mujoco_ros2_control + moveit2 + pick'n'place

[uahic]

Hi @ all,

I was experimenting lately to grasp objects using Moveit's task constructor and mujoco_ros2_control. As there are limited possibilities regarding effort-interface contrrollers in moveit2, I've tried using the JointTrajectoryController and was wondering if the solution would be to set as a goal the gripper fully closed but having an effort limit (on the HW interface side). I am not sure if this is common to implement and would like to know how other people solve grasping objects like boxes in mujoco?

The problem with pure position control without effort limits is that the controller will squeeze the boxes until they jump around/away

Thank you!

[sangteak601]

I think you should use the JointTrajectoryController with the position_pid interface. That will give you a more realistic result. Here is an example of it.

[uahic]

@sangteak601 the issue that closing the gripper just position based leaves 2 options:

1. closing it entirely (object jumps away or hand "explodes")
2. trying to figure out the exact apperature for each object and hope friction will hold it (didnt worked so far)

therefore the hope was that there is something available already to get it working based on (maximal) efforts

[AbdElRahmanFarhan]

@sangteak601 the issue that closing the gripper just position based leaves 2 options:

1. closing it entirely (object jumps away or hand "explodes")
2. trying to figure out the exact apperature for each object and hope friction will hold it (didnt worked so far)

therefore the hope was that there is something available already to get it working based on (maximal) efforts

Hi, I am also facing the same problem. Initially, I thought maybe it is because of the position_controllers/GripperActionController as it will close the gripper immediately. But even when I replaced it with joint trajectory controller and enforced a scaling factor. I still face the same issue.

This is weird because if you use the Mujoco model for a panda robot from here directly with Mujoco GUI, without ros altogether, it will work just fine. But when I try to do the same with mujoco ros2 controller, the object jumps once the pads touches it.

[abuibaid]

that is true I have the same problem too, I'm using robotiq gripper 2f85 with ur5e and I have the same issue. The gripper moves rapidly!!

[AbdElRahmanFarhan]

that is true I have the same problem too, I'm using robotiq gripper 2f85 with ur5e and I have the same issue. The gripper moves rapidly!!

I tried to move it very very very slowly with max_effort = 1, the object will also fly once the pads touch it. When trying the same model and object MJCF but using Mujoco GUI directly, the pads can touch the object and grip it normally.

I am starting to think that this plugin has a bug when simulating contacts.

[sangteak601]

That's interesting. I will take a look at this.

[Bigenlight]

Hello all!
For me setting the Kd value lower for the robot arm helped out.
Check for panda.ros2_control.xacro in your folder.

I'm using a different arm, so the params may differ. But I think around 10 for position_kd is enough.
<param name="position_kd">10</param>
Test with 2f85 gripper:
https://github.com/user-attachments/assets/8d92fa4d-4401-4621-8ca7-20ffcb53d0cf

[abuibaid]

Hi @Bigenlight, actually it didn't work as what you proposed even though the video really shows the smootness of the gripper movements!

could you please share with us, the ros2_control.urdf.xacro of the gripper plus the .yaml ? like what controller did you use? is it gripperactioncommand?

[Bigenlight]

Hello @abuibaid.
I'm sorry to hear that. Since I didn't use moveit2 for my case, the environment might be different. But I can still share the code I could merged in a public repo recently.

I simply use default ROS2 controller for the 2f85 gripper. Which rotate left_driver_joint. You can see the code and info here:

• gripper YAML, arm + gripper YAML
• ros2_control.xacro
• model XML
• doc to use it

Hope this helps!