warning

This page is describing the upcomming ROS2 version of the MRS UAV System (however, it may be still outdated). If you are looking for ROS1 version of the docs, follow to https://ctu-mrs.github.io/docs/1.5.0/introduction/.

Gazebo Motor parameters

• Pixhawk controller output is shaped via function

  output = (original_output + input_offset) * input_scaling + zero_position_armed

  in gazebo_mavlink_interface.cpp. The parameters are loaded from component_snippets.xacro from the rotor block:

  <channel name="rotor2">
    <input_index>1</input_index>
    <input_offset>0</input_offset>
    <input_scaling>1</input_scaling>
    <zero_position_disarmed>0</zero_position_disarmed>
    <zero_position_armed>0.15</zero_position_armed>
    <joint_control_type>velocity</joint_control_type>
  </channel>

  The original_output is scaled from 0 to 1. The new output has zero_position_armed added, which offsets the signal up and emulates the "minimal rotor speed" set in PixHawk.

• Gazebo receives the signals from PixHawk ([0, 1])

  • A simulated rotor speed (rad/s) is generated by dividing the signal by the rotor_velocity_slowdown_sim constant
    • that is the speed of the actual model in gazebo
  • A thrust [N] is generated from the signal (NOT the simulated rotor speed) by the function thrust = motor_constant * signal^2
  • the parameters are in the .xacro file

  <xacro:property name="rotor_velocity_slowdown_sim" value="0.0159236" />
  <xacro:property name="motor_constant" value="8.3" /> <!-- [kg.m/s^2] -->
  • rotor_velocity_slowdown_sim is set so the max velocity is 10 revolutions per second