Add kv damping attribute to position and intvelocity actuator shortcuts.

PiperOrigin-RevId: 588377097
Change-Id: I8ded2ff982e52ed8673019979e29b706ef65c743

doc/XMLreference.rst

@@ -5317,13 +5317,13 @@ This element does not have custom attributes. It only has common attributes, whi
 
 This element creates a position servo. The underlying :el:`general` attributes are set as follows:
 
-========= ======= ========= =======
+========= ======= ========= =========
 Attribute Setting Attribute Setting
-========= ======= ========= =======
+========= ======= ========= =========
 dyntype   none    dynprm    1 0 0
 gaintype  fixed   gainprm   kp 0 0
-biastype  affine  biasprm   0 -kp 0
+biastype  affine  biasprm   0 -kp -kv
-========= ======= ========= =======
+========= ======= ========= =========
 
 
 This element has one custom attribute in addition to the common attributes:
@@ -5377,6 +5377,11 @@ This element has one custom attribute in addition to the common attributes:
 :at:`kp`: :at-val:`real, "1"`
    Position feedback gain.
 
+.. _actuator-position-kv:
+
+:at:`kv`: :at-val:`real, "0"`
+   Damping applied by the actuator.
+   When using this attribute, it is recommended to use the implicitfast or implicit :ref:`integrators<geIntegration>`.
 
 .. _actuator-velocity:
 
@@ -5385,7 +5390,9 @@ This element has one custom attribute in addition to the common attributes:
 
 This element creates a velocity servo. Note that in order create a PD controller, one has to define two actuators: a
 position servo and a velocity servo. This is because MuJoCo actuators are SISO while a PD controller takes two control
-inputs (reference position and reference velocity). The underlying :el:`general` attributes are set as follows:
+inputs (reference position and reference velocity).
+When using this actuator, it is recommended to use the implicitfast or implicit :ref:`integrators<geIntegration>`.
+The underlying :el:`general` attributes are set as follows:
 
 ========= ======= ========= =======
 Attribute Setting Attribute Setting
@@ -5456,14 +5463,14 @@ This element creates an integrated-velocity servo. For more information, see the
 :ref:`Activation clamping <CActRange>` section of the Modeling chapter. The underlying
 :el:`general` attributes are set as follows:
 
-==========   =========== ========= =======
+==========   =========== ========= =========
 Attribute    Setting     Attribute Setting
-==========   =========== ========= =======
+==========   =========== ========= =========
 dyntype      integrator  dynprm    1 0 0
 gaintype     fixed       gainprm   kp 0 0
-biastype     affine      biasprm   0 -kp 0
+biastype     affine      biasprm   0 -kp -kv
 actlimited   true
-==========   =========== ========= =======
+==========   =========== ========= =========
 
 This element has one custom attribute in addition to the common attributes:
 
@@ -5518,6 +5525,11 @@ This element has one custom attribute in addition to the common attributes:
 :at:`kp`: :at-val:`real, "1"`
    Position feedback gain.
 
+.. _actuator-intvelocity-kv:
+
+:at:`kv`: :at-val:`real, "0"`
+   Damping applied by the actuator.
+   When using this attribute, it is recommended to use the implicitfast or implicit :ref:`integrators<geIntegration>`.
 
 .. _actuator-damper:
 
@@ -5525,8 +5537,9 @@ This element has one custom attribute in addition to the common attributes:
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 This element is an active damper which produces a force proportional to both velocity and control: ``F = - kv * velocity
-* control``, where ``kv`` must be nonnegative. :at:`ctrlrange` is required and must also be nonnegative. The underlying
+* control``, where ``kv`` must be nonnegative. :at:`ctrlrange` is required and must also be nonnegative.
-:el:`general` attributes are set as follows:
+When using this actuator, it is recommended to use the implicitfast or implicit :ref:`integrators<geIntegration>`.
+The underlying :el:`general` attributes are set as follows:
 
 =========== ======= ========= =======
 Attribute   Setting Attribute Setting
@@ -7680,6 +7693,8 @@ slidersite, cranksite.
 
