How to install

Install ros2:

https://docs.ros.org/en/humble/Installation/Ubuntu-Install-Debians.html

Install ros control:

sudo apt install ros-rolling-ros2-control

Install ros topic based control:

https://github.com/PickNikRobotics/topic_based_ros2_control/tree/main?tab=readme-ov-file

sudo apt install ros-humble-topic-based-ros2-control

Install python dependencies:

pip3 install python-can

pip3 install pyserial

pip3 install numpy

Navigate to folder /src:

sudo rosdep init

sudo rosdep update

sudo rosdep install --from-paths ./ -i -y --rosdistro ${ROS_DISTRO}

How to integrate robot

Navigate to the control ros2 control .xacro file and in the <hardware> section include topic based plugin together with topic definition for state and command:

<plugin>topic_based_ros2_control/TopicBasedSystem</plugin>
<param name="joint_commands_topic">/mks_servo_joints_cmd</param>
<param name="joint_states_topic">/mks_servo_joints</param>

Topics use sensor_msgs/JointState.msg format

How to configure driver

In src/python_driver/python_driver/driver.py file specify joint count of your robot by modifying JOINT_CNT variable. Interfaces with servos are created automatically with IDs in ascending order and starting with ID 1.

Alternativelly you can specify interfaces manually by replacing:

self.servos = [ MksServo(self.bus, self.notifier, i+1) for i in range(self.JOINT_CNT) ]

with:

self.servos = [
    MksServo(self.bus, self.notifier, 1),
    MksServo(self.bus, self.notifier, 5)
]

where the last argument specifies servo CAN ID.

It is also impartant to specify usb device path of your can usb interface by changing channel argument:

self.bus = can.interface.Bus(interface='slcan', channel='/dev/ttyACM0', bitrate=125000)

How to build

In workspace root

colcon build

source install/setup.bash 

How to run

ros2 run python_driver mks_interface 

In case of permision denied error, update usb device permissions by running:

sudo chmod 666 /dev/ttyACM0 

How to use

By default, the driver is in standby mode (mode 0). In this mode joint states are published and all commands are ignored.

Mode can be changed by calling mks_servo_change_mode service:

ros2 service call /mks_servo_change_mode python_driver_interfaces/srv/ChangeMode "{mode: 1}"

Don't forget to source the workspace before running the command.

Driver supports 3 different modes:

• 0 - Standby (joint states are published, command are ignored)
• 1 - Position (joint states are published, position commands are used)
• 2 - Speed (joint states are published, velocity commands are used)

Driver also allows user to reset the servo axis to 0 by calling:

ros2 service call /mks_servo_reset_axis python_driver_interfaces/srv/ResetAxis

How to run test demo

This demo works with at least 2 servos connected i.e. JOINT_CNT in driver should be 2.

ros2 launch ros2_control_demo_example_1 rrbot.launch.py 

Limitations

During testing we have observed that servos continue to run even when the communitacion is lost.