Troubleshooting

This page contains the most common errors that could happen when using PyCRAM and how to resolve them.

Ros Init Exception

ROSInitException: time is not initialized. Have you called init_node()

This exception usually occurs when trying to load an Object into the BulletWorld or when creating a Pose. The reason for this exception is that the ROS node of PyCRAM could not be initialized, this is usually the case when the PyCRAM launch file was not launched.

To solve this problem you just have to launch the ik_and_description file of PyCRAM. This can be done via the following command.

roslaunch pycram ik_and_description

Robot Description not Loaded

In PyCRAM a lot of things are base on the robot description that is currently loaded and in turn the robot description that will be loaded depends on the robot description that is on the ROS parameter server at the time PyCRAM is started.

If you get an error that looks similar to the following exception the most likely case is that the robot description was not loaded.

     763 with open(self.path) as f:
     764     self.urdf_object = URDF.from_xml_string(f.read())
 --> 765     if self.urdf_object.name == robot_description.name and not BulletWorld.robot:
     766         BulletWorld.robot = self
     768 self.links[self.urdf_object.get_root()] = -1

 AttributeError: 'NoneType' object has no attribute 'name'
There could be a few reasons for this behaviour:
  • The name of the URDF on the parameter server and the name in the PyCRAM robot description are different

    • The PyCRAM robot description is matched by the name of the robot in the URDF

    • You can check the assignment of the PyCRAM robot description in this function update_robot_description() (there is a link to the source code)

  • You only started a roscore

  • You did not start the ik_and_description launch file

Stop Iteration

Stop iterations usually happen when you try to resolve a designator for which there is no solution or if you iterate over a designator and reached the end of all possible solutions.

When you try to resolve a designator which has no solution the error will look something like this.

    753 def ground(self) -> Union[Object, bool]:
    754     """
    755     Return the first object from the bullet world that fits the description.
    756
    757     :return: A resolved object designator
    758     """
--> 759     return next(iter(self))

StopIteration:

If you encounter such an error the most likely reason is that you put the wrong arguments into your DesignatorDescription. The best solution is to double check the input arguments of the DesignatorDescription.

BulletWorld crashes after loading an URDF

It can happen that the BulletWorld crashes when loading a URDF. This happens when loading a URDF with more than 127 links. This is a limitation of PyBullet which can not deal with objects with more links.

Only real solution here is to either delete links such that you have at max 127 links or split up the URDF and load the split parts individually.

Error when performing Actions or Motions

     30 def perform(self):
     31     pm_manager = ProcessModuleManager.get_manager()
---> 32     return pm_manager.navigate().execute(self)

AttributeError: 'NoneType' object has no attribute 'navigate'

If you get an error like this when trying to perform an action or motion designator, then you did not specify how the designator should be executed. You can specify how the designator should be performed by using the simulated_robot or real_robot environments. This is also explained in the Action Designator Example.

with simulated_robot:
   NavigateAction([Pose()]).resolve().perform()