RBDL - Rigid Body Dynamics Library Copyright (c) 2018-2022 Martin Felis [email protected] Felix Richter [email protected]

Introduction

RBDL is a highly efficient C++ library that contains some essential rigid body dynamics algorithms such as the Articulated Body Algorithm (ABA) for forward dynamics, Recursive Newton-Euler Algorithm (RNEA) for inverse dynamics and the Composite Rigid Body Algorithm (CRBA) for the efficient computation of the joint space inertia matrix. It further contains code for Jacobians, forward and inverse kinematics, handling of external constraints such as contacts and collisions, and closed-loop models.

The code was originally developed by Martin Felis [email protected] at the research group Optimization in Robotics and Biomechanics (ORB) of the Interdisciplinary Center for Scientific Computing (IWR) and Institute of Computer Engineering at Heidelberg University. The code closely follows the notation used in Roy Featherstone's book "Rigid Body Dynamics Algorithm".

Documentation

The documentation is contained in the code and can be extracted with the tool doxygen.

To create the documentation simply run

    doxygen Doxyfile

which will generate the documentation in the subdirectory ./doc/html. The main page will then be located in ./doc/html/index.html.

An online version of the generated documentation can be found at https://rbdl.github.io.

VCPKG package manager (for Windows, Linux and Mac)

As of 08-2021 rbdl is part of microsofts vcpkg, a tool to manage c++ dependencies on all major operating systems. The luamodel and urdfmodel addon are installed via vcpkg as well, other addons may be added in the future as well.

Install vcpkg by making a local clone from its GitHub repo Microsoft/vcpkg. Then run the vcpkg-bootstrapper script to set it up. For detailed installation instructions, see Install vcpkg. To integrate vcpkg with your Visual Studio or Visual Studio Code development environment, see Integrate vcpkg. Then, to use vcpkg to install or update a library, see Manage libraries with vcpkg. For more information about vcpkg commands, see vcpkg command-line reference.

Building RBDL from Source

The official rbdl git repository can be cloned from

    https://github.com/rbdl/rbdl

(See https://git-scm.com/downloads/guis/ for git clients.)

To make sure all submodules are correctly downloaded, clone the repository recursively!

git clone --recursive https://github.com/rbdl/rbdl

Upgrading from an older version of RBDL

For convenience there is a script to upgrade to the newest RBDL repository version.

./upgrade.sh

It pulls the latest commits from master and also checks out the correct version of all sub repositories. Manual upgrading requires doing the following:

git pull origin master
git submodule update --init

Building and Installation

Linux: RBDL

1. Prior to installation update the apt system. Open a terminal and type

  sudo apt update
  sudo apt upgrade

2. Install git

  sudo apt install git-core

3. Install cmake

  sudo apt install cmake

4. Install Eigen3 RBDL uses Eigen3 for efficient computations (http://eigen.tuxfamily.org).

  sudo apt install libeigen3-dev

5. Install a c++ compiler The choice of compiler can have a large effect on performance. Consider evaluating a few different compilers, such as Clang, for the best performance.

  sudo apt-get install build-essential

6. Install cmake-curses (optional) If you are planning on taking advantage of the many addons and other build options we recommend that you use cmake-curses as it makes the build configuration process faster and less prone to error.

  sudo apt install cmake-curses-gui

7. Install Catch2 (optional) Install Catch2 if you want to run RBDL's test code.

At the moment most linux distributions do not have catch2 in their repositories yet. So the recommended install approach is to build it from source.

