Physics: remove *VelocityCmd at each time step

Part of #1926.

Signed-off-by: Steve Peters <[email protected]>

Migration.md

@@ -5,6 +5,13 @@ Deprecated code produces compile-time warnings. These warning serve as
 notification to users that their code should be upgraded. The next major
 release will remove the deprecated code.
 
+## Gazebo Sim 8.x to 9.0
+
+ * **Modified**:
+   + In the Physics system, all `*VelocityCmd` components are deleted after
+     each time step. Persistent velocity commands should be reapplied at
+     each time step.
+
 ## Gazebo Sim 7.x to 8.0
 * **Deprecated**
     + `gz::sim::components::Factory::Register(const std::string &_type, ComponentDescriptorBase *_compDesc)` and

src/systems/physics/Physics.cc

@@ -3629,9 +3629,9 @@ void PhysicsPrivate::UpdateSim(EntityComponentManager &_ecm,
       });
 
   _ecm.Each<components::JointVelocityCmd>(
-      [&](const Entity &, components::JointVelocityCmd *_vel) -> bool
+      [&](const Entity &_entity, components::JointVelocityCmd *) -> bool
       {
-        std::fill(_vel->Data().begin(), _vel->Data().end(), 0.0);
+        _ecm.RemoveComponent<components::JointVelocityCmd>(_entity);
         return true;
       });
 
@@ -3644,16 +3644,16 @@ void PhysicsPrivate::UpdateSim(EntityComponentManager &_ecm,
   GZ_PROFILE_END();
 
   _ecm.Each<components::AngularVelocityCmd>(
-      [&](const Entity &, components::AngularVelocityCmd *_vel) -> bool
+      [&](const Entity &_entity, components::AngularVelocityCmd *) -> bool
       {
-        _vel->Data() = math::Vector3d::Zero;
+        _ecm.RemoveComponent<components::AngularVelocityCmd>(_entity);
         return true;
       });
 
   _ecm.Each<components::LinearVelocityCmd>(
-      [&](const Entity &, components::LinearVelocityCmd *_vel) -> bool
+      [&](const Entity &_entity, components::LinearVelocityCmd *) -> bool
       {
-        _vel->Data() = math::Vector3d::Zero;
+        _ecm.RemoveComponent<components::LinearVelocityCmd>(_entity);
         return true;
       });