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