Tools for simulating humanoid robot dynamics: A survey based on user feedback
---
paper_title: Extensive analysis of Linear Complementarity Problem (LCP) solver performance on randomly generated rigid body contact problems

paper_content:

The Linear Complementarity Problem (LCP) is a key problem in robot dynamics, optimization, and simulation. Common experience with dynamic robotic simulations suggests that the numerical robustness of the LCP solver often determines simulation usability: if the solver fails to find a solution or finds a solution with significant residual error, interpenetration can result, the simulation can gain energy, or both. This paper undertakes the first comprehensive evaluation of LCP solvers across the space of multi-rigid body contact problems. We evaluate the performance of these solvers along the dimensions of solubility, solution quality, and running time.
---
paper_title: MIRA - middleware for robotic applications

paper_content:

In this paper, we present MIRA, a new middleware for robotic applications. It is designed for use in real-world applications and for research and teaching. In comparison to many other existing middlewares, MIRA employs novel techniques for communication that are described in this paper. Moreover, we present benchmarks that analyze the performance of the most commonly used middlewares ROS, Yarp, LCM, Player, Urbi, and MOOS. Using these benchmarks, we can show that MIRA outperforms the other middlewares in terms of latency and computation time.
---
paper_title: An evaluation of methods for modeling contact in multibody simulation

paper_content:

Modeling contact in multibody simulation is a difficult problem frequently characterized by numerically brittle algorithms, long running times, and inaccurate (with respect to theory) models. We present a comprehensive evaluation of four methods for contact modeling on seven benchmark scenarios in order to quantify the performance of these methods with respect to robustness and speed. We also assess the accuracy of these methods where possible. We conclude the paper with a prescriptive description in order to guide the user of multibody simulation.
---
paper_title: Three-dimensional impact: energy-based modeling of tangential compliance

paper_content:

Impact is indispensable in robotic manipulation tasks in which objects and/or manipulators move at high speeds. Applied research using impact has been hindered by underdeveloped computational foundations for rigid-body collision. This paper studies the computation of tangential impulse as two rigid bodies in the space collide at a point with both tangential compliance and friction. It extends Stronge's spring-based planar contact structure to three dimensions by modeling the contact point as a massless particle able to move tangentially on one body while connected to an infinitesimal region on the other body via three orthogonal springs. Slip or stick is indicated by whether the particle is still or moving. Impact analysis is carried out using normal impulse rather than time as the only independent variable, unlike in previous work on tangential compliance. This is due to the ability to update the energies stored in the three springs. Collision is governed by a system of differential equations that are solvable numerically. Modularity of the impact model makes it easy to be integrated into a multibody system, with one copy at each contact, in combination with a model for multiple impacts that governs normal impulses at different contacts.
---
paper_title: Control of elastic soft robots based on real-time finite element method

paper_content:

In this paper, we present a new method for the control of soft robots with elastic behavior, piloted by several actuators. The central contribution of this work is the use of the Finite Element Method (FEM), computed in real-time, in the control algorithm. The FEM based simulation computes the nonlinear deformations of the robots at interactive rates. The model is completed by Lagrange multipliers at the actuation zones and at the end-effector position. A reduced compliance matrix is built in order to deal with the necessary inversion of the model. Then, an iterative algorithm uses this compliance matrix to find the contribution of the actuators (force and/or position) that will deform the structure so that the terminal end of the robot follows a given position. Additional constraints, like rigid or deformable obstacles, or the internal characteristics of the actuators are integrated in the control algorithm. We illustrate our method using simulated examples of both serial and parallel structures and we validate it on a real 3D soft robot made of silicone.
---
paper_title: Realistic Haptic Rendering of Interacting Deformable Objects in Virtual Environments

paper_content:

