A interface for the the system dynamics of a legged robot. More...

#include <dynamic_model.h>

Inheritance diagram for towr::DynamicModel:

Public Member Functions
double	g () const
virtual BaseAcc	GetDynamicViolation () const =0
	The violation of the system dynamics incurred by the current values.
int	GetEECount () const
	the number of endeffectors that this robot has.
virtual Jac	GetJacobianWrtBaseAng (const EulerConverter &base_angular, double t) const =0
	How the base orientation affects the dynamic violation.
virtual Jac	GetJacobianWrtBaseLin (const Jac &jac_base_lin_pos, const Jac &jac_base_lin_acc) const =0
	How the base position affects the dynamic violation.
virtual Jac	GetJacobianWrtEEPos (const Jac &ee_pos, EE ee) const =0
	How the endeffector positions affect the dynamic violation.
virtual Jac	GetJacobianWrtForce (const Jac &ee_force, EE ee) const =0
	How the endeffector forces affect the dynamic violation.
double	m () const
void	SetCurrent (const ComPos &com_W, const Vector3d com_acc_W, const Matrix3d &w_R_b, const AngVel &omega_W, const Vector3d &omega_dot_W, const EELoad &force_W, const EEPos &pos_W)
	Sets the current state and input of the system.
Protected Member Functions
	DynamicModel (double mass, int ee_count)
	Construct a dynamic object. Protected as this is abstract base class.
virtual	~DynamicModel ()
Protected Attributes
Vector3d	com_acc_
	x-y-z acceleration of the Center-of-Mass.
ComPos	com_pos_
	x-y-z position of the Center-of-Mass.
EELoad	ee_force_
	The endeffector force expressed in world frame.
EEPos	ee_pos_
	The x-y-z position of each endeffector.
AngVel	omega_
	angular velocity expressed in world frame.
Vector3d	omega_dot_
	angular acceleration expressed in world frame.
Matrix3d	w_R_b_
	rotation matrix from base (b) to world (w) frame.
Private Attributes
double	g_
	gravity acceleration [m/s^2]
double	m_
	mass of the robot

Detailed Description

A interface for the the system dynamics of a legged robot.

This class is responsible for verifying that the current acceleration of a system given a specific robot state and input forces ensure the system dynamics, so g = xdd(t) - f(x(t), f(t)).

Dynamic models can for example be: Linear Inverted Pendulum (LIP), SingleRigidBodyDynamics (SRBD), Centroidal Dynamics, Full Rigid Body Dynamics (RBD).

An overview of all these models can be found here: https://doi.org/10.3929/ethz-b-000272432

This model is used in DynamicConstraint to ensure that the optimized motion trajectory complies to this. Currently, only SingleRigidBodyDynamics is implemented.

Definition at line 66 of file dynamic_model.h.

Constructor & Destructor Documentation

towr::DynamicModel::DynamicModel	(	double	mass,
		int	ee_count
	)		`[protected]`

Construct a dynamic object. Protected as this is abstract base class.

Parameters:

mass	The mass of the system.

Definition at line 34 of file dynamic_model.cc.

virtual towr::DynamicModel::~DynamicModel ( ) [protected, virtual]

Member Function Documentation

double towr::DynamicModel::g ( ) const [inline]

Returns:: The gravity acceleration [m/s^2] (positive)

Definition at line 144 of file dynamic_model.h.

virtual BaseAcc towr::DynamicModel::GetDynamicViolation ( ) const [pure virtual]

The violation of the system dynamics incurred by the current values.

Returns:: The 6-dimension generalized force violation (angular + linear).

Implemented in towr::SingleRigidBodyDynamics.

int towr::DynamicModel::GetEECount ( ) const [inline]

the number of endeffectors that this robot has.

Definition at line 154 of file dynamic_model.h.

virtual Jac towr::DynamicModel::GetJacobianWrtBaseAng	(	const EulerConverter &	base_angular,
		double	t
	)		const `[pure virtual]`

How the base orientation affects the dynamic violation.

Parameters:

base_angular	provides Euler angles Jacobians.
t	Time at which euler angles values are queried.

Returns:: The 6xn Jacobian of dynamic violations with respect to variables defining the base angular spline (e.g. node values).

Implemented in towr::SingleRigidBodyDynamics.

virtual Jac towr::DynamicModel::GetJacobianWrtBaseLin	(	const Jac &	jac_base_lin_pos,
		const Jac &	jac_base_lin_acc
	)		const `[pure virtual]`

How the base position affects the dynamic violation.

Parameters:

jac_base_lin_pos	The 3xn Jacobian of the base linear position.
jac_base_lin_acc	The 3xn Jacobian of the base linear acceleration.

Returns:: The 6xn Jacobian of dynamic violations with respect to variables defining the base linear spline (e.g. node values).

Implemented in towr::SingleRigidBodyDynamics.

virtual Jac towr::DynamicModel::GetJacobianWrtEEPos	(	const Jac &	ee_pos,
		EE	ee
	)		const `[pure virtual]`

How the endeffector positions affect the dynamic violation.

Parameters:

ee_force	The 3xn Jacobian of the foot position x,y,z.
ee	The endeffector for which the senstivity is required.

Returns:: The 6xn Jacobian of dynamic violations with respect to variables defining the foot positions (e.g. node values).

Implemented in towr::SingleRigidBodyDynamics.

virtual Jac towr::DynamicModel::GetJacobianWrtForce	(	const Jac &	ee_force,
		EE	ee
	)		const `[pure virtual]`

How the endeffector forces affect the dynamic violation.

Parameters:

ee_force	The 3xn Jacobian of the foot force x,y,z.
ee	The endeffector for which the senstivity is required.

Returns:: The 6xn Jacobian of dynamic violations with respect to variables defining the endeffector forces (e.g. node values).

Implemented in towr::SingleRigidBodyDynamics.

double towr::DynamicModel::m ( ) const [inline]

Returns:: The mass of the robot [kg].

Definition at line 149 of file dynamic_model.h.

void towr::DynamicModel::SetCurrent	(	const ComPos &	com_W,
		const Vector3d	com_acc_W,
		const Matrix3d &	w_R_b,
		const AngVel &	omega_W,
		const Vector3d &	omega_dot_W,
		const EELoad &	force_W,
		const EEPos &	pos_W
	)

Sets the current state and input of the system.

Parameters:

com_W	Current Center-of-Mass (x,y,z) position in world frame.
com_acc_W	Current Center-of-Mass (x,y,z) acceleration in world.
w_R_b	Current rotation from base to world frame.
omega_W	Current angular velocity in world frame.
omega_dot_W	Current angular acceleration in world frame.
force_W	Force at each foot expressed in world frame.
pos_W	Position of each foot expressed in world frame