zmoth/mecanum_controller

Mecanum Controller

This package offers a controller module designed to oversee a mecanum wheel platform utilizing the ROS2 Control framework. Presently, the controller is optimized for a mecanum platform equipped with four wheels, although this specification could evolve in the coming times.

The underlying architecture of the controller draws from the principles of the differential drive controller.

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Table of Content

• Updates
• Installation
• Usage
  • Parameters
• TODO

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Updates

2023-08-30

• Resolved mathematical issues related to wheel velocities and odometry
• Added functionality to check and adjust maximum wheel rotational speed

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Installation

1. Install the ROS2 Humble distribution

   Follow the ROS2 Humble installation guide.

2. Install the ros2_control framework and ros2_controllers

   Install the necessary packages using the following commands:

   sudo apt install -y ros-<ROS_DISTRO>-ros2-control ros-<ROS_DISTRO>-ros2-controllers
   

3. Create a new workspace

   Create a workspace and navigate to the source directory:

   mkdir -p ~/ros2_ws/src
   cd ~/ros2_ws/src
   

4. Clone this controller repository into '~/ros2_ws/src/'

   Clone the controller repository using the following command:

   git clone https://github.com/roboTHIx/mecanum_controller.git --branch=humble
   

5. Build and source

   Build the workspace and source the workspace:

   cd ~/ros2_ws
   colcon build --symlink-install --packages-select mecanum_controller
   source ~/ros2_ws/install/setup.bash
   

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Usage

Parameters

Parameter File

• publish_rate:
  • Defines the rate at which the controller calculates the required wheel velocities and, if chosen, the odometry based on these velocities.
• DIR_SIDE_wheel_name:
  • Specifies the name of each wheel joint (e.g., "wheel_front_left_joint"), which must be defined in the URDF file for the robot's description.
• wheel_separation_AXIS:
  • Represents the separation between the wheel treads in the X and Y directions. [m]
• wheel_max_rotational_speed:
  • Sets the maximum rotational speed of the wheels. Setting this to 0.0 will disregard this option. [rad/s]
• wheel_radius:
  • Defines the radius of the wheels. [m]
• wheel_separation_multiplier_AXIS:
  • Provides a correction factor for the wheel separation in the X and Y directions.
• DIR_SIDE_wheel_radius_multiplier:
  • Offers a correction factor when the radius of the front left wheel deviates from the nominal value specified in the DIR_SIDE_wheel_radius parameter.
• tf_frame_prefix:
  • Prefix appended to the tf frames; added to odom_id and base_frame_id before publishing. If empty, the controller's namespace will be used.
• odom_frame_id:
  • Name of the frame for odometry. This frame is the parent of base_frame_id when the controller publishes odometry.
• base_frame_id:
  • Name of the robot's base frame, which is a child of the odometry frame.
• pose_covariance_diagonal:
  • Odometry covariance for the robot's pose based on encoder output. Initial values: [0.001, 0.001, 0.001, 0.001, 0.001, 0.01]
• twist_covariance_diagonal:
  • Odometry covariance for the robot's speed based on encoder output. Initial values: [0.001, 0.001, 0.001, 0.001, 0.001, 0.01]
• open_loop:
  • When set to true, the robot's odometry will be calculated from the calculated wheel speed values rather than using feedback.
• position_feedback:
  • Indicates the presence of position feedback from the hardware.
• enable_odom_tf:
  • Publishes the transformation between odom_frame_id and base_frame_id.
• publish_limited_velocity:
  • Publish the limited velocity value.
• use_stamped_vel:
  • Uses the timestamp from the input velocity message to calculate the command's actual age.
• MOTION.DIR.LIMIT:
  • Limits for each motion direction and limit (velocity, acceleration, or jerk). Refer to the parameter file for more information.

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TODO

• Implement a wheel max rotational speed checker and scaler
• Revise wheel setup to be parametric, allowing for an arbitrary number of wheels instead of being limited to 4.