Why can't my robot arm move to specific positions?

[Niek Jonkman]

  Hi, I am using MoveIT with ROS to try to move my robot to a pre defined (hardcoded) position. The problem that I have is that the "easiest" to reach targets cannot be reached, and "harder" targets can be reached. The start state of the robot looks like this:

I have drawn a red box where I want to be able to reach targets. Now, I am using move_group from MoveIT (C++) like this:

    int main(int argc, char **argv)

    {

      ros::init(argc, argv, "cpp_arm");

    

      ros::NodeHandle node_handle;

   

      ros::AsyncSpinner spinner(1);

      spinner.start();

   

      static const string PLANNING_GROUP = "arm"; 

    

      moveit::planning_interface::MoveGroupInterface move_group(PLANNING_GROUP);

    

      moveit::planning_interface::PlanningSceneInterface planning_scene_interface;

      

      const robot_state::JointModelGroup *joint_model_group = move_group.getCurrentState()->getJointModelGroup(PLANNING_GROUP);

      

      ROS_INFO_NAMED("arm", "Reference frame: %s", move_group.getPlanningFrame().c_str());

      ROS_INFO_NAMED("gripper", "End effector link: %s", move_group.getEndEffectorLink().c_str());

    

      geometry_msgs::Pose target_pose1;

     

      target_pose1.orientation.w = 1.0;

      target_pose1.position.x = -0.2;

      target_pose1.position.y = 0.1;

      target_pose1.position.z = 0.60;

    

      move_group.setPoseTarget(target_pose1);

   

      moveit::planning_interface::MoveGroupInterface::Plan my_plan;

      

      bool success = move_group.plan(my_plan);

    

      ROS_INFO_NAMED("arm", "Visualizing plan 1 (pose goal) %s", success ? "" : "FAILED");

   

      move_group.move();

    }

This results in the robot to move to the specific location:

When you look at this video, you can see the robot twists around itself and move in a strange way to its location.

(ignore the stuttering, its an camera issue):

https://youtu.be/UfdCbqkBx-4

Now, because of this strange movement ( I think ) the robot cannot reach simple positions in front or behind it like this:

And this:

I have used the same positions to move to as where the cubes are located at but it cannot reach them. I am getting the following erros:

    Fail: ABORTED: No motion plan found. No execution attempted

And

    RRTConnect: Unable to sample any valid states for goal tree

This is my URDF file:

https://pastebin.com/iuE3DG1L

Why is this happening and how can I reach goal states in front of my robot?

Thanks in advance