$ git clone --branch v2.x https://github.com/catchorg/Catch2.git
$ cd Catch2
$ cmake -Bbuild -H. -DBUILD_TESTING=OFF
$ sudo cmake --build build/ --target install 

8. Build RBDL using CMake (http://www.cmake.org). To compile the library in a separate directory in Release mode use:

  mkdir /rbdl-build
  cd rbdl-build/
  cmake -D CMAKE_BUILD_TYPE=Release ../rbdl
  make

If you have installed cmake-curses-gui you can see all of the available build options by running cmake-curses

  mkdir /rbdl-build
  cd rbdl-build/
  ccmake ../rbdl 

at which point you will see full list of build options for RBDL. We recommend that you build and run RBDL's test code at least once by building RBDL with

RBDL_BUILD_TESTS                 ON
RUN_AUTOMATIC_TESTS              ON

Linux: RBDL's documentation

1. Install doxygen

    sudo apt install doxygen

2. Build the doxygen:

• Open a terminal in the RBDL source directory and type

doxygen Doxyfile

3. Open the file doc/html/index.html in a web-browser.

Linux: RBDL's examples

1. Install Boost (optional) Boost is needed to run many of the example simulations that come with RBDL.

sudo apt install libboost-all-dev

Linux: RBDL's addon dependencies

1. luamodel addon:

• If you'd like to load model files written in Lua to RBDL. Without this addon you will need to build models programmatically, or read them in using the URDF addon. To do so:
• Install Lua51

  sudo apt install lua5.1
  sudo apt install liblua5.1-0-dev

• Build RBDL with

  RBDL_BUILD_ADDON_LUAMODEL        ON

2. urdf addon

• If you'd like to load model files written in URDF to RBDL. This addon uses the URDF_Parser library which is included as a submodule. You will need to have cloned the repository recursively! If you missed doing that you can intialize the submodules (from a terminal within the source directory) after the fact with:

git submodule init
git submodule update

• Build RBDL with

RBDL_BUILD_ADDON_URDFREADER        ON

3. muscle addon

• If you'd like to include muscles in your RBDL muscles, such as those in Millard et al., then build RBDL with

  RBDL_BUILD_ADDON_GEOMETRY ON
  RBDL_BUILD_ADDON_MUSCLE   ON

• The geometry addon is a dependency which cmake will automatically include
• Millard M, Emonds AL, Harant M, Mombaur K. A reduced muscle model and planar musculoskeletal model fit for the simulation of whole-body movements. Journal of biomechanics. 2019 Apr 10.

4. muscle addon: muscle fitting option

• If you'd like to make use of the muscle fitting algorithms detailed in Millard et al.
• Install Ipopt. One of the easier ways to do this is to follow these instructions from Ipopt's online documentation which guides you through the process. Instructions to build the code appear in the README located in the Ipopt folder
• Configure RBDL's cmake file with these flags set to 'On'

        RBDL_BUILD_ADDON_GEOMETRY        ON
        RBDL_BUILD_ADDON_LUAMODEL        ON
        RBDL_BUILD_ADDON_MUSCLE          ON
        RBDL_BUILD_ADDON_MUSCLE_FITTING  ON

• Set the CUSTOM_IPOPT_PATH to the main Ipopt directory.
• Build RBDL
• Update your .bashrc file so that Ipopt's lib folder is in LD_LIBRARY_PATH

      export IPOPT_HOME=/home/mjhmilla/dev/Ipopt-3.12.8
      export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:$IPOPT_HOME/lib

• As of March 2019 all of the muscle fitting code has been tested with Ipopt-3.12.8.
• Millard M, Emonds AL, Harant M, Mombaur K. A reduced muscle model and planar musculoskeletal model fit for the simulation of whole-body movements. Journal of biomechanics. 2019 Apr 10.

Windows

Although RBDL can be installed on Windows, none of the ORB members currently uses Windows and so we are unable to provide detailed instructions.

Python Bindings

RBDL can also build an experimental python wrapper that works with python 3 and python 2. To do this enable the the RBDL_BUILD_PYTHON_WRAPPER cmake options. This will build the wrapper for python 3, if you want to use python 2 instead you will also have to enable the RBDL_USE_PYTHON_2 cmake option. The result of this is an extra python directory in the build directory. From within which you can install it using setup.py. This is done automatically when using make install

Linux: Python wrapper dependencies

1. Install Python3, NumPy, SciPy, & Matplotlib (optional) Most of RBDL is accessible through Python. If you are interested in using the RBDL through Python these instructions:

• If you are using Ubuntu 18.04 or later python3 comes pre-installed.
• To check if you have python3, in a command shell type

python3 -V

• If you already have python3 installed system-wide then you can get the remaining libraries with

sudo apt install cython3 python3-numpy python3-scipy python3-matplotlib

• If you are not using Ubuntu 18.04, and do not currently have python3, please look for instructions online to install these libraries on your system.

