Add contact sensor or example

#1

Did someone already use a contact sensor in the NRP or knows an experiment with an example?

I already added the sensor to my robot, can stream the data via "gz topic -e ā€œ/gazebo/default/robot/base_link/my_contactā€ and set a topic in my model.sdf. But I canā€™t see it with ā€œrostopic listā€, so I think that my sensor plugin is not working.

How can I find the needed argument/attributes to get it into the TF?

[SOLVED] Contact sensor - transfer function issue
#2

Hello, @FloAui!

To get sensor data for contact (bumper-style) sensors in a transfer function, Iā€™d recommend to use a ROS-based solution instead: The bumper sensor plugin included in GazeboRosPackages. This plugin publishes ROS messages (type gazebo_msgs/ContactsState) that you can subscribe to from a transfer function.
As of now, transfer functions donā€™t have support for subscribing to Gazebo topics.

Putting something like:

<!-- contact sensor -->
<sensor type="contact" name="your_link_contact_sensor">
  <update_rate>1000.0</update_rate>
  <always_on>1</always_on>
  <contact>
    <collision>bumper_collision</collision>
    <topic>/bumper_contact</topic>
  </contact>
<plugin name="gazebo_ros_bumper_controller" filename="libgazebo_ros_bumper.so">
        <alwaysOn>true</alwaysOn>
        <updateRate>1000.0</updateRate>
        <bumperTopicName>/robot_bumper</bumperTopicName>
        <frameName>world</frameName>
</plugin>
</sensor>

(taken from: https://answers.ros.org/question/240076/gazebo-ros-collision-detection/)

in each link you want to act as a contact sensor (take care to keep the sensor names unique) should get you started.

With best regards,
Fabian

#3

Hello, @faichele!

thank for your help! I implemented the code into the sdf-model and are able to listen to it via

 rostopic echo /robot_bumper/states   <img src="/uploads/default/original/1X/00dc558d62ec7a789b8ea1939d57a97254fdc003.png" width="690" height="421">

an example output is attached.

I tried to subscribe and print the sensor data with the following TF:

# Imported Python Transfer Function
@nrp.MapRobotSubscriber("collision2_name", Topic('/robot_bumper/states/collision2_name', gazebo_msgs.msg.ContactsState))
@nrp.Robot2Neuron()
def read_sensor(t, collision2_name):
    clientLogger.info(collision2_name)

I checked the data format with the following command.

rosmsg show gazebo_msgs/ContactsState

I thought that I could print it directly, since collision2_name has the format string, but the output is:

  [17:52:17]
  <hbp_nrp_cle.robotsim.RosCommunicationAdapter.RosSubscribedTopic object at 0x7fe89d1c0410>

I assume that I either only get the address or missed a converting step. Am I subscribing the topic correct? Do you know what I missed?

With best regards,
Florian

#4

Hi, @FloAui!

Transfer function that worked for me is:

# Imported Python Transfer Function
@nrp.MapRobotSubscriber("bumper", Topic('/robot_bumper', gazebo_msgs.msg.ContactsState))
@nrp.Robot2Neuron()
def read_sensor(t, bumper):
    clientLogger.info(bumper.value) # type(bumper.value) = gazebo ContactsState
#5

Hi,

I am working on the same topic. I implemented the contact sensor in all links I need, and I can listen to all of them via

rostopic echo /robot_bumper/states

as well as in a transfer function as suggested.
However, the ā€œstatesā€ tab of the contact sensor output remains empty, even if there is an obvious collision.

Do you have any ideas on how to fix this issue?

Thanks,
Michael

#6

Hi cyb3,

Could you share your robot sdf file on this forum? It would help us figure out what the culprit is.
Best regards,
Luc

#7

Hi Luc,

thanks for answering!
I already got a solution on one of my other posts:

That solved the problem for me :smile:

Have a nice day!
Michael