Quaternion MPC

This codebase is used for the quaternion MPC experiments. It contains C++ implementations of quaternion MPC as well as Euler angle-based MPCs, and Gazebo simulation environments for MIT humanoid and Unitree quadruped robots.

Robots with Attitude: Singularity-Free Quaternion-Based Model-Predictive Control for Agile Legged Robots, Zixin Zhang, John Z. Zhang, Shuo Yang, Zachary Manchester, pdf, video.

@misc{zhang2024robotsattitudesingularityfreequaternionbased,
      title={Robots with Attitude: Singularity-Free Quaternion-Based Model-Predictive Control for Agile Legged Robots}, 
      author={Zixin Zhang and John Z. Zhang and Shuo Yang and Zachary Manchester},
      year={2024},
      eprint={2409.09940},
      archivePrefix={arXiv},
      primaryClass={cs.RO},
      url={https://arxiv.org/abs/2409.09940}, 
}

Branches:

• main: Quaternion MPC and Euler MPC for Unitree Go1 walking control. Can be deployed in Gazebo and on hardware.
• spider_dog: Quaternion MPC for Unitree Go1 chimney climbing control. Can be deployed in Gazebo and on hardware.
• falling_cat: Quaternion MPC for quadruped airborne attitude control.
• humanoid: Quaternion MPC and Euler MPC for MIT humanoid balancing control.

Installation

• Run in Ubuntu 20.04.
• Make sure git and ROS Noetic have been installed properly.
• Necessary dependencies are installed using the bash script install.bash.

All you need to do is enter the following commands (if you are using other shells, such as zsh, please modify the commands and install.bash script accordingly):

cd PATH_TO_YOUR_CATKIN_WORKSPACE/src
git clone https://github.com/zixinz990/quaternion-mpc.git
cd quaternion-mpc
git submodule init
git submodule update --recursive
bash ./install.bash
cd ../..
catkin build
echo "export PATH_TO_YOUR_CATKIN_WORKSPACE/devel/setup.bash" >> ~/.bashrc
source ~/.bashrc

Run the Controller

If you want to run the controller in Gazebo, you need to launch the simulation first:

roslaunch unitree_gazebo normal.launch rname:=${robot_type}

If you are using a real robot, make sure it is connected to the computer and the power is on. To check if your computer has connected to the robot, try:

ping 192.168.123.161

If there is no messgae received, try:

sudo ifconfig enpxxx down  # enpxxx is your network device
sudo ifconfig enpxxx 192.168.123.162/24
sudo ifconfig enpxxx up
ping 192.168.123.161

Make sure the robot is in a safe environment. Press L2 + B and L1 + L2 + START to get the robot down to the ground.

To run the controller, enter the following command:

roslaunch legged_ctrl ${env_type}_go1_${controller_type}.launch

• env_type can be gazebo or hardware.
• controller_type can be convex_mpc or quat_mpc.

The following two commands can help you reset the robot's pose in Gazebo without restarting the simulation:

rosrun unitree_controller unitree_servo # reset joint angles
rosrun unitree_controller unitree_move_kinetic # reset body pose

Control the Robot using a Joystick

joy_node will be automatically open when you launch the controller. You can do rostopic echo /joy to check the connection.

Default joystick settings (Xbox Controller):

Button	Function
Left stick	Control yaw angle and body's height
Right stick	Control walking direction and speed
Left cross	Control pitch and roll angle (only available for Quaternion MPC)
A	Switch mode between "stand" and "walk"
B	Enter/exit default position mode (only available in Gazebo)
Y	Input sinusoidal attitude commend (only available for Quaternion MPC)
LB	Shut down controller

To change this, modify the YAML files in src/legged_ctrl/config.

Debug Instructions

1. Sometimes ROS cannot find some packages. Make sure you have sourced the devel/setup.bash file in your catkin workspace.
2. The install.bash file automatically installs CMake 3.24.3, because the program requires CMake 3.23+. If you think this will mess up your computer, feel free to delete the related commands in install.bash. But to use the controller, you need to make sure you have CMake 3.23+ installed.
3. Sometimes you may need to manually copy the .so file from the legged_ctrl/src/estimation/casadi_ekf/casadi_lib folder to the /tmp folder (sudo is required to do this).

Development Guide

Any contribution is welcome. Please ensure that the following naming rules are followed:

Naming rules in legged_ctrl package

1. The name of folders should be lowercase. Use underscores to connect words, eg., my_folder, etc.
2. The name of C++ header and source files should follow the PascalCase rule (also known as UpperCamelCase), eg., MyMpc.h, etc.
3. The name of XML-based files and YAML files should be lowercase. Use underscores to connect words, eg., my_launch_file.launch.
4. The name of classes, structures and enumerated types should follow the PascalCase rule, eg., MyMpc, etc.
5. The name of namespace, variables, parameters, enumerators and functions should be lowercase. Use underscores to connect words, eg., my_namespace.
6. The name of macros or constants appear in the preprocessor should be uppercase. Use underscores to connect words, eg., #define MY_CONST 1.

Acknowledgement

Dr. Shuo Yang made major contributions to the development of the first version of this codebase (September 2022), particularly in the development of the state estimators and the code structure. John Ziyang Zhang made significant contributions to the chimney climbing experiment. The solver was developed based on Dr. Brian E. Jackson's C++ implementation of ALTRO. Thank you all for your support. Finally, special thanks to Dr. Zachary Manchester for all the insightful guidance along the way.