problems with a simple realtime joint controller in Gazebo

asked 2011-10-25 12:40:42 -0500

andrew-unit
283 ●11 ●14 ●21

updated 2011-11-03 06:01:20 -0500

Wim
2915 ●14 ●34 ●43

Hello,

I'm trying to follow along with the Writing a realtime joint controller tutorial. I've got the class all set up, and I believe I've got it installed correctly using the plugin lib, as I can see the controller when I do

rosrun pr2_controller_manager pr2_controller_manager list

and I can see that the plugin is running OK. The problem is that even when I set the joint_state_->commanded_effort_ to a fixed value, I don't see any change in the joints of my simulation in gazebo. However, when I do a rostopic echo of the /mechanism_statistics, I can see that the commanded effort is non-zero and that the limits haven't been violated:

name: p_one_joint_4
timestamp: 
  secs: 54
  nsecs: 5000000
position: 0.0
velocity: 0.0
measured_effort: 0.0
commanded_effort: -100.0
is_calibrated: True
violated_limits: False
odometer: 0.0
min_position: 0.0
max_position: 0.0
max_abs_velocity: 0.0
max_abs_effort: 0.0

Also, it is interesting that when I go into gazebo and tinker with the joints manually by using the little hand tool and making the joints move, I don't see anything when I add a printf into the controller to print the joint position (it stays 0). I know that putting a printf in the controller is a bad idea for real-time behavior... Any hints on why I can't get the joint to move with my simple controller would be appreciated. Also in my joint definition in my URDF file I do not have a limit or safety_controller tag currently in it (they're below but commented out):

    <joint name="${parent}_${suffix}_joint_4" type="continuous">
        <origin xyz="${link_4_len} 0 0" rpy="0 0 0" />
        <axis xyz="0 1 0" />
        <!-- <limit effort="10" velocity="10" /> -->
        <!-- <safety_controller soft_lower_limit="-1.5" soft_upper_limit="1.5" k_position="1" k_velocity="1"/> -\-> -->
        <joint_properties damping="0.0" friction="0.0" />
        <parent link="${parent}_${suffix}_link_4" />
        <child link="${parent}_${suffix}_link_5" />
    </joint>

I have also verified that the links look OK in the simulation as well as in rviz, and the TF tree looks like it's being published.

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Comments

Hmm. Another observation is that when I fire up the simulation and grab the robot with the hand tool to get it to move the joints, and I try to do a rostopic echo of /joint_states, I see all the joints in my urdf file, but the positions, velocities, and effort are all zero. Also in rviz it looks like the joints aren't moving at all.

andrew-unit ( 2011-10-26 00:55:18 -0500 )edit

Puting printfs in the realtime loop won't crash it, though it will diminish its performances you can try it. Have you been through this tutorial : http://www.ros.org/wiki/pr2_mechanism/Tutorials/Running%20a%20controller%20in%20simulation ?

Guido ( 2011-11-15 21:13:55 -0500 )edit

Is this joint connected to any actuators?

sglaser ( 2012-02-14 13:24:55 -0500 )edit

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2

answered 2012-02-14 13:56:28 -0500

hsu
5735 ●31 ●62 ●89

updated 2012-02-14 13:56:40 -0500

Do you have gazebo_ros_controller_manager or an equivalent gazebo plugin in your simulated robot XML?

<gazebo>
  <controller:gazebo_ros_controller_manager name="gazebo_ros_controller_manager" plugin="libgazebo_ros_controller_manager.so">
    <alwaysOn>true</alwaysOn>
    <updateRate>1000.0</updateRate>
  </controller:gazebo_ros_controller_manager>
</gazebo>