 .. _default-position-kp:
 
+.. _default-position-kv:
+
 :el-prefix:`default/` |-| **position** (?)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -7736,6 +7751,8 @@ tendon, slidersite, cranksite.
 
 .. _default-intvelocity-kp:
 
+.. _default-intvelocity-kv:
+
 :el-prefix:`default/` |-| **intvelocity** (?)
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

doc/XMLschema.rst

@@ -778,7 +778,7 @@
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 |                                    |    |    | :ref:`jointinparent<actuator-position-jointinparent>`           | :ref:`tendon<actuator-position-tendon>`                         | :ref:`slidersite<actuator-position-slidersite>`                 | :ref:`cranksite<actuator-position-cranksite>`                   | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`site<actuator-position-site>`                             | :ref:`refsite<actuator-position-refsite>`                       | :ref:`kp<actuator-position-kp>`                                 |                                                                 | |
+|                                    |    |    | :ref:`site<actuator-position-site>`                             | :ref:`refsite<actuator-position-refsite>`                       | :ref:`kp<actuator-position-kp>`                                 | :ref:`kv<actuator-position-kv>`                                 | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 +------------------------------------+----+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 | |_| actuator |br| |_| |L|          |    | .. table::                                                                                                                                                                                                                                                                   |
@@ -810,6 +810,8 @@
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 |                                    |    |    | :ref:`cranksite<actuator-intvelocity-cranksite>`                | :ref:`site<actuator-intvelocity-site>`                          | :ref:`refsite<actuator-intvelocity-refsite>`                    | :ref:`kp<actuator-intvelocity-kp>`                              | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
+|                                    |    |    | :ref:`kv<actuator-intvelocity-kv>`                              |                                                                 |                                                                 |                                                                 | |
+|                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 +------------------------------------+----+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 | |_| actuator |br| |_| |L|          |    | .. table::                                                                                                                                                                                                                                                                   |
 | :ref:`damper                       | \* |    :class: mjcf-attributes                                                                                                                                                                                                                                                   |
@@ -1440,7 +1442,7 @@
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 |                                    |    |    | :ref:`gear<default-position-gear>`                              | :ref:`cranklength<default-position-cranklength>`                | :ref:`user<default-position-user>`                              | :ref:`group<default-position-group>`                            | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`kp<default-position-kp>`                                  |                                                                 |                                                                 |                                                                 | |
+|                                    |    |    | :ref:`kp<default-position-kp>`                                  | :ref:`kv<default-position-kv>`                                  |                                                                 |                                                                 | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 +------------------------------------+----+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 | |_| default |br| |_| |L|           |    | .. table::                                                                                                                                                                                                                                                                   |
@@ -1462,7 +1464,7 @@
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 |                                    |    |    | :ref:`actrange<default-intvelocity-actrange>`                   | :ref:`gear<default-intvelocity-gear>`                           | :ref:`cranklength<default-intvelocity-cranklength>`             | :ref:`user<default-intvelocity-user>`                           | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
-|                                    |    |    | :ref:`group<default-intvelocity-group>`                         | :ref:`kp<default-intvelocity-kp>`                               |                                                                 |                                                                 | |
+|                                    |    |    | :ref:`group<default-intvelocity-group>`                         | :ref:`kp<default-intvelocity-kp>`                               | :ref:`kv<default-intvelocity-kv>`                               |                                                                 | |
 |                                    |    |    +-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+-----------------------------------------------------------------+ |
 +------------------------------------+----+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
 | |_| default |br| |_| |L|           |    | .. table::                                                                                                                                                                                                                                                                   |

doc/changelog.rst

@@ -12,6 +12,10 @@ General
   robust for very small or large geom sizes.
 - Added :ref:`frame<frame>` to MJCF, a :ref:`meta-element<meta-element>` which defines a pure coordinate transformation
   on its direct children, without requiring a :ref:`body<body>`.
+- Added the :at:`kv` attribute to the :ref:`position<actuator-position>` and :ref:`intvelocity<actuator-intvelocity>`
+  actuators, for specifying actuator-applied damping. This can be used to implement a PD controller with 0 reference
+  velocity. When using this attribute, it is recommended to use the implicitfast or implicit
+  :ref:`integrators<geIntegration>`.
 
