in its capability are evaluated, and a number of biologically based improvements are suggested for future work.

Efficient worm-like locomotion: slip and control of soft-bodied peristaltic robots

In this work, we present a dynamic simulation of an earthworm-like robot moving in a pipe with radially symmetric Coulomb friction contact. Under these conditions, peristaltic locomotion is efficient if slip is minimized. We characterize ways to reduce slip-related losses in a constant-radius pipe. Using these principles, we can design controllers that can navigate pipes even with a narrowing in radius. We propose a stable heteroclinic channel controller that takes advantage of contact force feedback on each segment. In an example narrowing pipe, this controller loses 40% less energy to slip compared to the best-fit sine wave controller. The peristaltic locomotion with feedback also has greater speed and more consistent forward progress

A controller for continuous wave peristaltic locomotion

While soft-bodied animals have an extraordinarily diverse set of robust behaviors, soft-bodied robots have not yet achieved this flexiblity. In this paper, we explore controlling a truly continuously deformable structure with a CPG-like network. Our recently completed soft wormlike robot with a continuously deformable outer mesh, along with a continuum analysis of peristalsis, has suggested the neural control investigated here. We use a Wilson-Cowan neuronal model in a continuum arrangement that mirrors the arrangement of muscles in an earthworm. We show that such a system is well suited to incorporate sensory input and can create both rhythmic and nonrhythmic activity. The system can be controlled using straightforward descending signals whose effects are largely decoupled and can modulate the properties from CPG-like behaviors to static waves. This approach will be useful for designing robotic systems that express multiple adaptive behavioral modes.

Worm-Like Robotic Locomotion with a Compliant Modular Mesh

In order to mimic and better understand the way an earthworm uses its many segments to navigate diverse terrain, this paper describes the design, performance, and sensing capabilities of a new modular soft robotic worm. The robot, Compliant Modular Mesh Worm CMMWorm, utilizes a compliant mesh actuated at modular segments to create waveforms along its body. These waveforms can generate peristaltic motion of the body similar to that of an earthworm. The modular mesh is constructed from 3-D printed and commercially available parts allowing for the testing of a variety of components that can be easily interchanged. In addition to having independently controlled segments and interchangeable mesh properties, CMMWorm also has greater range of contraction 52% of maximum diameter than our previous robot Softworm 73% of maximum diameter. The six-segment robot can traverse flat ground and pipes. We show that a segment is able to detect the wall of a pipe and return to its initial position using actuator-based load-sensing. A simple kinematic model predicts the outer diameter of the worm robots mesh as a function of encoder position.

Designing responsive pattern generators: stable heteroclinic channel cycles for modeling and control

A striking feature of biological pattern generators is their ability to respond immediately to multisensory perturbations by modulating the dwell time at a particular phase of oscillation, which can vary force output, range of motion, or other characteristics of a physical system. Stable heteroclinic channels (SHCs) are a dynamical architecture that can provide such responsiveness to artificial devices such as robots. SHCs are composed of sequences of saddle equilibrium points, which yields exquisite sensitivity. The strength of the vector fields in the neighborhood of these equilibria determines the responsiveness to perturbations and how long trajectories dwell in the vicinity of a saddle. For SHC cycles, the addition of stochastic noise results in oscillation with a regular mean period. In this paper, we parameterize noise-driven Lotka-Volterra SHC cycles such that each saddle can be independently designed to have a desired mean sub-period. The first step in the design process is an analytic approximation, which results in mean sub-periods that are within 2% of the specified sub-period for a typical parameter set. Further, after measuring the resultant sub-periods over sufficient numbers of cycles, the magnitude of the noise can be adjusted to control the mean period with accuracy close to that of the integration step size. With these relationships, SHCs can be more easily employed in engineering and modeling applications. For applications that require smooth state transitions, this parameterization permits each states distribution of periods to be independently specified. Moreover, for modeling context-dependent behaviors, continuously varying inputs in each state dimension can rapidly precipitate transitions to alter frequency and phase.