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Robot arm falls over on spawn (Gazebo)

asked 2019-05-25 15:03:30 -0500

tswie gravatar image

updated 2019-05-27 17:44:46 -0500

I'm using ROS Melodic with the denso_robot_ros package ( https://github.com/DENSORobot/denso_r... ).

I'm currently trying to adapt my own arm to utilize the package. The package comes with a functioning example using the VS060 model, whereas I'm attempting to use the VS6577 A-B model with a custom end effector. I have created my own URDF (in xacro format) by using data obtained from the VS6577 controller for the arm and the custom end effector files.

When running the VS060 example, the arm will spawn in both Gazebo and RViz, with RViz providing the ability to control the arm by moving the position indicator located at the tip. When executing a trajectory in RViz, the model in Gazebo will make movements corresponding to the trajectory.

When running the VS6577 arm, the arm will spawn in both Gazebo in RViz, however it will flop over in both and fail to respond to commands. The arm in RViz will mimic the movement of the arm in Gazebo and doesn't exert any force to correct itself/stand up. The RViz VS6577 will still display the clickable indicator on the end of the robot arm that allows me to move it to a hypothetical position that it can then successfully plan to move it. Once I decide to execute the trajectory however, the arm doesn't make any attempt at movement while the terminal indicates that it has successfully moved.

 [ INFO] [1558814233.787314221, 39.284000000]: Combined planning and execution request received for MoveGroup action. Forwarding to planning and execution pipeline.
[ INFO] [1558814233.787400526, 39.284000000]: Planning attempt 1 of at most 1
[ INFO] [1558814233.787467946, 39.284000000]: Starting state is just outside bounds (joint 'joint_2'). Assuming within bounds.
[ INFO] [1558814233.787630107, 39.284000000]: Found a contact between 'EEF_robot_magnet' (type 'Robot link') and 'J4' (type 'Robot link'), which constitutes a collision. Contact information is not stored.
[ INFO] [1558814233.787663090, 39.284000000]: Collision checking is considered complete (collision was found and 0 contacts are stored)
[ INFO] [1558814233.787701964, 39.284000000]: Start state appears to be in collision with respect to group arm
[ INFO] [1558814233.789812451, 39.287000000]: Found a valid state near the start state at distance 1.286259 after 3 attempts
[ INFO] [1558814233.790373357, 39.287000000]: Planner configuration 'arm' will use planner 'geometric::RRTConnect'. Additional configuration parameters will be set when the planner is constructed.
[ INFO] [1558814233.790927439, 39.288000000]: RRTConnect: Starting planning with 1 states already in datastructure
[ INFO] [1558814233.790988817, 39.288000000]: RRTConnect: Starting planning with 1 states already in datastructure
[ INFO] [1558814233.791059312, 39.288000000]: RRTConnect: Starting planning with 1 states already in datastructure
[ INFO] [1558814233.791120209, 39.288000000]: RRTConnect: Starting planning with 1 states already in datastructure
[ INFO] [1558814233.801353892, 39.298000000]: RRTConnect: Created 5 states (2 start + 3 goal)
[ INFO] [1558814233.801434857, 39.298000000]: RRTConnect: Created 5 states (2 start + 3 goal)
[ INFO] [1558814233.801546992, 39.298000000]: RRTConnect: Created 5 states (2 start + 3 goal)
[ INFO] [1558814233.801651412, 39.298000000]: RRTConnect: Created 5 states (2 start ...
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1

It sounds like the joint controllers are not set up correctly, so each joint is freely moving. Can you show us the launch files and controller yaml flies you're using.

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2019-05-25 17:51:19 -0500 )edit

Sure thing! Adding them to the OP now.

tswie gravatar image tswie  ( 2019-05-27 17:27:59 -0500 )edit
1

At a quick glance it looks like your PID controllers need to be tuned. I would expect some of those values to be significantly higher than they are. If you have a look at this page for a slightly different controller it gives you some hints to tune these parameters using dynamic reconfigure. You can also echo the joint effort topics and see what sort of forces the controllers are outputting.

PeteBlackerThe3rd gravatar image PeteBlackerThe3rd  ( 2019-05-28 04:37:39 -0500 )edit

Thank you! Looking into the joint efforts led to me the solution, as found here: https://answers.ros.org/question/1108...

tswie gravatar image tswie  ( 2019-05-30 14:22:26 -0500 )edit

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answered 2019-05-30 14:22:05 -0500

tswie gravatar image

Was able to solve it by changing the effort limits in my URDF. Previously they were set to 1 (found in the joint tags in my URDF). After setting them higher, the robot can now stand on its own and manipulating PID gains leads to visible changes in error control while running the sim. I'll be fixing these values as I go along to something more reasonable.

Found a solution by going here: https://answers.ros.org/question/1108...

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answered 2019-05-27 16:42:42 -0500

Bonadio gravatar image

updated 2019-05-27 16:43:04 -0500

Have you checked this collision?

[ INFO] [1558814233.787630107, 39.284000000]: Found a contact between 'EEF_robot_magnet' (type 'Robot link') and 'J4' (type 'Robot link'), which constitutes a collision. Contact information is not stored.

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Could you explain where I would go to check it? The move_it configuration didn't show any contacts in it while I was setting it up and I believe the pose I was using for the example above didn't have any visual indicators of a contact between the two links (the link turning red upon contact detection I mean).

EDIT: Could you also explain what it means when it says contact information is not stored? I would have thought that means it was choosing to ignore it.

tswie gravatar image tswie  ( 2019-05-27 17:58:35 -0500 )edit

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Asked: 2019-05-25 15:02:35 -0500

Seen: 780 times

Last updated: May 30 '19