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

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Niek Jonkman

Jun 27, 2017, 7:23:12 AM6/27/17
to MoveIt! Users

  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);
      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;
      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");

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):

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


    RRTConnect: Unable to sample any valid states for goal tree

This is my URDF file:

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

Thanks in advance

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