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Gazebo Motor parameters
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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.
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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
- A simulated rotor speed (rad/s) is generated by dividing the signal by the rotor_velocity_slowdown_sim constant