Bio-inspired Controllers Facilitate Sim-to-Real Transfer

The 11th International Symposium on Adaptive Motion of Animals and Machines. Kobe University, Japan. 2023-06-06/09. Adaptive Motion of Animals and Machines Organizing Committee.Poster Session P7

Where to place cameras on a snake robot: Focus on camera trajectory and motion blur

Visual information is heavily used in robotics, in particular for SLAM applications. Visual SLAM algorithms depend on robust feature extraction and reliable state estimation. Quality of the visual information highly depends on how that information is captured. The nature of snake robots' locomotion presents considerable challenges on the quality of images captured by an onboard mobile camera. Although placing the camera on the "head" of the snake robot has advantages when the robot is stationary since the body can be used as a manipulator observing for the environment, how to place the camera in order to capture more useful images for navigation during locomotion is not clear. In this paper, we present a comparative study to discuss implications of the camera location on field coverage and types of image quality for three snake gaits: Rolling, sidewinding and linear progression. Camera pose during locomotion is examined in detail and quality of images are quantified using a motion blur metric which relates camera egomotion to blur. Linear progression is found to be very promising in terms of supplying sharper images. But, there are also other merits that can be exploited in different locomotion types and camera locations

Mechanical Stability Margin for Scouting Poses in Modular Snake Robots

This paper presents an algorithm to calculate mechanical stability margins of a Modular Snake Robot (MSR) during scouting poses. Scouting poses are defined as robot configurations in which one or two of the end modules of the robot are raised up to increase the range of perception of sensors that might be placed in its distal parts. The robot center of mass (CoM) and each of the module's contact pad positions are calculated by computing the robot kinematics. Then, this kinematic model is placed in an environment that consist of a height map (the terrain), built on a 2D grid base of defined size and resolution. Due the hyper-stability of the MSR structure, as it features many static contact points with the terrain, we approximate by weighting the distribution of forces to ensure an iso-static simplified problem. Using this information as input, the algorithm calculates a representation of the supporting surface (not necessarily horizontal), and then, it computes the minimum distance of the CoM projection into this surface to one of its edges to define a mechanical stability margin. The effectiveness and robustness of the method is demonstrated by comparisons of simulation and the real robot results. Moreover, a sequence of quasi-static motions bounded by a threshold in the stability margin, keeps the robot stable as it rises. Thus, demonstrating qualitatively the convenience of the method

The simple reason why pressure sensors are not adequate to replicate the lateral line in free swimming fish-like robots

The 9.5th international symposium on Adaptive Motion of Animals and Machines. Ottawa，Canada (Virtual Platform). 2021-06-22/25. Adaptive Motion of Animals and Machines Organizing Committee

Model predictive control based framework for CoM control of a quadruped robot

Model Predictive Control is becoming more and more present in robotic applications. It has been successfully used in control of humanoid robots to adjust positions of the footsteps in order to satisfy stability constraints. In this paper we show how to adapt such scheme for a quadruped robot utilizing a static walking. The MPC is used to provide a center of mass projection reference, keeping it within support polygons to ensure stability. User is given freedom in choosing the desired dynamical behavior of the reference. The proposed control framework is tested in simulation and on a real quadruped robot. An emphasize is put on generality of such approach which is independent of gait parameters

Spine Controller for a Sprawling Posture Robot

More and more biologically inspired robots present spines with multiples degrees of freedom to resemble their biological counterparts. The function of the spine on both animal and robot can play an important role in locomotion. If it has enough degrees of freedom to allow independent control of both shoulder and pelvic girdle (i.e., the points of attachment of body and limb), it can be used to extend the reach of the legs or to increase turning capabilities. In this letter, we present the spine controller for a sprawling quadrupedal robot. The controller achieves a synchronization between spine and legs and allows a precise control of the girdle positions by solving the inverse kinematics of the spine. The controller is validated in simulation and experiments with the real robot showing an ease in the control of the locomotion and achieving a very good tracking between the girdle trajectories with a very small, noncumulative error (less than 6% of the inter-girdle distance). This controller enables both the human operation and the implementation of autonomous path planning and navigation algorithms for these type of amphibious robots, making them more suitable for scenarios with limited maneuverability such as inside pipes or in collapsed buildings

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 robot’s shape to the environment. The gait control remains simple by acting directly in the robot’s 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 robot’s 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

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”

Challenges in visual and inertial information gathering for a sprawling posture robot

We discuss challenges a sprawling posture legged robot faces when moving in a complex environment. These kind of robots can be used for search and rescue applications when proper sensors are used and placed correctly. Finding an adequate position for placing sensors on legged robots with a segmented spine to maximize the information retrieval is not trivial. In this paper, we talk about equipping the salamanderlike robot Pleurobot with necessary sensors to understand its challenges. Our setup gathers visual and inertial information for 3D mapping and localization. To do so, we have come up with three different experimental terrains to analyze the sensing behavior. The results are examples to understanding the behavior of quadrupedal legged robots similar to Pleurobot in search and rescue scenarios

Adaptive Compliant Foot Design for Salamander Robots

Aquatic stepping gaits in animals arguably display higher speed performance as well as energetic efficiency compared to other gaits using the limbs (i.e walking). This suggest that the foot structure and function contributes at a great extent on the propulsive force generation. This work presents the design of a salamander foot, in which the dimensions, angle range, aspect ratios and the kinematics of different salamander species were condensed in simple parameters. The foot implementation was based in the compliant SoftHand design of Pisa/IIT, in which one motor actuates the whole foot. The prototype design parameters are scaled up from the dimensions of a Tiger salamander (Ambystoma tigrinum's) foot. The results from experiments using a motion capture system to retrieve the kinematics of the foot and the force plates to measure normal forces, allow to describe when and how each of the fingers act during the whole stride, impacting the ground reaction forces (GRFs). We attempt to provide a richer understanding in locomotion schemes of salamanders featuring robust ground placement and to make robotic platforms more accurate W.r.t. biology. Qualitative comparisons between the animal and the prototype show that the robotic foot is capable to generate a GRF pattern similar to that of the animals. As additional features, the foot also shows terrain adaptability and simultaneous high resilience to hitting obstacles during operation