This node handles the communication between MAB's md80 drives in ROS2 environment. The node was designed to act as operational endpoint - to control the drives and get information from them, thus it is not capable of configuring the drives, for this use mdtool or Candle library or a custom FDCAN application.

The node normally communicates via services for setup, and via topics for regular data transfers. Services are:

• /add_md80s
• /zero_md80s
• /set_mode_md80s
• /enable_md80s
• /disable_md80s

Topics subscribed by the node are:

• /md80/motion_command
• /md80/impedance_command
• /md80/velocity_pid_command
• /md80/position_pid_command

Topic published by the node is:

• /md80/joint_states

After starting the node, it will wait for configuration messages.

Firstly, the node should be informed which drives should be present on the FDCAN bus. This can be done via /add_md80s service. For example:

ros2 service call /candle_ros2_node/add_md80s candle_ros2/srv/AddMd80s "drive_ids: [81, 97]"

Should produce the following output:

waiting for service to become available...
requester: making request: candle_ros2.srv.AddMd80s_Request(drive_ids=[81, 97])

response:
candle_ros2.srv.AddMd80s_Response(drives_success=[True, True], total_number_of_drives=2)

informing, that both drives (ids: 81 and 97), have been successfully contacted, and were added to the node's drives list.

Next the desired control mode should be selected. This is accomplished with /set_mode_md80s service. For example:

ros2 service call /candle_ros2_node/set_mode_md80s candle_ros2/srv/SetModeMd80s "{drive_ids: [81, 97], mode:["IMPEDANCE", "IMPEDANCE"]}"

Should produce:

requester: making request: candle_ros2.srv.SetModeMd80s_Request(drive_ids=[81, 97], mode=['IMPEDANCE', 'IMPEDANCE'])

response:
candle_ros2.srv.SetModeMd80s_Response(drives_success=[True, True])

Informing that for both drives mode has been set correctly.

Often when starting, setting a current position to zero is desired. This can be accomplished with a call to /zero_md80s service.

ros2 service call /candle_ros2_node/zero_md80s candle_ros2/srv/GenericMd80Msg "{drive_ids:[81, 97]}"

Using services /enable_md80s and /disable_md80s the drives and the node publishers and subscribers can be enabled/disabled. NOTE: After calling /enable_md80s service, no calls to services other than /disable_md80s should be done.

After enabling, the node will publish current joint states to /md80/joint_states at a frequency of 100Hz. Joint names are generated based on drive ID, for example, a drive with id 546 will be called Joint 546.

The node will also listen for the messages on topics for controlling the drives. All of the above topics are listened to all the time, but currently applied settings are dependent on the md80 mode set before enabling.

ros2 service call /candle_ros2_node/enable_md80s candle_ros2/srv/GenericMd80Msg "{drive_ids:[81, 97]}"

ros2 service call /candle_ros2_node/disable_md80s candle_ros2/srv/GenericMd80Msg "{drive_ids:[81, 97]}"

Controlling the drives is done via the four topics listed above. For commands to be viable, all fields of each message must be filled properly. For example, to set up custom gains for IMPEDANCE mode use:

ros2 topic pub /md80/impedance_command candle_ros2/msg/ImpedanceCommand "{drive_ids:[81, 97], kp:[0.25, 1.0], kd:[0.1, 0.05], max_output:[2.0, 2.0]}"

Setting desired position, velocity, and torque is done via /md80/motion_command topic. Note that for it to take effect, all fields in the message should be correctly filled. For example, to move the drives in impedance mode, it is possible to use the following command

ros2 topic pub /md80/motion_command candle_ros2/msg/MotionCommand "{drive_ids:[81,97], target_position:[3.0, -3.0], target_velocity:[0.0, 0.0], target_torque:[0, 0]}" -1