Add tendon velocity sensor to MJX.

PiperOrigin-RevId: 685689974
Change-Id: Ib5e65b19c20b74e20cffa66c6baca0d8faaaf3ae

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"/>