 Plugins
 ^^^^^^^

src/user/user_objects.cc

@@ -3876,7 +3876,7 @@ void mjCActuator::Compile(void) {
     throw mjCError(this, "invalid control range for actuator '%s' (id = %d)", name.c_str(), id);
   }
   if (actrange[0]>=actrange[1] && actlimited) {
-    throw mjCError(this, "invalid activation range for actuator '%s' (id = %d)", name.c_str(), id);
+    throw mjCError(this, "invalid actrange for actuator '%s' (id = %d)", name.c_str(), id);
   }
   if (actlimited && dyntype == mjDYN_NONE) {
     throw mjCError(this, "actrange specified but dyntype is 'none' in actuator '%s' (id = %d)",

src/xml/xml_native_reader.cc

@@ -166,16 +166,16 @@ static const char* MJCF[nMJCF][mjXATTRNUM] = {
             "dyntype", "gaintype", "biastype", "dynprm", "gainprm", "biasprm", "actearly"},
         {"motor", "?", "8", "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
             "gear", "cranklength", "user", "group"},
-        {"position", "?", "9", "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
+        {"position", "?", "10", "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
             "gear", "cranklength", "user", "group",
-            "kp"},
+            "kp", "kv"},
         {"velocity", "?", "9", "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
             "gear", "cranklength", "user", "group",
             "kv"},
-        {"intvelocity", "?", "10", "ctrllimited", "forcelimited",
+        {"intvelocity", "?", "11", "ctrllimited", "forcelimited",
             "ctrlrange", "forcerange", "actrange",
             "gear", "cranklength", "user", "group",
-            "kp"},
+            "kp", "kv"},
         {"damper", "?", "8", "forcelimited", "ctrlrange", "forcerange",
             "gear", "cranklength", "user", "group",
             "kv"},
@@ -379,22 +379,22 @@ static const char* MJCF[nMJCF][mjXATTRNUM] = {
             "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
             "lengthrange", "gear", "cranklength", "user",
             "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite"},
-        {"position", "*", "19", "name", "class", "group",
+        {"position", "*", "20", "name", "class", "group",
             "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
             "lengthrange", "gear", "cranklength", "user",
             "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
-            "kp"},
+            "kp", "kv"},
         {"velocity", "*", "19", "name", "class", "group",
             "ctrllimited", "forcelimited", "ctrlrange", "forcerange",
             "lengthrange", "gear", "cranklength", "user",
             "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
             "kv"},
-        {"intvelocity", "*", "20", "name", "class", "group",
+        {"intvelocity", "*", "21", "name", "class", "group",
             "ctrllimited", "forcelimited",
             "ctrlrange", "forcerange", "actrange", "lengthrange",
             "gear", "cranklength", "user",
             "joint", "jointinparent", "tendon", "slidersite", "cranksite", "site", "refsite",
-            "kp"},
+            "kp", "kv"},
         {"damper", "*", "18", "name", "class", "group",
             "forcelimited", "ctrlrange", "forcerange",
             "lengthrange", "gear", "cranklength", "user",
@@ -1895,19 +1895,26 @@ void mjXReader::OneActuator(XMLElement* elem, mjCActuator* pact) {
     pact->biastype = mjBIAS_NONE;
   }
 
-  // position servo
+  // position or integrated velocity servo
-  else if (type=="position") {
+  else if (type=="position" || type=="intvelocity") {
-    // clear bias
-    mjuu_zerovec(pact->biasprm, mjNBIAS);
-
     // explicit attributes
     ReadAttr(elem, "kp", 1, pact->gainprm, text);
     pact->biasprm[1] = -pact->gainprm[0];
 
