Kamilo Melo

Experimental determination of control parameter intervals for repeatable gaits in modular snake robots

Controlling motion in a Modular Snake Robot can be achieved by reducing the high dimensionality of the robots configuration space Q. This can be done by using cyclic motions programed by functions whose parameters conform to a parameterized space P. In the scope of this research P = ℝ9, wich leads to an infinite set of possible gaits. However, not every combination of parameters leads to feasible and effective gaits. The paper outlines practical limitations of P related to mechanical constraints and theoretical rules that analyze the behavior of the parameterized functions that control the robots motion. Once these limits were imposed on the parameterized space, an experimental sweep along the feasible parameter intervals was carried out. The aim of this sweep was to verify and analyze the type of locomotion output produced, in order to select a set of gaits according to a criteria that measures their repeatability. The value of select repeatable gaits based on the control parameters relies on the possibility of using them as a basis for determining general locomotion models that are scalable to different numbers of DoF.

Modular snake robot gaits on horizontal pipes

In this paper, a comparative analysis of different gaits were done using modular snake robots. They move along different sizes of horizontal pipes. Pipe sizes were chosen according to robots length. Gaits were chosen to match robot stability and effectiveness criteria on these surfaces. A description of gait design process is shown. Parametrized schemes were used to control the robot. A visualization tool was used to validate the gait designs prior their implementation on the real robot. Performance metrics, regarding robots locomotion speed and energy efficiency were developed. A series of experiments were carried out to compare the performance of the selected gaits under these criteria. The experiments can be observed on the accompanying video. Among selected gaits, lateral rolling has demonstrated to be suitable for every pipe size. The fastest speed v = 46.5cm/s, and the most efficient locomotion, under the metrics proposed here, are also shown.

Center of mass displacements using rolling gaits for modular robots on the outside of pipes

This paper addresses the problem of find modular robots center of mass displacements when a rolling gait is executed on the outside of a pipe. Parametrization of the gait and a complete forward kinematic model was determined in order to find the center of mass position. The displacements the robots center of mass during a gait will be used as a energy efficiency metric. A stability issue also will be studied, defining a stability margin for this specific gait. Travel in joint space of the actuators depending of the pipes radius during the locomotion, will also serve as a metric of energy efficiency and at the same time, a measure of gait smoothness. Considerations for energy efficiency, stability and performance of the gait are presented.

From cineradiography to biorobots: an approach for designing robots to emulate and study animal locomotion.

Robots are increasingly used as scientific tools to investigate animal locomotion. However, designing a robot that properly emulates the kinematic and dynamic properties of an animal is difficult because of the complexity of musculoskeletal systems and the limitations of current robotics technology. Here, we propose a design process that combines high-speed cineradiography, optimization, dynamic scaling, three-dimensional printing, high-end servomotors and a tailored dry-suit to construct Pleurobot: a salamander-like robot that closely mimics its biological counterpart, Pleurodeles waltl. Our previous robots helped us test and confirm hypotheses on the interaction between the locomotor neuronal networks of the limbs and the spine to generate basic swimming and walking gaits. With Pleurobot, we demonstrate a design process that will enable studies of richer motor skills in salamanders. In particular, we are interested in how these richer motor skills can be obtained by extending our spinal cord models with the addition of more descending pathways and more detailed limb central pattern generator networks. Pleurobot is a dynamically scaled amphibious salamander robot with a large number of actuated degrees of freedom (DOFs: 27 in total). Because of our design process, the robot can capture most of the animals DOFs and range of motion, especially at the limbs. We demonstrate the robots abilities by imposing raw kinematic data, extracted from X-ray videos, to the robots joints for basic locomotor behaviours in water and on land. The robot closely matches the behaviour of the animal in terms of relative forward speeds and lateral displacements. Ground reaction forces during walking also resemble those of the animal. Based on our results, we anticipate that future studies on richer motor skills in salamanders will highly benefit from Pleurobots design.

The Modular Snake Robot Open Project: Turning animal functions into engineering tools

This paper introduces the KM-RoBoTas Modular Snake Robot Open Project, as a part of the research and development activities of this Colombian institution. The contents of the paper are divided in two main parts. First, the aim of this bio-inspired project is presented, which is built upon the relationships between animal physiology and engineering tools. Second, the extension and re-categorization of the entire project using different research and development achievements of our institution, is presented. This includes developments of hardware, which can be summarized as the description of the machine, the sensors and the processing unit. Developments in software as loco-manipulation controllers, simulation tools and a robot architecture implementation to integrate either software and hardware. This paper is an insight of the outlooks in modular snake robot research by our institution, particularly modeling locomotion and implementing or improving perception and task capabilities under the bio-inspired gaze.