A new computer haptics algorithm to be used in general interactive manipulations of deformable virtual objects is presented. In multimodal interactive simulations, haptic feedback computation often comes from contact forces. Subsequently, the fidelity of haptic rendering depends significantly on contact space modeling. Contact and friction laws between deformable models are often simplified in up to date methods. They do not allow a "realistic" rendering of the subtleties of contact space physical phenomena (such as slip and stick effects due to friction or mechanical coupling between contacts). In this paper, we use Signorini's contact law and Coulomb's friction law as a computer haptics basis. Real-time performance is made possible thanks to a linearization of the behavior in the contact space, formulated as the so-called Delassus operator, and iteratively solved by a Gauss-Seidel type algorithm. Dynamic deformation uses corotational global formulation to obtain the Delassus operator in which the mass and stiffness ratio are dissociated from the simulation time step. This last point is crucial to keep stable haptic feedback. This global approach has been packaged, implemented, and tested. Stable and realistic 6D haptic feedback is demonstrated through a clipping task experiment.
---
paper_title: Convex and analytically-invertible dynamics with contacts and constraints: Theory and implementation in MuJoCo

paper_content:

We describe a full-featured simulation pipeline implemented in the MuJoCo physics engine. It includes multi-joint dynamics in generalized coordinates, holonomic constraints, dry joint friction, joint and tendon limits, frictionless and frictional contacts that can have sliding, torsional and rolling friction. The forward dynamics of a 27-dof humanoid with 10 contacts are evaluated in 0.1 msec. Since the simulation is stable at 10 msec timesteps, it can run 100 times faster than real-time on a single core of a desktop processor. Furthermore the entire simulation pipeline can be inverted analytically, an order-ofmagnitude faster than the corresponding forward dynamics. We soften all constraints, in a way that avoids instabilities and unrealistic penetrations associated with earlier spring-damper methods and yet is sufficient to allow inversion. Constraints are imposed via impulses, using an extended version of the velocitystepping approach. For holomonic constraints the extension involves a soft version of the Gauss principle. For all other constraints we extend our earlier work on complementarity-free contact dynamics – which were already known to be invertible via an iterative solver – and develop a new formulation allowing analytical inversion.
---
paper_title: Robot and Multibody Dynamics: Analysis and Algorithms

paper_content:

Part I Basics: Serial Chain Dynamics.- Spatial vectors.- Single rigid body dynamics.- Differential kinematics for a serial-chain system.- The mass matrix.- Equations of motion for a serial chain system.- Articulated body models for serial chains.- Operator factorization and inversion of the mass matrix.- Forward dynamics.- Part II General Multibody Systems.- Tree topology systems.- The operational space inertia.- Closed chain system dynamics.- Multi-arm manipulators.- Systems with hinge flexibility.- Systems with link flexibility.- Part III Advanced Topics and Applications.- Under-actuated systems.- Free-flying space manipulators.- Mass matrix sensitives.- Linearized dynamics models.- Sensitivity of innovations factors.- Diagnolized lagrangian dynamics.- Overview of optimal linear estimation theory.
---
paper_title: Extensive analysis of Linear Complementarity Problem (LCP) solver performance on randomly generated rigid body contact problems

paper_content:

The Linear Complementarity Problem (LCP) is a key problem in robot dynamics, optimization, and simulation. Common experience with dynamic robotic simulations suggests that the numerical robustness of the LCP solver often determines simulation usability: if the solver fails to find a solution or finds a solution with significant residual error, interpenetration can result, the simulation can gain energy, or both. This paper undertakes the first comprehensive evaluation of LCP solvers across the space of multi-rigid body contact problems. We evaluate the performance of these solvers along the dimensions of solubility, solution quality, and running time.
---
paper_title: A convex, smooth and invertible contact model for trajectory optimization

paper_content:

Trajectory optimization is done most efficiently when an inverse dynamics model is available. Here we develop the first model of contact dynamics defined in both the forward and inverse directions. The contact impulse is the solution to a convex optimization problem: minimize kinetic energy in contact space subject to non-penetration and friction-cone constraints. We use a custom interior-point method to make the optimization problem unconstrained; this is key to defining the forward and inverse dynamics in a consistent way. The resulting model has a parameter which sets the amount of contact smoothing, facilitating continuation methods for optimization. We implemented the proposed contact solver in our new physics engine (MuJoCo). A full Newton step of trajectory optimization for a 3D walking gait takes only 160 msec, on a 12-core PC.
---
paper_title: MuJoCo: A physics engine for model-based control

paper_content:

