Perceptive and torque-control NMPC

qh1. Perceptive and torque-control NMPC wiki

I - Software Overview¶

I.1. Openrobots¶

Collections of all the open-source software used at LAAS. You can find more details in Openrobots Wiki-Homepage

I-2. Robotpkg¶

Robotpkg is a packaging system for installing robotics software developed by the robotic community.
We will use robotpkg to install the required modules for the simulations (state estimation, gazebo interface...) as well as third-party dependencies (qpOases).

I-3. GenoM¶

GenoM is a generator of modules, designed to be middleware independant, i.e. the same module can be compiled for, e.g., ROS, YARP, or Pocolibs, without any modification.
This allows a great code re-usability and to abstract the user from any specific choice of a middleware.
Originally GenoM has been developed tightly with Pocolibs, then from version 3, aka GenoM3, ROS templates has been provided.

Another specificity of GenoM is the interaction with and between components.
Each component is started independantly like a linux executable (within a roscore, for ROS, or a h2 intance, for Pocolibs), then the connection between ports (or topics) is made using a supervisor, Genomix, either with Matlab or TCL.

I-4. Pocolibs¶

Pocolibs is a middleware, like ROS.
It aims at being lighter and faster than ROS, when running on a single machine, thanks to the exploitation of shared memory. ROS, on the other hand, uses a network layer for sending messages between nodes, this leads to greater delays and loss of performances.

I-5. TeleKyb¶

The TeleKyb software platform provides the aerial-robotic oriented softwares developped at LAAS-CNRS.
In particular, we will use:

• mrsim, a Multi-Robot SIMulator. It is design to be a transparent interface w.r.t. the real aerial vehicles used in LAAS-CNRS. It makes the transition between simulation and experiment transparent, from the software point of view.
• pom, a UKF-based state estimator merging state feedback for different sources (e.g. mocap + IMU)
• optitrack,, to export the motion capture data to the genom software stack
• rotorcraft, the low-level interface, with either the simulated or real platform
• nhfc, near-hovering flight controller, used for unmodeled take-off and post-failure recoverues
• maneuver, a global trajectory planner, providing position and attitude (as quaternions) as well as first and second derivatives. It implement take-off and waypoint-to-waypoint motions. A joystick-based velocity control is implemented, but not used in this project.

I-6. Gazebo¶

To simulate the platform, we use the Gazebo simulator. To interface it with the genom software stack, we use two dedicated components:

• mrsim-gazebo a plugin to interface the simulated multi-rotor with the genom components (in place of mrsim)
• optitrack-gazebo emulates the optitrack network interface to publish the model poses

II - Installation procedure¶

This section is a tutorial on how to install the software architecture to run the simulations.
Note that everything has been tested on Ubuntu 18.04 since it is the OS used by the LAAS-CNRS robotic platform. It should work seamlessly on other OS, but there is no guarantee.

II-0. Clone the Perceptive and torque-control NMPC repository¶

Clone the repo associated to this project. Its root will act as the devel folder for the following.

git clone git://redmine.laas.fr/laas/perceptive-torque-nmpc.git
cd ./perceptive-torque-nmpc/

To simplify the installation, we provide some environment variables in the env.sh file.
In order to run all the installed executables, we need to setup the path to the newly created folders.
We provide a env.sh script that exports all the required variables. In the root folder, do:

source env.sh

II-1. Setup robotpkg¶

(Steps taken from http://robotpkg.openrobots.org/install.html)

1. Clone the robotpkg lastest release:¶

git clone git://git.openrobots.org/robots/robotpkg

2. Check that the openrobots/ folder exists in the repository root, and update the environement variables accordingly if you didn't source the env.sh file:¶

export ROBOTPKG_BASE=`pwd`/openrobots

3. Install robotpkg¶

cd robotpkg/bootstrap
./bootstrap --prefix=$ROBOTPKG_BASE

4. Install the required components and there dependencies¶

The installation can be done 'manually' by navigating to the desired folder in ./robotpkg/ and install with make update; but we will simplify the process using a set.
To do so, we need to edit the config file: $ROBOTPKG_BASE/etc/robotpkg.conf. Add the following at the end of the file:

PKG_OPTIONS.%-genom3 = \
        codels \
        pocolibs-server \
        pocolibs-client-c

PKGSET.mpcset = \
    sysutils/arduio-genom3 \
    architecture/genom3 \
    architecture/genom3-pocolibs \
    robots/rotorcraft-genom3 \
    localization/pom-genom3 \
    localization/optitrack-genom3 \
    motion/nhfc-genom3 \
    path/libkdtp \
    optimization/qpoases \
    net/genomix \
    supervision/matlab-genomix \
    supervision/tcl-genomix \
    shell/eltclsh \
    simulation/mrsim-genom3 \
    simulation/mrsim-gazebo \
    simulation/libmrsim \
    simulation/optitrack-gazebo

PREFER.lapack = robotpkg
PREFIX.matlab = <path/to/Matlab>

The last line need to point to the Matlab root folder in the system (e.g. /opt/Matlab).
It is recommanded to use Matlab for the proposed simulations since the syntax is more intuitive and comprehensible for the user to modify them. However, we also provide all the launch files in tcl, as well as the environment to run them (shell/eltclsh in the above list is a custom tcl script shell).
If Matlab is not installed on the system, remove the lines supervision/matlab-genomix \ and PREFIX.matlab = <path/to/Matlab> from the above list.
Also, all the above is meant for using Pocolibs, not ROS. Futur version of this tutorial might come to use the ROS install.

