oscillation_ctrl

Repo containing oscillation damping controller for tether missions + instructions how to to set up

Cesar Rodriguez

cesar.rodriguez@spirirobotics.com

February 2022

Steps to recreate stable PX4 environment + working repo

WARNING

Currently repo is only for Ubuntu 18.04 and ROS Melodic, work is being made to be upgraded to Ubuntu 20.04 and ROS Noetic

Setup

1) Set up oscillation_ctrl

Install xterm

sudo apt-get update -y
sudo apt-get install -y xterm

Clone oscillation_ctrl

cd ~/catkin_ws/src
git clone https://git.spirirobotics.com/cesar.alejandro/oscillation_ctrl.git

Run bash script and build

bash /.oscillation_ctrl/px4_setup/ubuntu_sim_ros_melodic.sh

This bash script is taken from PX4 Firmware but sets certain versions of dependencies to work with oscillation_ctrl. It also installs common ROS dependencies, ROS Melodic, Gazebo 9, and MAVROS. It should build oscillation_ctrl and add the source path to your .bashrc. If it does not, then run:

cd ~/catkin_ws
catkin build
source devel/setup.bash

If you do not want to source every time, add 'source ~/catkin_ws/devel/setup.bash' to your .bashrc

2) PX4 Environment Development

Install PX4 firmware and dependencies:

git clone https://github.com/PX4/PX4-Autopilot.git --recursive
git checkout 601c588294973caf105b79a23f7587c6b991bb05
bash ./PX4-Autopilot/Tools/setup/ubuntu.sh

There will be prompts on the screen, hit 'u' and 'enter' as they come up.

Add models, world, and airframe files

To add the necessary Spiri Mu files to PX4, run:

cd ca
bash /.oscillation_ctrl/px4_setup/px4_bash.sh

Add airframes to cmake targets

add 'spiri' and 'spiri_with_tether' airframe names in ~/PX4-Autopilot/platforms/posix/cmake/sitl_target.cmake under set(models...

do not add their airframe number! e.i. 4000 or 4001

Download QGroundControl:

cd to desired directory to install QGroundControl. For example, Desktop.

cd ~/<example_Desktop>
wget https://github.com/mavlink/qgroundcontrol/releases/download/v4.2.0/QGroundControl.AppImage
chmod +x QGroundControl.AppImage

Finish Building PX4 package

cd ~/PX4-Autopilot
DONT_RUN=1 make px4_sitl_default gazebo

If if fails and you see

gzerver: symbol lookup error...

then run:

sudo apt upgrade libignition-math2

If all is good, run: source Tools/setup_gazebo.bash (pwd) (pwd)/build/px4_sitl_default export ROS_PACKAGE_PATH=ROS_PACKAGE_PATH:(pwd) export ROS_PACKAGE_PATH=ROS_PACKAGE_PATH:(pwd)/Tools/sitl_gazebo roslaunch px4 posix_sitl.launch

PX4 should launch with MAVROS

Change devel/setup.bash

In catkin_ws (or any working directory) add to devel/setup.bash:

CURRENT_DIR=$(pwd)
cd ~/PX4-Autopilot
source Tools/setup_gazebo.bash $(pwd) $(pwd)/build/px4_sitl_default
export ROS_PACKAGE_PATH=$ROS_PACKAGE_PATH:$(pwd)
export ROS_PACKAGE_PATH=$ROS_PACKAGE_PATH:$(pwd)/Tools/sitl_gazebo

cd $CURRENT_DIR

Finally, source your setup.bash file

cd ~/catkin_ws
source devel/setup.bash

Jinja tether file

• spiri_with_tether.sdf.jinja can be altered to create desired tether model
• changes need to be made in px4 directory and will only take effect after running: "make px4_sitl gazebo"
  • can do "DONT_RUN=1 make px4_sitl gazebo" to avoid starting px4 shell and gazebo
• First two elements can be changed to tweak tether parameters
  • number_elements: number of segments tether will be composed of
  • tl: segment length (should be no shorter than 0.3 meters)

oscillation_ctrl info

Info pertaining to oscillation_ctrl repo such as what the ROS nodes do, different ROS parameters, etc.

