Thruster Class Reference

This plugin simulates a maritime thruster for boats and underwater vehicles. It uses the equations described in Fossen's "Guidance and Control of Ocean Vehicles" in page 246. This plugin has two modes of operation. In the default mode it takes in a force in Newtons and applies it to the thruster. It also calculates the theoretical angular velocity of the blades and spins them accordingly. Alternatively, one may send angular velocity commands to calculate the force to be applied using the said equation. In the default mode the plugin will publish angular velocity in radians per second on /model/{ns}/joint/{joint_name}/ang_vel as a gz.msgs.double. If <use_angvel_cmd> is set to true it publishes force in Newtons instead to /model/{ns}/joint/{joint_name}/force. More...

#include <Thruster.hh>

Public Member Functions
	Thruster ()
	Constructor.
void	Configure (const Entity &_entity, const std::shared_ptr< const sdf::Element > &_sdf, EntityComponentManager &_ecm, EventManager &) override
	Documentation inherited.
void	PostUpdate (const UpdateInfo &_info, const EntityComponentManager &_ecm) override
	Documentation inherited.
void	PreUpdate (const UpdateInfo &_info, EntityComponentManager &_ecm) override
	Documentation inherited.
Public Member Functions inherited from System
	System ()=default
	Constructor.
virtual	~System ()=default
	Destructor.

Additional Inherited Members
Public Types inherited from System
using	PriorityType = int32_t
	Signed integer type used for specifying priority of the execution order of PreUpdate and Update phases.
Static Public Attributes inherited from System
static constexpr PriorityType	kDefaultPriority = {0}
	Default priority value for execution order of the PreUpdate and Update phases.
static constexpr std::string_view	kPriorityElementName
	Name of the XML element from which the priority value will be parsed.

Detailed Description

This plugin simulates a maritime thruster for boats and underwater vehicles. It uses the equations described in Fossen's "Guidance and Control of Ocean Vehicles" in page 246. This plugin has two modes of operation. In the default mode it takes in a force in Newtons and applies it to the thruster. It also calculates the theoretical angular velocity of the blades and spins them accordingly. Alternatively, one may send angular velocity commands to calculate the force to be applied using the said equation. In the default mode the plugin will publish angular velocity in radians per second on /model/{ns}/joint/{joint_name}/ang_vel as a gz.msgs.double. If <use_angvel_cmd> is set to true it publishes force in Newtons instead to /model/{ns}/joint/{joint_name}/force.

System Parameters

• <namespace>: The namespace in which the robot exists. The plugin will listen on the topic /model/{namespace}/joint/{joint_name}/cmd_thrustor /model/{namespace}/joint/{joint_name}/cmd_vel depending on the mode of operation. If {topic} is set then the plugin will listen on {namespace}/{topic} [Optional]
• <topic>: The topic for receiving thrust commands. [Optional]
• <joint_name>: This is the joint in the model which corresponds to the propeller. [Required]
• <use_angvel_cmd>: If set to true will make the thruster plugin accept commands in angular velocity in radians per seconds in terms of newtons. [Optional, Boolean, defaults to false]
• <fluid_density>: The fluid density of the liquid in which the thruster is operating in. [Optional, kg/m^3, defaults to 1000 kg/m^3]
• <propeller_diameter>: The diameter of the propeller in meters. [Optional, m, defaults to 0.02m]
• <thrust_coefficient>: This is the coefficient which relates the angular velocity to thrust. A positive coefficient corresponds to a clockwise propeller, which is a propeller that spins clockwise under positive thrust when viewed along the parent link from stern (-x) to bow (+x). [Optional, no units, defaults to 1.0]

  omega = sqrt(thrust /
      (fluid_density * thrust_coefficient * propeller_diameter ^ 4))

  where omega is the propeller's angular velocity in rad/s.
• <velocity_control>: If true, use joint velocity commands to rotate the propeller. If false, use a PID controller to apply wrenches directly to the propeller link instead. [Optional, defaults to false].
• <p_gain>: Proportional gain for joint PID controller. [Optional, no units, defaults to 0.1]
• <i_gain>: Integral gain for joint PID controller. [Optional, no units, defaults to 0.0]
• <d_gain>: Derivative gain for joint PID controller. [Optional, no units, defaults to 0.0]
• <max_thrust_cmd>: Maximum input thrust or angular velocity command. [Optional, defaults to 1000N or 1000rad/s]
• <min_thrust_cmd>: Minimum input thrust or angular velocity command. [Optional, defaults to -1000N or -1000rad/s]
• <deadband>: Deadband of the thruster. Absolute value below which the thruster won't spin nor generate thrust. This value can be changed at runtime using a topic. The topic is either /model/{ns}/joint/{jointName}/enable_deadband or {ns}/{topic}/enable_deadband depending on other params

• <wake_fraction>: Relative speed reduction between the water at the propeller (Va) vs behind the vessel. [Optional, defults to 0.2]

  See Thor I Fossen's "Guidance and Control of ocean vehicles" p. 95:

  Va = (1 - wake_fraction) * advance_speed

• <alpha_1>: Constant given by the open water propeller diagram. Used in the calculation of the thrust coefficient (Kt). [Optional, defults to 1]

• <alpha_2>: Constant given by the open water propeller diagram. Used in the calculation of the thrust coefficient (Kt). [Optional, defults to 0]

  See Thor I Fossen's "Guidance and Control of ocean vehicles" p. 95:

  Kt = alpha_1 * alpha_2 *
      (Va / (propeller_revolution * propeller_diameter))

Example

An example configuration is installed with Gazebo. The example uses the LiftDrag plugin to apply steering controls. It also uses the thruster plugin to propell the craft and the buoyancy plugin for buoyant force. To run the example:

gz sim auv_controls.sdf

To control the rudder of the craft run the following:

gz topic -t /model/tethys/joint/vertical_fins_joint/0/cmd_pos \
   -m gz.msgs.Double -p 'data: -0.17'

To apply a thrust you may run the following command:

gz topic -t /model/tethys/joint/propeller_joint/cmd_thrust \
   -m gz.msgs.Double -p 'data: -31'

The vehicle should move in a circle.

Constructor & Destructor Documentation

Thruster()

Thruster

(

)

Constructor.

Member Function Documentation

Configure()

void Configure ( const Entity &  _entity, const std::shared_ptr< const sdf::Element > &  _sdf, EntityComponentManager &  _ecm, EventManager &    )

overridevirtual

Documentation inherited.

Implements ISystemConfigure.

PostUpdate()

void PostUpdate ( const UpdateInfo &  _info, const EntityComponentManager &  _ecm  )

overridevirtual

Documentation inherited.

Implements ISystemPostUpdate.

PreUpdate()

void PreUpdate ( const UpdateInfo &  _info, EntityComponentManager &  _ecm  )

overridevirtual

Documentation inherited.

Implements ISystemPreUpdate.

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The documentation for this class was generated from the following file:

• Thruster.hh