Role of compliance on the locomotion of a reconfigurable modular snake robot

This paper presents the results of a study on the effect of in-series compliance on the locomotion of a simulated 8-DoF Lola-OP™ Modular Snake Robot with added compliant elements. We explore whether there is an optimal stiffness for gait, terrain type, or several gaits and several terrains (i.e. a good “general-purpose” stiffness). Compliance was simulated using ball joints with eight different levels of stiffness. Two snake locomotion gaits (rolling and sidewinding) were tested over flat ground and three different types of rough terrains. We performed grid search and Particle Swarm Optimization to identify the locomotion parameters leading to fast locomotion and analyzed the best candidates in terms of locomotion speed and energy efficiency (cost of transport). Contrary to our expectations, we did not observe a clear trend that would favor the use of compliant elements over rigid structures. For sidewinding, compliant and stiff elements lead to comparable performances. For rolling gait, the general rule seems to be “the stiffer, the better”.

Inverse kinematics and reflex based controller for body-limb coordination of a salamander-like robot walking on uneven terrain

Search and rescue (SAR) missions are being carried out by several types of robots. They include ground, marine and air vehicles depending on the terrain and mission to be tackled. A particular niche for SAR activities are shallow waters. They present high difficultly for conventional ground or marine robots because of the mix of water and ground. Such an environment is difficult to be accessed for a robot without some built-in amphibious capabilities. Our lab has experience in the design of amphibious salamander-like robots. In order to consider whether these robots would be suited for SAR missions in shallow waters, a key requirement is the ability to tackle rough terrains. In this paper we present a control framework for a highly redundant salamander-like robot. It involves bio-inspired spine control, inverse kinematics-based limb control, proper limb-spine coordination, reflex mechanisms and attitude control. The framework is validated in a simulation and on the real robot. In both cases, the robot is used in two different configurations: with and without its tail, in order to investigate how the tail (which is necessary for swimming) affects ground locomotion. With this exploration, we aim to set the precedent for improving the problem of dynamic locomotion of salamander-like robots over unperceived rough terrain. Our results confirm that the design of reflexes like stumbling and extension, combined with an attitude controller, allows for the improving of the performance of the robot in a generic rough terrain which includes stairs, holes and bumps with several levels of complexity adjusted according to the robot dimensions.

Compliant snake robot locomotion on horizontal pipes

In this paper we introduce a body-compliant Modular Snake Robot executing rolling gaits on different cylindrical geometries. In the state of the art it is considered that an active shape adaptation to the terrain while a gait is executed produces better performances than a simple pre-programmed stiff motion without feedback. Several attempts to reproduce such behaviors in snake robots range from compliant shape controllers (acting in joint space) to torque control strategies of elastic actuated joints. In our proposal, we incorporate compliant elements in a modular snake robot structure to passively adapt the robots shape to the environment. The gait control remains simple by acting directly in the robots joint space with known gait generation schemes. To validate our results we performed experiments with compliant modular snake robots rolling on pipes with different geometry characteristics such as different diameters, smooth surfaces, surfaces with presence of obstacles (terrain bumps), and considerable changes in diameter in a single robot run. We evaluated the performance across different robots body-compliance values, measuring the speed of locomotion as well as the power consumption. Our results show that providing a good selection of body compliant elements is a way to maintain high locomotion performance (at least while rolling on pipes) without including additional complex control artifacts to the simple open-loop cyclic gait controller.

Modular snake robot velocity for side-winding gaits

This paper considers a kinematic model that captures the speed and heading angle of a modular snake robot performing side-winding gaits. Modular snake robot locomotion is controlled in joint space. Consequently, the motion is achieved by continuous changes of the robots body shape. In light of this behavior, this work describes a method to determine the position and orientation of a floating frame of reference to capture the robots attitude in real-time, while executing side-winding gaits. A simple velocity model based on ground static contacts that determine the magnitude and direction of the robots motion is proposed based on that frame. This model is validated by comparisons with experiments. The benefit of the proposed floating frame formulation and the velocity model for side-winding gaits depends on the fact that their calculation relied only in the gait control parameters, hence they could be determined analytically on-line.

A preliminary review on metrics for modular snake robots locomotion

Without changing its mechanical structure, a modular snake robot (MSR) can move using different gaits. In order to evaluate their locomotion, different metrics according to specific research goals have been developed in the last decades. However, there is a lack of homogeneity in the use of these metrics between robot types and the tasks executed. In this paper, a set of metrics is presented. These metrics were divided in performance and efficiency metrics to capture such characteristics in a MSR. Related work on metrics for this kind of robots was reviewed in detail. A description of each metric was provided. Friction coefficients, translational speed, orientation of the velocity vector and a stability margin, define the first set of metrics aimed to measuring the robots performance. On the other hand, energy efficiency, mechanical energy efficiency and dissipated power conform the set of efficiency metrics. Hence, a metric framework for MSRs locomotion was presented. The use of this framework is oriented to spatial motion of modular snake robots.