+    if (ReadAttr(elem, "kv", 1, pact->biasprm + 2, text)) {
+      if (pact->biasprm[2] < 0)
+        throw mjXError(elem, "kv cannot be negative");
+      pact->biasprm[2] *= -1;
+    }
+
     // implied parameters
-    pact->dyntype = mjDYN_NONE;
     pact->gaintype = mjGAIN_FIXED;
     pact->biastype = mjBIAS_AFFINE;
+
+    if (type=="intvelocity") {
+      pact->dyntype = mjDYN_INTEGRATOR;
+      pact->actlimited = 1;
+    }
   }
 
   // velocity servo
@@ -1925,22 +1932,6 @@ void mjXReader::OneActuator(XMLElement* elem, mjCActuator* pact) {
     pact->biastype = mjBIAS_AFFINE;
   }
 
-  // integrated velocity
-  else if (type=="intvelocity") {
-    // clear bias
-    mjuu_zerovec(pact->biasprm, mjNBIAS);
-
-    // explicit attributes
-    ReadAttr(elem, "kp", 1, pact->gainprm, text);
-
-    // implied parameters
-    pact->dyntype = mjDYN_INTEGRATOR;
-    pact->gaintype = mjGAIN_FIXED;
-    pact->biastype = mjBIAS_AFFINE;
-    pact->actlimited = 1;
-    pact->biasprm[1] = -pact->gainprm[0];
-  }
-
   // damper
   else if (type=="damper") {
     // clear gain

test/engine/testdata/actuation/refsite.xml

@@ -13,7 +13,7 @@
 
   <default>
     <default class="translation">
-      <general gainprm="100" biasprm="0 -100 -10" biastype="affine" ctrlrange="-.25 .25"/>
+      <position kp="100" kv="10" ctrlrange="-.25 .25"/>
     </default>
     <default class="rotation">
       <!--
@@ -22,7 +22,7 @@
       Increase this range to pi or bigger in order to see the instabillity.
       See here for more details https://mujoco.readthedocs.io/en/latest/XMLreference.html#actuator
       -->
-      <general gainprm=".5" biasprm="0 -.5 -.05" biastype="affine" ctrlrange="-1.571 1.571"/>
+      <position kp=".5" kv=".05" ctrlrange="-1.571 1.571"/>
     </default>
     <!--
     Clamping the total actuator torque at the joints means that the motion produced by the Cartesian
@@ -62,11 +62,11 @@
   </worldbody>
 
   <actuator>
-    <general name="x"  site="end_effector" refsite="reference" gear="1 0 0 0 0 0" class="translation"/>
+    <position name="x"  site="end_effector" refsite="reference" gear="1 0 0 0 0 0" class="translation"/>
-    <general name="y"  site="end_effector" refsite="reference" gear="0 1 0 0 0 0" class="translation"/>
+    <position name="y"  site="end_effector" refsite="reference" gear="0 1 0 0 0 0" class="translation"/>
-    <general name="z"  site="end_effector" refsite="reference" gear="0 0 1 0 0 0" class="translation"/>
+    <position name="z"  site="end_effector" refsite="reference" gear="0 0 1 0 0 0" class="translation"/>
-    <general name="rx" site="end_effector" refsite="reference" gear="0 0 0 1 0 0" class="rotation"/>
+    <position name="rx" site="end_effector" refsite="reference" gear="0 0 0 1 0 0" class="rotation"/>
-    <general name="ry" site="end_effector" refsite="reference" gear="0 0 0 0 1 0" class="rotation"/>
+    <position name="ry" site="end_effector" refsite="reference" gear="0 0 0 0 1 0" class="rotation"/>
-    <general name="rz" site="end_effector" refsite="reference" gear="0 0 0 0 0 1" class="rotation"/>
+    <position name="rz" site="end_effector" refsite="reference" gear="0 0 0 0 0 1" class="rotation"/>
   </actuator>
 </mujoco>

