Sandeep Manjanna

Using Gait Change for Terrain Sensing by Robots

In this paper we examine the interplay between terrain classification accuracy and gait in a walking robot, and show how changes in walking speed can be used for terrain-dependent walk optimizations, as well as to enhance terrain identification. The details of a walking gait have a great influence on the performance of locomotive systems and their interaction with the terrain. Most legged robots can benefit from adapting their gait (and specifically walk speed) to the particular terrain on which they are walking. To achieve this, the agent should first be capable of identifying the terrain in order to choose the optimal speed. In this work we are interested in analyzing the performance of a legged robot on different terrains and with different gait parameters. We also discuss the effects of gait parameters, such as speed, on the terrain identification computed by a legged robot. We use an unsupervised classification algorithm to classify terrains based on inertial measurement samples and actuator feedback collected over different terrains and operation speeds. We present the effects of speed on the terrain classification in our classification results.

Ninja legs: Amphibious one degree of freedom robotic legs

In this paper we propose a design of a class of robotic legs (known as “Ninja legs”) that enable amphibious operation, both walking and swimming, for use on a class of hexapod robots. Amphibious legs equip the robot with a capability to explore diverse locations in the world encompassing both those that are on the ground as well as underwater. In this paper we work with a hexapod robot of the Aqua vehicle family (based on a body plan first developed by Buehler et al. [1]), which is an amphibious robot that employs legs for amphibious locomotion. Many different leg designs have been previously developed for Aqua-class vehicles, including both robust all-terrain legs for walking, and efficient flippers for swimming. But the walking legs have extremely poor thrust for swimming and the flippers are completely unsuitable for terrestrial operations. In this work we propose a single leg design with the advantages of both the walking legs and the swimming flippers. We design a cage-like circular enclosure for the flippers in order to protect the flippers during terrestrial operations. The enclosing structure also plays the role of the walking legs for terrestrial locomotion. The circular shape of the enclosure, as well, has the advantages of an offset wheel. We evaluate the performance of our design for terrestrial mobility by comparing the power efficiency and the physical speed of the robot equipped with the newly designed legs against that with the walking legs which are semi-circular in shape. The swimming performance is examined by measuring the thrust generated by newly designed legs and comparing the same with the thrust generated by the swimming flippers. In the field, we also verified that these legs are suitable for swimming through moderate surf, walking through the breakers on a beach (and thus through slurry), and onto wet and dry sand.

Efficient Terrain Driven Coral Coverage Using Gaussian Processes for Mosaic Synthesis

In this paper we present an efficient method for visual mapping of open water environments using exploration and reward identification followed by selective visual coverage. In particular, we consider the problem of visual mapping a shallow water coral reef to provide an environmental assay. Our approach has two stages based on two classes of sensors: bathymetric mapping and visual mapping. We use a robotic boat to collect bathymetric data using a sonar sensor for the first stage and video data using a visual sensor for the second stage. Since underwater environments have varying visibility, we use the sonar map to select regions of potential value, and efficiently construct the bathymetric map from sparse data using a Gaussian Process model. In the second stage, we collect visual data only where there is good potential pay-off, and we use a reward-driven finite-horizon model akin to a Markov Decision Process to extract the maximum amount of valuable data in the least amount of time. We show that a very small number of sonar readings suffice on a typical fringing reef. We validate and demonstrate our surveying technique using real robot in the presence of real world conditions such as wind and current. We also show that our proposed approach is suitable for visual surveying by presenting a visual collage of the reef.

