[planning] Match RobotDiagram default time step to MbP's default

This fixes some crashes when using models that need discrete-time-only modeling features, such as implicit PD control.
RobotLocomotion · Mar 6, 2024 · 2dc0143 · 2dc0143
1 parent bbafc14
commit 2dc0143
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Showing 3 changed files with 11 additions and 3 deletions.
diff --git a/bindings/pydrake/planning/planning_py_robot_diagram.cc b/bindings/pydrake/planning/planning_py_robot_diagram.cc
@@ -55,7 +55,8 @@ void DefinePlanningRobotDiagram(py::module m) {
       auto cls = DefineTemplateClassWithDefault<Class>(
           m, "RobotDiagramBuilder", GetPyParam<T>(), cls_doc.doc);
       cls  // BR
-          .def(py::init<double>(), py::arg("time_step") = 0.0, cls_doc.ctor.doc)
+          .def(py::init<double>(), py::arg("time_step") = 0.001,
+              cls_doc.ctor.doc)
           .def("builder",
               overload_cast_explicit<systems::DiagramBuilder<T>&>(
                   &Class::builder),

diff --git a/planning/robot_diagram_builder.h b/planning/robot_diagram_builder.h
@@ -30,7 +30,7 @@ class RobotDiagramBuilder {
   DRAKE_NO_COPY_NO_MOVE_NO_ASSIGN(RobotDiagramBuilder)
 
   /** Constructs with the specified time step for the contained plant. */
-  explicit RobotDiagramBuilder(double time_step = 0.0);
+  explicit RobotDiagramBuilder(double time_step = 0.001);
 
   ~RobotDiagramBuilder();
 

diff --git a/planning/test/robot_diagram_test.cc b/planning/test/robot_diagram_test.cc
@@ -18,6 +18,7 @@ namespace {
 
 using geometry::SceneGraph;
 using multibody::MultibodyPlant;
+using multibody::MultibodyPlantConfig;
 using multibody::Parser;
 using symbolic::Expression;
 using systems::Context;
@@ -33,7 +34,13 @@ std::unique_ptr<RobotDiagramBuilder<double>> MakeSampleDut() {
   return builder;
 }
 
-GTEST_TEST(RobotDiagramBuilderTest, TimeStep) {
+GTEST_TEST(RobotDiagramBuilderTest, TimeStepDefault) {
+  const MultibodyPlantConfig default_plant_config;
+  auto builder = std::make_unique<RobotDiagramBuilder<double>>();
+  EXPECT_EQ(builder->plant().time_step(), default_plant_config.time_step);
+}
+
+GTEST_TEST(RobotDiagramBuilderTest, TimeStepExplicit) {
   const double time_step = 0.01;
   auto builder = std::make_unique<RobotDiagramBuilder<double>>(time_step);
   EXPECT_EQ(builder->plant().time_step(), time_step);