test/user/user_objects_test.cc

@@ -940,7 +940,7 @@ TEST_F(ActRangeTest, ActRangeBad) {
   std::array<char, 1024> error;
   mjModel* model = LoadModelFromString(xml, error.data(), error.size());
   ASSERT_THAT(model, IsNull());
-  EXPECT_THAT(error.data(), HasSubstr("invalid activation range"));
+  EXPECT_THAT(error.data(), HasSubstr("invalid actrange"));
 }
 
 TEST_F(ActRangeTest, ActRangeUndefined) {
@@ -960,7 +960,7 @@ TEST_F(ActRangeTest, ActRangeUndefined) {
   std::array<char, 1024> error;
   mjModel* model = LoadModelFromString(xml, error.data(), error.size());
   ASSERT_THAT(model, IsNull());
-  EXPECT_THAT(error.data(), HasSubstr("invalid activation range"));
+  EXPECT_THAT(error.data(), HasSubstr("invalid actrange"));
 }
 
 TEST_F(ActRangeTest, ActRangeNoDyntype) {

test/xml/xml_native_reader_test.cc

@@ -531,92 +531,6 @@ TEST_F(XMLReaderTest, ReadShellParameter) {
   mj_deleteModel(model);
 }
 
-TEST_F(XMLReaderTest, ReadsDamper) {
-  static constexpr char xml[] = R"(
-  <mujoco>
-    <compiler autolimits="true"/>
-    <worldbody>
-      <body>
-        <geom size="1"/>
-        <joint name="jnt" type="slide" axis="1 0 0" range="-10 10"/>
-      </body>
-    </worldbody>
-    <actuator>
-      <damper joint="jnt" ctrlrange="0 1"/>
-      <general joint="jnt" ctrllimited="true" ctrlrange="0 1" gaintype="affine" biastype="none"/>
-    </actuator>
-  </mujoco>
-  )";
-  std::array<char, 1024> error;
-  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
-  ASSERT_THAT(model, NotNull());
-  EXPECT_THAT(model->actuator_gaintype[0], Eq(mjGAIN_AFFINE));
-  EXPECT_THAT(model->actuator_gaintype[1], Eq(mjGAIN_AFFINE));
-  EXPECT_THAT(model->actuator_biastype[0], Eq(mjBIAS_NONE));
-  EXPECT_THAT(model->actuator_biastype[1], Eq(mjBIAS_NONE));
-  mj_deleteModel(model);
-}
-
-TEST_F(XMLReaderTest, RequiresPoisitiveDamping) {
-  static constexpr char xml[] = R"(
-  <mujoco>
-    <worldbody>
-      <body>
-        <geom size="1"/>
-        <joint name="jnt" type="slide" axis="1 0 0" range="-10 10"/>
-      </body>
-    </worldbody>
-    <actuator>
-      <damper joint="jnt" kv="-1"/>
-    </actuator>
-  </mujoco>
-  )";
-  std::array<char, 1024> error;
-  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
-  ASSERT_THAT(model, IsNull());
-  EXPECT_THAT(error.data(),
-              HasSubstr("damping coefficient cannot be negative"));
-}
-
-TEST_F(XMLReaderTest, RequiresControlRange) {
-  static constexpr char xml[] = R"(
-  <mujoco>
-    <worldbody>
-      <body>
-        <geom size="1"/>
-        <joint name="jnt" type="slide" axis="1 0 0" range="-10 10" limited="true"/>
-      </body>
-    </worldbody>
-    <actuator>
-      <damper joint="jnt" kv="1"/>
-    </actuator>
-  </mujoco>
-  )";
-  std::array<char, 1024> error;
-  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
-  ASSERT_THAT(model, IsNull());
-  EXPECT_THAT(error.data(), HasSubstr("invalid control range"));
-}
-
-TEST_F(XMLReaderTest, PositiveControlRange) {
-  static constexpr char xml[] = R"(
-  <mujoco>
-    <worldbody>
-      <body>
-        <geom size="1"/>
-        <joint name="jnt" type="slide" axis="1 0 0" range="-10 10"/>
-      </body>
-    </worldbody>
-    <actuator>
-      <damper joint="jnt" kv="1" ctrlrange="-1 0"/>
-    </actuator>
-  </mujoco>
-  )";
-  std::array<char, 1024> error;
-  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
-  ASSERT_THAT(model, IsNull());
-  EXPECT_THAT(error.data(), HasSubstr("control range cannot be negative"));
-}
 