We describe a new physics engine tailored to model-based control. Multi-joint dynamics are represented in generalized coordinates and computed via recursive algorithms. Contact responses are computed via efficient new algorithms we have developed, based on the modern velocity-stepping approach which avoids the difficulties with spring-dampers. Models are specified using either a high-level C++ API or an intuitive XML file format. A built-in compiler transforms the user model into an optimized data structure used for runtime computation. The engine can compute both forward and inverse dynamics. The latter are well-defined even in the presence of contacts and equality constraints. The model can include tendon wrapping as well as actuator activation states (e.g. pneumatic cylinders or muscles). To facilitate optimal control applications and in particular sampling and finite differencing, the dynamics can be evaluated for different states and controls in parallel. Around 400,000 dynamics evaluations per second are possible on a 12-core machine, for a 3D homanoid with 18 dofs and 6 active contacts. We have already used the engine in a number of control applications. It will soon be made publicly available.
---
paper_title: An evaluation of methods for modeling contact in multibody simulation

paper_content:

Modeling contact in multibody simulation is a difficult problem frequently characterized by numerically brittle algorithms, long running times, and inaccurate (with respect to theory) models. We present a comprehensive evaluation of four methods for contact modeling on seven benchmark scenarios in order to quantify the performance of these methods with respect to robustness and speed. We also assess the accuracy of these methods where possible. We conclude the paper with a prescriptive description in order to guide the user of multibody simulation.
---
paper_title: Extensive analysis of Linear Complementarity Problem (LCP) solver performance on randomly generated rigid body contact problems

paper_content:

The Linear Complementarity Problem (LCP) is a key problem in robot dynamics, optimization, and simulation. Common experience with dynamic robotic simulations suggests that the numerical robustness of the LCP solver often determines simulation usability: if the solver fails to find a solution or finds a solution with significant residual error, interpenetration can result, the simulation can gain energy, or both. This paper undertakes the first comprehensive evaluation of LCP solvers across the space of multi-rigid body contact problems. We evaluate the performance of these solvers along the dimensions of solubility, solution quality, and running time.
---
paper_title: An opensource simulator for cognitive robotics research: The prototype of the icub humanoid robot simulator

paper_content:

This paper presents the prototype of a new computer simulator for the humanoid robot iCub. The iCub is a new open-source humanoid robot developed as a result of the "RobotCub" project, a collaborative European project aiming at developing a new open-source cognitive robotics platform. The iCub simulator has been developed as part of a joint effort with the European project "ITALK" on the integration and transfer of action and language knowledge in cognitive robots. This is available open-source to all researchers interested in cognitive robotics experiments with the iCub humanoid platform.
---
paper_title: MuJoCo: A physics engine for model-based control

paper_content:

We describe a new physics engine tailored to model-based control. Multi-joint dynamics are represented in generalized coordinates and computed via recursive algorithms. Contact responses are computed via efficient new algorithms we have developed, based on the modern velocity-stepping approach which avoids the difficulties with spring-dampers. Models are specified using either a high-level C++ API or an intuitive XML file format. A built-in compiler transforms the user model into an optimized data structure used for runtime computation. The engine can compute both forward and inverse dynamics. The latter are well-defined even in the presence of contacts and equality constraints. The model can include tendon wrapping as well as actuator activation states (e.g. pneumatic cylinders or muscles). To facilitate optimal control applications and in particular sampling and finite differencing, the dynamics can be evaluated for different states and controls in parallel. Around 400,000 dynamics evaluations per second are possible on a 12-core machine, for a 3D homanoid with 18 dofs and 6 active contacts. We have already used the engine in a number of control applications. It will soon be made publicly available.
---
paper_title: Yarp Based Plugins for Gazebo Simulator

paper_content:

