Heading control

description of the file heading_controller.py

The class Heading_controller implements a PD controller in order to follow the heading desired.

ROS

Node

heading_controller

Topics

ROS topics subscribed	Message	Description
/BlueRov2/imu/attitude	bluerov_ros_playground/Attitude	Yaw in [-π,π]rad
/Settings/set_heading	bluerov_ros_playground/Set_heading	Settings for the controller
/Settings/set_target	bluerov_ros_playground/Set_target	Yaw to follow

The heading targeted must be in [0, 360]deg range where 0 is North, 180 is South

ROS topics published	Message	Description
/Command/heading	Uint16	Pwm send by the controller to the commander

Heading estimation

PD controller

The PD controller uses the difference between current yaw and the yaw desired, but also the derivative value to compute a command in the interval [-400,+400]. This command is added to 1500, the pwm neutral of thrusters.

To calculate the command the current yaw and the yaw desired are in [-pi,pi]rad range

Sawtooth

To deal with the 2 PI modulo for angles, difference between yaw desired and current yaw goes through this function sawtooth.

Saturation

A saturation method is added on pwm output before the publication on the command topic in case of a will to limit thruster power.

Send heading target

The heading target is defined by the publication of a Set_target message on the topic /Settings/set_target. This message is shared with the depth and the velocity controller to set their target

Several methods exist to publish the message : the GUI, command line, script, ....

Set_target message :		Units
float64	depth_desired	m
float64	heading_desired	deg
float64	velocity_desired	pwm range [-400,400]

The heading targeted must be in [0, 360]deg range where 0 and 360 is North, 180 is South

Tune PD and set saturation

PD coefficients and maximum pwm for saturation of the command can be modified in real time by the Set_heading message published on the topic /Settings/set_heading.

These values send are not saved and the controller will get its initial value. To change permanently the values of those parameters you must change it in the code, in the __init__ method.

Set_heading message
bool	enable_heading_ctrl
uint16	pwm_max
uint32	KP
uint32	KD

See Commander to know how enable_heading_ctrl is used