raisim::Tendon

class · #include <raisim/constraints/Tendon.hpp>

A scalar transmission: routed spatial length or a weighted sum of scalar joints. Positive tension shortens the tendon; positive actuation force lengthens it. Geometry is massless. Optional armature adds inertia only along tendon length. World owns tendons and removes them when a referenced object is removed.

Nested classes

• struct Drive — Actuator acting along the tendon.
• struct JointGradient — Length gradient with respect to one joint of a fixed tendon.
• struct JointTerm — One term of a fixed tendon: length += coefficient * q(joint). Only revolute and prismatic joints are supported.
• struct PathElement — One element of a spatial tendon route. Create elements with the static factory functions.
• struct PointGradient — Length gradient with respect to one world-space application point.
• struct Properties — Passive and limit parameters of a tendon. Forces are in tendon coordinates (N for spatial tendons). Validated by setProperties().
• struct Site — An attachment point on a body (or in the world frame) used by spatial tendon paths.
• struct VisualSegment — A straight piece of the routed tendon in world coordinates.

Public types

Type

enum class Type

Spatial: routed through sites/obstacles (World::addSpatialTendon()). Fixed: weighted sum of joint coordinates (World::addFixedTendon()).

Enumerator
Spatial
Fixed

Constructors & destructor

~Tendon

~Tendon()

Tendon

Tendon(const Tendon &) = delete

Public member functions

operator=

Tendon &operator=(const Tendon &) = delete

getType

Type getType() const

Returns whether this is a spatial or a fixed tendon.

getName

const std::string &getName() const

Returns the tendon's unique name.

setName

void setName(const std::string &name)

Rename the tendon.

Parameters

Parameter	Description
name (in)	new name; must be non-empty and unique among the world's tendons (throws std::invalid_argument otherwise).

getProperties

const Properties &getProperties() const

Returns the current properties. NaN spring bounds are replaced by the reference length.

setProperties

void setProperties(const Properties &properties)

Replace the tendon properties and wake the attached bodies.

Parameters

Parameter	Description
properties (in)	new properties. Throws std::invalid_argument if invalid. NaN/NaN spring bounds use getReferenceLength().

getDrive

const Drive &getDrive() const

Returns the current drive settings.

setDrive

void setDrive(const Drive &drive)

Replace the drive settings and wake the attached bodies.

Parameters

Parameter	Description
drive (in)	must have finite force/targets and nonnegative gains/activation time (throws std::invalid_argument otherwise).

setTension

void setTension(double tension)

Set the feedforward drive force to -tension (positive tension shortens the tendon).

Parameters

Parameter	Description
tension (in)	tension (N for spatial tendons), finite

setActuationForce

void setActuationForce(double force)

Set the feedforward drive force (Drive::force); positive lengthens the tendon.

Parameters

Parameter	Description
force (in)	force (N for spatial tendons), finite

setEnabled

void setEnabled(bool enabled)

Enable or disable the tendon. A disabled tendon applies no force.

Parameters

Parameter	Description
enabled (in)	true to enable

isEnabled

bool isEnabled() const

Returns true if the tendon is enabled.

updateGeometry

void updateGeometry(bool visuals=false)

Refresh length, velocity, gradients and (on request) visual segments at current state. Simulation-side: mutates the tendon, so call it only from the thread that steps the world.

Parameters

Parameter	Description
visuals (in)	also refresh getVisualSegments()

computeVisualSegments

void computeVisualSegments(std::vector<VisualSegment> &segments) const

Route segments at the current object poses, written to a caller-owned buffer. Does not touch the tendon's own length, gradients or visual cache; safe for renderers.

Parameters

Parameter	Description
segments (out)	cleared and filled with the route segments

getLength

double getLength() const

Returns the tendon length at the last geometry update (m for spatial tendons).

getVelocity

double getVelocity() const

Returns the rate of change of the tendon length.

getReferenceLength

double getReferenceLength() const

Returns the length when the tendon was created.

getForce

double getForce() const

Returns the sum of all tendon force contributions in the last step; positive lengthens the tendon. Last-step signed total tendon force.

getTension

double getTension() const

Returns -getForce(); positive when the tendon pulls.

getActuationForce

double getActuationForce() const

Returns the drive's contribution to the last-step force.

getLimitForce

double getLimitForce() const

Returns the length limits' contribution to the last-step force.

getFrictionForce

double getFrictionForce() const

Returns the friction loss's contribution to the last-step force.

getPotentialEnergy

double getPotentialEnergy() const

Returns spring energy 0.5*stiffness*e^2, where e is the length's distance outside [springLower, springUpper] (J).

getKineticEnergy

double getKineticEnergy() const

Returns armature kinetic energy 0.5*armature*velocity^2 (J).

getPath

const std::vector<PathElement> &getPath() const

Returns the route of a spatial tendon (empty for fixed tendons).

getJoints

const std::vector<JointTerm> &getJoints() const

Returns the joint terms of a fixed tendon (empty for spatial tendons).

getPointGradients

const std::vector<PointGradient> &getPointGradients() const

Returns the length gradients w.r.t. application points from the last geometry update.

getJointGradients

const std::vector<JointGradient> &getJointGradients() const

Returns the length gradients w.r.t. the joints of a fixed tendon.

getVisualSegments

const std::vector<VisualSegment> &getVisualSegments() const

Returns the segments cached by the last updateGeometry(true) call.