This paper presents a set of plugins for the Gazebo simulator that enables the interoperability between a robot, controlled using the YARP framework, and Gazebo itself. Gazebo is an open-source simulator that can handle different Dynamic Engines developed by the Open Source Robotics Foundation. Since our plugins conform with the YARP layer used on the real robot, applications written for our robots, COMAN and iCub, can be run on the simulator with no changes. Our plugins have two main components: a YARP interface with the same API as the real robot interface, and a Gazebo plugin which handles simulated joints, encoders, IMUs, force/torque sensors and synchronization. Different modules and tasks for COMAN and iCub have been developed using Gazebo and our plugins as a testbed before moving to the real robots.
---
paper_title: Convex and analytically-invertible dynamics with contacts and constraints: Theory and implementation in MuJoCo

paper_content:

We describe a full-featured simulation pipeline implemented in the MuJoCo physics engine. It includes multi-joint dynamics in generalized coordinates, holonomic constraints, dry joint friction, joint and tendon limits, frictionless and frictional contacts that can have sliding, torsional and rolling friction. The forward dynamics of a 27-dof humanoid with 10 contacts are evaluated in 0.1 msec. Since the simulation is stable at 10 msec timesteps, it can run 100 times faster than real-time on a single core of a desktop processor. Furthermore the entire simulation pipeline can be inverted analytically, an order-ofmagnitude faster than the corresponding forward dynamics. We soften all constraints, in a way that avoids instabilities and unrealistic penetrations associated with earlier spring-damper methods and yet is sufficient to allow inversion. Constraints are imposed via impulses, using an extended version of the velocitystepping approach. For holomonic constraints the extension involves a soft version of the Gauss principle. For all other constraints we extend our earlier work on complementarity-free contact dynamics – which were already known to be invertible via an iterative solver – and develop a new formulation allowing analytical inversion.
---
paper_title: Convex and analytically-invertible dynamics with contacts and constraints: Theory and implementation in MuJoCo

paper_content:

We describe a full-featured simulation pipeline implemented in the MuJoCo physics engine. It includes multi-joint dynamics in generalized coordinates, holonomic constraints, dry joint friction, joint and tendon limits, frictionless and frictional contacts that can have sliding, torsional and rolling friction. The forward dynamics of a 27-dof humanoid with 10 contacts are evaluated in 0.1 msec. Since the simulation is stable at 10 msec timesteps, it can run 100 times faster than real-time on a single core of a desktop processor. Furthermore the entire simulation pipeline can be inverted analytically, an order-ofmagnitude faster than the corresponding forward dynamics. We soften all constraints, in a way that avoids instabilities and unrealistic penetrations associated with earlier spring-damper methods and yet is sufficient to allow inversion. Constraints are imposed via impulses, using an extended version of the velocitystepping approach. For holomonic constraints the extension involves a soft version of the Gauss principle. For all other constraints we extend our earlier work on complementarity-free contact dynamics – which were already known to be invertible via an iterative solver – and develop a new formulation allowing analytical inversion.
---
paper_title: Robot and Multibody Dynamics: Analysis and Algorithms

paper_content:

Part I Basics: Serial Chain Dynamics.- Spatial vectors.- Single rigid body dynamics.- Differential kinematics for a serial-chain system.- The mass matrix.- Equations of motion for a serial chain system.- Articulated body models for serial chains.- Operator factorization and inversion of the mass matrix.- Forward dynamics.- Part II General Multibody Systems.- Tree topology systems.- The operational space inertia.- Closed chain system dynamics.- Multi-arm manipulators.- Systems with hinge flexibility.- Systems with link flexibility.- Part III Advanced Topics and Applications.- Under-actuated systems.- Free-flying space manipulators.- Mass matrix sensitives.- Linearized dynamics models.- Sensitivity of innovations factors.- Diagnolized lagrangian dynamics.- Overview of optimal linear estimation theory.
---
paper_title: Extensive analysis of Linear Complementarity Problem (LCP) solver performance on randomly generated rigid body contact problems

paper_content:

