Hiwonder xArm ESP32 Control with ROS2

This repository is intended for the control of a Hiwonder xArm, that utilises 6 bus servos, with an ESP32 micro and micro-ROS for control on a master machine. The ESP32 is essentially utilised as a motor driver, while micro-ROS is utilized to set and read parameters of the motors using defined ROS publishers, subscribers and messages.

• Parameters that can be set: Servo angle/position (and time to execute respective movements)
• Parameters that can be read: Servo angle/position, servo input voltage, servo temperature

For the use of these motors with an ESP32 and ROS1-Rosserial, please go to this link.

For the setup of the environment, including ROS2 installation and workspace, micro-ROS installation and setup of the IDE please see the Setup README.

Test System: Ubuntu 22.04 on WSL, ROS2 Humble Hawksbill, Micro-ROS, ESP32-DevkitC-32E with PlatformIO in VS Code as the dev environment

Author: Miguel Garcia Naude

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Hardware Setup

• Hiwonder xArm ESP32
• ESP32-DevKitC-32e

Front View	Side View

Servo Number	Model	Range (deg.)	Rotation Speed	Parameter Feedback
1	ID1 Servo	160 deg.	0.39 sec/60deg	Position, Temperture, Voltage
2	LX-15D Servo	240 deg.	0.22 sec/60deg	Position, Temperture, Voltage
3	LX-15D Servo	240 deg.	0.22 sec/60deg	Position, Temperture, Voltage
4	LX-15D Servo	240 deg.	0.22 sec/60deg	Position, Temperture, Voltage
5	LX-225 Servo	240 deg.	0.23 sec/60deg	Position, Temperture, Voltage
6	LX-15D Servo	240 deg.	0.22 sec/60deg	Position, Temperture, Voltage

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Electronics Setup

Servos can be daisy chained together. Thus all six servos may be chained together and connected as a single pin at GPIO pin 33 on the ESP32. It was found that the system experiences communication errors with the servos regularly when more than three servos are daisy chained together. As such they can be connected in parallel at pin 33. Two pairs of three chained servos are thus connected in parallel to pin 33.

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Basic Operation

Power On

1. Ensure that the servos are powered on (their LEDs will light up) with the 7.5V source.
2. Power on the ESP32 by plugging it in with the micro-USB.
3. Ensure that the Serial lines of the servos are connected to Pin 33 of the ESP32
4. Ensure that the servos and the ESP32 have a common ground.

Build & Run

Note again: see setup readme for installation instructions.

Change directory to that of your micro-ROS. In my case this is done with:

cd esp32_microros_ws
pwd
/home/miguel_u22/esp32_microros_ws

Inside this directory there should be the following:

miguel_u22@miguelpc:~/esp32_microros_ws$ ls
build  install  log  src

Source the setup.bash file in the install folder:

source install/setup.bash

If you are confident this will not create any conflicts, you can add this line to the ~/.bashrc so you do not have to source the micro-ROS workspace everytime:

echo "source /home/miguel_u22/microros_ws/install/setup.bash" >> ~/.bashrc    # replace with file path with your own

Run

1. Plug the ESP32 into the host PC with the USB.

2. In the micro-ros directory (for me /home/miguel_u22/esp32_microros_ws), run the micro-ROS agent: ros2 run micro_ros_agent micro_ros_agent serial --dev /dev/ttyUSB0 -v6

   This should produce the following response:

    [1696498217.465170] info     | TermiosAgentLinux.cpp | init                     | running...             | fd: 3
    [1696498217.465918] info     | Root.cpp           | set_verbose_level        | logger setup           | verbose_level: 6
    [1696498226.028623] info     | Root.cpp           | create_client            | create                 | client_key: 0x340D845A, session_id: 0x81
    [1696498226.028907] info     | SessionManager.hpp | establish_session        | session established    | client_key: 0x340D845A, address: 0
    [1696498226.029119] debug    | SerialAgentLinux.cpp | send_message             | [** <<SER>> **]        | client_key: 0x340D845A, len: 19, data:
    0000: 81 00 00 00 04 01 0B 00 00 00 58 52 43 45 01 00 01 0F 00
    [1696498226.041597] debug    | SerialAgentLinux.cpp | recv_message             | [==>> SER <<==]        | client_key: 0x340D845A, len: 52, data:
    0000: 81 80 00 00 01 07 2A 00 00 0A 00 01 01 03 00 00 1B 00 00 00 00 01 FB 3F 13 00 00 00 48 69 77 6F
    0020: 6E 64 65 72 5F 78 41 72 6D 5F 6E 6F 64 65 00 00 00 00 00 00
    [1696498226.064239] info     | ProxyClient.cpp    | create_participant       | participant created    | client_key: 0x340D845A, participant_id: 0x000(1)
    [1696498226.064379] debug    | SerialAgentLinux.cpp | send_message             | [** <<SER>> **]        | client_key: 0x340D845A, len: 14, data:
    0000: 81 80 00 00 05 01 06 00 00 0A 00 01 00 00
    [1696498226.064408] debug    | SerialAgentLinux.cpp | send_message             | [** <<SER>> **]        | client_key: 0x340D845A, len: 13, data:
    0000: 81 00 00 00 0A 01 05 00 01 00 00 00 80
    [1696498226.075602] debug    | SerialAgentLinux.cpp | recv_message             | [==>> SER <<==]        | client_key: 0x340D845A, len: 13, data:
    0000: 81 00 00 00 0A 01 05 00 01 00 00 00 80
    [1696498226.082373] debug    | SerialAgentLinux.cpp | recv_message             | [==>> SER <<==]        | client_key: 0x340D845A, len: 96, data:

The agent is now running, and we can begin communicating with the ESP32 via ROS2 to control the servos. The LED on pin 4 (should you connect one) should light on.