 TEST_F(XMLReaderTest, ReadsSkinGroups) {
   static constexpr char xml[] = R"(
@@ -779,6 +693,186 @@ TEST_F(ActuatorTest, ReadsByte) {
 
 using ActuatorParseTest = MujocoTest;
 
+TEST_F(ActuatorParseTest, ReadsDamper) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <worldbody>
+      <body>
+        <geom size="1"/>
+        <joint name="jnt" type="slide" axis="1 0 0" range="-10 10"/>
+      </body>
+    </worldbody>
+    <actuator>
+      <damper joint="jnt" ctrlrange="0 1"/>
+      <general joint="jnt" ctrllimited="true" ctrlrange="0 1" gaintype="affine" biastype="none"/>
+    </actuator>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, NotNull());
+  EXPECT_THAT(model->actuator_gaintype[0], Eq(mjGAIN_AFFINE));
+  EXPECT_THAT(model->actuator_gaintype[1], Eq(mjGAIN_AFFINE));
+  EXPECT_THAT(model->actuator_biastype[0], Eq(mjBIAS_NONE));
+  EXPECT_THAT(model->actuator_biastype[1], Eq(mjBIAS_NONE));
+  mj_deleteModel(model);
+}
+
+TEST_F(ActuatorParseTest, DamperRequiresPositiveDamping) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <worldbody>
+      <body>
+        <geom size="1"/>
+        <joint name="jnt" type="slide" axis="1 0 0" range="-10 10"/>
+      </body>
+    </worldbody>
+    <actuator>
+      <damper joint="jnt" kv="-1"/>
+    </actuator>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, IsNull());
+  EXPECT_THAT(error.data(),
+              HasSubstr("damping coefficient cannot be negative"));
+}
+
+TEST_F(ActuatorParseTest, DamperRequiresControlRange) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <worldbody>
+      <body>
+        <geom size="1"/>
+        <joint name="jnt" type="slide" axis="1 0 0" range="-10 10" limited="true"/>
+      </body>
+    </worldbody>
+    <actuator>
+      <damper joint="jnt" kv="1"/>
+    </actuator>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, IsNull());
+  EXPECT_THAT(error.data(), HasSubstr("invalid control range"));
+}
+
+TEST_F(ActuatorParseTest, DamperPositiveControlRange) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <worldbody>
+      <body>
+        <geom size="1"/>
+        <joint name="jnt" type="slide" axis="1 0 0" range="-10 10"/>
+      </body>
+    </worldbody>
+    <actuator>
+      <damper joint="jnt" kv="1" ctrlrange="-1 0"/>
+    </actuator>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, IsNull());
+  EXPECT_THAT(error.data(), HasSubstr("control range cannot be negative"));
+}
+
+TEST_F(ActuatorParseTest, ReadsPositionIntvelKv) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <worldbody>
+      <body>
+        <geom size="1"/>
+        <joint name="jnt" type="slide" axis="1 0 0"/>
+      </body>
+    </worldbody>
+    <actuator>
+      <position joint="jnt" kv="2"/>
+      <intvelocity joint="jnt" actrange="-1 1" kv="3"/>
+    </actuator>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, NotNull());