The Linear Complementarity Problem (LCP) is a key problem in robot dynamics, optimization, and simulation. Common experience with dynamic robotic simulations suggests that the numerical robustness of the LCP solver often determines simulation usability: if the solver fails to find a solution or finds a solution with significant residual error, interpenetration can result, the simulation can gain energy, or both. This paper undertakes the first comprehensive evaluation of LCP solvers across the space of multi-rigid body contact problems. We evaluate the performance of these solvers along the dimensions of solubility, solution quality, and running time.
---
paper_title: Tools for dynamics simulation of robots: a survey based on user feedback

paper_content:

The number of tools for dynamics simulation has grown in the last years. It is necessary for the robotics community to have elements to ponder which of the available tools is the best for their research. As a complement to an objective and quantitative comparison, difficult to obtain since not all the tools are open-source, an element of evaluation is user feedback. With this goal in mind, we created an online survey about the use of dynamical simulation in robotics. This paper reports the analysis of the participants' answers and a descriptive information fiche for the most relevant tools. We believe this report will be helpful for roboticists to choose the best simulation tool for their researches.
---
paper_title: A convex, smooth and invertible contact model for trajectory optimization

paper_content:

Trajectory optimization is done most efficiently when an inverse dynamics model is available. Here we develop the first model of contact dynamics defined in both the forward and inverse directions. The contact impulse is the solution to a convex optimization problem: minimize kinetic energy in contact space subject to non-penetration and friction-cone constraints. We use a custom interior-point method to make the optimization problem unconstrained; this is key to defining the forward and inverse dynamics in a consistent way. The resulting model has a parameter which sets the amount of contact smoothing, facilitating continuation methods for optimization. We implemented the proposed contact solver in our new physics engine (MuJoCo). A full Newton step of trajectory optimization for a 3D walking gait takes only 160 msec, on a 12-core PC.
---
paper_title: MuJoCo: A physics engine for model-based control

paper_content:

We describe a new physics engine tailored to model-based control. Multi-joint dynamics are represented in generalized coordinates and computed via recursive algorithms. Contact responses are computed via efficient new algorithms we have developed, based on the modern velocity-stepping approach which avoids the difficulties with spring-dampers. Models are specified using either a high-level C++ API or an intuitive XML file format. A built-in compiler transforms the user model into an optimized data structure used for runtime computation. The engine can compute both forward and inverse dynamics. The latter are well-defined even in the presence of contacts and equality constraints. The model can include tendon wrapping as well as actuator activation states (e.g. pneumatic cylinders or muscles). To facilitate optimal control applications and in particular sampling and finite differencing, the dynamics can be evaluated for different states and controls in parallel. Around 400,000 dynamics evaluations per second are possible on a 12-core machine, for a 3D homanoid with 18 dofs and 6 active contacts. We have already used the engine in a number of control applications. It will soon be made publicly available.
---
paper_title: An evaluation of methods for modeling contact in multibody simulation

paper_content:

Modeling contact in multibody simulation is a difficult problem frequently characterized by numerically brittle algorithms, long running times, and inaccurate (with respect to theory) models. We present a comprehensive evaluation of four methods for contact modeling on seven benchmark scenarios in order to quantify the performance of these methods with respect to robustness and speed. We also assess the accuracy of these methods where possible. We conclude the paper with a prescriptive description in order to guide the user of multibody simulation.
---
paper_title: Three-dimensional impact: energy-based modeling of tangential compliance

paper_content:

Impact is indispensable in robotic manipulation tasks in which objects and/or manipulators move at high speeds. Applied research using impact has been hindered by underdeveloped computational foundations for rigid-body collision. This paper studies the computation of tangential impulse as two rigid bodies in the space collide at a point with both tangential compliance and friction. It extends Stronge's spring-based planar contact structure to three dimensions by modeling the contact point as a massless particle able to move tangentially on one body while connected to an infinitesimal region on the other body via three orthogonal springs. Slip or stick is indicated by whether the particle is still or moving. Impact analysis is carried out using normal impulse rather than time as the only independent variable, unlike in previous work on tangential compliance. This is due to the ability to update the energies stored in the three springs. Collision is governed by a system of differential equations that are solvable numerically. Modularity of the impact model makes it easy to be integrated into a multibody system, with one copy at each contact, in combination with a model for multiple impacts that governs normal impulses at different contacts.
---
paper_title: Realistic Haptic Rendering of Interacting Deformable Objects in Virtual Environments

paper_content:

