DiffDrive.cc

/*
 * Copyright (C) 2012-2015 Open Source Robotics Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
*/

// ALL THE MEASUREMENTS ARE OF Pinoneer2DX

#include <gazebo/transport/transport.hh>
#include "gazebo/util/system.hh"
#include <gazebo/math/gzmath.hh>
#include <gazebo/gazebo_client.hh>
#include <boost/bind.hpp>
#include <gazebo/gazebo.hh>
#include <gazebo/physics/physics.hh>
#include <gazebo/common/common.hh>
#include <stdio.h>

enum {RIGHT, LEFT};

namespace gazebo
{
  class DiffDrive : public ModelPlugin
  {
    public: DiffDrive() : ModelPlugin()
    {
      this->wheelSpeed[LEFT] = this->wheelSpeed[RIGHT] = 0;
      this->wheelSeparation = 0.34;
      this->wheelRadius = 0.11;
    }
    public: virtual void Load(physics::ModelPtr _model, sdf::ElementPtr _sdf);
    public: virtual void Init();

    private: void OnUpdate();

    private: void OnVelMsg(ConstPosePtr &_msg);

    private: transport::NodePtr node;
    private: transport::SubscriberPtr velSub;

    private: physics::ModelPtr model;
    private: physics::JointPtr leftJoint, rightJoint;
    private: event::ConnectionPtr updateConnection;
    private: double wheelSpeed[2];
    private: double wheelSeparation;
    private: double wheelRadius;
    private: common::Time prevUpdateTime;

    private: physics::LinkPtr link, leftWheelLink, rightWheelLink;
  };

  GZ_REGISTER_MODEL_PLUGIN(DiffDrive)
}


/////////////////////////////////////////////////
void gazebo::DiffDrive::Load(physics::ModelPtr _model,
                           sdf::ElementPtr _sdf)
{
  this->model = _model;

  this->node = transport::NodePtr(new transport::Node());
  this->node->Init(this->model->GetWorld()->GetName());

  this->velSub = this->node->Subscribe(std::string("~/") +
      this->model->GetName() + "/vel_cmd", &DiffDrive::OnVelMsg, this);

  if (!_sdf->HasElement("left_joint"))
    gzerr << "DiffDrive plugin missing <left_joint> element\n";

  if (!_sdf->HasElement("right_joint"))
    gzerr << "DiffDrive plugin missing <right_joint> element\n";

  this->leftJoint = _model->GetJoint(
      _sdf->GetElement("left_joint")->Get<std::string>());
  this->rightJoint = _model->GetJoint(
      _sdf->GetElement("right_joint")->Get<std::string>());

  if (!this->leftJoint)
    gzerr << "Unable to find left joint["
          << _sdf->GetElement("left_joint")->Get<std::string>() << "]\n";
  if (!this->rightJoint)
    gzerr << "Unable to find right joint["
          << _sdf->GetElement("right_joint")->Get<std::string>() << "]\n";

  this->updateConnection = event::Events::ConnectWorldUpdateBegin(
          boost::bind(&DiffDrive::OnUpdate, this));
}

/////////////////////////////////////////////////
void gazebo::DiffDrive::Init()
{
  this->wheelSeparation = this->leftJoint->GetAnchor(0).Distance(
      this->rightJoint->GetAnchor(0));

  physics::EntityPtr parent = boost::dynamic_pointer_cast<physics::Entity>(
      this->leftJoint->GetChild());

  math::Box bb = parent->GetBoundingBox();
  // This assumes that the largest dimension of the wheel is the diameter
  this->wheelRadius = bb.GetSize().GetMax() * 0.5;
}

/////////////////////////////////////////////////
void gazebo::DiffDrive::OnVelMsg(ConstPosePtr &_msg)
{
  double vr, va;

  // My method to calculate wheel velocities

  // vr = _msg->position().x();
  // va =  msgs::ConvertIgn(_msg->orientation()).Euler().Z();

  this->wheelSpeed[LEFT] = vr + va * this->wheelSeparation / 2.0;
  this->wheelSpeed[RIGHT] = vr - va * this->wheelSeparation / 2.0;
}

/////////////////////////////////////////////////
void gazebo::DiffDrive::OnUpdate()
{
  /* double d1, d2;
  double dr, da;

  this->prevUpdateTime = currTime;

  // Distance travelled by front wheels
  d1 = stepTime.Double() * this->wheelRadius * this->leftJoint->GetVelocity(0);
  d2 = stepTime.Double() * this->wheelRadius * this->rightJoint->GetVelocity(0);

  dr = (d1 + d2) / 2;
  da = (d1 - d2) / this->wheelSeparation;
  common::Time currTime = this->model->GetWorld()->GetSimTime();
  common::Time stepTime = currTime - this->prevUpdateTime;
  */

  double leftVelDesired = (this->wheelSpeed[LEFT] / this->wheelRadius);
  double rightVelDesired = (this->wheelSpeed[RIGHT] / this->wheelRadius);

  this->leftJoint->SetVelocity(0, leftVelDesired);
  this->rightJoint->SetVelocity(0, rightVelDesired);
}