ROS Nodes

LinkState.py

determines payload load angles and their rates (theta and phi) using Gazebo (needs to be made more robust), as well as determines tether length and keeps track of variables needed in case of a step or square test.

Publishes to:

/status/twoBody_status # no longer used but keeps track of payload and vehicle position
/status/load_angles    # payload angles (and states) relative to vehicle
/status/path_follow    # boolean to run trajectory test

Subscribes to:

none

wpoint_tracker.py

Sets original waypoints to be (in meters): [x=0,y=0,z=5]. This node listens to topic to keep track of desired waypoints. If any other node wants to change the waypoints, they publish to "reference/waypoints" and wpoint_tracker creates these new waypoints.

Publishes to:

none

Subscribes to:

/reference/waypoints 

ref_signalGen.py

takes in desired position (xd) and determines smooth path trajectory.

Publishes to:

/reference/path         # smooth path

Subscribes to:

/status/load_angles
/mavros/local_position/pose
/mavros/local_position/velocity_body
/mavros/imu/data
/mavros/state
/reference/waypoints

klausen_control.py

determines forces on drone needed based on smooth path and feedback to dampen oscillations. From the forces needed, it publishes attitude commands.

Publishes to:

/command/att_target # attitude commands

Subscribes to:

/status/load_angles
/reference/path
/mavros/local_position/pose
/mavros/local_position/velocity_body
/mavros/imu/data

set_ploadmass.py

sets the payload mass to be pload_mass value in the spiri_param.yaml

path_follow.cpp

sets the vehicle in OFFBOARD mode (PX4) and takes off to a set height for 25 seconds before starting to publish attitude and thrust commands.

Publishes to:

mavros/setpoint_position/local # needed to hover @ set height	
mavros/setpoint_raw/attitude   # attitude and thrust commands 	

Subscribes to:

/command/att_target	
/command/bodyrate_command	
/mavros/state

Launching simulation

To launch a simulation, run the following command:

roslaunch oscillation_ctrl oscillation_damp.launch

This simulation is set to have a Spiri Mu hover at an alitude of 5 m. The launch file itself has two usable arguments:

model:

spiri_with_tether           # Spiri Mu with a tethered payload			
spiri                       # Spiri Mu without tethered paylaod
headless_spiri_with_tether  # headless mode: launches with no Gazebo GUI. This is the default model

test:

none   # default
step   # step input - default is 5 m
square # square trajectory

To run the simulation with a tethered payload headless mode and perform a step test:

roslaunch oscillation_ctrl oscillation_damp.launch model:=headless_spiri_with_tether test:=step

Whenever the oscillation_ctrl is used, the scripts are written such that the vehicle will hover for about 30 seconds in "Position Mode". This is used to take advantage of the takeoff procedure PX4 has, as this controller assumes the vehicle is already in flight when determining the necessary thrust.

ROS parameters

All these values will be under the '/status/' namespace during simulation

use_ctrl: needs to be set to false to take off. Once Spiri has reached desired altitude, it get be set to 'true' to use oscillation damping controller. This is needed as PX4 has a takeoff procedure which is neglected when using the oscillation damping controller due to attitude setpoints needed a thrust value

pload_mass: sets the payload mass in simulation without having to change the spiri_with_tether jinja file (which needs px4 package to be rebuilt in order to make changes)

Frequent Issues

Will populate this section with frequently faces issues

No header files error:

In oscillation_ctrl/CMakeLists.txt, change:

add_dependencies(pathFollow_node ${${PROJECT_NAME}EXPORTEDTARGETS} ${catkin_EXPORTED_TARGETS})

to:

add_dependencies(pathFollow_node oscillation_ctrl_generate_messages_cpp)

Cannot build px4_sitl

Normally, this is solved by running:

make clean

And redo command you were trying to run. If problem persists, rerun ubuntu_sim_ros_melodic.sh and ubuntu.sh and try again.