raisim::Joint

class · #include <raisim/object/ArticulatedSystem/JointAndBodies.hpp>

Joint connecting a body to its parent; used to build an articulated system (see Child).

Public types

Type

enum Type : int

Joint type.

Enumerator	Value	Description
FIXED	0	No degree of freedom. At the root, it means a fixed base; elsewhere, the child is merged into its movable parent.
REVOLUTE		1 rotational DOF about the axis (gc: 1, gv: 1).
PRISMATIC		1 translational DOF along the axis (gc: 1, gv: 1).
SPHERICAL		Ball joint (gc: quaternion w,x,y,z; gv: angular velocity in the child body frame).
FLOATING		Free 6-DOF joint, only allowed at the root (gc: position + quaternion; gv: linear + angular velocity in the world frame).

Constructors & destructor

Joint

Joint()

Joint(
    const Vec<3> &joint_axis,
    const Vec<3> &joint_pos_P,
    const Mat<3, 3> &joint_rot,
    const Vec<2> &joint_limit,
    Type joint_type,
    const std::string &joint_name)

if upper and lower bounds of the limit are the same, the limit is ignored

Parameters

Parameter	Description
joint_axis (in)	joint axis in the joint frame
joint_pos_P (in)	joint position in the parent body frame [m]
joint_rot (in)	joint frame orientation relative to the parent body frame
joint_limit (in)	{lower, upper} [rad or m]
joint_type (in)	joint type
joint_name (in)	joint name

Public member functions

jointAxis

void jointAxis(std::initializer_list<double> a)

Parameters

Parameter	Description
a (in)	joint axis {x, y, z} (first 3 values are used)

jointPosition

void jointPosition(std::initializer_list<double> p)

Parameters

Parameter	Description
p (in)	joint position in the parent body frame {x, y, z} [m] (first 3 values are used)

void jointPosition(const Vec<3> &p)

Parameters

Parameter	Description
p (in)	joint position in the parent body frame [m]

getGcDim

size_t getGcDim()

Returns generalized coordinate dimension: 0 (fixed), 1 (revolute/prismatic), 4 (spherical), 7 (floating)

getGvDim

size_t getGvDim()

Returns generalized velocity dimension: 0 (fixed), 1 (revolute/prismatic), 3 (spherical), 6 (floating)

Static member functions

getFloatingBaseJoint static

static Joint getFloatingBaseJoint()

Returns a default joint of type FLOATING

Public attributes

axis

Vec<3> axis

Joint axis expressed in the joint frame (the parent body frame rotated by rot).

pos_P

Vec<3> pos_P

Joint position in parent frame.

rot

Mat<3, 3> rot

Joint frame orientation relative to the parent body frame.

limit

Vec<2> limit

Joint limits (lower, upper) [rad or m]. For a spherical joint, limit[0] is the maximum angle. Equal bounds mean no limit.

type

Type type

Joint type.

effort

double effort

Effort limit (torque/force). If positive, the actuation limits are set to [-effort, effort].

damping

double damping

Joint damping coefficient.

friction

double friction

Joint friction coefficient. Stored, but currently not used by the ArticulatedSystem dynamics.

stiffness

double stiffness

Joint spring stiffness. If positive, a spring element with rest configuration springMount is created.

rotor_inertia

double rotor_inertia

Rotor inertia about the joint axis (added to the mass matrix diagonal).

velocity_limit

double velocity_limit

Joint velocity limit. Infinity means "no limit configured" – do NOT overload 0 for that, since an explicit velocity="0" (URDF) or maxJointVelocity=0 (USD) is a legitimate request to hold the joint still and must still be enforced. Loaders that do not read a velocity limit leave this at infinity; ArticulatedSystem enforces the limit whenever it is finite.

springMount

Vec<4> springMount

Spring rest configuration: springMount[0] for revolute/prismatic joints, a rotation quaternion (w,x,y,z) for spherical joints, which a positive stiffness requires (it is normalized; a zero one is fatal).

jointRef

double jointRef

Reference joint position (MJCF "ref") of a revolute/prismatic joint: the joint is offset so that the model's nominal pose corresponds to this coordinate, which is also the initial generalized coordinate.

name

std::string name

Joint name.