A new computer haptics algorithm to be used in general interactive manipulations of deformable virtual objects is presented. In multimodal interactive simulations, haptic feedback computation often comes from contact forces. Subsequently, the fidelity of haptic rendering depends significantly on contact space modeling. Contact and friction laws between deformable models are often simplified in up to date methods. They do not allow a "realistic" rendering of the subtleties of contact space physical phenomena (such as slip and stick effects due to friction or mechanical coupling between contacts). In this paper, we use Signorini's contact law and Coulomb's friction law as a computer haptics basis. Real-time performance is made possible thanks to a linearization of the behavior in the contact space, formulated as the so-called Delassus operator, and iteratively solved by a Gauss-Seidel type algorithm. Dynamic deformation uses corotational global formulation to obtain the Delassus operator in which the mass and stiffness ratio are dissociated from the simulation time step. This last point is crucial to keep stable haptic feedback. This global approach has been packaged, implemented, and tested. Stable and realistic 6D haptic feedback is demonstrated through a clipping task experiment.
---
paper_title: Three-dimensional impact: energy-based modeling of tangential compliance

paper_content:

Impact is indispensable in robotic manipulation tasks in which objects and/or manipulators move at high speeds. Applied research using impact has been hindered by underdeveloped computational foundations for rigid-body collision. This paper studies the computation of tangential impulse as two rigid bodies in the space collide at a point with both tangential compliance and friction. It extends Stronge's spring-based planar contact structure to three dimensions by modeling the contact point as a massless particle able to move tangentially on one body while connected to an infinitesimal region on the other body via three orthogonal springs. Slip or stick is indicated by whether the particle is still or moving. Impact analysis is carried out using normal impulse rather than time as the only independent variable, unlike in previous work on tangential compliance. This is due to the ability to update the energies stored in the three springs. Collision is governed by a system of differential equations that are solvable numerically. Modularity of the impact model makes it easy to be integrated into a multibody system, with one copy at each contact, in combination with a model for multiple impacts that governs normal impulses at different contacts.
---
paper_title: Control of elastic soft robots based on real-time finite element method

paper_content:

In this paper, we present a new method for the control of soft robots with elastic behavior, piloted by several actuators. The central contribution of this work is the use of the Finite Element Method (FEM), computed in real-time, in the control algorithm. The FEM based simulation computes the nonlinear deformations of the robots at interactive rates. The model is completed by Lagrange multipliers at the actuation zones and at the end-effector position. A reduced compliance matrix is built in order to deal with the necessary inversion of the model. Then, an iterative algorithm uses this compliance matrix to find the contribution of the actuators (force and/or position) that will deform the structure so that the terminal end of the robot follows a given position. Additional constraints, like rigid or deformable obstacles, or the internal characteristics of the actuators are integrated in the control algorithm. We illustrate our method using simulated examples of both serial and parallel structures and we validate it on a real 3D soft robot made of silicone.
---
paper_title: Realistic Haptic Rendering of Interacting Deformable Objects in Virtual Environments

paper_content:

A new computer haptics algorithm to be used in general interactive manipulations of deformable virtual objects is presented. In multimodal interactive simulations, haptic feedback computation often comes from contact forces. Subsequently, the fidelity of haptic rendering depends significantly on contact space modeling. Contact and friction laws between deformable models are often simplified in up to date methods. They do not allow a "realistic" rendering of the subtleties of contact space physical phenomena (such as slip and stick effects due to friction or mechanical coupling between contacts). In this paper, we use Signorini's contact law and Coulomb's friction law as a computer haptics basis. Real-time performance is made possible thanks to a linearization of the behavior in the contact space, formulated as the so-called Delassus operator, and iteratively solved by a Gauss-Seidel type algorithm. Dynamic deformation uses corotational global formulation to obtain the Delassus operator in which the mass and stiffness ratio are dissociated from the simulation time step. This last point is crucial to keep stable haptic feedback. This global approach has been packaged, implemented, and tested. Stable and realistic 6D haptic feedback is demonstrated through a clipping task experiment.
---
paper_title: Tools for dynamics simulation of robots: a survey based on user feedback

paper_content:

