Add tendon velocity sensor to MJX.

PiperOrigin-RevId: 685689974
Change-Id: Ib5e65b19c20b74e20cffa66c6baca0d8faaaf3ae

doc/changelog.rst

@@ -24,7 +24,7 @@ MJX
 - Added support for :ref:`spatial tendons <tendon-spatial>` with pulleys and external sphere and cylinder wrapping.
 - Added sphere-cylinder and sphere-ellipsoid collision functions (:github:issue:`2126`).
 - Fixed a bug with frictionloss constraints.
-- Added ``TENDONPOS`` sensor.
+- Added ``TENDONPOS`` and ``TENDONVEL`` sensors.
 - Fixed a bug with the computation of tangential contact forces in ``_decode_pyramid``.
 
 Bug fixes

doc/mjx.rst

@@ -219,9 +219,9 @@ The following features are **fully supported** in MJX:
    * - :ref:`Sensors <mjtSensor>`
      - ``MAGNETOMETER``, ``CAMPROJECTION``, ``RANGEFINDER``, ``JOINTPOS``, ``TENDONPOS``, ``ACTUATORPOS``, ``BALLQUAT``,
        ``FRAMEPOS``, ``FRAMEXAXIS``, ``FRAMEYAXIS``, ``FRAMEZAXIS``, ``FRAMEQUAT``, ``SUBTREECOM``, ``CLOCK``,
-       ``VELOCIMETER``, ``GYRO``, ``JOINTVEL``, ``ACTUATORVEL``, ``BALLANGVEL``, ``FRAMELINVEL``, ``FRAMEANGVEL``,
-       ``SUBTREELINVEL``, ``SUBTREEANGMOM``, ``ACCELEROMETER``, ``FORCE``, ``TORQUE``, ``ACTUATORFRC``, ``JOINTACTFRC``,
-       ``FRAMELINACC``, ``FRAMEANGACC``.
+       ``VELOCIMETER``, ``GYRO``, ``JOINTVEL``, ``TENDONVEL``, ``ACTUATORVEL``, ``BALLANGVEL``, ``FRAMELINVEL``,
+       ``FRAMEANGVEL``, ``SUBTREELINVEL``, ``SUBTREEANGMOM``, ``ACCELEROMETER``, ``FORCE``, ``TORQUE``, ``ACTUATORFRC``,
+       ``JOINTACTFRC``, ``FRAMELINACC``, ``FRAMEANGACC``.
 
 The following features are **in development** and coming soon:
 

mjx/mujoco/mjx/_src/sensor.py

@@ -330,6 +330,8 @@ def sensor_vel(m: Model, d: Data) -> Data:
       adr = (adr[:, None] + np.arange(3)[None]).reshape(-1)
     elif sensor_type == SensorType.JOINTVEL:
       sensor = d.qvel[m.jnt_dofadr[objid]]
+    elif sensor_type == SensorType.TENDONVEL:
+      sensor = d.ten_velocity[objid]
     elif sensor_type == SensorType.ACTUATORVEL:
       sensor = d.actuator_velocity[objid]
     elif sensor_type == SensorType.BALLANGVEL:

mjx/mujoco/mjx/_src/types.py

@@ -321,6 +321,7 @@ class SensorType(enum.IntEnum):
     VELOCIMETER: 3D linear velocity, in local frame
     GYRO: 3D angular velocity, in local frame
     JOINTVEL: joint velocity
+    TENDONVEL: scalar tendon velocity
     ACTUATORVEL: actuator velocity
     BALLANGVEL: ball joint angular velocity
     FRAMELINVEL: 3D linear velocity
@@ -352,6 +353,7 @@ class SensorType(enum.IntEnum):
   VELOCIMETER = mujoco.mjtSensor.mjSENS_VELOCIMETER
   GYRO = mujoco.mjtSensor.mjSENS_GYRO
   JOINTVEL = mujoco.mjtSensor.mjSENS_JOINTVEL
+  TENDONVEL = mujoco.mjtSensor.mjSENS_TENDONVEL
   ACTUATORVEL = mujoco.mjtSensor.mjSENS_ACTUATORVEL
   BALLANGVEL = mujoco.mjtSensor.mjSENS_BALLANGVEL
   FRAMELINVEL = mujoco.mjtSensor.mjSENS_FRAMELINVEL

mjx/mujoco/mjx/test_data/sensor/sensor.xml

@@ -19,6 +19,7 @@
 -velocimeter
 -gyro
 -jointvel
+-tendonvel
 -actuatorvel
 -ballangvel
 -framelinvel
@@ -122,6 +123,7 @@
   <sensor>
     <torque site="site_torque"/>
     <tendonpos tendon="fixed"/>
+    <tendonvel tendon="fixed"/>
     <magnetometer name="magnetometer0" site="site0"/>
     <velocimeter name="velocimeter0" site="site0"/>
     <velocimeter name="velocimeter0cutoff" site="site0" cutoff="3e-4"/>
@@ -131,6 +133,7 @@
     <accelerometer name="accelerometer1" site="site1"/>
     <force site="site_force"/>
     <tendonpos tendon="spatial"/>
+    <tendonvel tendon="spatial"/>
     <jointpos name="jointpos0" joint="hinge0"/>
     <jointpos name="jointpos0cutoff" joint="hinge0" cutoff="1e-4"/>
     <jointvel name="jointvel0" joint="hinge0"/>