A system that updates wheel slip parameters based on linear wheel spin velocity (radius * spin rate). More...

#include <WheelSlip.hh>

Public Member Functions
	WheelSlip ()
	Constructor.

	~WheelSlip () override=default
	Destructor.

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

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

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

A system that updates wheel slip parameters based on linear wheel spin velocity (radius * spin rate).

System parameters

It currently assumes that the fdir1 friction parameter is set parallel to the joint axis (often [0 0 1]) and that the link origin is on the joint axis.

The slip parameter is a Force-Dependent Slip (slip1, slip2) and it has units of velocity / force (m / s / N), similar to the inverse of a viscous damping coefficient.

The slip_compliance parameters specified in this plugin are unitless, representing the lateral or longitudinal slip ratio (see https://en.wikipedia.org/wiki/Slip_(vehicle_dynamics) ) to tangential force ratio (tangential / normal force).

Note that the maximum force ratio is the friction coefficient. At each time step, these compliances are multiplied by the linear wheel spin velocity and divided by the wheel_normal_force parameter specified below in order to match the units of the slip parameters.

A graphical interpretation of these parameters is provided below for a positive value of slip compliance. The horizontal axis corresponds to the slip ratio at the wheel, and the vertical axis corresponds to the tangential force ratio (tangential / normal force).

As wheel slip increases, the tangential force increases until it reaches the maximum set by the friction coefficient. The slip compliance corresponds to the inverse of the slope of the force before it reaches the maximum value. A slip compliance of 0 corresponds to a completely vertical portion of the plot below. As slip compliance increases, the slope decreases.

  |                                            .
  |      _________ friction coefficient        .
  |     /                                      .
  |    /|                                      .
  |   /-┘ slope is inverse of                  .
  |  /    slip compliance                      .
  | /                                          .
  |/                                           .
--+-------------------------- slipRatio
  |

Examples

<plugin filename="gz-sim-wheel-slip-system"
 name="systems::WheelSlip">
  <wheel link_name="wheel_front_left">
    <slip_compliance_lateral>0</slip_compliance_lateral>
    <slip_compliance_longitudinal>0.1</slip_compliance_longitudinal>
    <wheel_normal_force>100</wheel_normal_force>
    <wheel_radius>0.1651</wheel_radius>
  </wheel>
  <wheel link_name="wheel_front_right">
    <slip_compliance_lateral>0</slip_compliance_lateral>
    <slip_compliance_longitudinal>0.1</slip_compliance_longitudinal>
    <wheel_normal_force>100</wheel_normal_force>
    <wheel_radius>0.1651</wheel_radius>
  </wheel>
  <wheel link_name="wheel_rear_left">
    <slip_compliance_lateral>0</slip_compliance_lateral>
    <slip_compliance_longitudinal>0.1</slip_compliance_longitudinal>
    <wheel_normal_force>80</wheel_normal_force>
    <wheel_radius>0.1651</wheel_radius>
  </wheel>
  <wheel link_name="wheel_rear_right">
    <slip_compliance_lateral>0</slip_compliance_lateral>
    <slip_compliance_longitudinal>0.1</slip_compliance_longitudinal>
    <wheel_normal_force>80</wheel_normal_force>
    <wheel_radius>0.1651</wheel_radius>
  </wheel>
</plugin>

Constructor & Destructor Documentation

◆ WheelSlip()

WheelSlip ( )

Constructor.

◆ ~WheelSlip()

~WheelSlip ( )

overridedefault

Destructor.

Member Function Documentation

◆ Configure()

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

overridevirtual

Configure the system.

Parameters

[in]	_entity	The entity this plugin is attached to.
[in]	_sdf	The SDF Element associated with this system plugin.
[in]	_ecm	The EntityComponentManager of the given simulation instance.
[in]	_eventMgr	The EventManager of the given simulation instance.