Why this->model->SetLinearVel doesn't work?

Question

I am trying to give velocity to a model by using SetLinearVel for the model and apparently it doesn't seem to work. I looked up this tutorial: http://gazebosim.org/tutorials?tut=set_velocity and they are doing model->GetLink("white_link_0")->SetLinearVel({0, 1, 0});. However, I am attempting to do this->model->SetLinearVel(ignition::math::Vector3d(2.0, 0.0, 0.0)); and it doesn't seem to work. I don't see my model moving. What is it that I am doing wrong?

The full code is given below:

namespace gazebo
{
    Sparkle::Sparkle()
    {
        
    }
    void Sparkle::Load(physics::ModelPtr _parent, sdf::ElementPtr _sdf)
    {
        ROS_INFO_STREAM("Load");
        this->model = _parent; /*Store the pointer to the model*/
        this->world = _parent->GetWorld();
        this->robotNamespace = "";
        this->physicsEngine = (this->world)->Physics(); 

        /*Get the update rate from sdf*/
        if (_sdf->HasElement("updateRate"))
        {
            this->updateRate = _sdf->GetElement("updateRate")->Get<double>();
        }
        if (_sdf->HasElement("robotNamespace"))
        {
            this->robotNamespace = _sdf->GetElement("robotNamespace")->Get<std::string>();
        }

        
        this->velTopic = this->robotNamespace + "/vel";

        //Start up ros_node
        int argc = 0;
        char** argv = NULL;
        ros::init(argc, argv, "sparkle_sim", ros::init_options::NoSigintHandler | ros::init_options::AnonymousName);
        rosnode_ = new ros::NodeHandle(this->robotNamespace);

        
        this->ros_spinner_thread_ = boost::thread( boost::bind( &Sparkle::SimROSThread, this ) );
       

    }

    void Sparkle::SimROSThread()
    {
        ROS_INFO_STREAM("SimROSThread,");
        ros::NodeHandle nodehandle;
        ros::Subscriber velsub = nodehandle.subscribe(this->velTopic, 1, &Sparkle::changeVel, this);
        ros::Rate loop_rate(10);

        while (this->rosnode_->ok())
        {
            ROS_INFO_STREAM("Looping");
            ros::spinOnce();
            loop_rate.sleep( );
        }
    }

    void Sparkle::changeVel(const geometry_msgs::Twist::ConstPtr& msg)
    {
        ROS_INFO_STREAM("ChangingVel");
        double x = msg->linear.x;
        
        ROS_INFO("Velocity to set is %f\n", x);

        this->model->SetLinearVel(ignition::math::Vector3d(x, 0.0, 0.0));
    }

    void Sparkle::changePos(const gazebo_msgs::ModelState::ConstPtr& msg)
    {
        gazebo_msgs::ModelState newMsgs;
        newMsgs.model_name = this->robotNamespace;
        newMsgs.pose.position = msg->pose.position;
        newMsgs.pose.orientation = msg->pose.orientation;
        this->modelPub.publish(newMsgs);
    }
   GZ_REGISTER_MODEL_PLUGIN(Sparkle)
}

Apart from the fact that tutorial is using old math library, what is the difference between these two methods and why my method doesn't seem to work?

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Originally posted by rahul on Gazebo Answers with karma: 53 on 2019-06-15

Post score: 0

Answer 1

Few questions:

1. Did you compile your plugin? Does it compile without errors?
2. How do you know the plugin is actually loaded?
3. Which version of Gazebo are you using?
4. What does the ROS_INFO("Velocity to set is %f\n", x); line actually print in the terminal?
5. What does the robot look like? What are its physical properties? Is it even able to move in the x direction? Wouldn't, for example, friction prevent the robot from moving?
6. Can you show us the header file?

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Originally posted by kumpakri with karma: 755 on 2019-06-20

This answer was ACCEPTED on the original site

Post score: 1

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Original comments

Comment by rahul on 2019-06-20:
Thanks for the suggestions. I took your steps into consideration. I am using Gazebo 9.0. The problem I found was in Point no. 5. My Inertial for robot model was not correct and upon fixing, it worked just fine.