2. Build and install RBDL with the

RBDL_BUILD_PYTHON_WRAPPER : ON

(Note: you may need sudo privileges to install the rbdl.egg_info file to usr/local/lib/python directory.) 3. Add RBDL to Python's path Update your .bashrc file so that python can find the python version of rbdl. To do this you need to add the path to 'rbdl-build/python' to the PYTHONPATH which can be done by adding the following line to your .bashrc file.

export PYTHONPATH=$PYTHONPATH:<path-to-the-RBDL-build-directory>/python

Resources to learn more

There are four main ways to learn about anything that appears in RBDL:

1. The examples folder

• There are a set of deep-dive examples which are accompanied by detailed documentation: if you are new to RBDL start here first.
• There are also a set of minimalistic examples
• The examples cover the basics reasonably well, but currently many advanced items (quaternion joints, custom-joints, custom-constraints, muscle-fitting) do not have examples.

2. The Doxygen documentation

• The Doxygen for methods and components that were developed recently are covered in great detail (e.g. the Millard2016TorqueMuscle class in the muscle addon).
• Doxygen for more well established methods are more sparsely documented.

3. The test code;

• A minimalistic example of every command and modeling component can be found in the test code (e.g. in rbdl/tests, addons/geometry/tests, addons/muscle/tests, etc).
• A specific command can be easily found by using a text editor that can search an entire directory (e.g. sublime text) of text files for a keyword.

4. The literature.

• In addition to Featherstone's text and Felis's papers there are a number of exciting methods and modeling tools which are included in RBDL.
• The appropriate literature references are mentioned in the doxygen for the method in question.

Citation

An overview of the theoretical and implementation details has been published in [https://doi.org/10.1007/s10514-016-9574-0](Felis, M.L. Auton Robot (2017) 41: 495). To cite RBDL in your academic research you can use the following BibTeX entry:

@Article{Felis2016,
  author="Felis, Martin L.",
  title="RBDL: an efficient rigid-body dynamics library using recursive algorithms",
  journal="Autonomous Robots",
  year="2016",
  pages="1--17",
  issn="1573-7527",
  doi="10.1007/s10514-016-9574-0",
  url="http://dx.doi.org/10.1007/s10514-016-9574-0"
}

Licensing

The library is published under the very permissive zlib free software license which should allow you to use the software wherever you need.

This is the full license text (zlib license):

RBDL - Rigid Body Dynamics Library
Copyright (c) 2011-2020 Martin Felis <[email protected]>

This software is provided 'as-is', without any express or implied
warranty. In no event will the authors be held liable for any damages
arising from the use of this software.

Permission is granted to anyone to use this software for any purpose,
including commercial applications, and to alter it and redistribute it
freely, subject to the following restrictions:

   1. The origin of this software must not be misrepresented; you must not
   claim that you wrote the original software. If you use this software
   in a product, an acknowledgment in the product documentation would be
   appreciated but is not required.

   2. Altered source versions must be plainly marked as such, and must not
   be misrepresented as being the original software.

   3. This notice may not be removed or altered from any source
   distribution.

Acknowledgements

Work on this library was originally funded by the Heidelberg Graduate School of Mathematical and Computational Methods for the Sciences (HGS), and the European FP7 projects ECHORD (grant number 231143) and Koroibot (grant number 611909).

Work on the geometry and muscle addons was completed by Matthew Millard [email protected]. Financial support from Deutsche Forschungs Gemeinschaft grant no. MI 2109/1-1 and from the European Commission within the H2020 project Spexor (GA 687662) is gratefully acknowledged.