Autonomous gait selection for energy efficient walking

In this paper, we investigate the question of how a legged robot can walk efficiently by taking advantage of its ability to alter its gait as a function of statistical (large-scale) terrain properties. One of the contributions of this paper is the algorithm to achieve real-time terrain identification and autonomous gait adaptation on a legged robot. We approach this problem by first classifying the terrains based on their proprioceptive responses and identifying the terrain in real-time. Then we choose an optimal gait to best suit the identified terrain type. We exploit our recent findings regarding gaits, estimated from terrain-contact signatures, in order to obtain an optimized mapping between terrain signatures and terrain-specific gaits. We evaluate our algorithm on synthetic data, and real robot data collected on different terrains and naturally occurring terrain transitions. Another key contribution of this work is the statistical verification that precise gait selection can lead to energy savings in practice in legged robots. This assessment of energy efficiency, achieved by gait adaptation, is among the firsts of its kind in gait adaptation literature. We also present an analysis of the effect of terrain transition frequency on our gait adaptation algorithm. Our results are supported by validation using both synthetic data and field testing.

Multi-target rendezvous search

In this paper, we examine multi-target search, where one or more targets must be found by a moving robot. Given the targets initial probability distribution or the expected search region, we present an analysis of three search strategies - Global maxima search, Local maxima search, and Spiral search. We aim at minimizing the mean-time-to-find and maximizing the total probability of finding the target. This leads to two types of illustrative performance metrics: minimum time capture and guaranteed capture. We validate the search strategies with respect to these two performance metrics. In addition, we study the effect of different target distributions on the performance of the search strategies. We also consider the practical realization of the proposed algorithms for multi-target search. The search strategies are analytically evaluated, through simulations and illustrative deployments, in open-water with an Autonomous Surface Vehicle (ASV) and drifting sensor targets.

Multi-target search strategies

This paper addresses the problem of searching multiple non-adversarial targets using a mobile searcher in an obstacle-free environment. In practice, we are particularly interested in marine applications where the targets drift on the ocean surface. These targets can be surface sensors used for marine environmental monitoring, drifting debris, or lost divers in open water. Searching for a floating target requires prior knowledge about the search region and an estimate of the targets motion. This task becomes challenging when searching for multiple targets where persistent searching for one of the targets can result in the loss of other targets. Hence, the searcher needs to trade-off between guaranteed and fast searches. We propose three classes of search strategies for addressing the multi-target search problem. These include, data-independent, probabilistic and hybrid search. The data-independent search strategy follow a pre-defined search pattern and schedule. The probabilistic search strategy is guided by the estimated probability distribution of the search target. The hybrid strategy combines data-independent search patterns with a probabilistic search schedule. We evaluate these search strategies in simulation and compare their performance characteristics in the context of searching multiple drifting targets using an Autonomous Surface Vehicle (ASV).

Data Correlation and Comparison from Multiple Sensors Over a Coral Reef with a Team of Heterogeneous Aquatic Robots

This paper presents experimental insights from the deployment of an ensemble of heterogeneous autonomous sensor systems over a shallow coral reef. Visual, inertial, GPS, and ultrasonic data collected are compared and correlated to produce a comprehensive view of the health of the coral reef. Coverage strategies are discussed with a focus on the use of informed decisions to maximize the information collected during a fixed period of time.

Fast and efficient rendezvous in street networks

We address the problem of rendezvous between two agents in urban street networks. Specifically, we consider the case where the agents have variable speeds and they need to schedule a rendezvous or a meeting under uncertainty in their travel times. Examples of such a scenario range from everyday life where two people would like to coordinate a meeting while going from office to home; to a futuristic case where automated taxis would like to meet each other for load balancing passengers. The scheduling for such scenarios can easily become challenging with uncertainties such as delayed departures, road blocks due to construction or traffic congestion. Any solution for such a task is required to minimize the waiting time and the planning overhead. In this paper, we propose an algorithm that optimizes the total travel time and the waiting time for two agents to complete their respective paths from start to rendezvous and from rendezvous to goal locations subject to delays along their paths. We validate our approach with a street network database which has a cost associated with every query made to the database server. Thus our algorithm intelligently optimizes for rendezvous trajectories that effectively mitigate the scourge of traffic delays, while simultaneously limiting the number of queries through careful analysis of the informative value of each potential query.