Removed modules from the simulation infrastructure and refactored FRCPlugin.

Pneumatics still have CAN modules. The refactored code is now eight
plugins for sensors and actuators. There is some code reuse that should
be refactored out, but that level of abstraction will wait until we
figure out how these plugins are integrating with gazebo proper.

Change-Id: I357e695ef05af6dda83a39ba60380686bd57d11a
Closes: artf2610, artf2623

simulation/frc_gazebo_plugins/potentiometer/src/potentiometer.cpp

@@ -0,0 +1,56 @@
+#include "potentiometer.h"
+
+#include <gazebo/physics/physics.hh>
+#include <gazebo/transport/transport.hh>
+#include <boost/algorithm/string.hpp>
+
+#include "msgs/msgs.h"
+
+GZ_REGISTER_MODEL_PLUGIN(Potentiometer)
+
+Potentiometer::Potentiometer() {}
+
+Potentiometer::~Potentiometer() {}
+
+void Potentiometer::Load(physics::ModelPtr model, sdf::ElementPtr sdf) {
+  this->model = model;
+
+  // Parse SDF properties
+  joint = model->GetJoint(sdf->Get<std::string>("joint"));
+  if (sdf->HasElement("topic")) {
+    topic = sdf->Get<std::string>("topic");
+  } else {
+    topic = "~/"+sdf->GetAttribute("name")->GetAsString();
+  }
+  
+  if (sdf->HasElement("units")) {
+    radians = sdf->Get<std::string>("units") != "degrees";
+  } else {
+    radians = true;
+  }
+
+  gzmsg << "Initializing potentiometer: " << topic << " joint=" << joint->GetName()
+        << " radians=" << radians << std::endl;
+
+  // Connect to Gazebo transport for messaging
+  std::string scoped_name = model->GetWorld()->GetName()+"::"+model->GetScopedName();
+  boost::replace_all(scoped_name, "::", "/");
+  node = transport::NodePtr(new transport::Node());
+  node->Init(scoped_name);
+  pub = node->Advertise<msgs::Float64>(topic);
+
+  // Connect to the world update event.
+  // This will trigger the Update function every Gazebo iteration
+  updateConn = event::Events::ConnectWorldUpdateBegin(boost::bind(&Potentiometer::Update, this, _1));
+}
+
+void Potentiometer::Update(const common::UpdateInfo &info) {
+  joint->GetAngle(0).Normalize();
+  msgs::Float64 msg;
+  if (radians) {
+    msg.set_data(joint->GetAngle(0).Radian());
+  } else {
+    msg.set_data(joint->GetAngle(0).Degree());
+  }
+  pub->Publish(msg);
+}