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ros_control: Difficulty getting custom hardware interface to run

asked 2015-02-03 04:47:41 -0500

onkel_keks gravatar image


I am trying to implement a custom hardware interface for a 3-joint manipulator with ros_control. I was following the tutorial on the matter pretty closely. The problem is that while the controller_manager apparently gets started, service calls like list_controllers just hang. I am also unable to load any controllers, as this call also hangs.

To narrow down the possible causes, I created a test node (called test_iface) which contains almost exactly the code from the tutorial mentioned above, i.e., two joints, "A" and "B", and the interface implements a JointStateInterface as well as a PositionJointInterface. The read() and write() methods simply write a message to stdout (ROS_INFO).

Now, when I start this test node, the read/write loop gets executed properly, as I get the ROS_INFO messages from them. Also, the output of rosservice list is:

user@ubuntu:~$ rosservice list

So the controller_manager seems to start up okay. However, when I try to call the list_controllers service (via rqt; expecting an empty list, since no controllers have been loaded yet), the request just hangs and nothing happens.

When I use gazebo instead of my custom HW interface, the service call to list_controllers returns an empty list, as expected. (on a side note, if I run "rosrun controller_manager controller_manager list", that always seems to hang).

What can I do to debug this? Do you have any suggestions as to what I might be doing wrong? The test_iface code is the MyRobot class from the tutorial, extended by a read() and write() that only print debug messages, and this main method:

int main(int argc, char** argv)
  ros::init(argc, argv, "test_iface_node");
  ros::NodeHandle nh;

  MyRobot robot;
  controller_manager::ControllerManager cm(&robot);

  ros::Time ts = ros::Time::now();
  while (true)
     ros::Duration d = ts - ros::Time::now(); 
     ts = ros::Time::now();;
     cm.update(ts, d);

  return 0;

Any hints or suggestions are welcome. Thanks!

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I was using your code as example (was in a real need for a simple one) ... well there is a little issue: ros::Duration d = ts - ros::Time::now(); //is negative because time now is later and bigger ...

Must be like ros::Duration d = ros::Time::now() - ts;

cyborg-x1 gravatar image cyborg-x1  ( 2015-12-01 02:20:34 -0500 )edit

My example if you anybody is interested: (based on yours, now with fixed time calculation ;-) )

cyborg-x1 gravatar image cyborg-x1  ( 2015-12-01 02:26:53 -0500 )edit

cyborg-x1, Your link was quite helpful for me. Thanks

bario gravatar image bario  ( 2017-02-07 05:55:52 -0500 )edit

hello, what needs to be added in cyborg-x1's example so that the robot can move? Can I add rostopic commands into the program? I am trying to write a program that will ask for user input, as to how to move a link and will give back the actual position of the link.

SofiaGr gravatar image SofiaGr  ( 2017-05-26 11:32:18 -0500 )edit

As far as I remember my example you should have the topic cmd_vel as in the launchfile there is a diff drive controller loaded. Set linear.x part of the message for forward backward speed and angular.z for left/right.

cyborg-x1 gravatar image cyborg-x1  ( 2017-05-31 14:53:30 -0500 )edit

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answered 2015-02-03 06:49:47 -0500

For service (and also topic) callbacks to be able to get called, ros::spin() has to be called. This does not happen in your example, which is the reason for the behavior you observe. The easiest way to make things work in your example is probably adding a ros::spinOnce() somewhere in your while loop (This will add potentially non-deterministic delays to your controller loop however).

A better option is using an AsyncSpinner, which spins using one or more separate threads in parallel to your main loop. An example of it's use can be found here.

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Thanks, that solved it! I guess sometimes you just don't think of the obvious. I have to say this though, it would be nice if the example on the ros_control wiki was actually working code...

onkel_keks gravatar image onkel_keks  ( 2015-02-03 09:55:37 -0500 )edit

Having a separate spinner thread (other than the control thread) is a requirement. This is explained in detail in minutes 20-24 of the ROSCON'14 talk on ros_control.

Adolfo Rodriguez T gravatar image Adolfo Rodriguez T  ( 2015-02-03 10:53:59 -0500 )edit

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Asked: 2015-02-03 04:47:41 -0500

Seen: 1,997 times

Last updated: Feb 03 '15