minimec_control

ROS2 package for controlling a mecanum wheel base. Made for controlling the Minimec, but can be extended for other platforms.

Nodes

• kinematics: node that implements forward kinematics, taking an input twist and outputting wheel commands.
• odometry: node that implements odometry - estimation of position according to encoder feedback. This takes in joint states and publishes the odometry transform to a topic and broadcasts it to the tf tree.
• path_generator: node that generates spline and circular paths.
• trajectory_tracking: node that publisher velocity commands to track a generated path using feedforward + PI feedback control

Configuration

A file for configuring basic parameters is included in config/params.yaml. Parameters include:

• wheel radius
• wheelbase
• wheel track

Launch files

• launch_control.launch.py - launches the kinematics and odometry nodes, passing them the parameter file.
• launch_path_gen.launch.py - launches the path generation node (standalone) and rviz to visualize generated paths

Running the path generation node

The path generation can work as standalone, you can just spin up the node using the provided launchfile: ros2 launch minimec_control launch_path_gen.launch.py

You can then call the service with this sample input:

• To generate a spline path with fixed orienation: ros2 service call /generate_spline_plan minimec_msgs/srv/SplinePlanRequest "{points: [{x: 0.0, y: 0.0},{x: 1.0, y: 0.0}, {x: 1.0, y: 1.0}, {x: 2.0, y: 1.0}, {x: 2.0, y: 0.0}, {x: 3.0, y: 0.0},{x: 3.0, y: 1.0},{x: 4.0, y: 1.0},{x: 4.0, y: 0.0},{x: 5.0, y: 0.0}], heading_mode: fixed, frame_id: odom, heading_angle: 0.0, resolution: 0.0075}""

• To generate a spline path with point orientation: ros2 service call /generate_spline_plan minimec_msgs/srv/SplinePlanRequest "{points: [{x: 0.0, y: 0.0},{x: 1.0, y: 0.0}, {x: 1.0, y: 1.0}, {x: 2.0, y: 1.0}, {x: 2.0, y: 0.0}, {x: 3.0, y: 0.0},{x: 3.0, y: 1.0},{x: 4.0, y: 1.0},{x: 4.0, y: 0.0},{x: 5.0, y: 0.0}], heading_mode: point, frame_id: odom, heading_point: {x: 6.0, y: 0.0}, resolution: 0.0075}"

• To generate a circular path: ros2 service call /generate_circular_plan minimec_msgs/srv/CircularPlanRequest "{frame_id: odom, center: {x: 0.75, y: 0.0}, resolution: 0.005, radius: 0.75}"

This will display the points in rviz and the generated path.

Attribution

This package makes use of the TinySpline library for generating the spline from reference points.

The kinematics and trajectory tracking are heavily based on Lynch, Park - Modern Robotics book and the corresponding Modern Robotics python library