Now return to the robotpkg folder and install all the set:

cd ..
make update-mpcset

During the installation, some required dependencies need to be install with the usual package manager (e.g. apt on Ubuntu). When the install stops, install the required packages and rerun the above command.

5. Matlab configuration¶

The last step is to update Matlab path to use the custom libraries, if relevant.
Add the following paths in the Matlab path window:

</path/to/openrobots>/lib/matlab
</path/to/openrobots>/lib/matlab/simulink
</path/to/openrobots>/lib/matlab/simulink/genomix

(change </path/to/openrobots> to the vlaue of $ROBOTPKG_BASE)

II-2. Install custom components¶

List of the components¶

The src/ folder contains some additional components, in particular:

• vision-idl: the type declaration regarding the camera modules
• camgazebo-genom3: read the data from the gazebo inate cameras, via the gazebo API
• camviz-genom3: record and/or display the images from a camera
• arucotag-genom3: detect and filter (EKF-based) the ArUco markers/tags
• maneuver-genom3: custom version of maneuver (already mentionned) that publishes the reference trajectory for a specified receding horizon
• uavmpc-genom3: the NMPC controller presented in the pape

Install the extra components¶

Since it they are not considered 'stable' as the one provided in robotpkg, we rather install them in a devel folder.
Go to the project root, check that the devel folder exists, export the path if you didn't source the env.sh. Then go to the sources folder:

export DEVEL_BASE=`pwd`/devel
cd src/

For the manual installation, asciidoctor is needed. It can be installed using apt or any package manager.
Each component here has to be installed manually, using autoconf. To do so, proceed as follow:

cd src/<component>/
./bootstrap.sh
mkdir build
cd build
../configure --prefix=$DEVEL_BASE --with-templates=pocolibs/client/c,pocolibs/server
make install

The component vision-idl has to be installed first since it defines some type headers used by others.
The installation of the main component, uavmpc-genom3, is described in the next subection.

Install the MPC controller¶

Before installing the MPC controller, we have to generate the C sources corresponding to the desired model.
To do so, go to the model_generation/ folder:

cd src/uavmpc-genom3/model_generation

There is a README.md file there, explaining the requirements.
In short, the model sources are exported to C using CasADi in python3.
python3 along with NumPy, SciPy and CasADi are required, and easily installable on most Linux distributions (e.g. with apt and pip3).
Then, the sources are generated using:

python3 gen_model.py <quad or hexa>

Then install the component as explained before, but add the following flags to the configure command:

../configure --prefix=$GENOM_DEVEL --with-templates=pocolibs/client/c,pocolibs/server CFLAGS='-Wall -O3 -march=native -mfpmath=sse' CXXFLAGS='-std=c++14 -Wall -O3 -march=native -mfpmath=sse' CPPFLAGS='-I$ROBOTPKG_BASE/include' LDFLAGS='-L$ROBOTPKG_BASE/lib -Wl,-R$ROBOTPKG_BASE/lib'

II-3. Setup the environment¶

In order to run all the installed executables, we need to setup the path to the newly created folders.
All the required variables are exported in the env.sh file.

III - Running the simulation¶

We ws/ folder contains all the material to run a basic simulation with the NMPC.
In a terminal, launch the launch.sh script. It starts all the genom components, in background. It is used as a console since it displays warnings or error during runtime.
In another terminal, start gazebo with one of the world file provided.
Finally, run matlab or eltclsh and go to the relevant subsection below.

III.1. Running the simulations with Matlab¶

Change the flag at the top of the script to use either the quadrotor or the hexarotor.
Change also the variable devel_path to the value of $DEVEL_BASE

The provided scripts are organised as follow

• The two param_*.m scripts provide the parameters for either a standard colinear quadrotor (denoted qr) and a tilted-propeller hexarotor (denoted hr).
• The init.m script that connects all the components together and call the initialization services for all provided components.
• The traj_*.m that runs the specific trajectories for a specific scenario.
  Launch the script then press enter between each step to proceed to the next one. The evolution can be watched in gazebo and in the console terminal in parallel.

III.2. Running the simulations with tcl¶

The TCL scripts are not included yet
I will wait for the the current matlab scripts to be tested by other users, include potential feedback, then finalize the tcl versions
The tcl scripts are called from the eltclsh shell environment.
In order to run the script and keep the variables in the environment, use the source command.
The script architecture is the same as the matlab one. Change the flag and devel_path in the init.tcl script, then:

source init.tcl
source traj_<name_name>.tcl

III.3. List of the provided trajectories¶

• traj_mpc runs a flight using the nmpc without any perceptive constraint, reaching successive waypoints.
• traj_track runs a flight using the nmpc with a couple of perceptive constraints, again reaching successive waypoints.
  It corresponds to the experiment presented in section V-B in the paper.
• traj_follow runs a flight where we follow a target quadrotor equipped with a marker. The NMPC-controlled UAV needs to stay on top of it, while the target quadrotor is given successive waypoints.
  It corresponds to the experiment presented in Section V-C in the paper.

In order to perform the exact simulation performed in Section V-E of the paper, one need first to uncomment the tracking of the second tag in the model_hexa.py file and recompile uavmpc-genom3.
Then, modify the parameters in init.m: z_desired = 2; and target_compliant = 0;