+  EXPECT_THAT(model->actuator_biasprm[0*mjNBIAS + 2], Eq(-2.0));
+  EXPECT_THAT(model->actuator_biasprm[1*mjNBIAS + 2], Eq(-3.0));
+  mj_deleteModel(model);
+}
+
+TEST_F(ActuatorParseTest, RequirePositiveKv) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <worldbody>
+      <body>
+        <geom size="1"/>
+        <joint name="jnt" type="slide" axis="1 0 0"/>
+      </body>
+    </worldbody>
+    <actuator>
+      <position joint="jnt" kv="-2"/>
+    </actuator>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, IsNull());
+  EXPECT_THAT(error.data(), HasSubstr("kv cannot be negative"));
+}
+
+TEST_F(ActuatorParseTest, PositionIntvelocityVelocityDefaultsPropagate) {
+  static constexpr char xml[] = R"(
+  <mujoco>
+    <default>
+      <default class="position">
+        <position kp="3" kv="4"/>
+      </default>
+      <default class="intvelocity">
+        <intvelocity kp="5" kv="6" actrange="-1 1"/>
+      </default>
+      <default class="velocity">
+        <velocity kv="7"/>
+      </default>
+    </default>
+    <worldbody>
+      <body>
+        <geom size="1"/>
+        <joint name="jnt" type="slide" axis="1 0 0"/>
+      </body>
+    </worldbody>
+    <actuator>
+      <position joint="jnt" class="position"/>
+      <intvelocity joint="jnt" class="intvelocity"/>
+      <velocity joint="jnt" class="velocity"/>
+    </actuator>
+  </mujoco>
+  )";
+  std::array<char, 1024> error;
+  mjModel* model = LoadModelFromString(xml, error.data(), error.size());
+  ASSERT_THAT(model, NotNull()) << error.data();
+  EXPECT_EQ(model->actuator_gainprm[0*mjNGAIN + 0], 3.0);
+  EXPECT_EQ(model->actuator_biasprm[0*mjNBIAS + 1], -3.0);
+  EXPECT_EQ(model->actuator_biasprm[0*mjNBIAS + 2], -4.0);
+  EXPECT_EQ(model->actuator_gainprm[1*mjNGAIN + 0], 5.0);
+  EXPECT_EQ(model->actuator_biasprm[1*mjNBIAS + 1], -5.0);
+  EXPECT_EQ(model->actuator_biasprm[1*mjNBIAS + 2], -6.0);
+  EXPECT_EQ(model->actuator_gainprm[2*mjNGAIN + 0], 7.0);
+  EXPECT_EQ(model->actuator_biasprm[2*mjNBIAS + 1], 0.0);
+  EXPECT_EQ(model->actuator_biasprm[2*mjNBIAS + 2], -7.0);
+  for (int i = 0; i < model->nu; i++) {
+    for (int j = 3; j < mjNBIAS; j++) {
+      EXPECT_EQ(model->actuator_biasprm[i*mjNBIAS + j], 0.0);
+    }
+    for (int j = 3; j < mjNGAIN; j++) {
+      EXPECT_EQ(model->actuator_gainprm[i*mjNGAIN + j], 0.0);
+    }
+  }
+  mj_deleteModel(model);
+}
+
+
 TEST_F(ActuatorParseTest, IntvelocityCheckEquivalence) {
   static constexpr char xml[] = R"(
   <mujoco>
@@ -871,7 +965,7 @@ TEST_F(ActuatorParseTest, IntvelocityNoActrangeThrowsError) {
   std::array<char, 1024> error;
   mjModel* model = LoadModelFromString(xml, error.data(), error.size());
   ASSERT_THAT(model, IsNull());
-  EXPECT_THAT(error.data(), HasSubstr("invalid activation range for actuator"));
+  EXPECT_THAT(error.data(), HasSubstr("invalid actrange for actuator"));
 }
 
 TEST_F(ActuatorParseTest, IntvelocityDefaultsPropagate) {