RigidJoint

class genesis.engine.entities.rigid_entity.rigid_joint.RigidJoint(entity, idx, link_idx, q_start, dof_start, desc: RigidJointDescription)

Bases: RBC

Joint class for rigid body entities. Each RigidLink is connected to its parent link via a RigidJoint.

get_pos()

Get the position of the joint in the world frame.

get_quat()

Get the quaternion of the joint in the world frame.

get_anchor_pos()

Get the anchor position of the joint in the world frame.

Mathematically, the anchor point corresponds to the point that is fixed wrt parent link and is coincident with the joint for the neutral configuration qpos0. This means that this point moves under the effect of the generalized coordinates corresponding to this joint (and all its ancestors in the kinematic tree). Physically, the anchor point is the “output” of the joint transmission, on which the child body is welded.

get_anchor_axis()

Get the anchor axis of the joint in the world frame.

See RigidJoint.get_anchor_pos documentation for details about the notion on anchor point.

set_sol_params(sol_params)

Set the solver parameters of this joint.

get_sol_params()

Get the solver parameters the simulation is currently using for this joint.

property uid

Returns the unique id of the joint.

property name

Returns the name of the joint.

property entity

Returns the entity that the joint belongs to.

property solver

The RigidSolver object that the joint belongs to.

property link

Returns the child link that of the joint.

property idx

Returns the global index of the joint in the rigid solver.

property idx_local

Returns the local index of the joint in the entity.

property init_qpos

Returns the initial joint position.

property n_qs

Returns the number of q (generalized coordinate) variables that the joint has.

property n_dofs

Returns the number of dofs that the joint has.

property type

Returns the type of the joint.

property pos

Returns the initial position of the joint in the world frame.

property quat

Returns the initial quaternion of the joint in the world frame.

property q_start

Returns the starting index of the q variables of the joint in the rigid solver.

property dof_start

Returns the starting index of the dofs of the joint in the rigid solver.

property q_end

Returns the ending index of the q variables of the joint in the rigid solver.

property dof_end

Returns the ending index of the dofs of the joint in the rigid solver.

property dofs_idx

Returns all the Degrees’ of Freedom (DoF) indices of the joint in the rigid solver as a sequence.

property dofs_idx_local

Returns the local Degrees of Freedom indices of the joint in the entity.

property qs_idx

Returns all the position indices of the joint in the rigid solver.

property qs_idx_local

Returns all the local q indices of the joint in the entity.

property dofs_length

Returns the characteristic length of each dof, used to put dof velocities on a common linear (m/s) scale. Shape is (n_dofs,), or (n_dofs, n_envs) for a heterogeneous entity whose variants differ per environment.

A translational dof has length 1, so its velocity is already a linear speed. A rotational dof has the swept radius of the body as its length, so that multiplying it by an angular velocity gives the linear surface speed that rotation produces; this makes a single velocity tolerance meaningful across mixed dofs (e.g. for hibernation). By default the radius is per-axis: the largest perpendicular distance from that dof’s own rotation axis (through the joint anchor) to the geometry. With MuJoCo compatibility it is instead MuJoCo’s dof_length: a single bounding-sphere radius about the body COM, shared by every rotational dof. For a heterogeneous entity each variant’s geoms are active in their own environments, so the radius is per env.

property is_built

Returns whether the entity the joint belongs to is built.

Joint types

The value returned by RigidJoint.type.

class genesis.constants.JOINT_TYPE