The number of tools for dynamics simulation has grown in the last years. It is necessary for the robotics community to have elements to ponder which of the available tools is the best for their research. As a complement to an objective and quantitative comparison, difficult to obtain since not all the tools are open-source, an element of evaluation is user feedback. With this goal in mind, we created an online survey about the use of dynamical simulation in robotics. This paper reports the analysis of the participants' answers and a descriptive information fiche for the most relevant tools. We believe this report will be helpful for roboticists to choose the best simulation tool for their researches.
---
paper_title: An opensource simulator for cognitive robotics research: The prototype of the icub humanoid robot simulator

paper_content:

This paper presents the prototype of a new computer simulator for the humanoid robot iCub. The iCub is a new open-source humanoid robot developed as a result of the "RobotCub" project, a collaborative European project aiming at developing a new open-source cognitive robotics platform. The iCub simulator has been developed as part of a joint effort with the European project "ITALK" on the integration and transfer of action and language knowledge in cognitive robots. This is available open-source to all researchers interested in cognitive robotics experiments with the iCub humanoid platform.
---
paper_title: Yarp Based Plugins for Gazebo Simulator

paper_content:

This paper presents a set of plugins for the Gazebo simulator that enables the interoperability between a robot, controlled using the YARP framework, and Gazebo itself. Gazebo is an open-source simulator that can handle different Dynamic Engines developed by the Open Source Robotics Foundation. Since our plugins conform with the YARP layer used on the real robot, applications written for our robots, COMAN and iCub, can be run on the simulator with no changes. Our plugins have two main components: a YARP interface with the same API as the real robot interface, and a Gazebo plugin which handles simulated joints, encoders, IMUs, force/torque sensors and synchronization. Different modules and tasks for COMAN and iCub have been developed using Gazebo and our plugins as a testbed before moving to the real robots.
---

Title: Tools for simulating humanoid robot dynamics: A survey based on user feedback

Section 1: INTRODUCTION
Description 1: Introduce the importance of dynamics simulation in humanoid robotics, the purpose of the survey, and the lack of existing comparisons among simulation tools.

Section 2: SIMULATION TECHNOLOGIES
Description 2: Discuss the origin of the technologies used for robot dynamics simulation, challenges for robotics simulation, and introduce the user experience based survey.

Section 3: Challenges for robotics simulation
Description 3: Explore the stricter requirements for robotics simulation compared to virtual character animation, including numerical stability, contact forces, and actuation systems.

Section 4: Physics engines and system simulators
Description 4: Differentiate between physics engines and system simulators, and elaborate on their specific characteristics and use cases in robot simulation.

Section 5: Assorted software tools
Description 5: List and briefly describe a variety of simulation tools, highlighting their main features and intended applications.

Section 6: THE USERS POINT OF VIEW
Description 6: Present the results of the online survey, detailing the demographics of participants, their preferences, and their evaluation criteria for simulation tools.

Section 7: A diversity of tools
Description 7: Examine the abundance of available dynamics simulators and the familiarity of researchers with these tools, as well as their experiences in abandoning or adopting them.

Section 8: The main currently used tools
Description 8: Identify the most currently used simulation tools and provide user ratings and satisfaction levels for specific aspects of these tools.

Section 9: A diversity of tools: too many?
Description 9: Highlight the lack of a dominant simulator and the significant variants used by researchers for different types of robotics applications.

Section 10: A use-case: the iCub simulator
Description 10: Detail the decision process and justification for choosing a new simulation platform for the iCub project based on the survey results.

Section 11: CONCLUSIONS
Description 11: Summarize the key findings of the survey, stressing the importance of open-source projects and community efforts towards improving simulation tools for robotics applications.