If there is an issue, ensure that this is the correct serial connection. This can be verified by plugging in the ESP micro and running the following:

dmesg | grep tty
[ 2256.333770] usb 1-1: cp210x converter now attached to ttyUSB0

Which indicates that the serial is connected to ttyUSB0.

3. To end the connection with micro-ROS press ctrl + c in the terminal. The LED on pin 4 will turn off. To restart the connection with micro-ROS just run ros2 run micro_ros_agent micro_ros_agent serial --dev /dev/ttyUSB0 -v6.

Before proceeding, cut power to the servos and then restore it, to restart them. I have found that this gives better responsiveness and less likely for the servos to fail on read or write commands.

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ROS Topics

Run the micro-ROS agent as in step 2 above.

Running ros2 topic list, the available ROS2 topics should be listed.

miguel_u22@miguelpc:~$ ros2 topic list
/multi_servo_cmd_sub
/parameter_events
/rosout
/servo_pos_publisher
/servo_temp_publisher
/servo_volt_publisher

Moving the servos

The position of the servos can be controlled using the /multi_servo_cmd_sub topic. Any number of servos can be moved at once by specifying the disired servo angle (centi-degrees) and the time (milli-seconds) for the servos to carry out this command. The publish message from the terminal is an Int16MultiArray msg structured as follows:

ros2 topic pub /multi_servo_cmd_sub --once std_msgs/Int16MultiArray "{layout: {dim: [{label: '', size: 0, stride: 0}], data_offset: 0}, data: [12000,12000,12000,12000,12000,12000,500,500,500,500,500,500]}"

The data component of the message contains the desired servo positions and the move time. It should always contain 12 integer entries. To be more clear it is structured as follows:

data:[servo1_desired_pos, servo2_desired_pos, ... , servo6_desired_pos, servo1_move_time, ... , servo6_move_time]. In this particular case, servos 2-6 are set to their middle position (120 deg) and the arm moves upright in 500 ms.

If the servos do not move following this command, kinda see the Issues section in the install readme.

The servos will only move if a positive position is given, and if a position is given outside of a servo angular range, the servo will move to its limit. For instance, to move only servo 1 and servo 3, one could give the following:

ros2 topic pub /multi_servo_cmd_sub --once std_msgs/Int16MultiArray "{layout: {dim: [{label: '', size: 0, stride: 0}], data_offset: 0}, data: [7000,-1,2000,-1,-1,-1,500,500,500,500,500,500]}"

Pick Up Object	Wave

Reading from the servos

As is shown in the table, Position, Temperature & Voltage can be read from the servos. Voltage and temperature are published on start-up and then every 5 seconds, while servo positions are published at approximately 25 Hz. If you have problems reading from the servos (especially servo 1) please see issues.

1. /servo_pos_publisher - publishes servo positions in a JointState message, that includes the servo numbers, positions and time stamps. run ros2 topic echo /servo_pos_publisher and observe the published servo positions.

   header:
   stamp:
     sec: 67
     nanosec: 3297586560
   frame_id: frame id
   name:
   - Servo1
   - Servo2
   - Servo3
   - Servo4
   - Servo5
   - Servo6
   position:
   - 15120.0
   - 11952.0
   - 12048.0
   - 11952.0
   - 11904.0
   - 11952.0
   ...
   

2. /servo_temp_publisher - publishes the servo temperature as a Int16MultiArray message. The data is structured as such:

   data:[servo1_temp, servo2_temp, ... , servo6_temp].

   Run ros2 topic echo /servo_temp_publisher and observe the published servo temperatures.

   layout:
   dim: []
   data_offset: 0
   data:
   - 47
   - 28
   - 33
   - 29
   - 31
   - 27
   ---
   

3. /servo_volt_publisher - publishes the servo input voltage (milli-volts) as a Int16MultiArray message. The data is structured as such:

   data:[servo1_vin, servo2_vin, ... , servo6_vin].

   Run ros2 topic echo /servo_temp_publisher and observe the published servo input voltages.

   layout:
     dim: []
     data_offset: 0
   data:
   - 7607
   - 7629
   - 7629
   - 7585
   - 7618
   - 7583
   ---
   

Simple Example ROS2 Package for Hiwonder xArm

An example of a simple package for this arm is given in the arm_servos_pubs_subs folder. This package can be copied into your workspace source folder (in this case /home/miguel_u22/esp32_microros_ws/src) and built using colcon build.

Its corresponding launch file, with an example of how to configuring the micro-ros-agent for the launch file is also given in launch. This launch folder can be copied into the workspace (/home/miguel_u22/esp32_microros_ws/src), and following the build of the package using colcon build, the package can be launched in the terminal using:

ros2 launch servo_arm_esp32_launch.py

This serves primarily as just a simple example, upon which users can expand upon and implement more complex functionality in their own packages.

Resources that maybe be useful in future

• Hiwonder xArm ESP32 google drive.
• Hiwonder ArmPI FPV google drive.
• Hiwonder ArmPI FPV Source Code google drive