How can we teleop the Gripper from xarm_moveit_servo?

[bchandaka]

We are using xarm_moveit_servo to teleop control our xarm 7 using an xbox controller, but we found that the gripper controller is not launched from the servo nodes. How can we open/close the xarm gripper in the servoing mode?

[penglongxiang]

Hi @bchandaka there are two ways currently to control gripper while using moveit servo to control the arm.

(1) Use the ros2 service defined in xarm_api package. You should first enable the gripper related services in the config yaml if you have not done so. Please follow the instruction here and enable set_gripper_mode, set_gripper_enable, set_gripper_speed, set_gripper_position and clean_gripper_error services. After colcon build, You can check if gripper can be successfully controlled by following terminal command:

$ ros2 service call /xarm/set_gripper_mode xarm_msgs/srv/SetInt16 "data: 0"
$ ros2 service call /xarm/set_gripper_enable xarm_msgs/srv/SetInt16 "data: 1"
$ ros2 service call /xarm/set_gripper_speed xarm_msgs/srv/SetFloat32 "data: 3000"
$ ros2 service call /xarm/set_gripper_position xarm_msgs/srv/GripperMove "{pos: 200, wait: false, timeout: 10.0}"

The position range (in pulses for our API) of the gripper is from 0 (CLOSED) to 850 (fully OPEN). You can adjust the speed and target position, the first three configuration only needs to be done once upon application start, then you can just change the position command afterwards.

(2) Use self-implemented move_group interface program to control the gripper. As you can see in the robot_description_semantic param of /servo_server node, there is a pre-defined planning group named "xarm_gripper" with 2 states "open" and "close", you can implement a moveit node for planning and execution of the gripper, if moveit planning way is preferred on your side.

[bchandaka]

Thank you! I could succesfully map some buttons on my controller to open/close the gripper using the xarm_api as you mentioned.
So, I currently control the gripper position in increments of +-50, and I hear many clicking sounds when operating it in this way. If I use the normal moveit gui to open/close gripper there is just one click and then just the smooth motor motion sound. If I control the gripper in this servoing way(remote controller button press--> update gripper position +- 50 through the xarm_api), is it okay for the gripper motor's durability?