Add a binding for LinearSpringDamper and a test for it.

This will be useful once RobotLocomotion#11090 is resolved and we can't add UniformGravityFieldElement anymore.
YinjieLin · Sep 11, 2019 · 5ed2f4d · 5ed2f4d
1 parent d2d1cc3
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diff --git a/bindings/pydrake/multibody/test/plant_test.py b/bindings/pydrake/multibody/test/plant_test.py
@@ -20,6 +20,7 @@
     JointActuator_,
     JointActuatorIndex,
     JointIndex,
+    LinearSpringDamper_,
     ModelInstanceIndex,
     MultibodyForces_,
     RevoluteJoint_,
@@ -318,6 +319,24 @@ def test_friction_api(self, T):
         CoulombFriction = CoulombFriction_[T]
         CoulombFriction(static_friction=0.7, dynamic_friction=0.6)
 
+    @numpy_compare.check_all_types
+    def test_multibody_force_element(self, T):
+        MultibodyPlant = MultibodyPlant_[T]
+        LinearSpringDamper = LinearSpringDamper_[T]
+        SpatialInertia = SpatialInertia_[float]
+
+        plant = MultibodyPlant()
+        spatial_inertia = SpatialInertia()
+        body_a = plant.AddRigidBody(name="body_a",
+                                    M_BBo_B=spatial_inertia)
+        body_b = plant.AddRigidBody(name="body_b",
+                                    M_BBo_B=spatial_inertia)
+        plant.AddForceElement(LinearSpringDamper(
+            bodyA=body_a, p_AP=[0., 0., 0.],
+            bodyB=body_b, p_BQ=[0., 0., 0.],
+            free_length=1., stiffness=2., damping=3.))
+        plant.Finalize()
+
     @numpy_compare.check_all_types
     def test_multibody_gravity_default(self, T):
         MultibodyPlant = MultibodyPlant_[T]

diff --git a/bindings/pydrake/multibody/tree_py.cc b/bindings/pydrake/multibody/tree_py.cc
@@ -16,6 +16,7 @@
 #include "drake/multibody/tree/frame.h"
 #include "drake/multibody/tree/joint.h"
 #include "drake/multibody/tree/joint_actuator.h"
+#include "drake/multibody/tree/linear_spring_damper.h"
 #include "drake/multibody/tree/multibody_forces.h"
 #include "drake/multibody/tree/multibody_tree.h"  // `JacobianWrtVariable`
 #include "drake/multibody/tree/multibody_tree_indexes.h"
@@ -297,6 +298,19 @@ void DoScalarDependentDefinitions(py::module m, T) {
     BindMultibodyTreeElementMixin(&cls);
   }
 
+  {
+    using Class = LinearSpringDamper<T>;
+    constexpr auto& cls_doc = doc.LinearSpringDamper;
+    auto cls = DefineTemplateClassWithDefault<Class, ForceElement<T>>(
+        m, "LinearSpringDamper", param, cls_doc.doc);
+    cls  // BR
+        .def(py::init<const Body<T>&, const Vector3<double>&, const Body<T>&,
+                 const Vector3<double>&, double, double, double>(),
+            py::arg("bodyA"), py::arg("p_AP"), py::arg("bodyB"),
+            py::arg("p_BQ"), py::arg("free_length"), py::arg("stiffness"),
+            py::arg("damping"), cls_doc.ctor.doc);
+  }
+
   {
     using Class = UniformGravityFieldElement<T>;
     constexpr auto& cls_doc = doc.UniformGravityFieldElement;