Model- and Acceleration-based Pursuit (MAP) controller

This project presents a novel trajectory tracking algorithm for a high-speed autonomous racing setting. Our controller uses a similar working principle to the Pure Pursuit algorithm but with some notable differences. Specifically, it calculates acceleration via L1 guidance and then converts this value to a steering angle using a lookup table generated from system model parameters and tire dynamics. By using this approach, the controller can achieve greater accuracy and performance than traditional geometric controllers.

This package provides a script for the lookup table generation and two controllers: the MAP controller and a Pure Pursuit controller. Additionally, it includes a simulator where you can test these controllers. With the simulator, you can evaluate the performance of the MAP controller with a linear tyre model (as the simulator models a linear tyre behaviour) and the Pure Pursuit controller and compare their results.

Click on the image for a brief video description:

Getting Started

Prerequisits

Before getting started with this project, make sure you have the following software installed:

• ROS Noetic
• Catkin tools: sudo apt install python3-catkin-tools

You can find instructions on how to install ROS for your operating system on the official ROS wiki page: http://wiki.ros.org/ROS/Installation

Dependencies

• tf2_geometry_msgs
• ackermann_msgs
• joy
• map_server
• scipy

You can install them by running:

sudo apt-get install ros-noetic-tf2-geometry-msgs ros-noetic-ackermann-msgs ros-noetic-joy ros-noetic-map-server python3-scipy

Installing

To install this package, first, create a new ROS workspace and navigate to the src folder:

mkdir -p ~/catkin_ws/src
cd ~/catkin_ws/src

Then, clone the repository into the src folder:

git clone https://github.com/ETH-PBL/MAP-Controller.git

Once the repository has been cloned, build the package:

cd ~/catkin_ws
source /opt/ros/noetic/setup.bash
catkin build

Running the Package

After building the package, source the setup.bash file to add the package to your ROS environment:

source ~/catkin_ws/devel/setup.bash

You can now run the MAP controller using the roslaunch command:

roslaunch map_controller sim_MAP.launch 

This will launch the simulator together with the MAP controller on a preselected map. You can change the map by specifying the desired map in the argument map_name:=desired_map where desired_map is the name of the desired map.

Alternatively, you can run the Pure Pursuit controller for comparison:

roslaunch map_controller sim_PP.launch 

Usage

Lookup Table Generation

The lookup table generation script expects a model.txt file in the folder /steering_lookup/src/LUT_Generation/models with the folowing parameters for the linear model:

Parameter	Description
mu	Friction coefficient [1]
C_Sf	Cornering stiffness front axle [1/rad]
C_Sr	Cornering stiffness rear axle [1/rad]
l_f	Distance from center of gravity to front axle [m]
l_r	Distance from center of gravity to rear axle [m]
h_cg	Center of gravity height of total mass [m]
m	Mass of the car [kg]
I_z	Inertia of center of gravity to yaw axis [kgm^2]

and following parameters for the pacjeka model:

Parameter	Description
mu	Friction coefficient [1]
C_Pf_0	Cornering stiffness front axle [1/rad]
C_Pf_1	Shape factor front axle [1]
C_Pf_2	Peak value front axle [1]
C_Pf_3	Curvature factor front axle [1]
C_Pr_0	Cornering stiffness rear axle [1/rad]
C_Pr_1	Shape factor rear axle [1]
C_Pr_2	Peak value rear axle [1]
C_Pr_3	Curvature factor rear axle [1]
l_f	Distance from center of gravity to front axle [m]
l_r	Distance from center of gravity to rear axle [m]
h_cg	Center of gravity height of total mass [m]
m	Mass of the car [kg]
I_z	Inertia of center of gravity to yaw axis [kgm^2]

You can run the script using the command: cd ~/catkin_ws/src/Map-Controller/steering_lookup/src/LUT_Generation/ pyhton3 simulate_model.py

The generated lookup tbale is placed in the /steering_lookup/src/LUT_Generation/modelsfolder. This file can be moved to the /steering_lookup/cfg folder to be used in the simulator.

MAP Controller

We experimentally evaluated the controller on the 1:10 scaled F1TENTH testing platform, but the control strategy is not limited to small-scale platforms. It can be applied to full-scale vehicles as well, making it a versatile solution for trajectory tracking in various settings.

The controller requires the current position and the waypoints of the trajectory which should be published as:

• PoseStamped on the /car_state/pose topic
• WpntArray on the /global_waypoints topic

The lookahead distance is caluclated with following formula: $m_{map}\cdot \text{targetspeed} + q_{map}$. To fine-tune the controller, you can adjust the tuning parameters in the map_params.yaml file located in /map_controller/cfg. The default settings generalize well to different trajectories and speeds, but the parameters can be adjusted to increase accuracy.

• m_map parameter determines the steepness of the slope
• q_map sets the offset
• t_clip_min is the minimum distance for the lookahead distance in meters to prevent oscillations
• t_clip_max is the maximum distance for the lookahead distance in meters to prevent corner cutting

The controller publishes the calculated steering and speed commands as an AckermannDriveStamped message on the /ackermann_cmd_mux/input/teleop topic.

Reference

The relative paper has been published at ICRA2023, see the pre-print. If you find our work useful in your research, please consider citing:

@inproceedings{Becker_2023,
	doi = {10.1109/icra48891.2023.10161472},
	url = {https://doi.org/10.1109%2Ficra48891.2023.10161472},
	year = 2023,
	month = {may},
	publisher = {{IEEE}}, 
	author = {Jonathan Becker and Nadine Imholz and Luca Schwarzenbach and Edoardo Ghignone and Nicolas Baumann and Michele Magno},
	title = {Model- and Acceleration-based Pursuit Controller for High-Performance Autonomous Racing},
	booktitle = {2023 {IEEE} International Conference on Robotics and Automation ({ICRA})}
}