Alexander S. Boxerbaum

Design of an autonomous amphibious robot for surf zone operation: part i mechanical design for multi-mode mobility

The capability of autonomous and semi-autonomous platforms to function in the shallow water surf zone is critical for a wide range of military and civilian operations. Of particular importance is the ability to transition between locomotion modes in aquatic and terrestrial settings. The study of animal locomotion mechanisms can provide specific inspiration to address these demands. In this work, we summarize on-going efforts to create an autonomous, highly mobile amphibious robot. A water-resistant amphibious prototype design, based on the biologically-inspired Whegstrade platform, has been completed. Through extensive field-testing, mechanisms have been isolated to improve the implementation of the Whegstrade concept and make it more suited for amphibious operation. Specific design improvements include wheel-leg propellers enabling swimming locomotion, an active, compliant, water resistant, non-backdrivable body joint, and improved feet for advanced mobility. These design innovations allow Whegstrade to navigate on rough terrain and underwater, and accomplish tasks with little or no low-level control, thus greatly simplifying autonomous control system implementation. Complementary work is underway for autonomous control. We believe these results can lay the foundation for the development of a generation of amphibious robots with an unprecedented versatility and mobility

Continuous wave peristaltic motion in a robot

We have developed several innovative designs for a new kind of robot that uses a continuous wave of peristalsis for locomotion, the same method that earthworms use, and report on the first completed prototypes. This form of locomotion is particularly effective in constrained spaces, and although the motion has been understood for some time, it has rarely been effectively or accurately implemented in a robotic platform. As an alternative to robots with long segments, we present a technique using a braided mesh exterior to produce smooth waves of motion along the body of a worm-like robot. We also present a new analytical model of this motion and compare predicted robot velocity to a 2D simulation and a working prototype. Because constant-velocity peristaltic waves form due to accelerating and decelerating segments, it has been often assumed that this motion requires strong anisotropic ground friction. However, our analysis shows that with smooth, constant velocity waves, the forces that cause accelerations within the body sum to zero. Instead, transition timing between aerial and ground phases plays a critical role in the amount of slippage, and the final robot speed. The concept is highly scalable, and we present methods of construction at two different scales.

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

Design of an autonomous amphibious robot for surf zone operations: part II - hardware, control implementation and simulation

This paper describes a work at The Naval Postgraduate School (NPS) and Case Western Reserve University (CWRU) to create an autonomous highly mobile amphibious robot. A first generation land-based prototype has been constructed and field tested. This robot design, based on a tracked element, is capable of autonomous waypoint navigation, self-orientation, obstacle avoidance, and has the capacity to transmit sensor (visual) feedback. A water-resistant second generation amphibious prototype design, based around the biologically inspired Whegstrade platform, has been completed. This design marries the unprecedented mobility of Whegstrade with the autonomous hardware and control architectures implemented in the first generation prototype. Furthermore, we have also implemented a dynamic simulation capturing salient features of Whegstrade for testing of robotic locomotion capabilities. The integration of these elements can lay the foundation for the development of a new generation of highly mobile autonomous amphibious robots

A new theory and methods for creating peristaltic motion in a robotic platform

We have developed several innovative designs for a new kind of robot that uses peristalsis for locomotion, the same method that earthworms use, and report on the first completed prototype (Fig. 1). This form of locomotion is particularly effective in constrained spaces, and although the motion has been understood for some time, it has rarely been effectively or accurately implemented in a robotic platform. We address some reasons for this, including some common misconceptions within the field. We present a technique using a braided mesh exterior to produce fluid waves of motion along the body of a worm-like robot. We also present a new analytical model of this motion and compare predicted robot velocity to a 2-D simulation. Unlike previous mathematical models of peristaltic motion, our model suggests that friction is not a limiting factor in robot speed, but only in acceleration. The concept is highly scalable, and we present methods of construction at two different scales.

The latest generation Whegs™ robot features a passive-compliant body joint

Current autonomous and semi-autonomous robotic platforms are limited to functioning in highly structured environments such as buildings and roads. Autonomous robots that could explore and navigate rugged terrain and highly unstructured environments such as collapsed buildings would have large dividends in civilian and military applications. In this work, we present the next generation of Whegstrade robots, DAGSI Whegstrade, which has been completed and extensively field tested. Several innovations have made the robot more rugged and well suited to autonomous operation. Specifically, an actively controlled, passively compliant body joint has been tested in three different modes of operation to judge the usefulness of the mechanism. A two-dimensional dynamic simulation of the robot has also been constructed, and has been used to study the effects of weight distribution on obstacle climbing and to investigate future autonomous climbing strategies. Moving the center of mass forward allowed the robot to climb taller obstacles. DAGSI Whegstrade can climb rectangular obstacles as tall as 2.19 times the length of a leg.

Design of a semi-autonomous hybrid mobility surf-zone robot

Surf-zone environments pose extreme challenges to robot operation. A robot that could autonomously navigate through the rocky terrain, constantly changing underwater currents, hard-packed moist sand, and loose dry sand characterizing this environment, would have very significant utility for a range of defence and civilian missions. The study of animal locomotion mechanisms can elucidate specific movement principles that can be applied to address these demands. In this work, we report on the design and optimization of a biologically inspired autonomous robot for deployment and operation in an ocean beach environment. Based on recent success with beach environment autonomy and a new rugged waterproof robotic platform, we propose a new design that will fuse a range of insect-inspired passive mechanisms with active autonomous control architectures to seamlessly adapt to and traverse through a range of challenging substrates both in and out of the water.

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.

Introducing DAGSI Whegs™: The latest generation of Whegs™ robots, featuring a passive-compliant body joint

DAGSI Whegs is the latest generation of full size Whegs robots. The robot is designed for collaborative work with the Air Force Institute of Technology (AFIT) in SLAM with active feature recognition. Whegs vehicles use abstracted biological principles to navigate over irregular and varied terrain with little or no low level control. Torsionally compliant devices in the drive train of each wheel-leg allow its gait to passively adapt when climbing large obstacles or steep inclines. Whegs is similar to the RHex line of robots that preceded Whegs in that the foot motion of all 6 legs is circular, but it differs in many aspects: 3 leg-spokes versus 1, 1 drive motor vs. 6, leg rotation for steering instead of skid steering, passive gait adaptation vs. active gait control, and Whegs has a body joint.

Electronic image stabilization using optical flow with inertial fusion

When a camera is affixed on a dynamic mobile robot, image stabilization is the first step towards more complex analysis on the video feed. This paper presents a novel electronic image stabilization (EIS) algorithm for highly dynamic mobile robotic platforms. The algorithm combines optical flow motion parameter estimation with angular rate data provided by a strapdown inertial measurement unit (IMU). A discrete Kalman filter in feedforward configuration is used for optimal fusion of the two data sources. Performance evaluations are conducted using a simulated video truth model (capturing the effects of image translation, rotation, blurring, and moving objects), and live test data. Live data was collected from a camera and IMU affixed to the DAGSI Whegs mobile robotic platform as it navigated through a hallway. Template matching, feature detection, optical flow, and inertial measurement techniques are compared and analyzed to determine the most suitable algorithm for this specific type of image stabilization. Pyramidal Lucas-Kanade optical flow using Shi-Tomasi good features in combination with inertial measurement is the EIS algorithm found to be superior. In the presence of moving objects, fusion of inertial measurement reduces optical flow root-mean-squared (RMS) error in motion parameter estimates by 40%.